Presence Of Cover Crop Research Articles

Determination of C-factor for conventional cultivation and soil conservation technique used in hop gardens

Abstract The research presented in the article was focused on determining the C-factor for hops for conventional cultivation (CT) and soil conservation technique, which is based on the presence of cover crops (CC) in the inter-rows. The values of the soil loss ratio, which are the basis for the calculation of the C-factor, are also presented. The research activities were carried out between 2016 and 2023 and a field rainfall simulator was used for the measurements. Rainfall simulations were conducted at three developmental stages of CC. The results show a high C-factor value for CT (0.73), which indicates insufficient erosion control efficiency. In contrast, a C-factor of 0.16 was determined for the cover crop technique. This means that cover crops in the inter-rows of hop gardens can effectively reduce the risk of water erosion. The values reported in the article can be used as input parameters in various erosion models and equations to refine the subsequent calculation.

Winter cover cropping increases albedo and latent heat flux in a Texas High Plains agroecosystem

AbstractWinter cover crops represent a land cover change that may sequester carbon in the soil and improve agricultural sustainability. Their adoption may also change the Earth's radiative balance and result in biophysical feedbacks to climate through alterations in albedo and latent heat fluxes. Understanding the mechanisms underlying these alterations to the radiative balance is important for making reliable future climate projections. However, data on cover crop biophysics are limited, requiring models to rely on data from summer plants for parameterization, likely biasing predictions. To address this gap, we measured the albedo and stomatal conductance of two summer crops and three winter crops on farms in the High Plains region of Texas. We also established a winter cover crop field experiment with two cover crops and fallow fields to estimate the change in albedo and latent heat flux that results from a switch to winter cover cropping. We found that albedo was significantly higher in winter‐like conditions than in summer‐like conditions due to an increase in plant albedo and a reduction in leaf area index. The albedo of winter cover crops was higher than the soil albedo, resulting in an increase in top‐of‐atmosphere reflected radiation of 7%–14% when converting from fallow fields to winter cover cropped fields. There was an additional cooling effect through doubling of the estimated latent heat flux caused by the presence of cover crops. The combined changes in albedo and latent heat resulted in a change in the surface energy balance that is associated with an overall cooling effect of winter cover crops on surface atmospheric temperatures. While this effect is likely to be region‐specific, these results strongly indicate that winter cover crops alter the surface albedo and latent heat flux of agricultural fields and provide a direct cooling effect in the High Plains region of Texas.

Cover crop impacts on nitrogen losses and environmental damage cost

There is a need to explore management practices that reduce nitrate (NO3-) leaching and aid in meeting current greenhouse gas reduction goals. Tile drainage involves using perforated pipes to remove excess subsurface water from agricultural fields, also removing nutrients. The inclusion of cover crops in tile-drained systems in the Midwest has been shown to reduce NO3- losses and is potentially a strategy to mitigate soil nitrous oxide (N2O) emissions. The objectives of this research were to 1) evaluate cumulative soil NO3- and soil N2O losses with and without the inclusion of cover crops in a corn-soybean rotation on a tile-drained landscape and; 2) assess the environmental damage cost (EDC) of N losses with and without the inclusion of cover crops in a corn-soybean rotation on a tile-drained landscape. Corn (Zea mays L.) was grown in 2017, and soybean (Glycine max L.) in 2018. The cover crop used in this experiment was a 92% cereal rye (Secale cereal L.) and 8% daikon radish (Raphanus sativus L.) blend. Treatments included cover crop inclusion, no cover crop inclusion, and a zero control, which did not include cover crops or receive N fertilization. Each treatment was replicated three times in individually tile-drained plots established in Lexington, IL during the 2017 and 2018 growing seasons. In 2017, cover crop inclusion led to a reduction in NO3– losses of over 50% when compared to the no cover and zero control. In 2018, total N losses were identical; however, there was an increase in soil N2O emissions across all treatments compared to 2017. Despite the apparent tradeoff between N loss pathways in 2018, the overall EDC was reduced primarily because of the reduction in NO3- loss in the presence of cover crops. The results of this study indicated that the inclusion of a cover crop resulted in a sizeable reduction in N loss during the corn year that equated to a 64% reduction in EDC across a two-year crop rotation.

Functionally diverse cover crops support ecological weed management in orchard cropping systems

Abstract Diverse agricultural management practices are critical for agroecosystem sustainability, and cover crops provide opportunity for varied management and increased biodiversity. Understanding how cover crops fill open ecological niches underneath the trees, interact with weeds, and potentially provide ecosystem services to decrease pest pressure is essential for ecological agricultural management. The goal of this study was to test the weed suppression potential of two cover crop treatments with varied functional diversity compared to standard weed management practices in commercial almond orchards in California. Transect plant surveys were used to evaluate orchard plant communities under a functionally diverse seed mix including grasses, legumes, and brassicas, and a relatively uniform cover crop mix that included only brassica species. Winter annual orchard cover crops reduced bare ground from 39.3% of total land area to 15.9 or 11.4%, depending on treatment. Furthermore, winter cover crops displaced weeds with a negative correlation of 0.74. The presence of cover crops did not consistently affect weed community composition for low-richness weed communities found in California orchards. Diverse cover crop mixes more reliably resulted in increased ground cover across site years compared to uniform cover crop mixes, with coefficients of variation for ground cover at 49.6 and 91.5%, respectively. Cover crops with different levels of functional diversity can contribute to orchard weed management programs at commercial scales. Functional diversity supports cover crop establishment, abundance, and competitiveness across varied agroecological conditions, and cover crop mixes could be designed to address an assortment of orchard management concerns.

Impact of Zulla cover crop in vineyard on the musts volatile profile of Vitis vinifera L. cv Syrah

Grape aromatic characteristics are very important for producing quality wines. There have been very few studies on concentrations of volatile compounds in grape berries from vines with cover crops. For this reason, the aim of this work was to evaluate the influence of “Zulla” cover crop on the volatile profiles of organically grown Syrah variety grapes. For this purpose, volatile profiles of grapes obtained from vines with three different amounts of cover crop (one line, two lines, and four lines) and without cover crop, over three harvests (2019, 2020, and 2021) were determined. Moreover, a comparative study of conventional and organic crops, both submitted to soil tillage, was performed. The grape samples came from a warm climate zone. Must volatile compounds were determined by sequential sorptive extraction with Twisters by immersion (SBSE) and headspace (HSSE), followed by GC–MS analysis. A total of 160 compounds were determined and most of them were influenced by the presence of cover crop. However, the results showed an important influence of the harvest year over agronomic practices. Therefore, organic cultivation using Zulla cover crop seems to be a suitable tool for the implementation of friendly ecosystem management in a warm climate Syrah vineyard.

Role of Cover Crop, Irrigation Systems and Different Tillage on Soil Physical Properties

The central and southern regions of Iraq are located within the arid and semi-arid regions. The deterioration of the physical properties of the soil due to the low content of organic matter that is less than 1%. The high temperatures, low rainfall and the absence of vegetation cover, as well as the poor use of land and the absence of proper management of irrigation and tillage operations have negative effects on the physical, chemical and biological properties of the soil, which in turn will negatively affect the growth and production of agricultural crops. The experiment was conducted in the Nile district, located within the Babil Governorate, 86 km south of the capital, Baghdad, in a silty clay loam in the fall season 2020, aimed to examine the role of cover crop, irrigation systems and different tillage systems in some physical properties of soil (bulk density, porosity, mean weight diameter, soil resistance to penetration, and saturated soil hydraulic conductivity). The experiment was designed according to the strip-split plot arrangement according to a complete randomized block design. The experiment included three factors, the first that occupied the main plots is the cover crop (C) and included on two levels: without cover crop (C ), and the presence of cover crop (C ), and the second factor was the tillage systems (T) and included on four levels: Zero tillage (T ), 0 1 0minimum tillage (T ), medium tillage (T ) and deep tillage (T ), and the third factor is irrigation systems (I) with three levels: surface drip irrigation 1 2 3 (I ), subsurface drip irrigation (I ) and surface irrigation in basins. (I ) The results showed the superiority of treatment C T I in obtaining the 1 2 3 1 1 2lowest value of bulk density, soil resistance to penetration, highest porosity, mean weight diameter rate, and soil hydraulic conductivity saturated while treatment C T I gave the highest bulk density, soil resistance to penetration, less porosity, mean weight diameter and soil 0 3 3 hydraulic conductivity saturated.

Understanding Arbuscular Mycorrhizal Colonization in Walnut Plantations: The Contribution of Cover Crops and Soil Microbial Communities

Soil microorganisms play a central role in biological soil functioning. One of the beneficial microbiota that has a symbiotic association with most of the plants is arbuscular mycorrhizal fungi (AMF). Nevertheless, little is known about the impact of cover crops—widely used in conservation agriculture or organic farming—on native mycorrhizal fungi. This study was conducted in Southern France, in 20-year-old walnut orchards, where faba bean (Vicia faba Roth) was intercropped. To find whether the native AM fungal community associated with walnut trees was influenced by cover crops and soil microbial communities, analyses of soil physicochemical and microbiological indicators were carried out with roots and soil samples collected from four modalities (walnut in conventional farming with and without cover crops, and walnut in organic farming with and without cover crops). Our results showed that the presence of cover crops mainly influenced the soil microbial abundance and activities in conventional plots. In contrast, cover crops stimulated AM fungal colonization of walnut roots in organic plots, reaching 35% and 54% for arbuscule abundance and mycorrhizal intensity, respectively. In conventional plots, ergosterol and mineral nitrogen contents were mainly correlated with mycorrhizal colonization, while only acid phosphatase activity in soil was positively correlated with mycorrhizal colonization in organic plots. The use of the faba bean showed the great role played by cover crops in the enhancement of walnut trees’ mycorrhizal colonization. Identification of the functional traits of AM fungi sensitive to walnut trees is required to inform decisions in specific agricultural practices.

Enzyme activities in a sandy soil of Western Bahia under cotton production systems: short-term effects, temporal variability, and the FERTBIO sample concept.

Enzyme activities (EAs) and the FERTBIO sample concept have been increasingly adopted as a novel approach to estimate the soil quality in Brazil. However, the performance of this strategy in sandy soils of the Cerrado biome remains unclear. During 2years, in a Cerrado's sandy soil, the short-term effects of ten different cropping systems (conventional tillage or no-tillage associated with monoculture, rotations, and/or successions) on the activities of β-glucosidase, acid phosphatase, and arylsulfatase were studied. Issues related to annual variability and the feasibility of using the FERTBIO sample concept for soil enzymes activities were also evaluated. Soil samples were collected at three different depths (0-10cm, 10-20cm, and 20-40cm) in March 2017 and February 2018. Five years since the beginning of the experiment, the presence of cover crops and no-till promoted improvements in EAs evidencing the importance of regenerative management practices for the sustainability of agroecosystems in sandy soils. Regardless of the cropping systems and depths evaluated, soil organic carbon and EAs showed low temporal variation during the 2years of monitoring. Our results also showed that it is possible to use the FERTBIO sample concept for the Quartzipsament soils of Western Bahia, Brazil.

Under-vine cover crops: impact on weed development, yield and grape composition

This study aims to evaluate the interest of using an under-vine cover crop as a sustainable management tool replacing herbicides or tillage to control weeds, evaluating its effects on yield and berry parameters in a semi-arid climate. The performance of Trifolium fragiferum as an under-vine cover crop was evaluated in 2018 and 2019 in a Merlot vineyard in Traibuenas (Navarra, Spain). This trial showed that the soil under the vines was covered by 80 % of the cover crop in August 2018 and 100 % in Aug 2019, with clover (T. fragiferum) comprising around 26 % and 70 % of the cover crop surface, respectively. The presence of the cover crop only reduced the number of shoots in the second year, although both years there was an increment in water stress. Neither yield, cluster weight nor berry weight were affected by the presence of the under-vine cover crop. Similarly, no changes in grape composition were observed. The use of T. fragiferum-like cover crops under the vine allows for better control of weeds, provided a good installation is achieved. In the first two years, this cover crop reduced vegetative growth and increased water deficit slightly. However, no changes in yield and grape composition were observed.In a context of herbicide suppression and search for sustainable management, under-vine clover cover crops constitute a viable alternative in semi-arid regions provided drip irrigation can be applied.

Slug Monitoring and Impacts on the Ground Beetle Community in the Frame of Sustainable Pest Control in Conventional and Conservation Agroecosystems.

In conservation agriculture, slugs are considered significant pests and their monitoring is a key option in the integrated pest management framework. Together with molluscicide applications, predators such as ground beetles can offer a tool for slug control in the field. Through the evaluation of slug and ground beetle monitoring strategies, this work compared their presence in conventional and conservation agricultural plots. The invasive Deroceras invadens was the dominant slug species to occur in all sampling periods. Among Carabidae, Poecilus cupreus and Pterostichus melas were the most abundant species, and Bembidion spp., Brachinus spp., and Harpalus spp. were also common. Beer-baited pitfall traps, whatever their alcoholic content, caught more slugs and ground beetles than wooden boards used as shelters. Slugs were more abundant in conventional plots than in conservation plots, possibly due to the lower presence of natural enemies such as ground beetles. Despite possible impacts on Carabidae, beer-baited pitfall traps should be considered a useful tool for slug monitoring and for the planning of molluscicide applications. Soil management such as minimum- or no-tillage and the presence of cover crops are important elements influencing both slug and ground beetle presence, possibly playing a key role in the maintenance of natural enemy populations.

Short‐Term Effects of Cover Crops on Soil Microbial Characteristics and Biogeochemical Processes across Actively Managed Farms

Core Ideas The effect of cover crops on soil microbes and biogeochemistry was examined. Cover crops increase microbial biomass and bioavailable soil carbon. Increasing cover crop biomass amplifies belowground effects. Agricultural soils are largely degraded or under threat of degradation. Given a growing human population and the subsequent need to feed this population, agricultural practices must maintain productivity and soil quality. Cover cropping regimes are a management approach that aims to address these dual goals. Although the use of cover crops has been linked to many positive effects on soil quality and crop yields, few studies have examined their effects on soil microbial community structure and function under active farm management. We assessed soil characteristics and microbial community structure and function between agricultural field plots with and without cover crops. We expected microbes would respond in the short‐term to increasing cover crop biomass, with increases in microbial activity and a shift in C acquisition toward substrates indicative of root exudation. In the presence of cover crops, we found active microbial biomass and bioavailable‐C increased by 64 and 37%, respectively, indicating the potential for increased C sequestration. Soil NH4+ increased by 64%, whereas soil NO3‐ decreased by 30%, indicating a shift toward less mobile N forms and the potential of greater nutrient retention under cover cropping regimes. Additionally, increasing cover crop biomass was related to lower microbial biomass C/N ratios and to decreased utilization of recalcitrant C substrates. These results potentially suggest a shift toward greater microbial utilization of root‐derived compounds with increasing cover crop biomass. Together, these results indicate that, in the short‐term, the presence of cover crops may improve soil quality, as measured by indices of microbial activity, and soil C and nutrients.

Pigeon bean allelopathy on the germination and development of carrot seedlings

Carrot is an edible tuberous root with high economic value in Brazil. Carrot seeds may present uneven germination due to the presence of inhibitors in the epithelium. The presence of cover crops in the growing area may generate allelopathic compounds, with the potential to inhibit or stimulate germination of cultivated species. The work objective was verifying effect of pigeon bean extract levels on germination and development of carrot seedlings. The research was conducted in a completely randomized design, in a 3x5 factorial scheme (cultivars,Danvers, Flakker Giant and Nantes Milena and extract concentrations, 0, 25, 50, 75 and 100%). Were evaluate germination (first germination count, speed and final percentage), seedling root length and seedling dry mass. The data obtained were submitted to variance and regression analysis.

Atlantic Forest soil as reference in the soil quality evaluation of coconut orchards (Cocos nucífera L) under different management

The evaluation of the soil quality is important to identify potential problems of soil degradation.The assessment of the soil quality requires the determination of several soil parameters and the integration of specific soil properties measurements into mathematical models, such as the soil quality index (SQI).The aims of this study were to: (i) determine the SQI for an Ultisol under a remnant of Atlantic Rain Forest; (ii) use the SQI for the Atlantic Rain Forest as a reference to evaluate the effects of conventional and integrated management in coconut orchards. It was hypothesized that the conventional management of coconut (Cocos nuciferaL.) orchards reduces the SQI compared with Atlantic Rain Forest. A soil quality index was constructed using an additive model that considered three main soil functions (the ability of the soil to promote root growth, water storage and flux, and nutrient supply) and a set of soil indicators. The SQI values were 0.66, 0.54 and 0.46 for the Atlantic Forest,integrated and conventional orchards, respectively; therefore, there was decline in soil quality in both orchards. Even though there was an increase in the organic matter content in the integrated coconut orchard as result of the maintenance of the organic residues on the soil surface and the presence of cover crops, the SQI indicated that, in that type of highly weathered soil, a more conservative approach needs to be applied to avoid further soil quality degradation.

Effect of cover crops on maize-velvet leaf competition: leaf area density and light interception

Cover crops influence on canopy structure and light interception of maize (Zea mays L.) and velvetleaf (Abutilon theophrasti Medik), was studied in a field experiment. Treatments included planting of bean (Phaseolus vulgaris L.), soybean (Glycine max (L.) Merr.) and berseem clover (Trifolium alexandrium L.) as cover crops at the same date and 21 days after maize. Sole cropping of maize under weed- free and weedy conditions were also included in this experiment. All tested cover crops significantly reduced leaf area density and height of velvetleaf up to 50 %, while maize leaf area density increased in the presence of cover crops. Among cover crops, bean and soybean were the most effective in reducing velvetleaf leaf area density and height. Bean and soybean also strongly reduced absorbed light by velvetleaf by up to 80 % compared to clover. Maize grain yields were significantly influenced by cover crops planting in the inter row space. Compared to weeds free plots, only treatment with soybean as a cover crop resulted in similar maize grain yields, while maize intercropping with bean and clover significantly reduced maize yields. Delayed planting of cover crops, 21 day after maize, increased maize grain yield compared to cover crops and maize planting at the same time.

Modelling soil organic carbon in Danish agricultural soils suggests low potential for future carbon sequestration

Soil organic carbon (SOC) is in active exchange with the atmosphere. The amount of organic carbon (OC) input into the soil and SOC turnover rate are important for predicting the carbon (C) sequestration potential of soils subject to changes in land-use and climate. The C-TOOL model was developed to simulate the dynamics of SOC storage on medium- to long-term trends in the whole soil profile (0–100cm), and was used to compare SOC changes under typical Danish farming conditions for two sites in Denmark having the greatest possible temperature differences for the period 1986 and 2012. For this purpose, various agricultural management scenarios were considered including characteristic crop rotations with and without the presence of cover crops, and the application of organic amendments. We compared these simulated management effects with management effects estimated from Danish SOC monitoring network over the same period of time. The results of the C-TOOL simulations demonstrated that application of organic manure, use of cover crop, and converting the croplands to grassland had the potential to increase SOC in Danish mineral soils. The simulated data also suggested that C-TOOL gave a reasonably good account of SOC changes when compared with measured SOC values from a Danish national monitoring network, and the simulated management effects agree well with results of long-term experimental trials. The estimates show rather small potential for increasing SOC in Danish cropping systems, even when there is conversion to rotations with more grasslands or the use of cover crops is increased.

Weed suppression by cover crops: comparative on‐farm experiments under integrated and organic conservation tillage

SummaryCover crops are increasingly being used for weed suppression and to enhance the sustainability of agro‐ecosystems. However, the suitability of cover crops for weed suppression in integrated and organic conservation tillage systems is still poorly investigated. Therefore, a 2‐year field study at eight sites was conducted to test the weed suppressive potential of six legume‐based cover crops, with the aim to reduce herbicide input or mechanical weed management interventions. In all experiments, cover crops were directly sown after cereals before next year's main crop (grain maize or sunflower). The presence of cover crops caused a 96% to 100% reduction of weed dry matter at the four sites managed under integrated production, while effects were lower at the four sited managed under organic production, ranging from 19% to 87%. Cover crops that covered soil quickly and which produced much dry matter had the best weed suppressive potential. However, their weed suppressing effect was difficult to predict, as it depended on the year of the investigation, experimental site, cover crop species, the speed of soil cover in autumn and the density of the resulting mulch layer in spring. The study demonstrated that cover crops are a useful tool to suppress weeds under integrated and organic conservation tillage practices. Our recommendation for supporting weed management in conservation tillage systems is to use locally adapted cover crops that have rapid establishment, good soil coverage and high dry matter production. However, additional weed management measures are required for reliable weed control under on‐farm conditions.

Weed species differ in their ability to emerge in no‐till systems that include cover crops

AbstractNo‐till cropping systems that include cover crops could lead to important changes in weed communities by decreasing some annual weed populations. In this study, we predicted that seed burial depth and the presence of cover crop would affect the emergence and initial growth success of annual weed species. We tested two factors on 14 weed species in a greenhouse: the seed burial depth of weeds (buried versus soil surface) and the presence/absence of a cover crop (ryegrass). We counted the emerged seedlings and measured the height of weeds and cover crops (Hweed, Hcover), the dry matter content of weeds and cover crops (DMCweed, DMCcover) and the number of leaves of weeds (NLweed) on 1433 weed and 390 ryegrass individuals. Emergence of five weed species (AMBEL, ANGAR, BROST, CENCY and EPHHE) was affected by the seed location (−10.3% on average for unburied seeds), five other weed species (ALOMY, CAPBP, SONAS, VERPE and VLPMY) were affected by cover (on average −9.5% for seeds emerged in the presence of cover crop), and four weed species (GERDI, LAMPU, POAAN and VIOAR) were not affected by either. Weed growth of all weed species also decreased with the presence of a cover crop (on average Hweed: −49.9%, DMCweed: −87.2% and NLweed: −55.4%) and for unburied seeds (on average Hweed: −33.7%, DMCweed: −70.6% and NLweed: −43.3%), with various responses according to species. This study indicates that annual weeds could be disadvantaged by no‐till systems using cover crops.

Adubação potássica para o milho cultivado sob palhada de Capim Marandu

No Brasil, muitos trabalhos referentes à adubação potássica para a cultura do milho apontam para a ausência de resposta a este nutriente mesmo que a maioria dessas pesquisas seja desenvolvida em solos com teores de K de médio a alto; outro aspecto que deve ser levado em consideração é a presença de plantas de cobertura no sistema que podem influenciar a resposta a este nutriente. Objetivou-se avaliar o efeito de doses de K2O associadas à cobertura vegetal do solo com capim Marandu sobre a produtividade do milho e o teor de K no solo. O experimento consistiu de 8 tratamentos estabelecidos em delineamento de blocos casualisados com parcelas subdivididas. Cada dose de K2O (0, 75, 150, 225 kg ha-1) correspondeu a uma parcela sendo as subparcelas formadas pela presença ou ausência de Brachiaria brizantha cv. Marandu. Em solo com baixo teor de K, o milho responde à adubação potássica, independente da presença de palha de capim Marandu. A adubação potássica aplicada em superfície com ou sem palhada, eleva os teores de K do solo mesmo em camadas mais profundas; como planta de cobertura, o capim Marandu aumenta a eficiência da adubação potássica com consequente aumento de produtividade da cultura do milho.

Winter Nitrate Leaching under Different Tillage and Winter Cover Crop Management Practices

The potential for nitrate (NO3–) to leach is enhanced following cultivation of pastoral land, due to rapid mineralization of labile soil organic matter (SOM). In a 7‐yr field trial in New Zealand, we examined the impacts of tillage intensity [intensive (plowing to 20 cm), minimum, or no‐tillage] and winter cover crops (forage rape) on NO3– leaching following cultivation of permanent (sheep [Ovis aries]‐grazed) pasture to grow arable crops (the rotation included barley [Hordeum vulgare L.], wheat [Triticum aestivum L.], and pea [Pisum sativum L.]). Permanent pasture and permanent fallow (maintained plant‐free using herbicides, i.e., not cultivated or fertilized) treatments were included as controls. Losses of NO3––N were calculated from soil solution NO3––N concentrations (measured in ceramic suction cups installed at 600 mm) and drainage volumes. Cumulative NO3––N leached over 7 yr ranged from 20 to 428 kg N ha– 1, with least N lost under pasture. Residual soil mineral N in autumn accounted for ∼30% of the variability in leaching. Nitrate leaching under arable crops generally increased rapidly as winter rainfall (range 78–352 mm yr– 1) increased. Winter cover crops were effective in reducing NO3––N leaching losses, particularly in drier winters when about 50% less N leached where cover crops were grown. On average, annual leaching was only 10 to 18 kg N ha– 1 in the presence of cover crops. Tillage had relatively little influence on leaching, though use of minimum tillage for autumn cultivation resulted in significantly (P < 0.001) less NO3––N leaching than either intensive or no tillage. Largest leaching losses were recorded in the unfertilized, permanent fallow where there was no plant sink for NO3–N derived from SOM mineralization. Growing a crop during the winter period, combined with good N management practices to minimize pre‐winter soil mineral N, provides the best option to keep NO3– leaching within the acceptable range for arable cropping in New Zealand.

Sorption and mineralisation of S-metolachlor in soils from fields cultivated with different conservation tillage systems

Conservation tillage is promoted to improve the sustainability of agricultural systems and reduce the environmental impact of agricultural activities. These techniques strongly influence soil properties that can modify the fate of pesticides. S-metolachlor (SMOC) is a selective chloroacetamide pre- and post-emergence herbicide used on a variety of crops including maize, soybean, sunflower and sorghum and frequently detected in natural waters. The purpose of this study was to evaluate the effects of conservation tillage management, crop rotation, fallow period management and soil type on sorption and mineralisation of SMOC. During spring 2010, soil samples were collected from 51 agricultural fields located in the central basin of the Midi-Pyrenees (south-west France) at two depths in the topsoil layers (0–5cm and 5–10cm). Soils were mainly Calcisols, Luvisols and Cambisols. The SMOC adsorption coefficient (Kd) was measured for each sample using a batch equilibration technique. Mineralisation was monitored during laboratory incubations made at field capacity and 25°C for 113 days. Kd values ranged from 0.8 to 8.7Lkg−1 with a mean of 3.0Lkg−1 and a CV of 44%. Sorption was positively correlated with organic carbon (OC) content (ρ=0.74) and negatively with pH (ρ=−0.42). The presence of cover crop during the fallow period was found to enhance SMOC sorption. The mineralisation of SMOC after 113 days was found to be highly variable between samples and ranged from 0.8% to 28.3% of applied 14C-SMOC with a higher mineralisation in the 5–10cm-depth samples. It was positively correlated with soil pH (ρ=0.58) and with total microbial biomass (ρ=0.32). Mineralisation was also negatively correlated with OC content (ρ=−0.34) and adsorption coefficient Kd (ρ=−0.49). A better correlation (ρ=0.66) was obtained between mineralisation and the ratio ‘total microbial biomass/adsorption coefficient (Kd)’ of each sample. This correlation could be interpreted as an illustration of the competition between retention and degradation, directly depending on the modification of soil organic matter and microbial activity by the different conservation tillage systems.