Article

Use of hydrogels in the planting of industrial wood plantations

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Abstract

The quantity of available water in soil is crucial for plant growth, especially after transplanting as this water will enable the growth of new roots to facilitate nutrient and water uptake. Water absorbed by a hydrogel (superabsorbent polymer) has the potential to reduce drought stress after planting and to improve seedling survival. This article provides an overview of the concepts of post-plant water stress, a review of trials that tested application of hydrogels to forest tree species, and discussion on probable reasons for failure or success in the use of hydrogels. Hydrogels applied in pot trials, under controlled conditions, tended to have a higher frequency of positive survival responses compared with field trials (14 studies of the 17 (82%) in pot trials vs 15 of the 25 (60%) in field trials). In field trials, the application of hydrogels at planting had no effect on survival in seven of the 25 (28%) trials and had a negative effect in three of the 25 (12%) field trials included in this review. In the trials showing a positive response a hydrogel and water application improved survival by 18% and across all trials by 8%. The efficiency of hydrogels was probably influenced by the (1) chemicals present in the soil, (2) hydrogel quantity applied, (3) type of polymer, (4) hydrogel particle size distribution, (5) soil texture, (6) physical restrictions to hydrogel expansion, (7) hydrophilic nature of hydrogels, (8) unsaturated hydraulic conductivity between the substrate and the hydrogel particles, (9) application method and (10) planting conditions and rewatering. Due to this complexity and interactions between these factors it is difficult to provide site-specific recommendations for successful application of hydrogels in a forestry field setting. In general, application of hydrogels has been found to be more beneficial in sand or clay soils and to be of limited benefit in loam soils. Use of a hydrogel is not a replacement for good silviculture and has limited use as insurance against short periods of low rainfall. All efforts should be made to plant when environmental conditions are favourable for tree growth (i.e. wet soil and high probability of rainfall).

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... However, the fate of the sapling after depletion of supplies stored in the endosperm of the seed is deter− mined by interactions with the environment (e.g., substrate, water, temperature, and other liv− ing organisms) (Grossnickle, 2012). Recently, increases in temperature and drought frequency during the growing season has drawn attention to development of strategies to improve adaptabil− ity of seedlings and saplings through an extended period after planting (Crous, 2017;Repáč et al., 2021). ...
... Recent studies suggest that application of special substances called hydrogels, which retain and provide plentiful water for plants, would be an efficient means for mitigation of seedling vulnerability to water supply imbalance during early growth stages (Crous, 2017). According to Landis and Haase (2012), improved management of water balance after hydrogel application also can be connected with the formation of a layer with properties similar to natural polymeric mucilage produced by healthy roots. ...
... reproductive material of tree species in harsher environmental conditions (Beniwal et al., 2011;Orikiriza et al., 2013;Crous, 2017;. ...
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Climate change mitigation strategies, which include distributing ecological risk over a greater number of tree species in forest ecosystems, increase the attractiveness of cultivating chestnut in selected areas of Slovakia. Artificial restoration practices are important tools for preservation and improvement of the current status of chestnut. However, ongoing technology advances have tended to provoke their revision and actualization. The aim of this study was to examine the effect of sowing on the early growth of saplings of selected chestnut taxa. Chestnut seeds collected from Castanea mollissima (C. moll.), C. crenata (L7) and hybrids C. crenata × C. sativa (C6, B12) were germinated and sowed into the following treatments: vegetation cells (VC), growing sub− strate enriched by hydrogel (H), or loam soil (C), then raised under standard cultivation condi− tions over one growing season. During the growing season, the aboveground height was measured every 2 weeks. Despite slightly higher values of height of the aboveground parts of saplings C.moll., B12, and C6 grown in VC, and L7 grown in H, than saplings grown in C, analysis of vari− ance did not reveal these differences as statistically significant. On the other hand, significant differences were observed in the aboveground height of the chestnut taxa. Saplings of C. moll. (28.9 cm) and L7 (25.3 cm) grew significantly taller than hybrids C6 and B12 (17.3 cm and 13.2 cm). Our findings suggest that cultivation of chestnut saplings in VC or H under standard growing conditions does not stimulate growth in height during early growth stages.
... El principal beneficio de los hidrogeles, es el aumento de la capacidad de retención de humedad del suelo o medio de crecimiento donde se incorpore (Chen et al., 2004). Sin embargo, la efectividad de estos polímeros dependerá de múltiples factores como el tipo de polímero, tamaño de sus partículas, la dosis, la cantidad de agua disponible, el método de aplicación, entre otros (Crous, 2017). También, las propiedades físicas y químicas del suelo suelen afectar la eficacia de los hidrogeles (Agaba et al., 2010;Crous, 2017). ...
... Sin embargo, la efectividad de estos polímeros dependerá de múltiples factores como el tipo de polímero, tamaño de sus partículas, la dosis, la cantidad de agua disponible, el método de aplicación, entre otros (Crous, 2017). También, las propiedades físicas y químicas del suelo suelen afectar la eficacia de los hidrogeles (Agaba et al., 2010;Crous, 2017). En este sentido, la respuesta variable de las plantas a la aplicación del hidrogel pudo relacionarse con las diferencias en las características fisicoquímicas de los sustratos. ...
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Enterolobium cyclocarpum es una especie arbórea multipropósito cuyo crecimiento y supervivencia en plantaciones se desconoce. El objetivo fue evaluar el efecto de tres medios de crecimiento en vivero y tratamientos auxiliares para mitigar el estrés hídrico en el desempeño de plantas de E. cyclocarpum establecidas en campo. Las semillas se sembraron en tres diferentes tipos de sustrato: 1) mezcla base (turba, vermiculita y agrolita), 2) composta aeróbica y 3) tierra de monte. Cada grupo de plantas por tipo de sustrato se dividió en cuatro subgrupos a los que se les asignó diferente tratamiento auxiliar para mitigar el estrés hídrico: 1) riego, 2) hidrogel (2 g planta-1), 3) hidrogel (4 g planta-1) y 4) condiciones naturales (testigo). Los resultados indican que el tipo de sustrato influye en la supervivencia y crecimiento de las plantas; la tierra de monte promueve mayores valores. La relación entre el diámetro de plantas con la probabilidad de supervivencia fue positiva, esta variable es un indicador de la supervivencia en campo durante los primeros años de la plantación. El tratamiento auxiliar para mitigar el estrés hídrico afectó significativamente el crecimiento en diámetro y altura; el riego aumentó los valores, con excepción del diámetro en mezcla base.
... Morong, Fonseca et al., 2017;Pontes Filho et al., 2018). However, the time and application methods of the hydrogel, as well as the irrigation frequency, polymer type, texture and other soil physical properties have an influence on the optimal doses and affect its performance depending on the species (Crous, 2017). ...
... After the application of the same dose of hydrogel in the middle of the driest season in P. patula, the reduction in mortality dropped from 31% to 8%, whereas at the beginning or the end, it was not significant (Mudhanganyi et al., 2018). Previous studies corroborate the fact that seedling survival is favored by the hydrogel when there is an intense and prolonged water deficit (Crous, 2017). Otherwise, as demonstrated for 30 tree species belonging to several successional stages, after a year of establishment in the field without water deficit, neither seedling growth nor survival were affected by the application of hydrogel (Barbosa et al., 2013). ...
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The effect of hydrogel (0, 3, 6, and 9 g per seedling) on the survival and growth of Cariniana pyriformis seedlings under different water regimes (absence of irrigation, 60% and 100% field capacity) in a sandy loam soil was assessed. The experiment was carried out in an agricultural nursery with drip irrigation, implementing a completely randomized block design in a split-plot scheme. After 20 weeks of evaluation in both treatments with irrigation, the maximum dose showed a slight increase (9%) in stem diameter and seedling height compared with the control treatment, although the aerial and root dry biomass did not show differences. For the treatment without irrigation, the survival had a linear response with increasing doses, from 24% (0 g per seedling) to 65% (9 g per seedling). C. pyriformis responds positively to hydrogel when a severe water deficit occurs.
... Due to more frequent occurrence of warmer weather and drought periods in central Europe, not only in early spring but also during the growing season (Gera et al. 2019), an efficient way to overcome plant drought stress could be the use of water-holding additives (Crous 2017). Hydrogels are macromolecular networks of hydrophilic polymer chains that are able to absorb, retain and provide great amount of water (Bhardwaj et al. 2007). ...
... The use of hydrogels in outplanting applications yielded an increased survival and biomass production of seedlings of Pinus sylvestris, Pinus nigra and Picea abies (Šijačić-Nikolić et al. 2011;Orikiriza et al. 2013). However, effectiveness of hydrogel on seedling development is influenced in many ways, such as type, quantity and application method of a hydrogel, soil properties, rewetting interval and others (Bhardwaj et al. 2007;Apostol et al. 2009;Crous 2017), sometimes inducing even negative effect of hydrogel (Sarvaš et al. 2007;Starkey et al. 2012). ...
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Planting of seedlings is the most reliable and speedy way of forest restoration. Routine spring planting of bareroot seedlings is frequently unsuccessful in central Europe. In this study, the effects of planting time and a spring-pre-planting application of ectomycorrhiza-hydrogel additive Ectovit and hydrogel Stockosorb on the development of bareroot and container Norway spruce and Scots pine seedlings on windthrow area in Western Carpathians, northwest Slovakia were estimated. Survival and aboveground growth parameters during three consecutive years and root dry weight, short root frequency, soil and needle nutrients concentration and ectomycorrhizal fungi root colonization and identification 2 years after planting were assessed. Regardless of planting time and additive, the best developed bareroot spruce (2 + 2) survived significantly better than container spruce (2 + 0), container pine (2 + 0) and especially small-size bareroot pine (1 + 0); bareroot pine was found unsuitable for planting in conditions of planting site. Both additives improved survival of spring-planted container spruce in the summer-drought second year after planting. Container spruce survived and grew significantly better following fall compared to spring planting time. Higher number of short roots was observed in spring than in fall planted bareroot spruce. Neither planting time nor additives affected root dry weight and abundance of ectomycorrhizae. No significant effects of the treatments on pine development were found. Except of K deficiency in container spruce, sufficient or overabundant foliar macro-nutrients concentration was detected. Visual morphotyping of short roots and identification of ectomycorrhizae by DNA analysis indicated inefficient ectomycorrhizal inoculation of seedlings with Ectovit. (https://rdcu.be/b59AV)
... In geotechnical engineering, ground hydraulic conductivity control is an important manner for soil liquefaction potential mitigation and ensuring the stability of soil dams or seepage structures [210]. In fact, the presence of biopolymer hydrogels or other biomaterials can affect the hydraulic conductivity of soils by altering the water retention characteristics (suction potential) [211] or inducing soil pore clogging [69,212]. Regardless of the biopolymer phase in soil (e.g., dried biofilm, moist hydrogel), when BPTSs are subjected to water, biopolymers swell via hydrophilic adsorption and decrease paths for fluid flow [54], resulting in a significant reduction to the hydraulic conductivity of BPTSs [52,54,147,213]. ...
... Generally, plants require water for their growth and metabolic processes (e.g., photosynthesis); however, most water supplied to vegetation is lost through transpiration, guttation [220], and gravitational infiltration of soils with low water retention capacity [221]. In fact, excessive water drainage in sandy soils can result in scarcity of water around the root zone, hindering vegetation growth [222], and severe drought conditions are known to be a limiting factor for seedling survival and germination [211]. ...
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Various applications of biopolymer-based soil treatment (BPST) in geotechnical engineering have been implemented in recent years, including dust control, soil strengthening and erosion control. Despite BPST methods can ensure the effectiveness of engineering while meeting environmental protection requirements, BPST technology requires further validation in terms of site applicability, durability, and economic feasibility. This study aims to provide a state-of-the-art review and future prospective of BPST. Current biopolymer types, engineered and assessed in laboratory scales, are described along with site implementation attempts. The effect of biopolymers on soil behavior is reviewed with regard to geotechnical engineering application and practice, including soil consistency limits, strength parameters, hydraulic conductivity, soil-water characteristics, and erosion control. The economic feasibility and sustainability of BPST application in ground improvement and earth stabilization practices is discussed. This review postulates biopolymers to be a promising new, environmentally friendly ground improvement material for geotechnical and construction engineering practice.
... En este trabajo encontramos que la dosis de ½ l de PAM y 1 l fueron efectivas. Sin embargo, debido a la complejidad de interacciones raízsuelo-hidrogel, nuestros resultados no pueden ser extrapolables a otros tipos de suelos (Crous, 2017;Landis & Hasse, 2012). Debe tenerse en cuenta que diferentes propiedades físico-químicas de los sustratos pueden incidir en la efectividad del hidrogel (Durovic et al., 2007;Agaba et al., 2011;Paim et al., 2020). ...
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Background and aims: The practice of restoration is a source of valuable experience that, analyzed and disseminated, contributes to the improvement of interventions for the recovery of degraded areas. From this conception, in this work we evaluate an outplanting of Prosopis denudans var. denudans in an arid zone located at Auca Mahuida Protected Area (Neuquén, Argentina). The objectives were: to analyze the effect of hydrogel applications after 11 months after planting; and determine the incidence of predation of herbivorous vertebrates in the same period. M&M: A total of 651 nursery seedlings were planted distributed in two abandoned quarries. We apply the treatments ½ l of hydrogel; 1 l of hydrogel and control (without hydrogel), and protection vs. no protection of metal mesh to evaluate survival and predation. The results were analyzed with generalized linear models. Results: The survival was significantly higher and statistically different for seedlings with ½ l of hydrogel and metal mesh protection. The protected plants were no predated, and survival in no protected plants was reduced 50% approximately. Conclusions: The results show that the chances of survival may be greater with protectors against herbivorous mammals and hydrogel in restoration plantations. However, it is necessary to increase studies on the relationships between root growth and hydrogel doses in different edaphic conditions, particularly in species that can be the framework for the recovery of degraded areas.
... Hydrogels are soft reactive materials with an extremely hydrophilic 3D network structure that swells rapidly in solution environment. Due to the hygroscopic expansion capacity, hydrogels have been widely applied in biomedicine [14], tissue engineering [15], precision instrument [16,17], agriculture [18] and other fields. The NHE metamaterials can be designed by using the swelling or shrinking capacity of hydrogels when exposed to solution environment. ...
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A design strategy for a mechanical metamaterial with large negative hygroscopic expansion (NHE) was proposed in this paper. Different from the reported structures, the present metamaterial is designed by constructing repeated lattice microstructure consisting of curved ligaments incorporating hydrogel active layers and polymer support layers and straight polymer bars. When immersed in the solution environment, the swelling of hydrogel layer of such composite structure induces the reversed bending of the ligament, leading to the overall ultra-large shrink (negative expansion) deformation of the metamaterial. Through the new structural design, large NHE effects can be achieved. The theoretical investigation and finite element analysis (FEA) were conducted to demonstrate the large negative expansion effects of such metamaterial. The results showed that the effective NHE ratio of the metamaterial is dependent of the curvature of the curved ligament and the size of both the ligament and the connecting rod. The ultra-large NHE ratios about −80% for the 2D structure and −90% for the 3D version can be obtained by adopting the structural parameters. The newly designed metamaterials have potential applications in medical and other fields. © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
... Pozitívny účinok hydrogelu na rast a prežívanie sadbového materiálu v podmienkach simulovaného vlahového deficitu bol potvrdený viacerými experimentmi zhrnutými v práci Crousa (2017 (Crous 2017). Navyše, všetka voda z hydrogelu môže byť po jeho aplikácii uvoľnená, zvlášť v suchej pôde, v dôsledku čoho medzi koreňmi obalenými zmršteným hydrogelom, neschopným absorbovať ďalšiu vodu, a okolitou pôdou dochádza k prerušeniu kontaktu a obmedzeniu prístupu k pôdnej vlahe (Rowe et al. 2005). ...
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This study estimates effects of hydrogel Stockosorb and slow-release fertilizer Silvamix on survival, damage, aboveground and root growth, and foliar nutrients concentration of bareroot and containerized Norway spruce (spruce) and European beech (beech) seedlings five years after planting on windthrow area in the Javorie Mts., Central Slovakia. The average survival rate of all seedlings was 74% and 54% one and five years after planting, respectively. Spruce survived better, but was damaged by game more and by drying leading shoot in a similar extent, when compared to beech. Within tree species, bareroot and containerized seedlings showed a comparable survival and growth. Silvamix decreased survival of spruce seedlings, and on the contrary, increased foliar concentration of some macronutrients in all seedlings, and temporarily the aboveground growth of bareroot seedlings; however, a significant effect of the additives neither on the aboveground growth nor on root dry weight, short root frequency and relative abundance of ectomycorrhizal roots was found five years after planting. The results suggest a relatively low survival rate of seedlings, the most probably due to a precipitation deficiency in the first growing season after planting and a certain but inconsistent effects of the additives tested on outplanting seedling performance depending on tree species and planting stocktype used. For more information see Summary at the end of the article.
... Green manuring and hydrogel application already have been tested in forestry and agriculture to provide weed control, maximize water availability, and improve microclimatic and edaphic conditions (Spencer & Faust 2006;Teasdale et al. 2007;Crous 2017;Agbede et al. 2018;Mudhanganyi et al. 2018); however, its potential beneficial effects on tree species performances in direct seeding techniques for forest restoration have not been studied yet. Therefore, we investigated (1) the effects of green manure and hydrogel soil amendment alone, or in combination, on seedling emergence, establishment, survival, and the early growth of native tree species used in a direct seeding system for the restoration of the tropical seasonal forest; and (2) how green manure affects the initial weed coverage in the study plots. ...
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Although direct tree seeding may be a potentially useful restoration practice, many biotic and abiotic barriers prevent seedling emergence and early development, reducing its success and applicability. To overcome these barriers, we undertook a field experiment to test the effects of using green manure and hydrogel alone, or in combination, on seedling performances of 14 native tree species that were planted by direct seeding in a deforested tropical seasonal forest area in southern Brazil and to examine how green manure affected the initial weed coverage in the study plots. We evaluated competing vegetation coverage and tree seedling emergence and early development for two years after sowing. Weed infestation was significantly higher in the experimental plots with no green manure; however, neither green manure nor hydrogel improved tree seedling emergence and early development at any time of measurement. Our results suggest that the use of green manure and hydrogel alone or in combination, were not effective in guaranteeing direct seeding success, however, green manure can be an effective method to reduce weed infestation. Direct seeding techniques for tree species still need to be improved in order to restore tropical seasonal forests on a larger scale. This article is protected by copyright. All rights reserved.
... The high water-absorbing properties of synthetic gel structures along with their ability to fix mineral fertilizers and plant protection products in the plant rhizosphere [1][2][3][4][5][6][7][8] are largely determined by the dispersion and surface energy of strongly swelling polymer hydrogels (SSPHs). However, until now, in soil science no data on the dispersion of SSHPs were available. ...
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The study is the first attempt in soil physics to estimate the effective specific surface area of strongly swelling polymer hydrogels as soil conditioners of a new generation. Along with the standard assessment of water vapor desorption isotherms by the BET method, a new method for determining the specific surface area deduced from the slope of water retention curves was used. Water desorption isotherms and water retention curves were obtained by a dynamic sorption equilibrium method and by a new method of thermodesorption. The specific surface area values of synthetic polymer hydrogels ranged from 468 to 1029 m ² /g. An innovative Russian product VM-P with amphiphilic filler in the form of dispersed peat had the maximum specific surface area among all studied types of hydrogels. Water absorption properties and dispersion of gels have a hysteresis caused, presumably, by the dynamics of dispersion in the cycles of wetting-drying.
... Synthetic gel structures are actively used in modern agronomy and landscaping to optimize waterretention and ion-exchange capacity of soils, their erosion resistance, as well as to fix trace elements and plant protection products in the rhizosphere [1][2][3][4][5][6][7][8][9]. The actual task of soil physics is a scientifically based forecast of the action of certain doses of hydrogels on the technological properties and characteristics of soils. ...
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The mechanism of disjoining pressure controlling the swelling and water absorption of gel structures for soil conditioning is discussed. Its quantitative description is based on the fundamental ion-electrostatic model of soil water sorption isotherms containing the phase variable of gel swelling degree and specific surface area index of the soil substrate. The model adequately reproduces the s-shape of soil water sorption isotherms in a wide range of water activity from 0.05 to 0.999 depending on the working doses of hydrogels in the range of 0.05-0.3 mass%. Reinforcement of gel structures with amphiphilic dispersed particles increases the effect of disjoining pressure and water absorption.
... Natural materials employed include clays, which have been traditionally used for the amendment of sandy soils in many arid and semiarid areas of the world (Ajayi and Horn, 2016), and natural polymers such as guar gum (Patil et al., 2011). Among the artificial additives, hydrogels are among the most widely employed for agricultural, horticultural or forestry applications (Hüttermann et al., 2009;Agaba et al., 2010;Shi et al., 2010;Kabiri et al., 2011;Paradelo et Crous, 2017); they are cross-linked crystalline forms of insoluble polyacrylamide gel that absorb and store water up to 500 times their own weight when saturated (Johnson, 1984). However, information regarding combinations of humectants and compost for use as substrates is still scarce. ...
Article
Humectant agents are used to improve seed germination and survival in hard environments through their effect on water-holding capacity. In this work, we have evaluated the combined effect of substrate composition and humectant agents on the water-holding capacity and growth of Lolium multiflorum in different mixtures based on municipal solid waste composts. A commercial polyacrylamide, bentonite or guar gum have been added to mixtures of two municipal solid waste composts with either manure vermicompost or pine bark compost. Water-holding capacity of the substrates and plant production after five weeks in the greenhouse were evaluated. Only bentonite increased water retention of the substrates, likely because the compost-based substrates already presented high water retention. None of the humectant agents had significant effects on the growth of Lolium multiflorum. The use of bentonite can be recommended for increasing water-holding capacity of organic substrates in this case, but given the overall small effects of the humectant agents, an adequate choice of the organic materials could suffice for the formulation of adequate plant substrates in this case.
... (1) stands planted at lower density in dry environments may display fairly small decreases in overall productivity but large decreases in hydraulic water stress (Hakamada et al. 2017); (2) balanced fertilisation (especially ensuring adequate potassium supplements) may increase water use efficiency; (3) under water stress conditions, adequate micronutrient nutrition is also paramount (especially for the element boron), as it is not adequately taken up in dry conditions and its deficiency may severely limit productivity through tip dieback; (4) adequate weed control will limit water stress in young plantations during the phase before canopy closure; (5) appropriate soil preparation may increase infiltration and give access to greater volumes of soil that the roots may explore for water; (6) residue retention and/or techniques to conserve the forest floor (such as minimum tillage) may limit evaporation from soil surfaces in newly established stands. Analyses of several experiments showed that hydrogel can improve survival and/or growth of plants, but its efficacy is influenced by interactions with site preparation and soil texture, and it cannot replace good silvicultural techniques (Crous et al. 2017). ...
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Eucalyptus grandis is a globally important tree crop. Greenhouse-grown tree seedlings often face water deficit after outplanting to the field, which can affect their survival and establishment severely.This can be alleviated by the application of superabsorbent hydrophilic polymers (SAPs). Growth promoting bacteria can also improve crop abiotic stress tolerance; however, their use in trees is limited, partly due to difficulties in the application and viability loss. In this work, we evaluated the improvement of drought tolerance of E. grandis seedlings by inoculating with two Pseudomonas strains (named M25 and N33), carried by an acrylic-hydrocellulosic SAP. We observed significant bacterial survival in the seedling rhizosphere 50 days after inoculation. Under gradual water deficit conditions, we observed a considerable increase in the water content and wall elasticity of M25-inoculated plants and a trend towards growth promotion with both bacteria. Under rapid water deficit conditions, which caused partial defoliation, both strains significantly enhanced the formation of new leaves, while inoculation with M25 reduced the transpiration rate. Co-inoculation with M25 and N33 substantially increased growth and photosynthetic capacity. We conclude that the selected bacteria can benefit E. grandis early growth and can be easily inoculated at transplant by using an acrylic hydrocellulosic SAP.
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El micro-riego (o riego deficitario y localizado) es conocido desde hace más de dos mil años por las culturas fenicia, romana y china, aplicado a cultivos de huerta y a árboles frutales. Desde entonces y hasta nuestros días, ha ido extendiéndose y evolucionando tanto en el sector agrícola como en el sector forestal. En este último encuentra su principal aplicación en el establecimiento de brinzales, cuando la causa mayoritaria de mortalidad de las plantas sea el estrés hídrico. Las dudas técnicas y económicas que su aplicación suscita deben ser estudiadas y respondidas. La presente tesis doctoral realiza una exhaustiva revisión bibliográfica de los distintos sistemas de micro-riego forestal existentes, clasificándolos en base a su principio hidráulico de funcionamiento y su eficiencia técnica. Seguidamente, se desarrolla un modelo matemático con el que se obtiene el umbral de marras a partir del cual el micro-riego resulta ventajoso desde el punto de vista económico frente a la tradicional reposición de planta. El modelo se informatiza y se aplica a un amplio conjunto de casos de estudio de repoblación para analizar su utilidad y determinar la sensibilidad de sus diferentes parámetros de entrada. A continuación, se estima el tamaño y evolución del mercado internacional del micro-riego. Los resultados obtenidos con el modelo permiten al repoblador adoptar una decisión razonada respecto a la conveniencia (o no) de incluir riegos de apoyo en sus proyectos. También pueden orientar al fabricante de sistemas de micro-riego para fijar una oferta de precios que resulte atractiva al selvicultor.
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The amendment of soil with superabsorbent polymers (SAPs) has been gaining interest in agriculture and forestry, in both dry and semi-dry lands since the late 1970s. Here, we review studies on the characterization, application, and evaluation of SAPs in forestry and revegetation fields worldwide. SAPs usually absorb amounts of pure water several hundred times their dry weight; however, their absorption capacity decreases significantly for water containing salts and SAP expansion by water is restricted to the soil pore space. Until now, the experiments with SAPs have been mainly conducted on 1) root dipping of seedlings, 2) soil water holding capacity and drought tolerance of tree seedlings, 3) field application of SAPs to planting holes, and 4) gel seeding. The water-holding capacity of the soil increases with the amount of SAP added but the effects of the SAP on soil available water content and plant growth were more evident in sandy soils than in clayey soils. The application of SAP exhibited both positive and negative effects, depending on the soil texture and tree species. Some studies show that overuse of SAPs resulted in low seedling growth rates. The limitations of SAPs included the following: reduction in water holding capacity by combined use of fertilizers, short durability of SAP effects, and lack of cost evaluation. Further systematic studies are necessary to 1) develop suitable application methods, 2) identify applicable tree species by systematic studies in dry and semidry lands, and 3) improve the SAP products.
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Mixing superabsorbents, such as cross-linked polyacrylamides (PAM), with sandy sods may decrease water percolation rates and increase water availability to crops. Four polymers were evaluated for their effects on water retention and hydraulic conductivity (HC) in the presence of either tap or distilled water and within sand mixtures. Water retained by the absorbents alone (at low suction) ranged between 200 and 500 kg kg(-1) of polymer; water retained by the polymers when mixed with sand ranged between 40 and 140 kg kg(-1). Water retained per kilogram of polymer increased with an increase to polymer concentration in the sand while undergoing desorption, but absorbed water decreased with polymer concentration during sorption, indicating an effect of hysteresis and absorption kinetics in the water absorption process. Applying a hydraulic head of tap water initially caused a decrease in the HC, explained by the decrease in the volume of the soil-absorbents mixtures, followed by a steady increase in HC ascribed to drainage of water from the swollen polymer granules that led to an increase in the size of pores available for water flow. Leaching the soil-absorbent mixtures with distilled water, simulating rainwater, increased the volume of the mixtures (due to polymer swelling) and decreased their HC due to pore blockage by the swollen polymer grains. Better understanding of the interaction among absorbents, soil, and water quality may produce an efficient and economic technology for improving the water management of sandy soils.
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The use of polymer in agriculture is gaining popularity in science, particularly in the field of polymer chemistry. This has provided solutions to the problems of the present day agriculture which is to maximize land and water productivity without threatening the environment and the natural resources. Superabsorbent polymer hydrogels potentially influence soil permeability, density, structure, texture, evaporation and infiltration rates of water through the soils. Functionalized polymers were used to increase the efficiency of pesticides and herbicides, allowing lower doses to be used and to indirectly protect the environment by reducing pollution and clean-up existing pollutants. This account; a detailed review study, has been put together as an expose on the myriad application of polymer in the field of agriculture, highlighting present research trend , impact on food security and future outlook.
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The study focused on the influence of hydrogel on seedlings. Hydrogel is a good absorbent of macromolecule compound that can effectively bind water. The possibility of hydrogel to retain water is very important in the case of poor soils, especially when seedlings are growing in unfavorable drought conditions. From a theoretical point of view, hydrogel and its positive influence on survival and growth of seedlings is proved, but the question arises how it may affect, for instance, soil water increasing potential, reduction of mycorrhizas or pollution absorption. The investigation was conducted on areas difficult for afforesta-tion, such as agricultural, after-military, post-industrial and post-drainage peat-bogs. The influence of hydrogel on soil moisture, pF curve, water consumption by seedlings was also observed under laboratory conditions and in greenhouse. Main objectives of the present study include detection of effects of hydrogel application on survival and growth processes of pine (Pinus sylvestris) seedlings.
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In order to study the effects of super absorbent polymer and plant growth promoting rhizobacteria (PGPR) on yield and yield components of maize (double cross 370), the experiment was done in Karaj region/ Iran in 2009. The experiment was conducted as a randomized complete block design with 4 replicates and in two separate experiments under drought stress and normal conditions. Seven different treatments have been studied in this experiment, including: T 1 : Grain inoculation with biofertilizer (Azospirillum lipoferum + Pseudomonas putida), T 2 : Applying super absorbent polymer as gel on a row, T 3 : Applying super absorbent polymer as powder on a row, T 4 : Grain inoculation with biofertilizer (A. lipoferum + P. putida) and applying super absorbent polymer as powder in rows, T 5 : Grain inoculation with biofertilizer (A. lipoferum + P. putida) and applying super absorbent polymer as gel in rows, T 6 : Mixing biofertilizer (A. lipoferum + P. putida) with super absorbent polymer (as gel) and applying in rows and T 7 : Non-application of super absorbent polymer and biofertilizer (Control). The result of this experiment showed that drought stress reduced grain yield, biological yield, number of grains per row, number of grains per ear and harvest index. But no significant decrease observed on stem and leaf dry yield The application of super absorbent polymer (powder or gel) and inoculation of grain with biofertilizer (A. lipoferum + P. putida) increased grain yield and biological yield in both stress and normal condition. Co-application of super absorbent with biofertilizer (T 4 , T 5 , T 6) in compare with T 7 treatment in both drought stress and normal condition increased grain yield, but under normal condition in compare with T 2 treatment and under stress condition in compare with T 2 and T 3 , it did not increase grain yield, biological yield and other traits.
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A study was conducted on PVC columns in the laboratory to investigate the effect of the application of hydrogel in modifying the hydraulic properties of different soil types. The main treatments consisted of four different soil types, namely sand, alluvial sandy loam, red sandy loam and black clay. The sub-treatments consisted of three levels of gel application: 0.7%, 0.5% and 0% (by weight). A given level of gel was mixed in the top 10 cm-layer of soil. In all soil columns, 5 cm of water was applied, and soil samples were taken with a core auger on the fourth, seventh, 14th and 22nd days after watering (DAW). The undisturbed soil of the rings of the core assembly was used for preparing the soil water retention curve, and the soil of the core was used for determining saturated hydraulic conductivity (Ks), bulk density and gravimetric soil water content.
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Many root hydrogel compounds are available for seedling nurseries for root treatment at the time of packing. They can differ based on composition (starch-based versus polyacrylamide), grade (fine, medium, or coarse), or by their range of particle size distributions. While the use of root hydrogels at the time of lifting, packing, and storing is a visual indicator to customers that something has been sprayed on the roots, trials with loblolly pine (Pinus taeda L. [Pinaceae]) indicate that the effect of hydrogels on seedling survival is dependent on the particle size, composition, and soil moisture availability. When subjected to moisture stress following outplanting, root hydrogels do not increase seedling survival, and in some cases may increase seedling mortality, counter to manufacturers’ claims. Cross-linked polyacrylamide gels with a peak particle size distribution >1000 microns (μm) caused significant reduction in survival when seedlings were outplanted in sandy soils. For optimal seedling survival, nurseries should evaluate their hydrogel to determine the particle size and target a product with a peak particle size distribution around 300 μm.
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Superabsorbent polymer (SAP) materials are hydrophilic networks that can absorb and retain huge amounts of water or aqueous solutions. They can uptake water as high as 100,000%. Common SAPs are generally white sugar-like hygroscopic materials, which are mainly used in disposable diapers and other applications including agricultural use. This article reviews the SAP literature, background, types and chemical structures, physical and chemical properties, testing methods, uses, and applied research works. Due to variability of the possible monomers and macromolecular structure, many SAP types can be made. SAPs are originally divided into two main classes; i.e., synthetic (petrochemical-based) and natural (e.g., polysac-charide- and polypeptide-based). Most of the current superabsorbents, however, are frequently produced from acrylic acid (AA), its salts, and acrylamide (AM) via solution or inverse-suspension polymerization techniques. The main synthetic (internal) and environmental (extemal) factors affecting the acrylic anionic SAP characteristics are described briefly. The methods for quantifying the SAP practical features, i.e., absorption capacity (both load-free and under load), swelling rate, swollen gel strength, wicking capacity, sol fraction, residual monomer, and ionic sensitivity were discussed. The SAP applications and the related research works, particularly the hygienic and agricultural areas are reviewed. Meanwhile, the research findings on the effects of SAP in soil and agricultural achievements in Iran, as an arid country are treated as well. Finally, the safety and environmental issues concerning SAP practical applications are discussed as well.
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In this study results of hydrogel application in reclamations are presented. The application of hydrogel af - fected the survival of pine seedlings during two vegetation periods after planting. Double application of STOCKOSORB AGRO (gel) on the root system after lifting caused an about 19% higher survival rate compared to control variants. The application of 7 g/planting hole of STOCKOSORB MICRO granules caused overdosage and plant mortality. The application of hydrogel granules is simple but it is very complicated not to cause the overdosage because of the very high swelling capacity of hydrogel. Research should be carried out to determine suitable hydrogel application rates for different environmental conditions and tree species. To design a technology with regard to the economic effectiveness of application will be a very important task.
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Two experiments were conducted to assess the ability of a water-absorbing synthetic polymer to reduce water stress injury of seedlings of Pinus pinea L. under greenhouse and field conditions. In both experiments, two rates of hydrated hydrogel, corresponding to 200 and 400 cm ³ of stored water, and a control treatment without hydrophilic polymer were tested. Survival periods for the pine seedlings were 1.4 and 2.0 times longer for the 200- and 400-cm ³ treatments, respectively, than for a control treatment in a greenhouse assay. In the field assay, only differences in seedling survival between both hydrogel treatments and control were measured. Leaf water potential values of control plants were significantly lower than hydrated polymer treatments in both experiments. From these results, we conclude that the use of hydrophilic polymers may be an important method of increasing the success of reforestation in semiarid regions.
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The effect of super absorbent polyacrylate (SAP) hydrogel amendment to different soil types on plant available water (PAW), evapotranspiration and survival of Eucalyptus grandis, Eucalyptus citriodora, Pinus caribaea, Araucaria cunninghamii, Melia volkensii, Grevillea robusta, Azadirachta indica, Maesopsis eminii and Terminalia superba was investigated. The seedlings were potted in 3 kg size polythene bags filled with sand, loam, silt loam, sandy loam and clay soils, amended at 0 (control), 0.2 and 0.4% w/w hydrogel. The tree seedlings were allowed to grow normally with routine uniform watering in a glass house set up for a period of eight weeks, after which they were subjected to drought conditions by not watering any further. The 0.4% hydrogel amendment significantly (p < 0.05) increased the PAW by a factor of about three in sand, two fold in silt loam and one fold in sandy loam, loam and clay soils compared to the control. Similarly, the addition of either 0.2 or 0.4% hydrogel to the five soil types resulted in prolonged tree survival compared to the controls. Araucaria cunninghammi survived longest at 153 days, while Maesopsis eminii survived least (95 days) in sand amended at 0.4% after subjection to desiccation. Evapotranspiration was reduced in eight of the nine tree species grown in sandy loam, loam, silt loam and clay soils amended at 0.4% hydrogel. It is probable that soil amendment with SAP decreased the hydraulic soil conductivity that might reduce plant transpiration and soil evaporation.
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The classical aim of the application of super absorbent polyacrylate (SAPs) hydrogels is the prolonging of plant survival under water stress. Their effect on plant growth during non-water stress conditions is not known. This study examined the root and shoot biomass of seedlings of nine tree species; Eucalyptus grandis, Eucalyptus citriodora, Pinus caribaea, Araucaria cunninghamii, Melia volkensii, Grevillea robusta, Azadirachta indica, Maesopsis eminii and Terminalia superba. The seedlings were potted in five soil types; sand, sandy loam, loam, silt loam and clay. These were amended at two hydrogel levels: 0.2 and 0.4% w/w and grown under controlled conditions in a green house. Root and shoot growth responses of the seedlings were determined by measuring the dry weight of the roots, stems, leaves and twigs. The addition of either 0.2 or 0.4% hydrogel to the five soil types resulted in a significant increase of the root dry weight (p < 0.001) in eight tree species compared to the controls after 8 wk of routine watering. Also, the dry weight of stems and leaves and twigs were significantly (p < 0.001) higher in the nine tree species potted in hydrogel amended soil types than in the hydrogel free controls. These results suggested that hydrogel amendment enhances the efficiency of water uptake and utilization of photosynthates of plants grown in soils which have water contents close to field capacity.
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In dryland ecosystems, post-transplant water stress produces high seedling mortality after the first summer following outplanting. Our aim was to assess the effects of clay and hydrogel, both on the water holding capacity of the growing media and on various morphological and physiological characteristics of Quercus suber seedlings in the nursery and, subsequently, during the first 2years in the field. Quercus suber L. seedlings were grown in four types of growing media: CS (Control growing media, standard mixture of limed peat and coconut peat, 1:1 v/v ratio), SC-10 (CS mixed with sepiolite clay at 10% v/v) and HS (CS mixed with hydrogel Stockosorb® K-400 at two doses, 0.7 and 1.5% w/w). HS-1.5 showed the best results, increasing the water holding capacity of the root plug, improving seedling water status and increasing seedling survival in the field. SC-10 showed an intermediate effect on seedling response in the field. Mixing hydrogel with a peat-based growing medium to form root plugs is a suitable technique for cultivating species to be planted in areas with a strong water deficit. This technique reduces post-transplant water stress in seedlings during their first months in the field and contributes to improve forest-restoration methods in dryland ecosystems. Keywords Quercus suber –Plant stock quality–Substrate–Water availability–Carbon isotope composition
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An approach to the quantitative description of superabsorbent polymer hydrogels is examplified by partially hydrolyzed polyacrylamide gels obtained by three-dimensional radical copolymerization or radiation cross-linking of the polymer. The modified swelling theory has been used to develop a system of experimental and computational methods for the evaluation of the supergels network parameters. The possibility of applying these methods to the analysis of the network formation process is also discussed.
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Using diverse technological approaches, many types of delivery devices have been used to supply plant nutrients at a controlled rate in the soil. One new approach is the use of hydrophilic polymers as carriers of plant nutrients. These polymers may be generally classified as 1) natural polymers derived from polysaccharides, 2) semi-synthetic polymers (primarily cellulose derivatives), and 3) synthetic polymers. By controlling the reaction conditions when forming the polymers, various degrees of cross-linking, anionic charge, and cationic charge can be added, thereby changing their effectiveness as fertilizer carriers. When fertilizer-containing solutions are mixed with hydrophilic polymers to form a “gel” prior to application in the soil, the release of soluble nutrients can be substantially delayed compared with soluble fertilizer alone. The effectiveness of a specific controlled-release polymeric system is determined in part by its specific chemical and physical properties, its biodegradation rate, and the fertilizer source used. Addition of some polymers with nutrients has been shown to reduce N and K leaching from well-drained soils and to increase the plant recovery of added N, P, Fe, and Mn in some circumstances
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Root hydrogel, a hydrophilic polymer, has been used to improve transplanting success of bareroot conifer seedlings through effects on water holding capacity. We examined mechanisms by which Terra-sorb® Fine Hydrogel reduces damage that occurs when roots of 1-year old, dormant northern red oak (Quercus rubra L.) were subjected to short-term (1, 3, and 5h) pre-transplanting desiccation and long-term (45days) drought stress following transplanting in a controlled environment chamber or greenhouse conditions. Hydrogel-treated seedlings had 80% greater root moisture content than non-root dipped control seedlings following the pre-transplanting desiccation period. Hydrogel reduced root membrane leakiness by 31% 5h after the desiccation exposure. Hydrogel-treated seedlings did not show greater differences in shoot length, plant dry mass, root volume, net photosynthesis, and stomatal conductance compared with control seedlings following the 45-day drought stress exposure. A reduction in mean number of days to bud break in hydrogel-treated seedlings, combined with delayed tissue moisture loss (linked to higher stem water potential), suggests that hydrogel may have provided stress protection to aid survival under short-term desiccation, which may be beneficial toward alleviating initial transplanting stress.
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Superabsorbent polymers (SAPs) are organic materials with lightly crosslinked three-dimensional structure possessing high to very high swelling capacity in aqueous media. These are in fact the most commercially successful members of the hydrogel family. The SAP production for personal care products (baby diapers and feminine incontinence products) accounts for about 80% of the overall hydrogel production. Research during the past 30years, although not affected the commercial status of SAPs, has led to more and more understanding of superabsorbent structures, their properties, and potential uses. Beyond the hygienic use, the SAPs have found very wide applications from the agricultural formulations to pharmaceutical dosage forms. Since hygiene applications of SAPs are very well established and well reviewed, this article reviews and highlights the SAP applications in other sectors, such as in agriculture, pharmaceutics, separation technology, fibers/textiles, water-swelling rubbers, soft actuators/valves, electrical and construction.
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Introduction The mortality of nursery-grown beech (Fagus sylvatica L.) seedlings after out planting into the field is usually high. Objectives The goal of this study was to characterize the response of beech seedlings to planting stress and to test if soil amendment with a mixture of hydrogel and the ectomycorrhizal fungus Paxillus involutus could rescue the establishment of stressed plants. For this purpose, bare-rooted, dormant seedlings were exposed for 0, 2 and 6 h to air before planting. Results Water loss in response to air exposure caused increasing concentrations of soluble carbohydrates in buds and fine roots suggesting only passive of osmoprotection. Short-term exposure for 2 h delayed bud burst in spring, whereas long-term stress for 6 h also increased mortality. Growth of the seedlings in amended soil improved plant performance compared with plant grown in untreated soil. In particular, mycorrhizal colonization, plant water status and biomass increased, whereas carbohydrate storage pools were decreased. Total plant nitrogen allocated to leaves but not the nitrogen or carbohydrate concentrations were correlated with the degree of ectomycorrhizal colonization. Conclusion This suggests that soil amendment enhanced nitrogen uptake via ectomycorrhizals, which in turn stimulated growth, thereby, increasing carbon consumption and preventing starch accumulation. In conclusion, soil amendment with hydrogel and an ectomycorrhizal fungus significantly improved the performance of both stressed and unstressed young beech trees.
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Both the morphological and physiological characteristics of forest planting stock vary widely with nursery culture and environment. Through the control of environmentally determined variation in phenotype, stock can be adapted to both the stress of transplanting from nursery to forest site and the particular environmental conditions of the forest site. Evidence is discussed that indicates that the stress of transplanting is primarily water stress, resulting from (i) the confinement of roots to the planting hole, (ii) poor root–soil contact, and (iii) low root permeability. These deficiencies are overcome by root growth, which is thus a central process in plantation establishment. Root growth depends largely on current photosynthesis. Photosynthesis depends on the assimilation of carbon dioxide at the expense of lost water in transpiration. Transpiration is limited by water uptake and hence depends on root growth. Root growth and photosynthesis in newly planted trees are thus mutually dependent. Because of this relationship, plant water status immediately after planting, or as soon as conditions favorable to root growth occur, is a crucial factor in determining plantation establishment success. High plant tissue water status immediately after planting, or as soon as environmental conditions permit root growth, allows the onset of a positive cycle of root growth supported by photosynthesis and photosynthesis supported by root growth; whereas low tissue water potential immediately after planting can lead to the inhibition or root growth by a lack of photosynthesis and the inhibition of photosynthesis by a lack of root growth. Stock characteristics that enhance plant water status immediately after planting are reviewed and the scope for their control considered. Stock characteristics affecting adaptation to particular planting site conditions, or capable of affecting postestablishment plantation performance, are also discussed.
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Root growth is critical to the establishment of planted seedlings. Seedlings can undergo stress just after planting if root growth is not sufficient to couple the seedling to available soil water. Stress occurs when a newly planted seedling's root system can not supply enough water to transpiring needles to maintain a proper water balance and ensure survival. Thus, a newly planted seedling's ability to overcome planting stress is affected by its root system size and distribution, root-soil contact, and root hydraulic conductivity. This paper describes how factors of root growth and water status of newly planted seedlings are important in overcoming the phenomenon of planting stress which then allows a newly planted seedling to enter the establishment phase of development.
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An appropriate blend of growing media components increases water holding capacity and reduces irrigation frequency. Synthetic commercial materials, referred to as hydrogels, have remarkable hydrating properties, but can add significantly (about 15%) to the cost of growing media. The literature generally states that the physical characteristics of hydrogels, such as polyacrylamide (PAM), are altered by the presence of divalent cations (Ca(2+) and Mg(2+)). Few studies, however, have simultaneously investigated plant growth and development and media characteristics on a daily basis throughout plant production. Thus, the mechanisms explaining the reported beneficial and/or detrimental effects from PAM incorporation remain hidden. In this study, canopy ground cover of two species [pansy (Viola xwittrockiana Gams) and new guinea impatiens (Impatiens hawkeri Bull)] was measured daily, from transplanting to marketable size, using digital imaging to determine growth differences of plants grown in media containing different amounts of PAM. Media water content was determined with time-domain reflectance probes every 10 minutes in media treatments. Total number of irrigation events, time between irrigation events, root development after 4 and 8 weeks of growth, flower number, flower longevity, and dry masses of the shoot were also measured. Scanning electron microscopy revealed significant structural differences in hydrated PAM depending on water quality. The pansy canopy coverage was significantly greater with hydrogels, and root growth early in production was enhanced with PAM. No such effect was observed for new guinea impatiens. Total flower numbers and flower longevity of new guinea impatiens decreased with increasing amount of PAM (16.7% or higher) in the media. PAM incorporation reduced the need for irrigation early in production for both species, but by the end of production, those new guinea impatiens plants were smaller (less shoot dry mass) and required irrigation as often as plants grown without PAM. This effect coincided with reduced media volume, air capacity, and total porosity in PAM-containing media. Theoretical analysis of the potential benefits from hydrogels confirms the potential benefit early in production with little to no benefit later in production and in post-production. These data will assist growers in determining if the benefits derived from the use of PAM justify the added cost of medium.
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Pocket planting reclamation techniques developed in the 1970s for revegetating blocky quarrying waste have met with very limited success, often because the low water-holding capacity of the waste and limited root development within a small volume of planting pocket material result in severe drought mortality. We tested pocket planting approaches for waste tip reclamation at Europe's largest slate quarry, and compared materials for enhancing the continuity of water- and nutrient-holding down into the interior of the waste tip. When small compost-filled pocket planting bags were placed above slate processing fines (SPF) or water absorbent cross-linked polyacrylamide gel ("hydrogel"), tree growth rates increased in comparison with pocket planting bags alone. The SPF significantly improved tree survival especially during severe drought, but survival was not enhanced by the use of hydrogel. The sorption characteristics of hydrogel indicated that its presence may help to reduce nutrient leaching, but that it may have a negative effect on nitrogen availability. A more likely explanation for the poor performance of pure hydrogel is that it did not maintain sufficient available water, because of discontinuities caused by shrinkage and movement of the hydrogel, and/or degradation of water-holding capacity with environmental exposure. However, the root growth observed in the hydrogel treatments suggests that this technique, if adapted to reduce the effects of hydrogel shrinkage by using finer-grade hydrogel, mixing it with other soil-forming material, and reducing its exposure to extremes of temperature or sunlight, might have the potential to improve the growth and survival of trees planted on sites where delivery of heavy materials such as SPF is impractical. Fine mineral processing waste is freely available at active quarries and should be seen as a key resource for reclamation schemes.
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The aims of this study were: 1. to determine the effect of desiccation treatment on the physiological quality of Norway spruce (Picea abies [L.] Karst.) seedlings by measurements of electrolyte leakage from the root system; b) to test the use of hydrogel STOCKOSORB® for protection of the root system of spruce seedlings during their transplanting. The results showed that desiccation treatment significantly affected the rate of electrolyte leakage (34% leakage for control seedlings and 53% in contrast with seedlings after 5 hours of desiccation). Likewise, significant differences were found in height and root collar increments after the first vegetation period that decreased with the duration of desiccation treatment The values of electrolyte leakage also increased with the duration of desiccation treatment for seedlings treated with hydrogel. On the other hand, the rate of electrolyte leakage was lower after 5 hours of stress factor than in untreated seedlings. The height and root collar increments were higher in seedlings treated with hydrogel for all variants. The obtained results showed a possibility of using the measurement of electrolyte leakage from the root system to determine the physiological quality of Norway spruce seedlings. The rate of electrolyte leakage over 40% signals the physiological damage to the root system of spruce seedlings. Next, the results confirmed the need of protection of seedling roots during handling. The seedlings without hydrogel had 35% height and 26% root collar diameter increment after two-hour desiccation stress. On the other hand, the same seedlings with STOCKOSORB had 42% height and 48% root collar increment.
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Superabsorbent Polymers (SAPs) are capable of swelling and retain large amounts of water. Knowledge of the ability of SAPs to retain the absorbed water under evaporative conditions is less understood. We saturated four SAPs, seven soils from the semiarid areas in Northwest China (control treatments), and mixtures of 100 g of soil with 0.5 g of SAP, with tap water (electrical conductivity [EC] = 0.5 dS m−1, sodium adsorption ratio [SAR] = 2 [mmolc L−1] 0.5) for 15 min. The water-saturated SAPs, soils and soil-SAP mixtures were then placed in an oven at 60°C, and loss of water to evaporation from each treatment was measured every hour for 7 h. Water content of the soils at saturation ranged between 0.306 and 0.522 g g−1 of soil, while after drying it dropped to <0.08 g g−1 of soil. Water content of the SAPs ranged between 30 and 199 g g−1 of SAP at saturation, and decreased to 17 and 108 g g−1 of SAP after 7 h of drying. The soil-SAP mixtures absorbed between 78.59 and 47.94 g of water and retained between 34.51 and 12.75 g of water after 7 h of drying. Generally, evaporative water loss from soil-SAP mixtures was slower than for SAPs alone. When the SAP particle size was larger (3–4 mm) the opposite trend was noted. Furthermore, the 3 to 4 mm sized SAP differed from its <1.5 mm counter parts, that is, the water content retained by the soil-SAP (3–4 mm) mixture exceeded the sum of that retained by each component material alone. This suggests a synergy between this SAP and the soils with respect to the mixtures’ ability to retain water during the 7 h of drying. Our results suggest that when use of SAPs in cultivated soils to mitigate water stress is being considered, the characteristics of water loss from the soil-SAP mixture should be taken into account and not just the amount of water that the SAPs can absorb when mixed with the soils.
Article
Mixing cross-linked polyacrylamides with semiarid soils may increase water availability to crops. The effects of soils, sand, and superabsorbent properties on water absorption by four superabsorbent polymers (SAPs) were studied. The amount of water absorbed by the SAPs in tap water increased with increasing polymer cation exchange capacity. Less water was absorbed by SAPs mixed with soil or sand than by the control. In the sand and soil mixtures with a large-grain (3-4 mm) SAP, water absorption increased with time (up to 40-50 min) to a steady-state value in the range of 90 to 160 kg kg(-1) in the sand-SAP mixture and 33-55 kg kg(-1) in the soil-SAP mixture. Conversely, in the other three soil-SAP mixtures, water absorption reached a maximum value aft er 10 to 20 min, followed by a decrease with time to values ranging between 20 and 60 kg kg(-1). At the initial stage of water absorption, confinement of the SAP grains by the soil particles was the dominant factor limiting water absorption by these SAPs; the confinement increased as soil texture became finer. The subsequent observed reduction was ascribed to the gradual replacement of Na or K cations that were adsorbed on the SAPs with Ca and Mg cations released from the soil. The results suggest that addition of a small amount of SAP to soils (5 g kg(-1) soil) is more effective at increasing water holding capacity in soils with low clay content than in soils with high clay content.
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T he objectives of this study are to evaluate the effects of a hydrophilic polymer (Superab A200) on the growth indices of an ornamental plant (Cupressus ari-zonica) under reduced irrigation regimes in the field and on the soil water reten-tion curve in a laboratory. The RETC computer programme was used for obtaining optimum model parameters. Superab A200 in two levels, 4 and 6 g/kg, were mixed with two soil textures of clay and sandy loam, respectively. The results of the soil water retention model showed that, Superab A200 caused the residual water content (θ r) and saturated water content (θ s) to increase. Air entry value (h b) was observed to decrease in the clay and increase in the sandy loam. The results of the statistical analysis showed that there is a significant difference between samples containing Superab A200 and without hydrophilic polymer (the control) and the levels of polymer application. Available water content increases 2.3 fold of the control at maximum, with hydrophilic polymers application of 6 g/kg in sandy loam soil. The field trials were con-ducted as a split plot on the random complete blocks design in which the main plot treatments were two irrigation regimes consisting 33% and 66% evapotranspiration (ET c) and two sub-plot treatments were soils containing 4 and 6 g/kg hydrogel, respec-tively. The control blocks had no hydrophilic polymer and irrigated with 100% ET c . The results indicated that plant height, shoot diameter and length of green, are the same in treatments containing 4 and 6 g/kg Superab A200 and receiving irrigation water 66% ET c with the control. Thus, application of 4 and 6 g/kg hydrophilic polymer reduced the required water to 1/3 of the control. Application of Superab A200 can result in signifi-cant reduction in the required irrigation frequency particularly for light soil texture. This is an important issue in arid and semi-arid regions of the world.
Article
The levels of hydration of several hydrophilic polymers (hydrogels) varied greatly. Starch-based polymers had the fastest rate of hydration (<2 hours), followed by a propenoate-propenamide copolymer. Polyacrylamide materials required 4 to 8 hours to become fully hydrated. Maximum water retention in distilled water varied from 400 to 57 g of water per gram of dry material. All hydrogels retained less water in the presence of metal ions or fertilizers in the soaking solution, with substances releasing Fe ⁺² being the most detrimental. After exposure to fertilizers and ions, the water-holding capacity of a polyacrylamide with a high degree of cross linkage, but not that of hydrogels of the other structures, was fully recovered by subsequently soaking in distilled water. Pots amended with a polyacrylamide polymer but without Micromax (a micronutrient source) reached maximum water retention after six irrigations, while those with Micromax required 10 irrigations to reach peak water retention. The amounts of water being held in pots decreased after repeated fertilization. Medium volume increased with increasing levels of the polyacrylamide Supersorb C (0, 2, 4, or 6 g/pot). Micromax incorporated in medium amended with Supersorb C caused a depression in volume. Medium bulk density, total water retention, and water retention per unit volume of medium were increased by the incorporation of the hydrogel, regardless of the presence of Micromax. Noncapillary porosity measured at container capacity in medium amended with Micromax progressively decreased as the amount of hydrogel increased, but remained unchanged in medium without Micromax. Repeated drying and dehydration of the medium resulted in reduced water retention and increased noncapillary pore space.
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Hydration of three commercial hydrophilic polyacrylamide gels in deionized water ranged from 340 to 420 g per gram of gel. Hydration was progressively inhibited by fertilizer salt concentrations from 0 to 20 meq·liter ⁻¹ . Hydration of the gels in the presence of divalent cations (Ca ²⁺ and Mg ²⁺ ) and monovalent cations (K+ and NH 4⁺ ) at 20 meq·liter ⁻¹ was reduced to ≈10% and 20% of maximum, respectively. The valence of the accompanying anion did not affect hydration. Gel hydration was unaffected by urea over the range of 2 to 20 m m . Sequential rinses of the hydrated gels with deionized water completely reversed the inhibition due to the monovalent, but not the divalent, cations. The electroconductivity (EC) of the external solution increased during gel hydration. In the presence of fertilizer salts, the physical properties of a 2 redwood sawdust : 1 sand (v/v) container mix were unaffected by hydrophilic gel additions of 1.2 and 2.4 kg·m ⁻³ (1 × and 2 × the recommended rate, respectively).
Article
The irrigated sandy soils in the arid regions have limited water retention capacity. A laboratory study was conducted on a sandy soil to investigate the effect of a gel-forming soil conditioner (Jalma) on the soil water retention relationship (ψ-θ), soil water diffusivity (D(θ)), and saturated hydraulic conductivity (KS). Zero, 0.2, 0.4, and 0.8% of Jalma (J) were uniformly mixed with a sandy soil (Typic Torripsamments). The soil water distribution, horizontal wetting front advance (X), and infiltration (I) were measured. The results indicate: (1) the available water content increased exponentially with increasing J, but KS decreased exponentially with increasing J; (2) the X and I decreased with increasing J, and their relationships with time can be described by power functions; (3) the D(θ) increased with increasing θ and decreased with increasing J. Two approaches were taken to calculate K(θ) by using: (1) the D(θ) functions and the complete θ-ψ relationship, and (2) the measured KS and a limited range of the θ-ψ relationship. The two approaches were found to be comparable, but the second approach is recommended since it required simpler and available data. The calculated K(θ) increased with increasing θ and decreased with increasing J. Generally, this study revealed that the addition of gel-conditioner improved the hydraulic properties of sandy soil and that the best rate of Jalma is 0.4%. This addition rate limited deep percolation losses while maintaining adequate infiltration and water retention characteristics.
Article
Research to minimize mortality and enhance early growth during the re-establishment of eucalypts includes the use of optimum growing stock and planting techniques, the application of adequate volumes of water at planting (where appropriate), correct fertilizer application and placement, and optimum environmental conditions at planting. The use of hydrogels at planting, Stockosorb® 400K in particular, has also shown improvements in seedling survival and initial growth when planted under adverse conditions. The reformulation of this hydrogel through the addition of plant nutrients (Aquasoil™) was marketed to enhance initial growth whilst retaining the inherent benefits of the hydrogel component. Whether Aquasoil™ could replace the use of a granular fertilizer thus needed to be tested. Three field trials were implemented covering a range of soils, climates and eucalypt species to compare the effect of Aquasoil™ together with various planting practices, including those of planting with, or without water, or Stockosorb® 400K (water and Stockosorb® 400K treatments were also tested with or without the application of a granular fertilizer) on eucalypt survival and initial growth. Results from these trials indicated that: i) planting without water generally resulted in poorer survival and growth, ii) although planting with water improved survival, growth was inconsistent and not always the best, iii) the application of a hydrogel (Stockosorb® 400K) consistently increased seedling survival and initial growth during sub-optimal planting conditions, iv) the surface application of granular fertilizer (whether used in combination with water or a hydrogel) at planting produced the fastest and largest growth responses of all treatments, and v) the use of Aquasoil™ (hydrogel combined with nutrients) to significantly improve survival and initial growth produced inconsistent results when compared to the application of a hydrogel only (no additional nutrients added).
Article
To ensure acceptable survival and growth of Eucalyptus grandis clonal material planted in the sandy clay loam soils of the Zululand interior of South Africa, the current planting season is limited to the summer rainfall period. A field trial was initiated with the primary objective of being able to successfully extend the planting period (May to September) within which Eucalyptus grandis clones could be planted. This was done by testing tree growth and survival by the addition of a soil-amended hydrogel (Stockosorb 400K) and comparing it to traditional water planting methods. Five levels of water (0 ml, 500 ml, 1000 ml, 2000 ml and 4000 ml) were combined with five levels of hydrogel (0 g, 3 g, 6 g, 9 g, and 12 g) and applied to the pit at planting in a 5x5 factorial design. The tree variates of mortality, height, groundline diameter, crown diameter, corrected leaf surface index (LSI c) and corrected biomass index (BI c) were assessed at 7, 47,86 and 118 days after planting.
Article
The water-retaining properties of four hydrogels were examined in distilled water, tap water and in various nutrient solutions. Dissolved salts had a significant effect on the water retained by hydrogels. High-quality tap water reduced absorbing capacity by an average of 30% and nutrient solutions by up to 75% compared with distilled water. Iron in the form of iron sulphate reduced absorbing capacity by a greater amount than chelated iron. A starch-based hydrogel incorporated in a peat moss, sand and rice hull medium at rates up to 1 kg m−3 had no effect on the final shoot dry weight (SDW) or time taken to wilt of petunia. An acrylamide co-polymer hydrogel incorporated at rates up to 500 g m−3 also had no effect either on the SDW or time taken to wilt of marigold. Potting media, however, did have a significant effect on SDW and wilting time, and media were ranked with respect to both parameters. Media containing 25–50% pinebark, or a peat, sand and rice hull medium had higher rankings than 50:50 (v/v) peat:sand or peat:perlite media and were considerably cheaper than the latter. A medium containing peat and polystyrene foam (60:40) had a lower ranking than all other media.
Article
This work focuses on synthetic polymeric materials that are designed to function as soil conditioners. A classification of the various polymeric soil conditioners is given and a historical review is attempted. One hundred and three examples are examined, covering the period from 1950 up to today. The routes followed for the preparation of a synthetic polymeric soil conditioner are discussed. In this way, materials and/or properties are tailored for certain applications. Water‐soluble, water‐insoluble (crosslinked or hydrophobic), ionic, or non‐ionic conditioners are examined and pictures of their shapes are given. Finally, a discussion on the combination(s) of materials and/or properties outlines the future trends of this topic. Interpenetrating networks, blends of soil conditioning polymers, polymers combined with slow‐releasing compounds as well as transformable materials are included by examining certain works that are concerned with such materials presenting combined properties that are used in specific applications.
Article
This reviews 509 articles via 505 refs. cover the period 1906–80. It surveys acrylamide preparation, polymerization by radiation and handling. A cheap method for PAM production is prospected.Chemical and technological means of solving tillage problems, soil reclamation and arable land creation are reviewed. The role of PAM on soil physico‐chemical properties, irrigation requirements and crops yield is discussed. Modification of PAM for imparting chemical and bacteriological fertilities besides conditioning soils is also prospected. This possibly creates cheaply arable fertile lands.
Article
Water retention and hydration rate of Aquasoil and Stockosorb polymers, the effects of these polymers on the water, ammonium and nitrate retention of a pine bark growth medium and the response of the polymers to fer- tilizer solutions were investigated. Aquasoil retained 129 g of distilled water g"1 of polymer, whereas Stockosorb retained 216 g"1 of polymer. Both polymers reached their maximum capacity in about one hour. The polymers when combined with 1 or 2 g 500 g"1 of pine bark, improved the water retention capacity of the growth medium. However, longer time was required in the growth medium for the polymers to reach maximum capacity than in the distilled water. All polymer-amended pine bark media retained more ammonium, compared to non-amended media. The 2 g polymer treatment retained greater amounts of N03 than the lower rates. Retention of water by the Aquasoil® and Stockosorb® polymers was reduced to 88% and 86% of capacity compared to distilled water, whereas fertilizer solution reduced water retention to 53% and 42% of capacity. Soaking in distilled or tap water improved water retention of the polymers over fertilizer solutions.
Article
Available soil moisture and quality of planting material are two important criteria affecting survival during plantation establishment. It has been observed that in northern NSW most seedling deaths occur within the first four weeks of planting. Reducing the rate that plants become stressed is important as less-stressed plants are more capable of exploiting available soil moisture required for survival beyond this four-week period. The health (leaf gas exchange, visual symptoms of leaf and stem wilt) and survival of Eucalyptus pilularis Smith seedlings and cuttings were examined following the application of water in the form of either a hydrogel solution or as irrigation. The main findings were that the rate at which stress developed was slower for cuttings than for seedlings; and that supplying more water, either as hydrogel or irrigation, reduced transplant stress and prolonged survival. Differences in morphology between seedlings and cuttings may explain why cuttings developed stress more slowly than did seedlings. Compared with seedlings, cuttings had reduced leaf area, an increased root : shoot ratio and lower leaf area : root dry mass ratio, all of which are traits that enhance water uptake and reduce water loss. The most effective treatments for reducing stress of seedlings and cuttings were either removing individual seedlings or cuttings from nursery trays and dipping the root ball into a 100% saturated hydrogel solution which coated it with a layer of saturated hydrogel, or supplying the equivalent volume of water as irrigation when transplanting the plants. Drenching nursery trays in 25% and 50% unsaturated hydrogel solutions prior to the removal of the plants delayed stress of transplanted cuttings to a similar extent as the 100% saturated hydrogel solution, but these solutions were ineffective in delaying stress in seedlings. It is thought the more open structure of the soil medium used for cuttings allowed the unsaturated hydrogel solutions to enter the root-ball during root drenching, and because the hydrogel solutions are more viscous than water the drainage of the solutions after removing the nursery trays from the root drench was reduced.
Article
In order to ensure the adequate survival of Eucalyptus grandis clonal hybrids on the sandy soils in the Zululand region of South Africa, seedlings are planted with large volumes of water (5 litres per planting pit). This results in a limited planting season, together with high establishment costs. A field trial was initiated with the primary objectives being to test whether tree growth and survival was affected by the volume of water added at planting, and to determine how this would be affected by the addition of a soil amended hydrogel (Stockosorb 400 K). Five levels of water (0 ml, 250 ml, 500 ml, 1000 ml and 5000 ml) were combined with five levels of hydrogel (0 g, 3 g, 6 g, 9 g and 12 g) and applied to the pit at planting in a 5 x 5 factorial treatment design. The trial was planted in summer (23 November 1998) with the tree variates of mortality, height, groundline diameter, corrected leaf surface index (LSIc) and corrected biomass index (BIc) being assessed at regular intervals. There was a highly significant (P>0,01) response of tree survival to the application of water, but not to the application of the hydrogel, this despite a significant rainfall event (146 mm) that occurred two days after planting. This response was quadratic (p > 0,001) with no further significant increase in survival above 500 ml of water. Both the variates LSIc and BIc indicated that growth was significantly enhanced with increasing levels of water or hydrogel. Optimum tree performance was found to occur at 1000 ml of water and 9 or 12 g of hydrogel. There was a 39,8% and 23,7% increase in the LSIc for water and hydrogel when comparing the best level against the worst, and a 24,8% and a 15,6% increase in BIc for water and hydrogel. Results from this trial indicate that increasing levels of water applied at planting had a positive impact on seedling survival. The lack of the expected response in terms of seedling survival with increasing levels of hydrogel could possibly be attributed to the significant rainfall event that fell two days after trial initiation. Increasing levels of both water and hydrogel resulted in enhanced growth. Further field trials have already been implemented under less favourable climatic and site conditions so that the full impact of the hydrogel on seasonal and un-seasonal planting can be more clearly understood.
Article
The effect of 0.0 (control), 0.1, 0.2, 0.4, and 0.6% of the hydrophilic polymer "Stockosorb K-400" hydrogel (HG) on survival and growth of buttonwood (Conocarpus erectus L.) seedlings grown in sandy soil under drought stress was investigated. The ability of the soil to retain water increased with increasing hydrogel concentrations. The highest level of the HG was capable of changing the typical sandy soil to a loam or even silty clay in terms of water potential and water content. The highest HG concentration prolonged the time of water loss from the soil by about 66% more than the control soil. During drought stress, the seedlings grown in 0.6% HG-mixed soil survived three times as long as those grown in the control soil. Shoot and root growth increased significantly in HG-amended soil as compared with non-amended soil. Plant water potential increased significantly with HG application, thus it aided in the establishment and growth of C. erectus seedlings under water stress conditions. There were no significant differences between 0.4% and 0.6%. The study indicated that an amendment of soil with 0.4% to 0.6% of the hydrophilic polymer "Stockosorb K-400" can be used in arid and semi-arid areas to enhance the drought tolerance of C. erectus seedlings.
Article
Tree seedlings are planted on sites of widely differing climatic, edaphic and vegetative characteristics. Seedling transplant shock, defined as seedling mortality or impaired growth soon after planting, has been reported across this spectrum of planting conditions. Thus, transplant shock is used to describe a phenomenon that embraces many distinct physiological responses to stress. This review lists and discusses the potential sources of transplant shock for containerised tree seedlings and suggests options for minimising its detrimental effects for a range of specific causes. Through an understanding of the physiological basis underlying transplant shock under a given set of conditions, it may be possible to eliminate, or at least minimise, the effects of transplant shock on containerised tree seedlings soon after planting.
Article
Batches of 2 + 0, bare-root lodgepole pine (Pinus contorta Dougl.) and white spruce (Picea glauca (Moench) Voss) seedings differing in provenance, lifting date, or nursery of origin varied greatly both in root growth capacity (RGC) as measured by a laboratory assay and in early survival and growth after field planting. Most of the variation in field performance was accounted for by the variation in RGC. The lateral roots of lodgepole pine seedlings were pruned chemically by raising them in containers coated on the inside with cupric carbonate in latex paint. When field planted, the chemically root- pruned stock grew appreciably faster than control stock raised in unpainted containers. The difference in growth rate was associated with a difference in root form 4 years after planting.
Article
We have investigated the effect of storage conditions (duration: 1, 8 or 15 days; temperature: 4C or 10C) and root coverage [bare root (BR) or soil-plugged root (PR)] on the water status, electrolyte leakage and root growth potential (number of new roots and new root length) of radiata pine (Pinus radiata D. Don) seedlings. We have also examined the effects that storage causes on plant quality and initial survival potential and their usefulness for detecting physiological damage to seedlings. We observed a gradual decrease of seedling water status and an increase in electrolyte leakage, both in root and shoot, with duration of storage, the latter indicating damage to membranes. Both storage temperature and duration influenced the ability of radiata pine seedlings to initiate and elongate new roots. The effect was more pronounced in BR than in container seedlings, suggesting that the rooting-plug medium provides protection against desiccation. The close relationship (r=0.923, P<0.05) between root growth potential and predawn xylem water potential before transplanting shows that water potential at the time of transplanting is a reliable predictor of the ability to generate new roots. Finally, we have observed a close relationship between survival and parameters such as electrolyte conductivity, post-storage water potential, new root length and root growth potential.
Article
The effect of an amendment of a sandy soil with superabsorbent hydrogels (Stockosorb K 400, a highly cross-linked polyacrylamide with about 40% of the amide group hydrolysed to carboxylic groups) on the survival of Pinus halepensis seedlings during water stress was studied, with the following concentrations added to the soils: 0.04%, 0.08%, 0.12%, 0.20%, and 0.40%. The water retention of the soil increased exponentially with increasing additions of hydrogel to the soil. The highest concentration used changed the water retention capacity and its change in water potential with regard to its water content from a typical sand to a loam or even silty clay. During desiccation under controlled conditions, the seedlings treated with 0.4% hydrogel survived twice as long in the soils amended with 0.4% hydrogel as in the control soils. During the drought, the seedlings exhibited a pronounced growth both of the shoot and the roots, which was about three-fold higher than the one of the plants in the control soils. The data indicate that an amendment of soils with this type of hydrogels at 0.4% (w/w) will greatly enhance the drought tolerance of the seedlings growing on this substrate. A comparison between the reaction of the plants in the hydrogel amended soils and the pF-curve measured with the plate test revealed that less water was actually available for the plants, as could be expected from the pF-curves.
Article
Plantation establishment requires high survival of transplanted seedlings. The experiments described in this paper examined methods to reduce death of Eucalyptus pilularis Smith and Corymbia citriodora subsp. variegata (F. Muell.) A.R. Bean & M.W. McDonald seedlings shortly after planting. Two products were tested: a fine grade water-retention hydrogel was examined as a means of providing water to seedlings, and a kaolin clay particle film mixture sprayed onto leaves was examined as a means of reducing leaf heating and dehydration. Both products were tested in a field and a glasshouse situation. Seedlings were planted with a pottiputki for field experiments or a hand trowel for glasshouse experiments. Seedlings were not watered in the glasshouse trial. Hydrogel was applied by immersing the seedlings’ root plug in a fully hydrated solution of hydrogel prior to planting which supplied each seedling with an additional 20 g weight corresponding to 20 ml of water. Kaolin clay particle film was applied by coating the leaves prior to planting. Field trials showed the majority of seedling death occurred between 1 and 4 weeks after planting with seedling health improving during this period following rainfall events. Five months after planting in the field hydrogel-treated seedlings had 12 and 5% death in E. pilularis and C. citriodora subsp. variegata seedlings compared to 26 and 14% death, respectively in control seedlings. The glasshouse trial showed hydrogel-treated seedlings remained healthier for longer. Hydrogel enhanced seedling survival because it provided extra moisture to seedlings, or it promoted contact between the root plug and the bulk soil. Kaolin clay particle film showed a non-significant trend of improving survival of field planted seedlings. There was also a non-significant trend indicating that kaolin clay delayed death of C. citriodora subsp. variegata seedlings when time between application and planting was increased. Species attributes such as presence of lignotubers and smaller leaf area in C. citriodora subsp. variegata than E. pilularis may account for its higher survival, although seedling morphology could not easily be related to seedling survival.
Article
An important window of opportunity to increase and sustain productivity in short-rotation plantations is the period from felling through re-establishment to canopy closure. This paper explores the effects, interactions and response mechanisms of intensive silvicultural practices on plantation productivity and sustainability, using five South African case studies (a–e). (a) Land preparation trials showed that complete surface cultivation by ploughing had a significant beneficial effect when afforestation is done for the first time in grasslands, improving basal area growth by 11–52% over pitting only. However, similar treatments have not resulted in significant growth responses under re-establishment conditions. (b) Stand growth suppression resulting chiefly from soil compaction during mechanised harvesting operations is strongly related to soil type, soil textural class and residue management options. Volume growth reduction in short-rotation eucalypt crops ranged from 25% on compaction sensitive loamy soils to less than 2% in resistant sandy soils. (c) The response mechanism whereby vegetation management improves stand productivity is a reduction in both inter-specific and intra-genotypic competition for resources, as well as a decrease in stand variability. Operationally, the most important criteria in a vegetation management programme relate to the timing of control operations across diverse site conditions. In local trials, the primary factors controlling the time taken for competition-induced tree growth suppression to occur were related to altitude, slash burning and the interaction between these factors, which facilitated the development of regional vegetation management strategies. (d) Empirical fertilizer trials in short-rotation hardwood stands have shown significant improvements in final productivity (commonly 20–90 m3 ha−1 in eucalypts and 30–50 m3 ha−1 in Acacia), as well as wood density (15–30 kg m−3 for eucalypts) following improvements in early nutrition. Improved nutrition was achieved through fertilization at planting or indirectly through residue management. The response mechanism is primarily due to early canopy development and associated increases in light capture, coupled with a more modest increase in canopy quantum efficiency and above-ground carbon allocation on a dry site. On sites with abundant water supply, increased quantum efficiency is likely to be the dominant response mechanism. (e) A series of operational gains trials tested the interactive effect of genetic tree improvement, site–genotype interaction, stand density and vegetation management + fertilization on eucalypt stand growth across five sites. There were no significant interactions between factors, but importantly, the results were additive, emphasizing the need to optimise each practice in the value chain to achieve maximum productivity.
Seedling processing, storage and outplanting. Agriculture Handbook 674
  • G A Ritchie
  • T D Landis
Ritchie GA, Landis TD. 2010. Assessing plant quality. In: Landis TD, Dumroese RK, Haase DL (eds), The container tree nursery manual. Vol. 7: Seedling processing, storage and outplanting. Agriculture Handbook 674. Washington, DC: US Department of Agriculture, Forest Service. pp 17-80.