Legume Rotation Research Articles

Tillage, residue burning and crop rotation alter soil fungal community and water-stable aggregation in arable fields

Abstract Soil microbiology is a key factor in soil organic matter decomposition, and nutrient turnover and availability in agricultural soils, which can be markedly influenced by management practices, such as placement of crop residues, tillage and crop rotation. The present field study was designed as long-term experiment in an experimental farm located in the suburb of Shanghai, China, to study the effects of agricultural management practices on community composition of soil fungi and soil structure. Treatments included burning (crop residues burnt vs . not burnt), tillage (tillage vs . no-tillage) and crop rotation (wheat–corn vs . wheat–soybean). The experiment started in June 2001 and soil samples were collected in March, July and November 2003, i.e. 2 years after establishment. Abundance, diversity and species composition of fungi and soil aggregate composition were analyzed. Hypothesis 1 was that abundance, species richness and diversity of soil fungi would increase in treatments with no-tillage, crop residue retention and wheat–legume rotation compared to tillage, burning and wheat–corn rotation, and Hypothesis 2 that size-distribution of stable aggregates would increase with the diversity of soil fungi. A total of 27 species of fungi of 15 genera were isolated. As the Hypothesis 1, overall soil fungal species richness (6.3 ± 0.4), diversity (2.2 ± 0.1) and total species number (26) in no-tillage significantly exceeded the species richness (4.4 ± 0.3), diversity (1.7 ± 0.1) and total species number (21) in tillage treatments, respectively. However, the effects of tillage depended on soil depth and were most pronounced deeper in soil (10–15 cm soil depth). The Hypothesis 2 was supported by the results: The content of large macro-aggregates (>2000 μm) (295 ± 94 g/kg soil) in no-tillage treatments significantly exceeded that (99 ± 25 g/kg soil) in tillage treatments in 10–15 cm but not in 0–5 cm soil depth, and coincidentally, soil fungal species richness (6.3 ± 0.5) and diversity (2.3 ± 0.1) in 10–15 and also the species richness (6.5 ± 0.5) and diversity (2.3 ± 0.1) in 5–10 cm in no-tillage treatments significantly exceeded the species richness (4.2 ± 0.7) and diversity (1.6 ± 0.3) in 10–15 cm and the species richness (4.3 ± 0.4) and diversity (1.7 ± 0.2) in 5–10 cm in tillage treatments, respectively, but the differences were also not in 0–5 cm soil depth. The results suggest that no-tillage favours fungi and that a more diverse fungal community beneficially affects the formation of large soil macro-aggregates. Further, the results indicate that species richness and diversity of cultivable fungi are useful and distinctive parameters reflecting the status and functioning of the soil fungal community.

Water Use by Five Warm‐Season Legumes in the Southern Great Plains

ABSTRACTGrowing warm‐season legumes during fallow periods associated with traditional continuous systems of winter wheat (Triticum aestivum L.) in the southern Great Plains (SGP) can provide supplemental forage, biological N, and protection from soil erosion, provided the legumes can tolerate drought stress and not deplete the available water in the soil profile. Our objective was to quantify water use by five species of pulse legumes {pigeon pea [(Cajanus Cajan (L.) Millsp.) cv. GA‐2], guar [Cyamopsis tetragonobloba (L.) Taub., cv. Kinman], cowpea [Vigna unguiculata (L.) Walp., cv. Chinese red], mung bean [Vigna radiate (L.) Wilcz., cv. Berkins], and soybean [Glycine max (L.) Merr., cv. Hutcheson (the control)]}. Seeds were inoculated and planted after wheat harvest in mid‐June 2003 through 2006. The amount of water in the upper 65 cm of the soil profile was measured on nine dates [from 45 d before planting legumes to 195 d since planting (DSP)]. Significant (P < 0.01) differences in soil water were recorded among treatments, dates, and years. Differences in soil water among fallow, cowpea, and mung bean were less following the 2003 and 2004 summer seasons and most noticeable in 2005 and 2006. Mung bean, guar, soybean, and pigeon pea used the greatest amounts of water in 2005, the wettest season, while cowpea and mung bean used the least in 2003. Mung bean, cowpea, and guar generated smaller water deficits and used less soil water, in three of four years, and could be effective in wheat‐summer legume rotations in the SGP.

Long-term effects of conservation tillage on organic fractions in two soils in southwest of Spain

Long-term field experiments can provide relevant information regarding soil organic carbon sequestration under different soil tillage systems. Especially, conservation tillage (CT) has been proved to be a practice that highly contributes to improve soil quality. For that reason, the study of soil quality indicators, such as organic fractions, are useful tools to assess changes caused by different soil tillage systems in long-term field experiments. We evaluated long-term effects of conservation tillage on soil carbon fractions and biological properties in a sandy clay loam Entisol (soil A) and in a clay Vertisol (soil B) located in semi-arid SW Spain. Cereal–sunflower–legume rotations under rainfed conditions were used in both soils in which conservation tillage (CT) was compared to traditional tillage (TT). Soil samples were collected at three depths (0–5, 5–10 and 10–20 cm) four months after sowing a pea crop ( Pisum arvense L.) in the Entisol and a wheat crop ( Triticum aestivum L.) in the Vertisol. Labile fractions of the total organic carbon (TOC) were determined as active carbon (AC) and water soluble carbon (WSC). Biological status was evaluated using soil microbial biomass carbon (MBC) and enzymatic activities [dehydrogenase activity (DHA), o-diphenol oxidase activity (Dphox), and β-glucosidase activity (β-glu)]. As a rule, the contents of AC, WSC, MBC, β-glu and Dphox in soil A and contents of TOC, AC and DHA in soil B were higher in CT than in TT, at the 0–5 cm depth. In both soils, the studied parameters decreased with depth under both tillage treatments (TT and CT). Values of AC, TOC, MBC and β-glu were positively correlated with each other ( p < 0.05) in both soils. The principal component analysis (PCA) showed that two principal components explained 44.17% and 21.2% of the total variability in the Entisol and 47.3% and 19.3% in Vertisol. The first principal component was influenced mostly by AC and β-glucosidase in the Entisol, while it was influenced by DHA, MBC and AC in Vertisol. Discriminant analysis (DA) showed as discriminant function was strongly correlated with MBC, AC and Dphox in soil A and with TOC, AC and WSC in soil B. From both analyses (PCA and DA) in this study, AC content was the most sensitive and consistent indicator for assessing the impact of different soil managements on soil quality in our two types of soil. Long-term conservation tillage in dryland farming systems improved the quality of both soils, especially at the surface, by enhancing soil organic carbon and biological status.

Modeling N2O flux from an Illinois agroecosystem using Monte Carlo sampling of field observations

We modeled the expected range of seasonal and annual N2O flux from temperate, grain agroecosystems using Monte Carlo sampling of N2O flux field observations. This analysis is complimentary to mechanistic biogeochemical model outcomes and provides an alternative method of estimating N2O flux. Our analysis produced a range of annual N2O gas flux estimates with mean values overlapping with results from an intermodel comparison of mechanistic models. Mean seasonal N2O flux was 1–4% of available N, while median seasonal N2O flux was less than 2% of available N across corn, soybean, wheat, ryegrass, legume, and bare fallow systems. The 25th–75th percentile values for simulated average annualized N2O flux rates ranged from 1 to 12.2 kg N ha−1 in the conventional system, from 1.3 to 8.8 kg N ha−1 in the cover crop rotation, and from 0.8 to 9.3 kg N ha−1 in the legume rotation. Although these modeling techniques lack the seasonal resolution of mechanistic models, model outcomes are based on measured field observations. Given the large variation in seasonal N gas flux predictions resulting from the application of mechanistic simulation models, this data-derived approach is a complimentary benchmark for assessing the impact of agricultural policy on greenhouse gas emissions.

Validating economic and environmental sustainability of a short-term summer forage legume in dryland wheat cropping systems in south-west Queensland

The present study set out to test the hypothesis through field and simulation studies that the incorporation of short-term summer legumes, particularly annual legume lablab (Lablab purpureus cv. Highworth), in a fallow–wheat cropping system will improve the overall economic and environmental benefits in south-west Queensland. Replicated, large plot experiments were established at five commercial properties by using their machineries, and two smaller plot experiments were established at two intensively researched sites (Roma and St George). A detailed study on various other biennial and perennial summer forage legumes in rotation with wheat and influenced by phosphorus (P) supply (10 and 40 kg P/ha) was also carried out at the two research sites. The other legumes were lucerne (Medicago sativa), butterfly pea (Clitoria ternatea) and burgundy bean (Macroptilium bracteatum). After legumes, spring wheat (Triticum aestivum) was sown into the legume stubble. The annual lablab produced the highest forage yield, whereas germination, establishment and production of other biennial and perennial legumes were poor, particularly in the red soil at St George. At the commercial sites, only lablab–wheat rotations were experimented, with an increased supply of P in subsurface soil (20 kg P/ha). The lablab grown at the commercial sites yielded between 3 and 6 t/ha forage yield over 2–3 month periods, whereas the following wheat crop with no applied fertiliser yielded between 0.5 to 2.5 t/ha. The wheat following lablab yielded 30% less, on average, than the wheat in a fallow plot, and the profitability of wheat following lablab was slightly higher than that of the wheat following fallow because of greater costs associated with fallow management. The profitability of the lablab–wheat phase was determined after accounting for the input costs and additional costs associated with the management of fallow and in-crop herbicide applications for a fallow–wheat system. The economic and environmental benefits of forage lablab and wheat cropping were also assessed through simulations over a long-term climatic pattern by using economic (PreCAPS) and biophysical (Agricultural Production Systems Simulation, APSIM) decision support models. Analysis of the long-term rainfall pattern (70% in summer and 30% in winter) and simulation studies indicated that ~50% time a wheat crop would not be planted or would fail to produce a profitable crop (grain yield less than 1 t/ha) because of less and unreliable rainfall in winter. Whereas forage lablab in summer would produce a profitable crop, with a forage yield of more than 3 t/ha, ~90% times. Only 14 wheat crops (of 26 growing seasons, i.e. 54%) were profitable, compared with 22 forage lablab (of 25 seasons, i.e. 90%). An opportunistic double-cropping of lablab in summer and wheat in winter is also viable and profitable in 50% of the years. Simulation studies also indicated that an opportunistic lablab–wheat cropping can reduce the potential runoff + drainage by more than 40% in the Roma region, leading to improved economic and environmental benefits.

Grain legume rotation benefits to maize in the northern Guinea savanna of Nigeria: fixed-nitrogen versus other rotation effects

The yield increases often recorded in maize following grain legumes have been attributed to fixed-N and ‘other rotation’ effects, but these effects have rarely been separated. Field trials were conducted between 2003 and 2005 to measure these effects on maize following grain legumes in the northern Guinea savanna of Nigeria. Maize was grown on plots previously cultivated to two genotypes each of soybean (TGx 1448-2E and SAMSOY-2) and cowpea (IT 96D-724 and SAMPEA-7), maize, and natural fallow. The plots were split into four N fertilizer rates (0, 30, 60 and 90 kg N ha−1) in a split plot design. The total effect was calculated as the yield of maize following a legume minus the yield following maize, both without added N and the rotation effect was calculated as the difference between rotations at the highest N fertilizer rate. The legume genotypes fixed between 14 and 51 kg N ha−1 of their total N and had an estimated net N balance ranging from −29.8 to 9.5 kg N ha−1. Positive N balance was obtained only when the nitrogen harvest index was greater than the proportion of N derived from atmosphere. The results also indicated that the magnitude of the fixed-N and other rotation effects varied widely and were influenced by the contributions of the grain legumes to the soil N-balance. In general, fixed-N effects ranged from 124 to 279 kg ha−1 while rotation effects ranged between 193 and 513 kg ha−1. On average, maize following legumes had higher grain yield of 1.2 and 1.3-fold compared with maize after fallow or maize after maize, respectively.

Rotation effects of grain legumes and fallow on maize yield, microbial biomass and chemical properties of an Alfisol in the Nigerian savanna

Understanding changes in soil chemical and biological properties is important in explaining the mechanism involved in the yield increases of cereals following legumes in rotation. Field trials were conducted between 2003 and 2005 to compare the effect of six 2-year rotations involving two genotypes each of cowpea (IT 96D-724 and SAMPEA-7) and soybean (TGx 1448-2E and SAMSOY-2), a natural bush fallow and maize on soil microbial and chemical properties and yield of subsequent maize. Changes in soil pH, total nitrogen (N tot), organic carbon (C org), water soluble carbon (WSC), microbial biomass carbon (C mic) and nitrogen (N mic) were measured under different cropping systems. Cropping sequence has no significant ( P > 0.05) effect on soil pH and C org, while WSC increased significantly when maize followed IT 96D-724 (100%), SAMPEA-7 (95%), TGx 1448-2E (79%) and SAMSOY-2 (106%) compared with continuous maize. On average, legume rotation caused 23% increase in N tot relative to continuous maize. The C mic and N mic values were significantly affected by cropping sequence. The highest values were found in legume–maize rotation and the lowest values were found in fallow–maize and continuous maize. On average, C mic made up to 4.8% of C org and N mic accounted for 4.4% of N tot under different cropping systems. Maize grain yield increased significantly following legumes and had strong positive correlation with C mic and N mic suggesting that they are associated with yield increases due to other rotation effects. Negative correlation of grain yield with C mic:N mic and C org:N tot indicate that high C:N ratios contribute to nitrogen immobilization in the soil and are detrimental to crop productivity. The results showed that integration of grain legumes will reverse this process and ensure maintenance of soil quality and maize crop yield, which on average, increased by 68% and 49% following soybean and cowpea, respectively compared to continuous maize.

Mixed-species legume fallows affect faunal abundance and richness and N cycling compared to single species in maize-fallow rotations

Rotation of nitrogen-fixing woody legumes with maize has been widely promoted to reduce the loss of soil organic matter and decline in soil biological fertility in maize cropping systems in Africa. The objective of this study was to determine the effect of maize-fallow rotations with pure stands, two-species legume mixtures and mixed vegetation fallows on the richness and abundance of soil macrofauna and mineral nitrogen (N) dynamics. Pure stands of sesbania ( Sesbania sesban), pigeon pea ( Cajanus cajan), tephrosia ( Tephrosia vogelii), 1:1 mixtures of sesbania + pigeon pea and sesbania + tephrosia, and a mixed vegetation fallow were compared with a continuously cropped monoculture maize receiving the recommended fertilizer rate, which was used as the control. The legume mixtures did not differ from the respective pure stands in leaf, litter and recycled biomass, soil Ca, Mg and K. Sesbania + pigeon pea mixtures consistently increased richness in soil macrofauna, and abundance of earthworms and millipedes compared with the maize monoculture (control). The nitrate-N, ammonium-N and total mineral N concentration of the till layer soil (upper 20 cm) of pure stands and mixed-species legume plots were comparable with the control plots. Sesbania + pigeon pea mixtures also gave higher maize grain yield compared with the pure stands of legume species and mixed vegetation fallows. It is concluded that maize-legume rotations increase soil macrofaunal richness and abundance compared with continuously cropped maize, and that further research is needed to better understand the interaction effect of macrofauna and mixtures of organic resources from legumes on soil microbial communities and nutrient fluxes in such agro-ecosystems.

The contribution of agricultural practices to nitrous oxide emissions in semi‐arid Mali

AbstractThe yield and flux of nitrous oxide (N2O) emitted from continuous cereals (with and without urea), legumes/cereal in rotation and cereal/legume in rotation all with or without organic manure was monitored from January 2004 to February 2005. All treatments except continuous cereals had phosphate added. The cereal grown July–October in 2003 and 2004 was pearl millet (Pennisetum glaucum) and the legume was a bean (Phaseolus vulgaris). The 10 m × 10 m plots were established in a semi‐arid climate in Mali. The addition of organic manure and both inorganic fertilizers increased yield and N2O emissions. Continuous cereals treated with both organic manure and urea emitted significantly less N2O (882 g N/ha per year) than plots receiving no organic manure(1535 g N/ha per year). Growing N‐fixing crops in rotation did not significantly increase N2O emissions. This study supports the new practice of growing cereal and legumes in rotation as an environmentally sustainable system in semi‐arid Mali.

A PARTICIPATORY APPROACH TO INCREASING PRODUCTIVITY OF MAIZE THROUGH STRIGA HERMONTHICA CONTROL IN NORTHEAST NIGERIA

SUMMARYStriga hermonthica is a parasitic weed that attacks maize, sorghum and other staple cereal crops and has long been considered one of the greatest biotic constraints to cereal production in Africa. Use of resistant or tolerant maize varieties, a maize–legume rotation using trap crops that stimulate suicidal germination of Striga and the application of nitrogen fertilizer are all effective in reducing infestation and damage. This paper reports on the use of a participatory research and extension approach in assessing the performance and scaling-up of integrated Striga control packages in three agro-ecological zones in Borno State, Nigeria. The participatory process which encourages close interaction between research, extension and farmers, involved 30 local communities and 228 farmers representing 193 farmer groups in identifying their own problems and seeking solutions to them. Results showed not only effective Striga control but productivity increases of over 200%. The involvement of local farmers and groups in the evaluation process, firstly, helped to confirm that Striga control can best be achieved using soyabean followed by Striga-resistant maize together with productivity-increasing management practices and, secondly, promoted farmer-to-farmer extension. A participatory adoption assessment exercise indicated widespread adoption of new varieties and management practices, despite the need for increased labour. Great potential exists to scale out the results to similar areas of Guinea and Sudan savannas in the West Africa region.

Short-term effects of crop rotation, residue management, and soil water on carbon mineralization in a tropical cropping system

The purpose of this study was to investigate the short-term effects of maize (Zea mays)-fallow rotation, residue management, and soil water on carbon mineralization in a tropical cropping system in Ghana. After 15 months of the trial, maize–legume rotation treatments had significantly (P < 0.001) higher levels of potentially mineralizable carbon, C0 (μg CO2–C g−1) than maize–elephant grass (Pennisetum purpureum) rotations. The C0 for maize–grass rotation treatments was significantly related to the biomass input (r = 0.95; P = 0.05), but that for the maize–legume rotation was not. The soil carbon mineralization rate constant, k (per day), was also significantly related to the rotation treatments (P < 0.001). The k values for maize–grass and maize–legume rotation treatments were 0.025 and 0.036 day−1 respectively. The initial carbon mineralization rate, m0 (μg CO2–C g−1 day −1), was significantly (P < 0.001) related to the soil water content, θ. The m0 ranged from 3.88 to 18.67 and from 2.30 to 15.35 μg CO2–C g−1 day−1 for maize–legume and maize–grass rotation treatments, respectively, when the soil water varied from 28% to 95% field capacity (FC). A simple soil water content (θ)-based factor, fw, formulated as: \(f_{\text{w}} = \left[ {\frac{{\theta - \theta _{\text{d}} }}{{\theta _{{\text{FC}}} - \theta _{\text{d}} }}} \right]\), where θd and θFC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m0 with respect to soil water (R2 = 0.91; RMSE = 1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions.

Role of Legume Fallow in Intensified Vegetable-Based Systems

Traditional shifting cultivation systems can no longer be sustained in intensive vegetable production systems of southwestern Nigeria. Alternative cropping systems include the use of site‐specific, weed‐suppressing, multipurpose cover legumes as short‐duration crops while reducing production costs. The purpose of this study was to investigate an integrated soil management system with leguminous cover crops in vegetable‐based systems. One year, planted fallow of leguminous cover crops Aeschynomene histrix, Canavalia ensiformis, Centrosema pubescens, Chamaecrista rotundifolia, Crotolaria ochroleuca cv. “Utiisp”, Mucuna Ghana, Mucuna pueraria cv. “IRZ”, Mucuna puriens cv. “Utilis”, Mucuna rajada, Pueraria phaseolodies, Stylosanthes hamata, and natural grass fallow as a control were followed by sweet maize (Zea mays cv. “TZSR‐sweet”) and vegetable amaranth (Amaranthus hybridus cv. “NHAc3”) in the second year, with 0 or 60 kg nitrogen (N) ha−1 as urea. Results showed that ground coverage by the cover crops within the first 3 months after planting (MAP) was highest in Crotolaria and lowest in Centrosema. At 5 MAP, Crotolaria had the highest biomass accumulation followed by Canavalia, Aeschynomene, and Mucuna cv. “IRZ”. Mucuna puriens cv. “Utilis” had a significantly higher soil total N compared with the grass fallow. Legume rotation increased vegetable yields and N accumulations. Legume fallow appeared to offer potential to sustain vegetable yields under intensified cropping. However, the absolute effect varied as a function of legume species and N‐management practices.

Meta-analysis of maize yield response to woody and herbaceous legumes in sub-Saharan Africa

A number of studies have tested the effect of woody and herbaceous legumes on soil fertility and maize yields in sub-Saharan Africa. However, their effects on maize productivity are much debated because results have been variable. A meta-analysis was conducted with the aim of evaluating the evidence in support of yield benefits from woody and herbaceous green manure legumes. A total of 94 peer-reviewed publications from West, East and southern Africa qualified for inclusion in the analysis. Maize yield from herbaceous green manure legumes (54 publications), non-coppicing legumes (48 publications), coppicing woody legumes (10 publications), natural fallows (29 publications), and fully fertilized monoculture maize (52 publications) were compared. Mixed linear modelling using yield differences (D) and response ratios (RR) indicated that the response to legumes is positive. The mean yield increase (D) over unfertilized maize was highest (2.3 t ha−1) and least variable (CV = 70%) in fully fertilized maize, while it was lowest (0.3 t ha−1) and most variable (CV = 229%) in natural fallows. The increase in yield over unfertilized maize was 1.6 t ha−1 with coppicing woody legumes, 1.3 t ha−1 with non-coppicing woody legumes and 0.8 t ha-1 with herbaceous green manure legumes. Doubling and tripling of yields relative to the control (RR > 2) was recorded in coppicing species (67% of the cases), non-coppicing legumes (45% of the cases), herbaceous green manure legumes (16% of the cases) and natural fallows (19% of the cases). However, doubling or tripling of yields occurred only in low and medium potential sites. Amending post-fallow plots with 50% of the recommended fertilizer dose further increased yields by over 25% indicating that legume rotations may play an important role in reducing fertilizer requirements. Except with the natural fallow, the 95% confidence intervals of D and RR were higher than 1 and 0, respectively indicating significant and positive response to treatments. Therefore, it is concluded that the global maize yield response to legumes is significantly positive and higher than unfertilized maize and natural vegetation fallows.

Nitrate‐Nitrogen Concentrations in the Perched Ground Water under Seepage‐Irrigated Potato Cropping Systems

Excessive nitrogen rates for potato production in northeast Florida have been declared as a potential source of nitrate pollution in the St. Johns River watershed. This 3-yr study examined the effect of N rates (0, 168, and 280 kg ha(-1)) split between planting and 40 d after planting on the NO(3)-N concentration in the perched ground water under potato (Solanum tuberosum cv. Atlantic) in rotation with sorghum sudan grass hybrid (Sorghum vulgare x Sorghum vulgare var. sudanese, cv. SX17), cowpea (Vigna unguiculata cv. Iron Clay), and greenbean (Phaseolus vulgare cv. Espada). Soil solution from the root zone and water from the perched ground water under potato were sampled periodically using lysimeters and wells, respectively. Fertilization at planting increased the NO(3)-N concentration in the perched ground water, but no effect of the legumes in rotation with potatoes on nitrate leaching was detected. Fertilization of green bean increased NO(3)-N concentration in the perched ground water under potato planted in the following season. The NO(3)-N concentration in the soil solution within the potato root zone followed a similar pattern to that of the perched ground water but with higher initial values. The NO(3)-N concentration in the perched ground water was proportional to the rainfall magnitude after potato planting. A significant increase in NO(3)-N concentration in the perched ground water under cowpea planted in summer after potato was detected for the side-dressing of 168 kg ha(-1) N applied to potato 40 d after planting but not at the 56 kg ha(-1) N side-dress. Elevation in NO(3)-N concentration in the perched ground water under sorghum was not significant, supporting its use as an effective N catch crop.

Recent Advances in Medicago truncatula Genomics.

Legume rotation has allowed a consistent increase in crop yield and consequently in human population since the antiquity. Legumes will also be instrumental in our ability to maintain the sustainability of our agriculture while facing the challenges of increasing food and biofuel demand. Medicago truncatula and Lotus japonicus have emerged during the last decade as two major model systems for legume biology. Initially developed to dissect plant-microbe symbiotic interactions and especially legume nodulation, these two models are now widely used in a variety of biological fields from plant physiology and development to population genetics and structural genomics. This review highlights the genetic and genomic tools available to the M. truncatula community. Comparative genomic approaches to transfer biological information between model systems and legume crops are also discussed.

Cross-pathogenicity of Rhizoctonia solani strains on pasture legumes in pasture-crop rotations

In Australia, in the past, pasture legumes were rotated mainly with cereals, but increasingly these rotations now involve pasture legumes with a wider range of crops, including legumes. This increasing frequency of the leguminous host in the rotation system may be associated with increased root rots in legumes in the current pasture-crop rotations. The primary aim of this study was to see whether the pathogenicity on pasture legumes of strains of Rhizoctonia solani sourced from lupins and cereals (common crops in rotation with pastures) is associated with increased incidence of root rots in pasture legumes in the disease conducive sandy soils of the Mediterranean regions of southern Australia. The second aim was to determine sources of resistance among newly introduced pasture legumes to R. solani strains originating from rotational crops as this would reduce the impact of disease in the pasture phase. Fifteen pasture legume genotypes were assessed for their resistance/susceptibility to five different zymogram groups (ZG) of the root rot pathogen R. solani under glasshouse conditions. Of the R. solani groups tested, ZG1–5 and ZG1–4 (both known to be pathogenic on cereals and legumes) overall, caused the most severe root disease across the genotypes tested, significantly more than ZG6 (known to be pathogenic on legumes), in turn significantly >ZG4 (known to be pathogenic on legumes) which in turn was >ZG11 (known to be pathogenic on legumes including tropical species). Overall, Ornithopus sativus Brot. cvs Cadiz and Margurita, Trifolium michelianum Savi. cvs Paradana and Frontier and T. purpureum Loisel. cv. Electro showed a significant level of resistance to root rot caused by R. solani ZG11 (root disease scores ≤1.2 on a 1–3 scale where 3 = maximum disease severity) while O. sativus cvs Cadiz and Erica showed a significant level of resistance to root rot caused by R. solani ZG4 (scores ≤1.2). O. compressus L. cvs Charano and Frontier, O. sativus cv. Erica, and T. purpureum cv. Electro showed some useful resistance to root rot caused by R. solani ZG6 (scores ≤1.8). This is the first time that cvs Cadiz, Electro, Frontier, Margurita and Paradana have been recognised for their levels of resistance to root rot caused by R. solani ZG11; and similarly for cvs Cadiz and Erica against ZG4; and for cvs Charano, Erica, and Electro against ZG6. These genotypes with resistance may also serve as useful sources of resistance in pasture legume breeding programs and also could potentially be exploited directly into areas where other rotation crops are affected by these R. solani strains. None of the tested genotypes showed useful resistance to R. solani ZG1–4 (scores ≥2.0) or ZG1–5 (scores ≥2.5). This study demonstrates the relative potential of the various R. solani ZG strains, and particularly ZG1–4, ZG1–5, ZG4 and ZG6 to attack legume pastures and pose a significant threat to non-pasture crop species susceptible to these strains grown in rotation with these pasture legumes. Significantly, the cross-pathogenicity of these strains could result in the continuous build-up of inoculum of these strains that may seriously affect the productivity eventually of legumes in all rotations. In particular, when choosing pasture legumes as rotation crops, caution needs to be exercised so that the cultivars deployed are those with the best resistance to the R. solani ZGs most likely to be prevalent at the location.

Productivity and rotational benefits of grass, medic pastures and faba beans in a rainfall limited environment

This study was undertaken to ascertain whether pulses, instead of pasture legumes, were more beneficial to grain yields by the following cereals in ley rotation systems. We evaluated growth processes for pastures or pulses and growth and yields for the following sequential crops of wheat and barley in a 3-crop rotation. The pasture or pulse phase that formed the main treatments consisted of grass pastures (Grass), medics (Medic) or faba beans that was either green manured (Faba-gm) or harvested for grain (Faba-gr). The rotations were initiated in two phases with Phase 1 starting in 1994 and Phase 2 in 1995, and each phase ran over 2 rotation cycles lasting 6 years. Despite differences in dry matter (DM) produced in the shoots and roots by the pastures and faba beans in the first years, they had similar seasonal evapotranspiration (ET) so water stored in the 100 cm profile of the soil was always similar when wheat was planted. By contrast, inorganic N in soil at wheat planting was always higher in legume rotations than in Grass and these differences persisted to the barley crop. Cereals in rotations with faba beans (Faba-gr and Faba-gm) produced more DM and grains than in Grass. In only 2 out of 8 croppings of cereals did wheat or barley in Medic out-yield those in Grass. These yield differences were not associated with uptake of soil N or use of soil-water by the cereals, but possibly due to lower levels of Pratylenchus neglectus in the soil under rotations with faba beans compared with pasture. Increased N supply after legumes or from fertilizer, however, increased grain protein in the cereals. This study showed that rotations with faba beans produced higher yields for the following cereals than with grassy or legume pastures, also green manuring of faba beans produced no advantage in yield for the cereals.

Water-use efficiency of wheat-based rotation systems in a Mediterranean environment

Crop production in Mediterranean-type environments is invariably limited by low and erratic rainfall (200–600 mm year −1), and thus soil moisture, and by high evapotranspiration resulting from high temperature. Consequently, a major research challenge is to devise cropping systems that maximize water-use efficiency (WUE). In a long-term trial in northern Syria (1986–1998) we compared the effects of seven wheat-based rotations on soil water dynamics and WUE in both the wheat and non-wheat phase. The cropping systems were durum wheat ( Triticum turgidum L.) in rotation with fallow, watermelon ( Citrullus vulgaris), lentil ( Lens culinaris), chickpea ( Cicer arietinum), vetch ( Vicia sativa), medic pasture ( Medicago spp.), and wheat. Seasonal recharge/discharge were identified using the neutron probe. Depth of wetting varied with seasonal rainfall (233–503 mm). Based on crop yields, WUE was calculated for each cropping option in relation to the durum wheat crop. The greatest limitation to growth was the supply of water and not the soil moisture storage potential. Wheat grain yield was dictated by the extent to which the alternative crops in the rotation dried out the soil profile, in addition to seasonal rainfall and its distribution. Chickpea and medic extracted as much water as continuous wheat. Wheat after these crops was solely dependent on current seasonal rainfall, but fallow, lentil, watermelon, and vetch did not deplete soil moisture to the same extent, leaving some residual soil moisture for the succeeding wheat crop. This difference in soil water resulted in a significant difference in wheat yield and hence WUE, which decreased in the following crop rotation sequence: fallow, medic, lentil, chickpea, and continuous wheat. However, on the system basis, the wheat/lentil or wheat/vetch systems were most efficient at using rainfall, producing 27% more grain than the wheat/fallow, while the wheat/chickpea system was as efficient as wheat/fallow system, with continuous wheat being least efficient. With N added to the cereal phase, system WUE of the system increased, being least for continuous wheat and greatest for wheat/lentil. Wheat–legume rotation systems with additional N input in the wheat phase not only can maintain sustainable production system, but also are more efficient in utilizing limited rainfall.

Nitrogen Contribution of Peanut Residue to Cotton in a Conservation Tillage System

ABSTRACT Leguminous crops, particularly winter annuals, have been utilized in conservation systems to partially meet nitrogen (N) requirements of succeeding summer cash crops. Previous research also highlights the benefits of utilizing summer annual legumes in rotation with non-leguminous crops. This study assessed the N contribution of peanut (Arachis hypogaea L.) residues to a subsequent cotton (Gossypium hirsitum L.) crop in a conservation system on a Dothan sandy loam (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) at Headland, AL during the 2003–2005 growing seasons. Treatments were arranged in a split plot design, with main plots of peanut residue retained or removed from the soil surface, and subplots as N application rates (0, 34, 67, and 101 kg ha− 1) applied in fall and spring. Peanut residue did not influence seed cotton yields, leaf N concentrations, or plant N uptake for either growth stage or year of the experiment. There was a trend for peanut residue to increase whole plant biomass measured at the first square in two of three years. Seed cotton yields and plant parameters measured at the first square and mid-bloom responded favorably to spring N applications, but the recommended 101 kg N ha− 1 did not maximize yields. The results from this study indicate that peanut residue does not contribute significant amounts of N to a succeeding cotton crop, however, retaining residue on the soil surface provides other benefits to soils in the southeastern U.S.

Comparison of Long‐Term Organic and Conventional Crop–Livestock Systems on a Previously Nutrient‐Depleted Soil in Sweden

An 18‐yr field study was performed to compare organic and conventional cropping on a highly P and K depleted soil in southern Sweden that had not received any inorganic fertilizers (or pesticides) since the mid‐1940s. The major management differences between the systems were (i) growth of legumes every second year and use of legumes as cover crops in the organic rotation; (ii) application of P in the organic system at higher rates than for the conventional system; (iii) exclusion of oilseed rape (Brassica napus L.) from the organic system but inclusion of potato (Solanum tuberosum L.); (iv) frequent mechanical weeding in the organic system; and (v) use of solid manure in the organic and liquid manure in the conventional system. Concentrations of soil‐exchangeable P increased more after application of large amounts of basic slag and apatite in the organic system than after application of P fertilizers in the conventional system. Organic systems, which rely mainly on legumes for their N supply, will acidify soils faster than systems with fewer legumes in rotation. Crop yields were, on average, 50% less and weed biomass was greater (1–3 Mg dry matter ha−1) in the organic system than in the conventional system. Nitrogen was identified as the main yield‐limiting nutrient for organically grown crops. Despite this, and even with use of cover crops, N leaching was not reduced by organic farming. Soil carbon (C) concentrations decreased in both systems, but less so in the organic system due to higher C inputs and lower soil pH values. Still, organic farming seems not be an option for sequestering C in soil in Sweden. After adjusting the two systems to the same boundary conditions for an unbiased modeling comparison, the C input is ≈60% higher in the conventional system than the organic system. The agronomic efficiency of N was 9 to 10 kg grain yield kg−1 N in the organic system compared with 16–18 kg grain yield kg−1 in the conventional system. The long‐term use efficiency of P was lower in the organic system (7%) than in the conventional system (36%). These results show that yield and soil fertility are superior in conventional cropping systems under cold‐temperate conditions.