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Weed density and diversity in a long-term cover crop experiment background
Abstract and Figures
Cover crops (CC) are biological tools with a great potential for weed control, but the suppression level depends on the CC species and management. A 2-year study was performed in the eighth year of a long-term experiment located in Central Spain to study the effect of replacing winter fallow by barley (Hordeum vulgare L.) or vetch (Vicia sativa L.), on the weed control. Moreover, two CC termination dates were evaluated. Weed biomass, density, diversity, population composition and the seed bank were assessed. Ground cover and CC biomass, soil inorganic N and topsoil water content were determined throughout the season. Barley achieved a greater weed control compared to vetch in winter and early spring. Later in May, both CC residues decreased weed density compared to fallow (63% in 2015, 55% in 2016), and reduced the density of some broadleaf species (i.e. Xanthium spinosum L. reduced >50%). The weed seedbank density was not affected by CC but the effect on specific species confirmed the control over Xanthium spp. (78% reduction), and also warned of the incomplete weed control by CC. The year in which the biomass and ground cover increased between termination dates, delaying the CC termination reduced weed density >75%. Therefore, delaying the termination date was a mean to increase weed control but should be performed with caution to avoid pre-emptive competition with the cash crop. Results underline the relevance of CC species and the termination date as management tools for weed control, and must be considered to plan specific management strategies in different scenarios.
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... In both graphs, the two orange markers represent the average (circle) and standard deviation (diamond), respectively, to all analyzed studies. [52,60,63,66,72,73,75,76,79,82,83] . In both graphs, the two orange markers represent the average (circle) and standard deviation (diamond), respectively, to all analyzed studies. ...
... A B Figure 5. Forest plot of the average N provided by (A) the chosen cover crops' biomass [53,60,63,64,66,69,70,72,79,[81][82][83] and (B) soil N at the end of the experiments [52,60,63,66,72,73,75,76,79,82,83]. In both graphs, the two orange markers represent the average (circle) and standard deviation (diamond), respectively, to all analyzed studies. ...
... A B Figure 5. Forest plot of the average N provided by (A) the chosen cover crops' biomass [53,60,63,64,66,69,70,72,79,[81][82][83] and (B) soil N at the end of the experiments [52,60,63,66,72,73,75,76,79,82,83]. In both graphs, the two orange markers represent the average (circle) and standard deviation (diamond), respectively, to all analyzed studies. ...
Cover crops are multifunctional, and contribute to improving soil properties and reducing environmental impact compared to no cover crops, thus could provide multiple soil, agricultural, and environmental benefits, and they are recognized as a valid strategy for the achievement of sustainable agriculture. However, cover crops’ impacts on subsequent cash crops and soil characteristics are dependent on several factors, such as pedoclimatic conditions, cover crop species, agricultural practices, method of termination, and irrigation management. The fact that cover crops are never applied as a single practice in the real agricultural sector, but are instead combined with other factors or agricultural practices, deeply affects their performance, but the scientific literature nevertheless keeps considering the use of cover crops alone. Moreover, the potential outcomes of cover crops that encompass other factors or agricultural practices affecting soil quality, weed control, and cash crops are still unclear. Additionally, cover crops are still poorly use in the Mediterranean type of climate. Therefore, this study reviewed the scientific literature to identify the most relevant factors or agricultural practices driving cover crops’ performance, and to outline future fields of investigation looking towards promising sustainable agriculture in Mediterranean areas with a view to minimizing the competition for soil water with the cropping systems and to reduce soil degradation. Furthermore, the investigation includes multiple factors or agricultural practices that better represent the real farming system, contributing to a comprehensive understanding of their interactions with cover crops, and suggests alternative strategies for reducing yield gap while seeking to achieve agricultural sustainability.
... The legume species (i.e. common vetch, fenugreek, and berseem clover) exhibited a very low weed control function. Legumes have been proven to be effective weed suppressor when used in mixtures and in long term experiments, also by enhancing soil properties (Alonso-Ayuso et al., 2018;Malaspina et al., 2023). For instance, common vetch showed a particular potential for long-term weed management, also due to biochemical inhibitory effects on root growth of some weed species (Adeux et al., 2021;Kunz et al., 2016;Rueda-Ayala et al., 2015). ...
... The use of mixed cover crops including legumes for long-term weed management might thus merit additional research. Additionally, by outcompeting weeds, cover crops can also influence weed seed bank composition in the long term (Alonso-Ayuso et al., 2018) and, in some cases, even reduce seed bank density in the years following the start of their employment (Moonen and Bàrberi, 2004;Schmidt et al., 2019). The potential of buckwheat, as well as cover mixtures, for long-term weed reduction also through seed bank reduction will thus deserve to be further investigated. ...
Cover crops can perform multiple ecosystem functions, including weed control, soil quality enhancement and support to pollinators. While the contribution of individual cover crop species or mixtures to each of these functions has been extensively investigated, experiments testing all these ecosystem functions simultaneously to select the best species or mixture overall are rare. In this study, we evaluated the performance of six summer cover crop species in terms of biomass production, weed suppression, soil fertility enhancement potential and support to wild and managed pollinators. Tested species included buckwheat (Fagopyrum esculentum Moench.), white mustard (Sinapis alba L.), berseem clover (Trifolium alexandrinum L.), blue tansy (Phacelia tanacetifolia Benth.), fenugreek (Trigonella foenum-graecum L.) and common vetch (Vicia sativa L.). Field work was carried out in four fields in Northern Italy during the summer months of 2020 and 2021. Buckwheat was identified as the overall best-performing species, by virtue of its high biomass production, ability to control weed growth, and abundant and long-lasting flowering that could support honeybees and hoverflies during a low-resource period without promoting competition. Buckwheat was, however, less promising regarding soil enhancement potential and support to wild bees, highlighting the need to continue searching for complementary cover crop species to be used alongside it in a mixture. Our results could improve cover crop selection schemes, suggesting the necessity for a comprehensive approach aimed at enhancing multiple ecosystem functions in agroecosystems.
... During these periods, autumn-emerging species and other indifferent species might have potentially had the temporal space to complete their life cycles and disseminate. However, introducing specific CC species rather than leaving the soil as 'weedy fallow' prevented the total weed density from soaring (Fig. 1), confirming the results of previous studies reviewed by Osipitan et al. (2019) and Sias et al. (2021) and the findings of Alonso- Ayuso et al. (2018). In this study, sowing triticale as a CC for three consecutive autumns led to a reduction in total weed density, whereas the succession of rye-clover-mustard CCs kept it steady. ...
A R T I C L E I N F O Keywords: Triticale Mustard Rye Clover Weed diversity Weed community shift A B S T R A C T Cover crops (CCs) are recognised as valuable for weed management, while fallow soil between cash crop seasons likely increases weed presence. Weeds may offer similar ecosystem services as CCs, although they pose a risk of seedbank buildup. This study evaluated the impact of two winter CC systems (3-year triticale cultivation, TRIT; and a 3-year succession of rye, clover, and mustard, RCM) compared to weedy fallow (WF) on weed seedbank size and composition in a 3-year 'maize (Zea mays L.)-maize-soybean (Glycine max (L.) Merr)' crop succession. After 3 years, seed density of spring/summer weeds reduced in all treatments, potentially stemming from her-bicide use during cash crop seasons and tillage operations. Triticale had the lowest seedbank density (9,487 seeds m − 2) and higher diversity (Shannon Index 6.9) compared to WF (28,543 seeds m-2 and 4.1, respectively). Furthermore, stochastic analysis revealed a lower risk of enlarging weed seedbanks in TRIT compared to WF (for seed densities above 900 seeds m − 2). Moreover, management practices (CCs, cash crop sowing, termination/ harvest) synchronised with weed seed production and germination likely contributed to the decreasing seed density of species including Portulaca oleracea and Chenopodium album, which were reduced by 90 and 80 %, respectively, by the study's end. Over three years, autumn/winter and indifferent weed seed densities increased 4.2 times more in WF and RCM (22,638 seeds m − 2) than in TRIT. This may be due to the varying growth rates among CC species in RCM, whereas TRIT consistently established rapidly, potentially outcompeting weeds until termination. Fallow periods between cash crops may increase weed species linked to that season and future crop-weed interference in varied crop rotations. Introducing CCs can mitigate this effect, although the choice of CC species may influence the extent of the impact.
... In the AC system, the mean values of WB were significantly lower for B, V and BV crops, in comparison to F, and had a downward trend over the three cropping seasons for all crops. However, for SC system mean values of WB in V and BV were close to F and lower for B. Our results agreed with those reported by Alonso-Ayuso et al. (2018), proving that barley achieved greater weed control than common vetch in a semi-arid climate. According to Smith, Warren, and Cordeau (2020), a cereal cover crop is more weed suppressive than the most stable mixture. ...
The use of cover crops within olive groves, be they legume, non-legume or a mixture, has become more widespread in recent years as a practice of environmental sustainability to improve soil organic matter. Using both SC: a sole-crop and AC: an alley-cropping, Hordeum vulgare L. and Vicia sativa L. were studied with olive trees 2016 to 2019. The aim was to determine the effects of both of these systems on: TB: total biomass, POXC: Permanganate oxidizable Carbon and SOC: Soil Organic Carbon, TN: Total Nitrogen, C:N ratio; and P: available Phosphorus. These parameters were measured on 192 soil samples collected at 0-20 and 20-40 cm soil depths before planting and after crop harvesting. The results showed that within the relatively short time of three seasons, cover crops increased SOC slightly overall. Compared to the SC, AC limited crop and weed growth and produced significantly less TB, especially in 2017-18, a particularly dry season. This can be explained by the initial state of the soil which was significantly affected by the cropping system. AC enhanced SOC and stabilized the POXC during all three cropping seasons for all treatments. Mixed crop (barley and vetch) significantly increased TN in the AC over the three cropping seasons and decreased the C:N ratio. However, with barley and vetch in pure stand, the mean TN was similar to that of fallow. Also, this type of agroforestry increased the mean available phosphorus with barley, vetch and a mixture of the two compared to fallow. ARTICLE HISTORY
... Our results confirm the importance of living mulch establishment and biomass accumulation in controlling weeds (e.g., Bybee-Finley et al., 2017;Alonso-Ayuso et al., 2018), and highlight the inherent Error bars represent ± standard error. Significant specified at *p < 0.05, **p < 0.01, ***p < 0.001. ...
Planting a cover crop living mulch between plastic mulch beds in fresh market vegetable production can reduce soil erosion and runoff, and offers an opportunity to grow an income generating cash crop alongside a soil building cover crop. However, potential negative impacts on yield, variable weed control, unclear impacts on soil health, and limited management recommendations challenge adoption of this practice, despite grower interest. In a two-year study in southwest Michigan, living mulches were evaluated in the production of plasticulture organic summer squash (Cucurbita pepo cv. Lioness) and bell pepper (Capsicum annuum cv. Paladin). Strategies evaluated included three common grower practices (cultivation, dead straw mulch, mowing ambient weeds) and three mowed living mulch treatments (Italian ryegrass [Lolium multiflorum] monoculture, rye [Secale cereale] monoculture, and a Dutch white clover [Trifolium repens]/rye mixture). We determined the impact of these strategies on weed control, organic matter inputs, vegetable crop performance, nitrogen retention, and soil microbial communities. We found that cultivation and dead mulch provided superior in-season weed control, reducing weed biomass by an average of 86% compared to 18% among living mulch treatments, with associated reductions in the weed seedbank compared to living mulches and mowed weeds. In most cases, living mulch establishment was a challenge and weed biomass on average accounted for 99, 74, and 94% of organic matter inputs in rye, ryegrass, and clover/rye treatments, respectively. Squash performance was unaffected by our treatments, but pepper yield reductions ranged from 41 to 54% in all treatments relative to cultivation in one of two years. Living mulches and the weedy treatment showed the ability to reduce end-of-season potentially leachable nitrogen by 61% compared to cultivation and dead mulching. Soil microbial abundance and functional diversity were similar across treatments, but extracellular enzyme activity was higher in dead mulch, living mulch and weedy treatments compared to cultivation. Results from this study help quantify tradeoffs between common grower practices for managing weeds and soil between plastic mulch beds, highlight key challenges with living mulch alternatives, and identify areas for future research.
... However, the presence of a cover crop can delay seasonal emergence patterns of Setaria spp. (Alonso-Ayuso et al., 2018). Further, green foxtail is somewhat tolerant of mowing, which can promote production of seeds in grass species (Black and Siddoway, 1977). ...
Agropyrum repens is a perennial plant from the grass family (Poaceae). In this paper, the use of Agropyrum repens in soil protection and phytoremediation of degraded areas, and as a medicinal and decorative plant is analyzed. The fact that Agropyrum repens can be grown even in marginal agro-ecological conditions gives us the opportunity to establish perennial grass areas on unused and degraded areas. Thanks to the development of new technologies for the processing of biological waste into energy products, the rate of increase in the use of alternative fuels is growing significantly, and tall mash, thanks to its modest requirements for water and heat, can be classified as a desirable energy crop. Agropyrum repens is one of the best crops for soil protection against all types of erosion, then for phytoremediation, absorption of harmful gases from the atmosphere, and it is valued as a decorative and ornamental plant. In order to ensure security in the supply of necessary energy sources, most countries in the world direct their research in the direction of finding the most rational way of using renewable energy sources. In folk medicine, pyrethrum is used in the prevention of gout, rheumatism, and inflammation of the urinary tract and renal stones.
The use of cover crops in conventional agriculture is not fully accepted. This is probably due to the substantial variability in outcomes reported and is complicated by the conflation of a host of techniques under the same umbrella term, often without the appropriate benchmarking. This review addresses these issues with a quantitative synthesis of the last 11 years of research on cover crops in cereal rotations in temperate climates. Strict inclusion criteria focus the scope of the review to studies offering comparisons with an equally treated bare fallow control. Coded variables included duration, fertiliser, irrigation and tillage regime, cover and cash crop type and termination mode. The result is a quantitative review of 100 parameters covered by multiple publications , with an additional overview on 124 parameters covered by single studies. The investigated response variables range from microbiology and chemical parameters to hydrology, soil structure, weed and pest control and crop performance. Relevant trends were identified regarding strengths and weaknesses of cover cropping, with predictions formulated about the conditions necessary for their successful implementation. Additionally, trade-offs specific to cover cropping are discussed, together with the variables at play in determining the final balance of net gain or loss. The main findings are that cash crop performance is best enhanced by legume cover crops and in low-tillage regimes, and the soil biotic effects of cover crops tend to be short-lived, fading by the end of the season. Most importantly, a positive effect of cover cropping on soil carbon is potentially offset by increased GHG emissions.
Weed management in agriculture is hampered by inefficient intensive methods, such as monoculture, deep plowing, and herbicides, leading to health and environmental problems. Furthermore, the prevalence of herbicide-resistant weed ecotypes in the Mediterranean, particularly in France (with over 61 ecotypes), Spain (41), and Italy (37), is a major concern, with a significant proportion of herbicides in the region. In this study, we examined the benefits of adopting agroecology as a sustainable approach for weed management in the Mediterranean region. Agroecology offers a variety of techniques and practices to improve sustainability and weed management, while preserving ecological balance and biodiversity.
However, solving these challenges is multifactorial and depends on local specificities, predominant weed species, crops, sowing dates, and pedo-climatic factors. In addition, this study included a systematic analysis of agroecological weed management in Mediterranean countries, assessing the effectiveness of existing practices, and identifying areas requiring further exploration in agroecosystems. A bibliometric analysis was also included to assess the literature on agroecology and weed management quantitatively, identifying major trends, influential studies, and research gaps. The bibliometric analysis highlighted
the importance of alternative herbicides in Mediterranean “weed” (with a link strength of 44), “agroecology” (22), and “biodiversity” (16). Italy has the strongest collaboration network, with a link strength of 61, followed by Turkey (44), and France (42). Using specific keywords to agroecological practices for weed management in Scopus, France worked the most in this context (around 25% of studies), followed by Spain (17%) and Italy (17%), while all other countries contributed to less than 40% of studies carried out in the Mediterranean
context. Clearly, it is imperative to foster collaboration between Mediterranean
countries to develop effective and sustainable weed control strategies. Understanding the challenges of herbicide-resistant weeds, exploring their reasons and mechanisms, and using systematic studies and bibliometric analyses will help to develop effective strategies for managing weeds in the Mediterranean. Agroecological management favors effective control, while promoting healthy and sustainable ecosystems, preserving biodiversity, and ensuring long-term food security.
Crop residues on the soil surface protect the soil against erosion, increase water infiltration and reduce agrochemicals in runoff water. Crop residues and soils are spectrally different in the absorption features associated with cellulose and lignin. Our objectives were to: (1) assess the impact of water on the spectral indices for estimating crop residue cover (fR); (2) evaluate spectral water indices for estimating the relative water content (RWC) of crop residues and soils; and (3) propose methods that mitigate the uncertainty caused by variable moisture conditions on estimates of fR. Reflectance spectra of diverse crops and soils were acquired in the laboratory over the 400–2400-nm wavelength region. Using the laboratory data, a linear mixture model simulated the reflectance of scenes with various fR and levels of RWC. Additional reflectance spectra were acquired over agricultural fields with a wide range of crop residue covers and scene moisture conditions. Spectral indices for estimating crop residue cover that were evaluated in this study included the Normalized Difference Tillage Index (NDTI), the Shortwave Infrared Normalized Difference Residue Index (SINDRI) and the Cellulose Absorption Index (CAI). Multivariate linear models that used pairs of spectral indices—one for RWC and one for fR—significantly improved estimates of fR using CAI and SINDRI. For NDTI to reliably assess fR, scene RWC should be relatively dry (RWC < 0.25). These techniques provide the tools needed to monitor the spatial and temporal changes in crop residue cover and help determine where additional conservation practices may be required.
Cover crops represent a potentially important biological filter during weed community assembly in agroecosystems. This filtering could be considered directional if different cover-crop species result in weed communities with predictably different species composition. We examined the following four questions related to the potential filtering effects of cover crops in a field experiment involving five cover crops grown in monoculture and mixture: (1) Do cover crops differ in their effect on weed community composition? (2) Is competition more intense between cover crops and weeds that are in the same family or functional group? (3) Is competition more intense across weed functional types in a cover-crop mixture compared with cover crops grown in monocultures? (4) Within a cover-crop mixture, is a higher seeding rate associated with more effective biotic filtering of the weed community? We found some evidence that cover crops differentially filtered weed communities and that at least some of these filtering effects were due to differential biomass production across cover-crop species. Monocultures of buckwheat and sorghum-sudangrass reduced the number of weed species relative to the no-cover-crop control by an average of 36 and 59% (buckwheat) and 25 and 40% (sorghum-sudangrass) in 2011 and 2012, respectively. We found little evidence that competition intensity was dependent upon the family or functional classification of the cover crop or weeds, or that cover-crop mixtures were stronger assembly filters than the most effective monocultures. Although our results do not suggest that annual cover crops exert strong directional filtering during weed community assembly, our methodological framework for detecting such effects could be applied to similar future studies that incorporate a greater number of cover-crop species and are conducted under a greater range of cover-cropping conditions.
Overwintered cover crops mechanically terminated into mulch can be a weed management tool for reduced-tillage organic agriculture. However, the impacts of management options for cover cropping are not well understood, including cover crop variety, termination timing and termination method. In a field experiment, conducted in 2012 and 2013 in Western Washington, we examined three grains, four vetches and one barley–vetch mix terminated with two mechanical methods and at two different times. We determined the influence of cover crop variety and termination time on cover crop biomass production and tissue nitrogen (N), effectiveness of cover crop termination, soil nitrate–N and percent weed cover. We also determined the influence of termination method on percent weed cover. Cover crop biomass ranged between 3 and 9 Mg ha
−1
and was not influenced by termination time; the greatest production was from three varieties of grain. Rye varieties were more effectively terminated with a roller–crimper than barley. Mean soil nitrate–N levels ranged from 1.9 to 18 mg kg
−1
and were the greatest with vetches. Post-termination weed cover was greater in 2013 than in 2012 and the cover crop variety influenced weed cover at the Late termination time only. Neither plant N concentration in the cover crop mulch nor soil nitrate influenced weed cover. The results of this study indicate that cover crop biomass and termination timing are important factors influencing weed cover and termination effectiveness in cover crop mulch.
Integrating cover crops (CC) in rotations provides multiple ecological services, but it must be ensured that management does not increase pre-emptive competition with the subsequent crop. This experiment was conducted to study the effect of kill date on: (i) CC growth and N content; (ii) the chemical composition of residues; (iii) soil inorganic N and potentially mineralizable N; and (iv) soil water content. Treatments were fallow and a CC mixture of barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) sown in October and killed on two different dates in spring. Above-ground biomass and chemical composition of CC were determined at harvest, and ground cover was monitored based on digital image analysis. Soil mineral N was determined before sowing and after killing the CC, and potentially mineralizable N was measured by aerobic incubation at the end of the experiment. Soil water content was monitored daily to a depth of 1.1 m using capacitance sensors. Under the present conditions of high N availability, delaying kill date increased barley above-ground biomass and N uptake from deep soil layers; little differences were observed in vetch. Postponing kill date increased the C/N ratio and the fiber content of plant residues. Ground cover reached >80% by the first kill date (∼1250°C days). Kill date was a means to control soil inorganic N by balancing the N retained in the residue and soil, and showed promise for mitigating N losses. The early kill date decreased the risk of water and N pre-emptive competition by reducing soil depletion, preserving rain harvested between kill dates and allowing more time for N release in spring. The soil potentially mineralizable N was enhanced by the CC and kill date delay. Therefore kill date is a crucial management variable for maximizing the CC benefits in agricultural systems.
The introduction of cover crops in the intercrop period may provide a broad range of ecosystem services derived from the multiple functions they can perform such as erosion control, recycling of nutrients or forage source. However, the achievement of these services in a particular agrosystem is not always required at the same time or to the same degree. Thus, species selection and definition of targeted objectives is capital when growing cover crops. The goal of this work was to describe the traits that determine the suitability of five species (barley, rye, triticale, mustard and vetch) for cover cropping. A field trial was established during two seasons (October-April) in Madrid (central Spain). Ground cover (GC) was monitored with 21 and 22 samples, and biomass measured 8 and 10 times, respectively for each season. A Gompertz model characterized GC until the decay observed after frosts, while biomass was fitted to Gompertz, logistic and linear-exponential equations. At the end of the experiment carbon (C), nitrogen (N), and fibre (neutral detergent, acid and lignin) contents, and the N fixed by the legume were determined. The grasses reached the highest GC (83-99%) and biomass (1226-1928 g/m2) at the end of the experiment. With the highest C/N ratio (27-39) and dietary fibre (527-600 mg/g) and the lowest residue quality (~680 mg/g), grasses were suitable for erosion control, catch crop and fodder. The vetch presented the lowest N uptake (2.4 and 0.7 g N/m2) due to N fixation (9.8 and 1.6 g N/m2) and low biomass accumulation. The mustard presented high N uptake in the warm year and could act as a catch crop, but low fodder capability in both years. The thermal time until reaching 30% GC was a good indicator of early coverage species. Variable quantification allowed finding variability among the species and provided information for further decisions involving cover crops selection and management.
Weeds are a major constraint for organic crop production. Previous research has found that cover crops in reduced tillage systems can provide weed interference, subsequently reducing inputs and improving crop yield. However, questions remain about effects of cover crop species identity and cover crop biomass on weed suppression and crop yield. This four-year study investigated how winter cover crops grown alone or in mixture influenced weed presence and crop yield in a reduced tillage organic vegetable system. Treatments were barley (Hordeum vulgare L.), crimson clover (Trifolium incarnatum L.), mixed barley + crimson clover, and a no-cover crop control. Plots were flail-mowed and strip-tilled prior to planting main crops (2011 and 2012: broccoli Brassica oleracea L.; 2013 and 2014: crookneck squash Cucurbita pepo L.). We measured density, diversity, and community composition of weeds and viable weed seeds, changes in weed percent cover within growing seasons, and crop yield. We found that the presence of barley, crimson clover, or barley + crimson clover reduced weed density by 50% relative to the control. Cover crop biomass negatively influenced weed density and weed seed diversity, and positively influenced squash yield. Weed percent cover within growing seasons did not respond differentially to cover crop treatment. Cover crop treatment and cover crop biomass had no influence on weed or weed seed community composition. These results suggest that reduced tillage winter cover crops in mixture or monoculture can similarly suppress weeds and improve yield, primarily due to biomass effects.
The symbiosis between plants and arbuscular mycorrhizal fungi (AMF) benefits the health, nutrition and abiotic stress tolerance of the host plant. The maintenance of potential AMF inoculum in the winter is important because it will affect the colonization process in the subsequent crop. The objective of this study was to evaluate the effect of winter cover crops (CC) on AMF parameters (root colonization, length of hyphae and number of AMF spores), other variables indirectly related to AMF (the easily extractable glomalin-related soil protein (EE-GRSP) and the enzymatic activity of β-glucosaminidase), along with water-stable aggregates (WSA) as a soil quality indicator. In addition, the effect of two sampling dates on the variables in maize and the relationships among all of the variables were studied. The samples were obtained from a field experiment established in 2006 located in Aranjuez (Central Spain) under a Mediterranean semiarid climate. The treatments were winter cover crops of barley (Hordeum vulgare L.) or vetch (Vicia villosa L.) and fallow as a control. The study covered two seasons in 2011–12 and 2012–13 with sunflower (Helianthus annuus L.) and maize (Zea mays L.) as the main crop, respectively, with both sown in the spring. The main crops were irrigated according to the crop demand. Compared with the bare fallow conditions, cover crops improved most of the variables, maintaining the benefits of CC on AMF under the semiarid conditions of the Mediterranean climate. Barley as a cover crop gave the best results, whereas the performance of vetch was poorer. In sunflower, barley increased by 80% the hyphae length and β-glucosaminidase activity and by 30% other variables compared with the fallow; whereas in maize, 60–70% increments were found in AMF spores and the hyphae length and 2-fold in the enzyme activity. The sampling date affected all of the variables analyzed in the maize crop, except for the EE-GRSP and the WSA. Positive relationships were found between the variables directly related to AMF, EE-GRSP content and β-glucosaminidase activity. This suggests that the variables indirectly related to AMF, mainly the EE-GRSP, could be used as indicators of AMF. Finally, the enhancement of soil aggregate stability by the CC via AMF promotion was corroborated.
Soil dispersion in an aqueous solution of sodium hexametaphosphate and sodium bicarbonate facilitates extraction of seeds by flotation with megnesium sulphate. The percentage viability of seeds collected in this manner subsequently can be determined with 2,3,5-triphenyl-tetrazolium chloride. Extraction of seeds usually is 100% efficient and enumeration of viable seeds via the tetrazolium test is accomplished much more rapidly than with conventional methods.