Deslocamento vertical de fósforo em condições controladas
Abstract
A aplicação de esterco bovino curtido é a forma mais comum de fertilização em sistemas de produção de agricultura familiar. No entanto, o modo de aplicação desta fonte orgânica é realizado sem muito controle o que contribui para o processo de lixiviação de nutrientes que podem contaminar o lençol freático. Objetivou-se avaliar o deslocamento vertical do fósforo (P), em um solo de textura arenosa sob adubação de longo período com esterco bovino, em condições de laboratório. O solo estudado foi coletado no município de Remígio - PB, em áreas de produção características de agricultura familiar onde a mais de 20 anos é realizada a adubação com esterco bovino curtido. O solo foi classificado como Neossolo Regolítico eutrófico. Utilizou-se o método de deslocamento miscível com utilização de colunas de solo e bomba peristáltica. Os parâmetros de adsorção e dessorção foram estimados pelo programa Sigma Plot 10, utilizando regressão não linear. Por intermédio das curvas de eluição do P identificou o mecanismo do processo de transporte do P e determinou os parâmetros hidrodispersivos por meio dos modelos convecção-dispersão (CDE), intermédio do programa CXTFIT 2.0. Os elevados coeficientes de correlação obtidos, a partir das equações linearizadas de Langmuir e Fleundlich, indicam que os modelos de adsorção foram significativamente capazes de estimar a adsorção de P nos solos, estimou-se uma perda de mais de 1 Kg/ha de P, nas camadas mais profundas. Os resultados obtidos mostram que a adubação com esterco bovino, em solo arenoso, oferece risco real de contaminação das águas subterrâneas da região
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This study was carried out from 1995 to 1996 at the the Laboratory of Irrigation and Salinity of the Department of Agricultural Engineering of the CCT/UFPB. The effects of the Primavera bentonite, from Boa Vista municipality, Paraíba state on the soil chemical properties, were evaluated in samples of a eutrophic rhegosol. Such soil samples of 0 - 20 cm depth were incubated for 120 days with doses of bentonite equivalent to 0, 30, 60 and 90t ha-1. After that, the chemical alterations were evaluated in the samples of the soil . The bentonite did not influence the levels of the exchangeable K and Al and available P, but increased soil pH and exchangeable Ca, Mg, Na and CEC. The results showed that the use of the bentonite Primavera increased the pH corresponding to the soil's ZPC.
Key words:
bentonite; eutrophic rhegosol; chemical properties
Hernani, L.C.; Freitas, P.L.de; Pruski, F.F.; De Maria, I,C.; Castro Filho, C.; Landers, J.N. A erosão e seu impacto. In: Manzatto, C.V.; Freitas Junior, E.; Peres, J.R.R. (eds.). Uso agrícola dos solos brasileiros. Rio de Janeiro, Brasil: Embrapa Solos, 2002. 174 p. [ISBN: 85-85864-10-9]. Cap. 5. pp. 47-60.
Disponível em www.alice.cnptia.embrapa.br/alice/bitstream/doc/328096/1/usoagricolasolosbrasileiros.pdf
Phosphorus (P), an essential nutrient for crop and animal production, can accelerate freshwater eutrophication, now one of the most ubiquitous forms of water quality impairment in the developed world. Repeated outbreaks of harmful algal blooms (e.g., Cyanobacteria and Pfiesteria) have increased society's awareness of eutrophication, and the need for solutions. Agriculture is regarded as an important source of P in the environment. Specifically, the concentration of specialized farming systems has led to a transfer of P from areas of grain production to animal production. This has created regional surpluses in P inputs (mineral fertilizer and feed) over outputs (crop and animal produce), built up soil P in excess of crop needs, and increased the loss of P from land to water. Recent research has shown that this loss of P in both surface runoff and subsurface flow originates primarily from small areas within watersheds during a few storms. These areas occur where high soil P, or P application in mineral fertilizer or manure, coincide with high runoff or erosion potential. We argue that the overall goal of efforts to reduce P loss to water should involve balancing P inputs and outputs at farm and watershed levels by optimizing animal feed rations and land application of P as mineral fertilizer and manure. Also, conservation practices should be targeted to relatively small but critical watershed areas for P export.
A produtividade em sistemas agrícolas de subsistência depende do nível de fertilidade natural do solo. Em condições de relevo forte ondulado, espera-se que a fertilidade do solo se modifique não apenas pelo tipo de uso mas, também, devido à sua posição no relevo. Para avaliar essas modificações, 260 amostras simples de solo (0-20 cm) da microbacia Vaca Brava, PB, representando combinações de três usos do solo, cinco posições no relevo e cinco classes texturais, foram analisadas quanto aos teores de P disponível, bases e acidez trocáveis. Ca e Mg compreenderam 75-80% dos cátions trocáveis, K e Na, de 10 a 15%, e H+Al, 10%; o valor de pH médio foi 5,5, enquanto P Mehlich-1 foi, em média, 3,8 mg kg-1 solo. Apesar dos efeitos significativos (p < 0,05) de uso, relevo e textura nos teores de alguns nutrientes, de forma geral a bacia pareceu relativamente uniforme. A principal diferença entre os usos decorreu da adição de esterco em áreas de roçado e capineira localizadas, preferencialmente, em áreas de pedimento e várzea. Ao redor de 80% das amostras apresentaram teores baixos de P enquanto 70% mostraram teores médios de K; entretanto, utilizando-se o índice K/(Ca+Mg)0,5 conclui-se que a quase totalidade das amostras se apresentou deficiente em K.
Com o objetivo de se quantificar o teor de fósforo no efluente de colunas com agregados de um Latossolo Vermelho distrófico em resposta ao tempo de difusão, realizou-se um experimento utilizando-se água destilada, extrator Mehlich-1 (HCl 0,05 mol -1 + H2SO4 0,0125 mol L-1) e solução de acetato de amônio 0,1 mol L-1, a pH 7, como eluentes. Os tratamentos corresponderam a um arranjo fatorial 4 x 5, sendo quatro classes de agregados (2,0-1,0; 1,0-0,5; 0,5-0,25 e 0,25-0,105 mm) e cinco tempos de difusão (0, 1, 2, 4 e 6 dias). As colunas receberam um volume de eluente igual a dez vezes o seu volume de poros, recolhendo-se cinco frações de efluente, cada uma de dois volumes de poros. Nas unidades experimentais correspondentes ao tempo de difusão zero, o volume do líquido foi aplicado de uma só vez, enquanto nas restantes foram realizadas eluições com dois volumes de poros, nos intervalos indicados para cada tempo de difusão. A água destilada eluiu maior quantidade de fósforo dos agregados de menor tamanho e teve incrementada a quantidade do fósforo eluído com o tempo de difusão. O extrator Mehlich-1 eluiu de três a sessenta vezes mais fósforo que a água destilada, mostrando comportamento inverso ao da lixiviação com água, em relação à classe de agregados e ao tempo de contato. As quantidades de fósforo eluídas com solução de acetato de amônio foram tão pequenas que não atingiram a concentração mínima necessária para permitir sua detecção.
A new and relatively simple equation for the soil-water content-pressure head curve is described. The particular form of the equation enables one to derive closed-form analytical expressions for the relative hydraulic conductivity, when substituted in the predictive conductivity models of N. T. Burdine or Y. Mualem. The resulting expressions contain three independent parameters which may be obtained by fitting the proposed soil-water retention model to experimental data. Results obtained with the closed-form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties.
Pastures cover nearly 50 million hectares in the Cerrado region. The Oxisols, which cover approximately half this area, are highly weathered soils composed mainly of kaolinite, iron and aluminum oxides. Iron and aluminum oxides have a great influence on the retention of phosphorus (P) in these soils. The aim of this study was to quantify the total phosphorus levels, as well as P availability and retention in Oxisols under pasture in the Cerrado region and to relate the data with soil mineralogical, textural and chemical characteristics. The relations between the studied parameters were analyzed by principal component analysis and linear correlation analysis. The ion-exchange resin extractable P was negatively correlated with mineralogical and texture soil characteristics, and positively with soil organic matter contents. Both the total free and the poorly crystalline oxides were negatively correlated with equilibrium P (Prem). Gibbsite, goethite as well as the total free and poorly crystalline oxides were negatively correlated with Prem, indicating their effects on P adsorption to Cerrado Oxisols. Conversely, kaolinite was not significantly correlated with Prem. The negative correlation between Prem and total carbon (C total) was due to the linear increase of soil carbon with the clay and silt contents. The iron and aluminum oxides were the characteristics that most influenced Prem of Cerrado Oxisols.
Phosphorus fractions were determined in soil samples from areas fertilized or not with farmyard cattle manure (FYM) and in samples of FYM used in the semi-arid region of Paraiba state, Brazil. Soil samples were taken from the 0-20; 20-40 and 40-60 cm layers of 18 cultivated areas, which, according to interviews with farmers, had been treated with 12 to 20 t ha-1 FYM annually, for the past 2 to 40 years. Soil samples were also collected from four unfertilized pasture areas as controls. Phosphorus in the soil samples was sequentially extracted with water (Pw), resin (Pres), NaHCO3 (Pi bic and Po bic), NaOH (Pi hid and Po hid), H2SO4 (Pacid) and, finally, by digestion with H2SO4/H2O2 (Presd). Nine FYM samples were extracted with water, resin, Mehlich-1, H2SO4, NaOH or digestion with H2SO4/H2O2, not sequentially, and the extracts analyzed for P. The sampled areas had homogeneous, sandy and P-deficient soils; increases in total soil P (Pt) above the mean value of the control areas (up to 274 mg kg-1 in the 0-20 cm layer of the most P-enriched samples) were therefore attributed to FYM applications, which was the only external P input in the region. Regression analysis was used to study the relationship between soil P fractions and Pt. The Pacid fraction, related to Ca-P forms, showed the greatest increases (p
A calagem é uma prática comum para elevar o pH do solo e aumentar a biodisponibilidade de fósforo (P) nas regiões tropicais. Todavia, o efeito da calagem na adsorção e biodisponibilidade de fósforo tem sido relatado de forma controversa. A dessorção de fósforo é um processo mais importante do que a adsorção para definir a biodisponibilidade de fósforo. Apesar disso, poucos estudos sobre a relação entre pH do solo e dessorção de fósforo são disponíveis, sobretudo nos solos tropicais. Os efeitos do pH do solo na adsorção e dessorção de fósforo num Ultissolo da Bahia, Brasil, foram investigados. A adsorção de fósforo diminuiu até 21 e 34% com o aumento do pH de 4,7 para 5,9 e 7,0, respectivamente. O parâmetro K da equação de Langmuir diminuiu e os coeficientes de partição (Kd) diminuíram junto com o pH, mantendo esta tendência. A dessorção de fósforo foi positivamente influenciada pelo aumento do pH, como reflexo da quantidade total de fósforo dessorvido e da taxa dessorvida do fósforo inicialmente adsorvido. O parâmetro K diminuiu e o valor de Kd aumentou, especialmente no valor de pH mais alto e no nível mais alto de adição de fósforo, reforçando a ocorrência do fenômeno. A calagem deste solo teve efeitos duplos de reduzir a adsorção de fósforo (até 4,5 kgha-1 de P na solução) e de aumentar a dessorção de fósforo (até 2,7kgha-1 de P liberado adicionalmente para a solução).
The objective of this work was to quantify changes on carbon and nutrient contents in soils under continuous manure additions. Eighteen cropped fields that had received annual additions of manure for at least two years and four fields under pasture with no history of manure addition were sampled to assess if this practice results in the accumulation or losses of added nutrients. Soils samples from the 0-20, 20-40 and 40-60 cm layers were taken from each field, and analyzed with regard to their physical (particle size and soil density) and chemical (pH, total C, N and P, extractable P by Mehlich-1 and water, and exchangeable cations) properties. Manure samples used in nine fields were also analyzed for chemical composition. Manure additions resulted in a build up of nutrient stocks near to 20 Mg ha-1 of C, 2 Mg ha-1 of N and Ca, and 0.5 to 1 Mg ha-1 of P, K and Mg (0-60 cm). Water-soluble P concentrations of 7 mg kg-1 in the 40-60 cm layer indicated losses of this nutrient, the less mobile in soils. Accumulation of exchangeable cations in the 0-60 cm layer, in comparison with control areas, indicates an even greater potential for losses of these nutrients.
O objetivo deste trabalho foi avaliar as alterações na atividade da biomassa microbiana como um indicador da dinâmica de C e N em solo submetido à sucessão de cobertura vegetal e de manejo na Amazônia Ocidental. Ostrabalhos foram realizados em duas cronosseqüências: CA sucessão floresta primária e cupuaçuzal (Theobroma grandiflorum) de três anos e CB sucessão floresta primária, pastagem de Brachiaria humidicola de oito anos e cupuaçuzal de três anos. A sucessão floresta primária-pastagem-cupuaçuzal afeta negativamente o estoque de C do solo, com diminuição significativa da matéria orgânica e do C da biomassa microbiana do solo, ao passo que na sucessão floresta primária-cupuaçuzal ocorre diminuição apenas do C da biomassa microbiana. Afloresta primária apresenta menor quociente metabólico e maior relação C/N da biomassa, o que resulta em menor perda de carbono. ON da biomassa microbiana na camada de 010cm, independentemente do manejo adotado, aumenta significativamente na área de cupuaçuzal, ao passo que o N total diminui. A concentração de amônio no solo diminui com a profundidade, de modo oposto ao verificado com o nitrato.
This experiment aimed at the evaluation of imazaquin sorption and transport in soils with different chemical, physical and mineralogical characteristics using batch and miscible-displacement techniques. The experiment was carried out with Neossolo Quartzarênico (RQ), Latossolo Vermelho-Amarelo (LVA) and Latossolo Vermelho distroférrico (LVdf) soils which were air-dried, passed through a 2 mm sieve and followed by chemical, physical and mineralogical characterization. A CaCl2 solution was applied in the miscible displacement experiment for the establishment of a Cl- elution curve that was used as tracer. The curves were adjusted to a model based on the convection-dispersion equation for ideal transport. Then a 14C-imazaquin solution was applied and the elution curves for this molecule obtained. The curve was adjusted to a bicontinuum model that considers non-equilibrium during the transport. In order to obtain the isotherms adjusted by Freundlich equation in the sorption experiment through the batch method, a radiolabel imazaquin solution was used with concentrations varying from 0.67 to 10.72 mmol L-1. The leaching was high for all soils and highest for the RQ soil. The Cl- elution curves were symmetric for all soils and adjusted well to the model that considers the ideal transport, showing that there was non-equilibrium related to the transport. The imazaquin elution curves were asymmetric with extension of the posterior part of the curve and well adjusted to the bicontinuum model, evidencing the occurrence of non-equilibrium in the sorption process. The sorption coefficient determined by the batch method was higher than the miscible displacement method. This result demonstrates that sorption in the leaching process can be overestimated by methods that assume chemical equilibrium during the sorption process.
Visou-se, com o presente estudo, avaliar os efeitos de seis anos de adubação orgânica sobre as características químicas de um Neossolo Regolítico cultivado com batata. Os tratamentos de adubação orgânica foram: 1) esterco (15 t ha-1); 2) cultivo e incorporação da Crotalaria juncea L.; 3) combinação de metade da dose de esterco (7,5 t ha-1) com o cultivo e incorporação da Crotalaria juncea L. e 4) testemunha, sem fertilização. Os ensaios de adubação orgânica e cultivo da batata foram realizados no período de 1996 a 2003, com exceção de 1998 e 1999, devido à escassez de chuvas. Ao final de 2003 amostras de solo coletadas nas camadas de 0-20 e 20-40 cm de profundidade foram analisadas. A aplicação anual de esterco, combinado ou não com a crotalária, elevou os teores de CO, N e P totais, e Zn na camada de 0-20 cm de profundidade, e os teores de P e K extraíveis, Mg e B nas duas camadas avaliadas. O cultivo e a incorporação anual da crotalária não exerceram efeito significativo nos teores de nutrientes do solo. Os resultados sugerem que a utilização de doses menores de esterco, combinadas com a incorporação de adubos verdes pode garantir a manutenção da fertilidade do solo em longo prazo.
Knowledge on the phosphorus capacity factor (PCF) of soils of the state of Paraíba is important to improve the interpretation of the available phosphorus (P) content and the recommendation of phosphate fertilization in soils of the State. The objective of this study was to evaluate the parameters of P adsorption isotherms (Langmuir and Freundlich) by the techniques of non-linear regression and linearization, in soil samples of the state of Paraíba, and to correlate the values of these parameters with chemical and physical soil properties. Samples of 12 representative soils of the state of Paraíba were collected in the 0-30 cm layer (six soils with a higher and six with a lower weathering degree), with a wide variation of values of physical and chemical properties within each group of six soils. The hyperbolic model of the Langmuir isotherm was adjusted by the technique of non-linear regression (single region) and of linearization (first region and second region). Correlation analyses were performed with the values of isotherm parameters and soil properties that reflect the FCP. In all soils, the model adjusted by non-linear regression fitted the data best, in comparison with the same model adjusted by linearization. In the most weathered soil group, the values of maximum adsorption capacity of phosphate (CMAP) were highly correlated with the contents of remaining (equilibrium) phosphorus (r = -0.95**), free Fe oxyhydroxides (r = 0.90**) and water retention (r = 0.88**), but did not correlate with the clay content (r = 0.64ns). Within the group of less weathered soils, the CMAP values were correlated with the contents of equilibrium phosphorus (r = -0.99**), water retention (r = 0.93**) and clay content (r = 0.97**), but did not correlate with free Fe oxyhydroxides (r = 0.10ns).
La materia orgánica de suelos tropicales se separó en diferentes fracciones de acuerdo con aspectos fisicoquímicos directamente ligados a la dinámica de nutrimentos en el suelo. Para ello, se de- sarrolló una metodología para la extracción de carbono orgánico (Corg) ligado a los sitios de intercambio de suelos tropicales, selec- cionando los mejores extractores, cuantificando el C org extraído (Cext) y correlacionándolo con otras formas de carbono. Los sue- los se sometieron a la extracción por K 2SO4, Na HSO4 y KNO3. También se midieron las concentraciones de carbono soluble en agua (CSA), mineralizable (Cmin) y oxidable (Coxid) y se fraccionó la materia orgánica en compuestos orgánicos de bajo peso molecular: ácidos fúlvicos, ácidos húmicos y humina. Las sales neutras extractoras (K2SO4 y KNO3) no fueron eficientes para re- mover el Ca 2+ +Mg 2+ ABSTRACT Physical and chemical aspects were used to separate the soil organic matter in different fractions directly related to the dynamic of nutrients in the soil. To this end, a methodology to extract organic carbon (Corg) connected to the exchange sites of tropical soils was developed; selecting the best extractors, quantifying extracted C org from the exchangeable sites (Cext), and correlating it withothers C-forms. The soils were submitted to the extraction by K 2SO4, KNO3 and NaHSO4. Concentrations of water soluble carbon (WSC), mineralizable carbon (Cmin), oxidizable carbon (Coxid) and organic matter was fractioned in organic compounds of low molecular weight: fulvic and, humic acids and humin Neutral salts (K2SO4 and KNO3) were not efficient to remove Ca 2+ , Mg 2+ and organic carbon from the exchange sites. Due to the effect of hydrogensulphate to displace the Corg from the exchange sites and the Na+ to displace the Ca2+ and Mg2+, the NaHSO4 had a satisfactory result to estimate the C ext. The acidity of this reagent also contributed to increase its efficiency. The C min and Coxid presented a correlation with the more stable fractions of C org, mainly with the humin fraction. The Cext presented a correlation to the Corg fractions less stable and more dynamic as WSC and Cmin in the first stage. This result supports the hypothesis that the Cext is formed by very dynamic carbon fraction.
The hydrodispersive characterization of two soils: an Yellow Ultisol and a Vertisol, both from the region of São Francisco Valley, was performed through displacement experiments in soil column in the laboratory. The experiment consisted of displacement of a pulse of 1 pore volume of a 0.1 M KBr solution in saturated soil column under steady-state flow conditions. The hydrodispersive parameters (D, R) ware obtained by fitting the analytical solution of the convection-dispersion equation (CDE) and the two-region transport model - MIM (D, R, ¿ and ¿) for the points of the experimental breakthrough curve. The soil dispersivity was found to be higher in the Vertisol than in the Yellow Ultisol, because of the higher aggregation of this soil. The retardation factor (R) represented the tracer interactions with the soils: anionic exclusion in the Vertisol and bromide retention in the Yellow Ultisol, due to the presence of iron-oxydes (Goethite). The CDE model presented a better performance than the MIM model, for fitting the bromide breakthrough curves in both soil columns, suggesting the absence of immobile water in the Yellow Ultisol and the Vertisol.
Land use changes in the Everglades Agricultural Area (EAA) in southern Florida may influence the distribution and availability of P. Cultivated soils in the EAA are being converted back to their historic use as seasonally-flooded prairies as part of Everglades restoration projects. The objectives of this study were to determine the distribution of P in soil chemical fractions in relation to long-term land management to predict P cycling and transformations for future land uses. Soil under pasture (100 yr) and planted to sugarcane (Saccharum sp.) for 50 yr were amended with P (0, 10, 50, 150 kg P ha−1), and its distribution in labile, Fe–Al bound P, Ca-bound P, humic–fulvic acid P, and residual P pools determined for surface soil (0–15 cm). Most P fertilizer entered Fe–Al and Ca-bound fractions. Cultivation contributed to higher pH and increased the Ca content in soil compared to pasture due to incorporation of bedrock limestone into soil by tillage. The land uses were differentiated by P storage in different pools. Subsequently, long-term fertilization increased soil total P for cultivated soil relative to pasture, but plant-available P constituted less than 1% of the total P. Labile P increased with increasing P application rate, ranging from 1.3 to 7.2 mg kg−1 for cultivated soil and 1.4 to 10.7 mg kg−1 for pasture. Most of the applied P was recovered in the Fe–Al fraction for pasture and the Ca-bound P fraction for cultivated soil. The Ca-bound P fraction represented the greatest proportion of total P for sugarcane (41%), but only 12% for pasture. The majority of P in the pasture was present in the humic–fulvic acid fraction (45%), compared to only 23% for sugarcane. The higher pH of the cultivated soil (6.8) favored retention in Ca fractions while the lower pH of pasture (5.3) favored P retention in the humic–fulvic acid fraction. The proportion of total P as organic P was greater for pasture (78%) than cultivated soil (52%). Higher P levels in more recalcitrant fractions for cultivated soils indicated that more of the applied fertilizer P was sequestered in stable fractions, which decreased P availability to crops and may subsequently increase P fertilizer requirements necessary to maintain optimal plant-available nutrient levels. Subsequently, continuation of current farming practices and tillage regimes promotes the redistribution of Ca from subsurface to surface soil, which leads to greater P sequestration in the Ca-bound fraction. However, P in inorganic fractions may be released upon onset of changes in land use. Thus, conversion to seasonally-flooded prairies may have a more dramatic effect on P release from cultivated than pasture soils since cultivated soils have more P in inorganic pools.
This paper gives a review of our current conceptual understanding of the basic processes of water flow and chemical transport in the untsaturated (vadose) zone and of various deterministic mathematical models that are being used to describe these processes. During the past few decades, tremendous effort has been directed toward unravelling the complexities of various interactive physical, chemical, and microbiological mechanisms affecting unsaturated flow and transport, with contributions being made by soil scientists, geochemists, hydrologists, soil microbiologists, and others. Unfortunately, segmented, disciplinary research has contributed to a lack of experimental and theoretical understanding of the vadose zone, which, in turn, has precluded the accurate prediction and management of flow and contaminant transport through it. Thus a more unified and interdisciplinary approach is needed that considers the most pertinent physical, chemical, and biological processes operative in the unsaturated zone. Challenges for both fundamental and applied researchers to reveal the intricacies of the zone and to integrate these with currently known concepts are numerous, as is the urgency for progress inasmuch as our soil and ground water resources are increasingly subjected to the dangers of long-term pollution. Specific research areas in need of future investigation are outlined.
The reactions of phosphate with natural samples of allophane, ferrihydrite, hematite and goethite were measured for up to 30 d. The amount of phosphate sorbed on allophane showed the biggest increase with time whereas the amount sorbed on goethite showed the least increase with time. The total amount of phosphate sorbed either at high levels of phosphate addition or after 10 d followed the order hematite < goethite < ferrihydrite < allophane and was probably related to the specific surface. Si was desorbed as phosphate was adsorbed on the minerals.
The reactions of phosphate on allophane involved rapid, strong adsorption, probably at defect sites, followed by weaker adsorption, followed, probably, by disruption of the allophane structure together with precipitation of aluminium phosphates. Previous suggestions either of diffusive penetration of phosphate into surfaces or about the formation of aluminium phosphate coatings, are unlikely to hold for allophane, if all the Al is at the surface and if the structure can be ruptured.
The reactions of phosphate with iron oxides involved a rapid, strong ligand exchange, followed by weaker ligand exchange, and, probably, by a relatively slow penetration at defect sites and pores. Highly crystalline goethite has virtually no slow reaction and therefore solid-state diffusion of phosphate does not readily occur. The extent of phosphate uptake during the slow penetration reactions probably depends on the degree of crystallinity or porosity of iron oxides.
The most reactive adsorbents, such as allophane, ferrihydrite and Al-humus complexes do not have planar surfaces, and this needs to be considered when modelling phosphate reactions.
Normalmente, o esterco disponível nas propriedades no Agreste paraibano é insuficiente para a manutenção da fertilidade do solo enquanto a adubação verde com Gliricidia sepium é uma alternativa para aumentar a disponibilidade de nutrientes. Objetivou-se, no presente trabalho, comparar a dinâmica de mineralização de N após a incorporação de esterco bovino ou de ramas de gliricídia a um Neossolo Regolítico em condições de campo e laboratório. O experimento de campo constou de três tratamentos: incorporação de 20 t ha-1 de esterco bovino, de 15 t ha-1de ramas frescas de gliricídia e testemunha sem adições. Logo após as adições semeou-se milho e se acompanhou o N mineralizado in situ no campo, durante 120 dias, na camada de 0-15 cm e o N absorvido pelo milho. A mineralização de N no laboratório foi acompanhada durante 56 dias em amostras de solo das camadas de 0-15, 15-30 e 30-60 cm; as de 0-15 cm receberam esterco ou gliricídia em quantidades equivalentes às de campo. No campo foram mineralizados 74 kg ha-1 de N até a colheita (120 dias), sem diferenças significativas entre tratamentos. No laboratório, a gliricídia levou a uma rápida mineralização líquida de N enquanto o esterco bovino provocou imobilização nos primeiros 14 dias.
The effects of fumigation on organic C extractable by 0.5 M K2SO4 were examined in a contrasting range of soils. EC (the difference between organic C extracted by 0.5 M K2SO4 from fumigated and non-fumigated soil) was about 70% of FC (the flush of CO2-C caused by fumigation during a 10 day incubation), meaned for ten soils. There was a close relationship between microbial biomass C, measured by fumigation-incubation (from the relationship Biomass C = FC/0.45) and EC given by the equation: Biomass C = (2.64 ± 0.060) EC that accounted for 99.2% of the variance in the data. This relationship held over a wide range of soil pH (3.9–8.0).ATP and microbial biomass N concentrations were measured in four of the soils. The ratios were very similar in the four soils, suggesting that both ATP and the organic C rendered decomposable by CHCl3 came from the soil microbial biomass. The C:N ratio of the biomass in a strongly acid (pH 4.2) soil was greater (9.4) than in the three less-acid soils (mean C:N ratio 5.1).We propose that the organic C rendered extractable to 0.5 m K2SO4 after a 24 h CHCl3-fumigation (EC) comes from the cells of the microbial biomass and can be used to estimate soil microbial biomass C in both neutral and acid soils.
In this study possible correlations between physical and chemical properties and the maximum phosphorus adsorption capacity (MAPC) were evaluated in soils with low activity clay from different regions of Brazil, using samples from the surface (A) and subsurface (B) horizons of 16 soil profiles. The dosages for the determination of MAPC were calculated from the level of remaining phosphorus and they ranged from 0 to 135 mg L-1. From this data isotherms of P adsorption were built. Correlations were tested between MAPC and the clay content, organic carbon, ki, kr, specific surface, Al content determined by sulfuric acid attack, and content of different forms of extracted iron. A high variation in the values of MAPC for the surface horizon (48 to 1429 mg kg-1) and for the subsurface horizon (455 to 1667 mg kg-1) was observed. The correlation coefficients showed a significant association between MAPC and clay content, iron and aluminium determined by sulfuric acid attack and iron extracted by dithionite-citrate-bicarbonate (DCB). The multiple regression analysis showed a good fit to MAPC values based in soil attributes.
This paper reviews the most important methods used to characterize the porosity of styrene-divinylbenzene resins. Methods such as adsorption of nitrogen for determination of surface area and mercury intrusion porosimetry for characterization of pore size distribution are related.
Soils under subsistence farming in semi-arid northeastern Brazil are showing progressive declines in soil fertility. In this study, we assessed the effects of subsistence farming on losses of organic nutrient pools in 10 independent sites that were distributed in five districts of two states. Each site had adjacent areas under dry forest and subsistence farming. Areas under each land use were separated in two groups that had different degrees of land degradation. Group assignment was based on land use history and visual observations of vegetation-soil degradation and was further evaluated using 137Cs activity to estimate erosion. Four combinations of land use degradation were defined: undisturbed (UDF) and disturbed (DDF) dry forest, and preserved (PC) and degraded (DC) cultivated land. Soils were sampled in the 0- to 7.5- and 7.5- to 15-cm layers. The 137Cs concentrations declined in the order UDF > DDF ≈ PC > DC. Soil C and N concentrations in DC (8.9 and 0.94 g kg-1 soil, respectively) were half of those in UDF (17.8 and 1.51 g kg-1 soil, respectively). The organic P (P 0)/ inorganic P (Pi) ratio was 1.47 in UDF and decreased to 0.82 in PC and DC. Carbon losses in DC were attributed to erosion (43%) and to mineralization (57%) processes. Differences between UDF and other land uses were greater in the 0 to 7.5 cm than in the 0- to 15-cm layer. Carbon and N losses in low-P status soils, in addition to limited water availability and unsuitable land management techniques, are likely to restrict the recovery of degraded soils by traditional bush fallow techniques.
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.
Phosphorus sorption is described mathematically for an ensemble of spherical oxide particles with a distributed particle size in order to show the effect of this size distribution on the surface reaction and on the diffusion/precipitation reaction. Then, using relationships resulting from this analysis we give a simplified sorption kinetics model for P sorption to soil which is of use even if the nature, geometries, and dimensions of the reactive phase minerals are unknown. For the slow reaction process, this model is in agreement with the one developed by Van Riemsdijk et al. (1984). Parameter assessment for the model is illustrated with some results of sorption and desorption experiments. -after Authors
Este estudo teve como objetivo avaliar o processo erosivo em um maciço residual em solos com diferentes coberturas, a saber; uma área plantada continuamente com milho em fileiras verticais, área em pousio há três anos e área de mata secundária. Foram colocadas nessas áreas placas de alumínio com 50 cm de largura com uma calha conectada na parte inferior para receber o material erodido. Foram coletadas amostras de solos próximo a cada calha, nas profundidades de 0-5; 5-10; 10-15; 15-20; 20-25 e 25-30cm. Foram realizadas análises químicas e físicas tanto nas amostras coletadas quanto no material erodido. Os solos apresentaram boas características químicas, sendo que houve um menor teor de matéria orgânica e fósforo no sistema com milho na camada de 0-5cm. O solo cultivado com milho mostrou uma maior densidade aparente e uma menor porosidade na mesma profundidade. Verificou-se uma diminuição da fração argila na camada superficial, e uma maior fertilidade nos sedimentos erodidos no sistema de plantio com milho. Os solos em pousio e de mata apresentaram uma menor de perda de sedimentos por erosão. A maior distribuição de chuvas favoreceu o processo erosivo.
Materiais de origem vegetal, como fibra de coco (MALVESTITI, 2004), esterco bovino (NEGREIROS et al., 2004), casca de arroz carbonizada (GUERRINI e TRIGUEIRO, 2004), mucilagem de sisal (LIMA et al., 2006) e bagaço de cana-de-açúcar (SEDIYAMA et al., 2000), dentre outros, têm-se destacado como ingredientes para compor substratos para produção de mudas; contudo, visando à viabilidade do uso desses materiais, é necessário conhecer, primeiro, sua composição química para a elaboração de formulações adequadas ou decidir sobre a necessidade de suplementação com fertilizantes minerais. A utilização de substratos orgânicos com características adequadas à espécie plantada possibilita redução do tempo de cultivo e do consumo de insumos, como fertilizantes químicos, defensivos e mão-de-obra (FERMINO e KAMPF, 2003). A qualidade do substrato resulta da combinação de suas propriedades químicas e físicas, as quais podem ser ajustadas pela formulação de misturas duplas ou triplas (NEGREIROS et al., 2004). Mesmo se conhecendo as grandes vantagens do uso de resíduos agrícolas como componentes na formulação do substrato para produção de mudas, muitos viveiristas ainda utilizam solo puro.
Mixing non-phosphate salts with phosphate fertilizer modifies the chemical environment of the soil-phosphorus (P) fertilizer reaction zone due to induced changes in soil pH and the interactions of P with soil components and other ions. The objective of this study was to examine the effects of cation and anion interactions on the solubility and diffusive transport of P in columns packed with a mixture of inert quartz sand and Ca2+-saturated cation exchange resin, buffered with CaCO3. The background pH of the resin-sand mixture was 9.4. Three types of cations (K+, NH +4, and Mg2+) were combined with four anions (NO3-, Cl-, SO2-4, and CO 2-3,) to produce 12 non-phosphate salts. Each of these salts was mixed with 0.4 g of KH2PO4 to provide 408.9 mg P kg-1 soil. The experiment was carried out in three replicates. Following 2 wk of incubation, columns were sectioned at 3-mm intervals and the pH of each section was measured. The samples were extracted with deionized water and subsequently with 1 mol L-1 HCl. Addition of KH 2PO4 alone reduced the pH at the surface (first 3-mm section) of the resin-sand column to 7.1, while pH remained unchanged at 9.1 on addition of K2CO3 and KH2PO4. Addition of MgCl2 and KH2PO4 resulted in the lowest pH in the column and the greatest depth of H+ penetration compared with other treatments. None of the treatments containing NO 3- or Cl- salts enhanced the solubility and movement of P. Addition of (NH4)2SO4 or (NH4)2CO3 to KH2PO4 produced the greatest amount of water-extractable P, followed by K 2SO4. The lowest solubility of P occurred on addition of K2CO3 (P < 0.05). We attributed the enhanced solubility of P by SO2-4 and CO2-3 associated with NH4+ to competition between these anions and HPO 2-4 for precipitation with solution Ca2+. Phosphate ion moved to depths of 5.0, 6.0 and 7.5 cm on addition of K2SO4, (NH4)2SO4, and MgSO4 to the column, respectively. These results suggested that salts such as K2SO 4, (NH4)2CO3, (NH4) 2SO4 and MgSO4 would enhance the lability of fertilizer P in a calcareous soil system.
Phosphorus (P) is the limiting nutrient for primary production in most freshwater ecosystems. The magnitude of P leaching from agricultural soils is therefore critical. Preferential flow has been proposed as a major cause for high P losses in structured clay soils. Undisturbed soil of two texturally different soils, that is, a clay soil in which preferential flow was expected to be the main mode of water transport and a sandy soil where piston flow is the dominant process, were used in this study. Use of labeled P made it possible to determine the origin of leached P. An equivalent of 100 kg P ha-1, labeled with 33P, was added to the soil surface of each lysimeter. Water equivalents to 100 mm were added on five occasions with 7 d between each watering event. Ponded flow conditions were established during periods when water was added, to trigger preferential flow behavior. Phosphorus leaching loads from clay columns were much higher than P loads from sand columns. The average P leaching load for the five clay columns was 4.0 kg ha-1, compared to only 56 g ha-1 for the three sand columns. The main part of leached P was in dissolved (PO4-P) form. The recently added P prevailed in leachate from the clay soil indicating rapid transport of added P from the soil surface through the profile via macropores.
A method is presented for determining organic carbon content of soils, extracts and plant tissue utilizing an acidic wet oxidation in modified culture tubes; samples containing carbonates are pretreated with dilute acid. Evolved CO2 is trapped in a NaOH solution and quantified titrimetrically. The method described has a range of 0.4–11 mg. carbon and the range can be extended in either direction by modifying the CO2 trapping/titration procedure. This method is as accurate and precise as more time consuming dry oxidation procedures.
The study of solute and water transport in non saturated soil is important by the environmental and economical conditions, so the use of computational models assumes important function, when allowing to preview the miscible displacement in a accurate and fast way. The objective of this work was evaluating the MIDI parameters (dispersivity and retardation factor) by a sensibility analysis in order to verify the consequence in the nitrate concentration in a vertical column of non saturated soil. The MIDI parameters (tirar a vírgula) evaluated in this work, dispersivity and retardation factor, were submitted to variations of -90 the + 90% and such effects were analyzed and the standard error was determined. For the obtained results, the model parameters, dispersivity and retardation factor, presented influence in the determination of the nitrate concentration. Among these two parameters the more sensitive was the retardation factor, mainly to the negative variations.
Long-term application of phosphorus (P) to soils as fertilizer or manure can increase the potential for P loss to ground and surface waters. Vertical P transport was investigated in a sandy soil material receiving seven different P fertilizer sources: poultry compost, poultry litter, triple superphosphate [Ca(H(2)PO(4))(2)center dot H(2)O], dairy lagoon liquid, swine lagoon liquid, swine lagoon sludge, and dissolved potassium dihydrogen phosphate (KH(2)PO(4)). The P sources were surface-applied to soil columns (6.35-cm diameter, 10-cm long) at two rates equivalent to 75 and 150 kg total P ha(-1), and columns were intermittently leached with deionized (DI) water. Column effluents were collected for up to 23 pore volumes and analyzed for dissolved reactive phosphorus (DRP) and dissolved organic carbon (DOC). In addition, a P retardation factor was determined for the soil from a P adsorption isotherm. Transport of P through soil columns receiving liquid P sources was simulated by a one-dimensional equilibrium convective-dispersive equation (CDE) based on water-extractable P (WEP) concentrations. Cumulative amounts of DRP leached were linearly related to the amounts of WEP in P source materials (r(2) = 0.87***). The recovery of DRP in the column effluents relative to WEP in the applied materials was 126 +/- 15% (mean +/- standard error) for organic P sources and 66 +/- 2% for inorganic P sources. The use of WEP in the CDE model underpredicted P transport in the columns amended with lagoon liquids compared with dissolved KH(2)PO(4). Results indicated that leaching losses of P from land-applied manures exceed the amounts of WEP in source materials because of organic P mineralization and competitive sorption of DOC.
Phosphorus (P) sorption properties are poorly documented for Swedish soils. In this study, P sorption capacity and its relation to soil properties were determined and evaluated in 10 representative Swedish topsoils depleted in available P. P sorption indices were estimated from sorption isotherms using Langmuir and Freundlich equations (Xm and aF, respectively) and P buffering capacity (PBC). Xm ranged from 6.0 to 12.2 mmol kg–1. All indices obtained from sorption isotherms were significantly correlated with each other (r=0.96*** to r=0.99***). Two single-point sorption indices (PSI1 and PSI2) were also determined, with additions of 19.4 and 50 mmol P kg–1 soil, respectively. Both PSI indices were well correlated with Xm (r0.98***), with PSI1 giving the highest correlation. As isotherms for determining P sorption capacities involve laborious analytical operations, PSI1 would be preferable for routine analyses. Xm was significantly correlated with Fe extracted by sodium pyrophosphate and ammonium oxalate, to Al extracted by ammonium oxalate and dithionite-citrate-bicarbonate and to organic c. Xm was also significantly correlated with the sum of Fe and Al extracted by ammonium oxalate. The best prediction of Xm through multiple regression was obtained when Fe extracted in ammonium oxalate and Al extracted in dithionite-citrate-bicarbonate were used. Based on the results obtained, both PSI1 and oxalate-extractable Fe plus Al can be used for predicting P sorption capacity in Swedish soils.
This work aimed to evaluate the impacts of the organic fertilization and the use of green manure (GrM) on the different soil P fractions in areas under organic agriculture in the municipality of Ubajara, state of Ceará, Brazil. The work was carried out in an organically cultivated farm situated in the Ubajara municipality, state of Ceará, Brazil. Soil samples of a sandy soil were collected at the 0- to 5-, 5- to 10-, 10- to 20-, 20- to 40- and 40- to 50-cm layers in areas of Caribbean cherry with (+) and without (−) previous incorporation of GrM in the rows (+GrMr and −GrMr) and between-rows (+GrMb-row and −GrMb-row). Area under natural vegetation (NV) was also sampled and considered as reference. P fractionation was performed by using a sequential extraction scheme adapted from Hedley. The cultivated systems presented higher P contents than NV, mainly in the most labile P pool (res-Pi + NaHCO3-P), indicating that organic management favoured greater P cycling of this fraction. In the cultivated areas labile P pool accounted for 20, 17, 21 and 27% of sum of soil total P in the −GrMr, −GrMb-row, +GrMr and +GrMb-row, respectively. There was an increment of 86% in the organic P pool in the organically cultivated areas in relation to the NV. The organic management promoted an increase on the available-P forms by avoiding and/or decreasing the rate of transformation of the Pi in more stable P forms, enhancing the P cycling. The use of green manure promoted increase on the most labile P pool (Resin-P+NaHCO3-P) and seems to contribute to the P incorporation into biological cycle. On the other hand, the risks of P losses in the organically managed areas should be considered and suggest a scientific remark to farmers for a better management of organic farming in sandy soils.
Soil structure exerts important influences on the edaphic conditions and the environment. It is often expressed as the degree of stability of aggregates. Aggregation results from the rearrangement, flocculation and cementation of particles. It is mediated by soil organic carbon (SOC), biota, ionic bridging, clay and carbonates. The complex interactions of these aggregants can be synergistic or disruptive to aggregation. Clay-sized particles are commonly associated with aggregation by rearrangement and flocculation, although swelling clay can disrupt aggregates. Organo-metallic compounds and cations form bridges between particles. The SOC originates from plants, animals and microorganisms, and their exudates. It enhances aggregation through the bonding of primary soil particles. The effectiveness of SOC in forming stable aggregates is related to its decomposition rate, which in turn is influenced by its physical and chemical protection from microbial action. Soil inorganic carbon (SIC) increases aggregation in arid and semi-arid environments, and the formation of secondary carbonates is influenced by the presence of SOC and Ca2+ and Mg2+. Soil biota release CO2 and form SOC which increase dissolution of primary carbonates while cations increase precipitation of secondary carbonates. The precipitation of (hydr)oxides, phosphates and carbonates enhances aggregation. Cations such as Si4+, Fe3+, Al3+ and Ca2+ stimulate the precipitation of compounds that act as bonding agents for primary particles. Roots and hyphae can enmesh particles together while realigning them and releasing organic compounds that hold particles together, a process with a positive impact on soil C sequestration. Soil structure can be significantly modified through management practices and environmental changes. Practices that increase productivity and decrease soil disruption enhance aggregation and structural development.
The reaction of ortho-phosphate (P) with sandy soil is described by two processes: a fast and reversible adsorption according to Langmuir kinetics, combined with a non-equilibrium, irreversible, precipitation-like process. The precipitation reaction involves the bulk of oxides and has diffusion of P through a metal phosphate coating, that surrounds the oxide, as the rate limiting step. Model parameters are assessed by performing sorption and desorption experiments. With the parameter values obtained, the transport of P in packed columns is simulated. Good agreement between measured and calculated breakthrough curves is found for the transport of high feed concentration of P and for the leaching of a column presaturated with P. Transport experiments appear to produce additional information that is necessary in the assessment of model parameters.
Substrate composition is one of the most important factors influencing the decomposition of plant residues in soils. The interaction of organic residue biochemistry with residue decomposition rates, soil aggregation and soil humus composition was determined in a laboratory experiment. Addition of seven different organic residues (2% w/w alfalfa, oat, canola, clover, soybean, corn and prairie grasses) to a Webster soil resulted in a rapid, transient increase in aggregate mean weight diameters (MWD) when incubated for 9 d with residues with low phenolic acid content (alfalfa, canola and clover) and was inversely correlated with soil carbohydrate content (r = -0.63). More pronounced improvement in aggregate size was noted upon increased incubation to 84 d with organic residues higher in phenolic acid content (corn, prairie grasses, oat and soybean) and was related to soil phenolic acid (r = 0.65) and soil carbohydrate content (r = 0.70). Total plant residue phenolic acid content was related to MWD measured after incubation for 84 d by a quadratic response and plateau function (r = 0.96) and the MWD quadratically increased with an increase in vanillin-vanillic acid concentrations in the plant residues (r = 0.997). Soil organic C after 84 d was related to the MWD (r = 0.82) and the residue's vanillin-vanillic acid content (r = 0.86), suggesting that C remaining in the soil following decomposition maybe related to the specific phenolic acid content. The results suggest that transient aggregate stability initiated by microbial decomposition of the carbohydrate and amino acid content of the residue, is then strengthened by the interaction with phenolic acids such as vanillin or vanillic acid released by microbial decomposition from residues structural components.
The contribution of nonpoint-source pollution of P leaching and P runoff from agricultural soils is very important, especially in those areas with intensive livestock production systems. Prediction of the impacts of fertilization reduction measures on P loads from agricultural soils to surface water requires a sound description of the accumulation of P. In this article an overview is given of the Dutch approach. The presented methodology has been developed for noncalcareous sandy soils in fiat areas where P loss by subsurface runoff is the dominating pathway. Based on the kinetics of P sorption and desorption of these soil types, P accumulation in soils, and inorganic P concentrations in soil solution can be modeled. Furthermore, methods have been deduced to translate the description of soil chemical P processes into commonly used soil P tests. As a result of this interaction, soil P tests can be used as an initial approach to estimate the potential risk of P leaching and runoff from agricultural soils in noncalcareous sandy areas. The description of the kinetics of inorganic P reactions and the modeling of soil P tests have been implemented in the ANIMO model in addition to an organic P cycle that is related to organic C and N dynamics. With this model, the fixation and immobilization of P by soil components can also be assessed. As a result of annual losses by fixation, immobilization, and subsurface runoff/leaching, changes in soil P test values with time can be estimated.
A study was conducted to examine the loss of P in subsurface flow from three cultivated soils of varying soil P concentrations. Measurements were made in flow waters from the soils before applying manure and then 3 weeks after sowing the soils to grass. An additional measurement of P in flow waters was made 1 year later. Dissolved reactive P (DRP) concentrations measured in flow water before (0.15-0.20 mg l(-1)) and after (0.39-0.51 mg l(-1)) manure application exceed current estimates of those required to promote surface water eutrophication (0.05 mg l(-1)). Concentrations of DRP1 year after manurial application increased compared to 3 weeks after application and was attributed to the slow movement of P down the cultivated soil. Concentrations of soil P were significantly increased down the soil profile and attributed to the P saturation of soils before manurial application. The results suggest that despite the establishment of fast growing grass, P concentrations would not be mitigated in the short-term (= 1 year), due to the large contribution of P in subsurface pathways.
Handbook of soil science
- J A Baldock
- P Nelson
BALDOCK, J.A.; NELSON, P.N. Soil organic matter. In: SUMNER, M.E. Handbook of
soil science. CRC Press, 2000. p. 325-375.