Legume Phase Research Articles

Soil nitrous oxide emissions from wheat-based rotations with different types of pulse crops

Production of agricultural crops with a low greenhouse gas (GHG) footprint is essential to mitigate the adverse effects of climate change. The inclusion of pulse crops in cereal-based rotations can enhance environmental quality by providing biologically fixed N and thereby reducing the amount of synthetic N fertilizer required for the crop rotation. The inclusion of pulse crop has the potential to reduce N2O emissions from the agricultural system in both the legume phase and the subsequent wheat phase of the rotation. However, long-term studies are necessary to thoroughly investigate N2O emissions from rotations with pulse crops, particularly in the semiarid region where pulse crops are frequently grown. In the present study, we evaluated cumulative N2O emissions and emission intensity during the rotation cycle. The assessment was conducted over 4 years, during two complete 2-yr cycles of an established rotation (years 9–12), under the climatological conditions of 2018–2021. Four rotations including wheat-wheat, pea-wheat, lentil-wheat, and chickpea-wheat were selected from a trial in Swift Current, Saskatchewan (semiarid prairies/Brown Chernozem). Our experiment was subjected to below normal precipitation, with interannual variations in climate and the last 2 years (2020–21) were drier than the first two years (2018–2019). Under such climate, PW and LW demonstrated to be environmentally sustainable, always exporting the highest N in grains (133 kg N ha−1 averaged across PW and LW and cycles) and consistently achieving the lowest N2O intensity (2.8 g N2O-N per kg exported N averaged across PW and LW and cycles). Continuous wheat presented inconsistent results, with a significant reduction in exported N from years 9–10 to 11–12 (the driest cycle). Because WW also promoted the highest cumulative N2O emissions, N2O intensity over the 2-yr was always the highest for WW. The CW consistently promoted the lowest N exports and was not resilient to dry soil conditions, with 23% lower exported N in years 11–12 than in years 9–10. Hence including pulse crops with pea or lentil in the rotation reduced N2O emissions and enhanced wheat yield resiliency.

Agronomic and economic performance of legume-legume and cereal-legume intercropping systems in Northern Tanzania

CONTEXTCereal-legume intercropping, a common practice among farmers in sub-Saharan Africa (SSA), is important for crop diversification, soil fertility improvement, household nutrition and climate adaptation. However, cereals often outcompete the intercropped legumes for growth resources resulting in low legume yields. OBJECTIVEThe objectives of this study were: i) assessing the effects of different intercropping options (crop spatial configurations) and maize crop (Zea mays L.) management innovations on productivity and economic benefits to farmers and ii) examining how farmers adapt new intercropping technologies to meet their household food security needs. METHODSThe study was undertaken in six on-farm researcher-designed and managed trials in high and low rainfall agro-ecological zones of Babati District in Tanzania, during four cropping seasons (2018–2021). The cropping systems tested included a sole maize system rotated with a legume-legume intercrop (Doubled-up legume), an innovation involving two maize rows intercropped with two legume species (Mbili-Mbili), maize-legume intercrop both with and without de-topping, maize-legume intercrop (2 maize plants at 50 cm intra-space, de-topped), maize-legume system (maize with vertical leaf architecture) and a farmer practice. The Mbili-Mbili technology adaptation assessment was conducted on 225 farmers during the 2021 cropping season. RESULTS AND CONCLUSIONSOverall, maize grain yields increased by up to 56% in improved compared to farmer intercropping practices (P ≤ 0.05). There were no significant differences in maize grain yield among the improved practices. Significantly higher pigeonpea (Cajanus cajan) yields of between 71% and 113% in 2020 and between 65% and 140% in 2021 were observed under Doubled-up legume and between 63% and 124% under local farmer practices in 2020 than in the improved cereal-legume practices. Across the study period, net revenues of sole maize and Doubled-up legume rotations were both the highest and lowest relative to other intercropping options, depending on the starting phase (US$ 653 sole maize and US$ 326 legume phase starting). These were also associated with the highest variances indicating instability. Mbili-Mbili intercropping system had not only high net revenue i.e., a mean of US$623 per hectare, but also more stable. Farmers perceived that Mbili-Mbili increased food security and 96% were willing to implement the system without project support. SIGNIFICANCEMbili-Mbili is recommended for adoption by farmers because of its potential economic benefits, food security and resilience in the current unpredictable weather and climate patterns.

Soil Organic Carbon Storage in Australian Wheat Cropping Systems in Response to Climate Change from 1990 to 2060

It is important to examine the effects of climate change on temporal variations in SOC storage, in order to optimize management practices for sustainable grain production. Using the denitrification–decomposition (DNDC) model to simulate biogeochemical processes in agro-ecosystems, SOC variability was evaluated in the Australian wheat cropping system from 1990 to 2060, under the Representative Concentration Pathway 85 (RCP85) climate change scenario. We analyzed the impacts of temperature and precipitation on SOC variability and further simulated six management scenarios for wheat cultivation over 71 years, which included wheat cropping under common nitrogen fertilizer (N-fertilizer) application rate (12 kg N/ha), adequate N-fertilizer application rate (50 kg N/ha), and legume–wheat rotation with N fertilizer application rates at 0, 12, and 50 kg N/ha. The results indicated that the DNDC model provided a good simulation of biogeochemical processes associated with wheat growth; the normalized root mean square error (NRMSE) of wheat yield was 15.16%, and the NRMSE of SOC was 13.21%. The SOC (0–30 cm) decreased from 3994.1 kg C/ha in 1990 to 2848.0 kg C/ha in 2060, an average decrease of 0.4% per year. Temperature and precipitation were the important factors affecting SOC storage, with contributions of 13% and 12%, respectively. Furthermore, adding a legume phase increased SOC and wheat yield in the low N-fertilizer scenario. In contrast, adding a legume phase in the adequate N-fertilizer scenario decreased SOC and wheat yield.

Broadening farmer options through legume rotational and intercrop diversity in maize-based cropping systems of central Malawi

• Evaluated diverse legume-maize systems in a 4-year, multi-site, on-farm study. • Pigeonpea-maize rotation had the most biomass, ideal for amending infertile soils. • In hot and dry environments, groundnut increased maize yield in a subsequent year. • Pigeonpea biomass was key to high N fixation yet suppressed by intercropping. Smallholder farmers across southern Africa have limited access to adequate quantities of inorganic fertilizers, and this limits crop productivity. Integration of legumes such as groundnut ( Arachis hypogaea L.) and pigeonpea ( Cajanus cajan L.) improve soil fertility and subsequent cereal crop productivity through biological nitrogen fixation (BNF), and high-quality residues. The objective of this four-year, multi-site, on-farm study in Malawi was to evaluate diverse legume systems, quantify crop production, economic viability, and total N accumulation in groundnut and pigeonpea. The study involved six research sites with different agricultural productivity potential based on precipitation, elevation, and temperature; to evaluate crop performance by environment. The six cropping systems evaluated were sole pigeonpea or sole groundnut rotated with maize ( Zea mays L.) (PP-MZ and GN-MZ), groundnut/pigeonpea intercrop rotated with maize (GNPP-MZ), maize/pigeonpea intercrop (MZPP), continuous unfertilized maize (MZ-MZ), and fertilized maize (MZ+F). Total N accumulated by cropping system was in the order GNPP > PP > MZPP > GN at 180, 130, 103 and 87 kg N/ha respectively. In the groundnut/pigeonpea intercrop, despite a reduction of pigeonpea biomass, pigeonpea was still the main driver for N cycling in the systems. The average percentage of N derived from BNF (BNF-N%) from all plant components and across sites was 66% for groundnut and 52% for pigeonpea. Average maize grain yield for response years when rotated with legumes was 4.82, 3.25, and 2.16 Mg/ha for sites with high (Linthipe), medium (Kandeu), and low (Golomoti) agricultural productivity potential. System performance in terms of gross margins ranged from $1145 (pigeonpea-maize rotation) to $1407/ha (groundnut/pigeonpea-maize rotation). The pigeonpea-maize rotation produced the most biomass but had modest economic and agronomic returns during the legume phase. This study highlighted that, for hot and dry environments, groundnut was the most effective species at increasing maize yield in a subsequent year. The groundnut/pigeonpea-maize rotation system met multiple goals including high pigeonpea biomass, profitable groundnut grain, and high maize yields during the rotational year. This system is recommended for ecological intensification, as it provided an economically feasible means to enhance BNF on smallholder farms, while ensuring multiple grain harvest goals in different environmental contexts.

Can legume species, crop residue management or no-till mitigate nitrous oxide emissions from a legume-wheat crop rotation in a semi-arid environment?

Soil emissions of nitrous oxide (N2O) are generally low in Australian semi-arid cropping systems, but can be reduced further by incorporating legumes into cereal-based rotations. We used automated and manual chambers to compare N2O emissions throughout a two-year legume-wheat field experiment. Two pulse crops [lupin (Lupinus angustifolius L.) and field pea (Pisum sativum L.)] and two forage legumes [vetch (Vicia sativa L.) and clover (a mixture of four Trifolium spp.)] were grown in the first year, followed by a wheat (Triticum aestivum L.) crop in the second year without additional nitrogen (N) fertilizer under either no-till or tillage systems. All legume crops were either (a) chemically terminated at anthesis (brown-manured, BM), or (b) cut for hay (forage legumes) or harvested for grain (pulses) (product-removed, PR). The fate of legume N in the BM treatment was traced using 15N labelled urea applied to soil in micro-plots. Results showed that N2O emissions during the legume and wheat phases were mostly unaffected by legume species, the exception being lower emissions from the BM clover pasture under the no-till treatment. Under the PR treatment, tillage tended to increase N2O emissions compared with the no-till treatment during both legume (121 vs. 104 g N2O-N ha−1 year−1) and wheat phases (91 vs. 79 g N2O-N ha−1 year−1). In contrast, a mixed result was found under the BM treatment with a significant tillage × crop management interaction during the legume phase, but no effect of tillage during the wheat phase. In general, the BM treatment promoted more N2O emissions due to more N input into soil compared to the PR treatment, with the impact extending into the subsequent wheat crop. The N2O emissions from the BM treatment during the legume (195 g N2O-N ha−1 year−1) and wheat phase (181 g N2O-N ha−1 year−1) were greater than those from the PR treatment for the corresponding phases (113 vs. 85 g N2O-N ha−1 year−1). The 15N study showed that the majority of legume-derived N was retained in the soil at the end of the legume phase and likely to be readily available for the subsequent cereal crop. The mitigation of N2O emissions derived from legumes in a semi-arid cereal-based cropping system can be optimized in a no-till system where product removal is practiced (cut for hay or harvested for grain) with legume species choice having little or no additional impact.

Green Manures in Continuous Wheat Systems Affect Grain Yield and Nitrogen Content

Continuous winter wheat (Triticum aestivum L. em Thell.) is the foundation for most US Southern Great Plains (SGP) agriculture. Inorganic N fertilizers are important to wheat production, but increasing N prices have caused producers to reconsider growing legumes during summer fallow for green N. This study was conducted during 2008 to 2012 to determine the potential for using lablab [Lablab purpureus (L.) Sweet cv. Rio Verde] to support wheat under conventional and no‐till management compared with soybean [Glycine max (L.) Merr. cv. Laredo] and three inorganic fertilizer treatments (none, 40, and 80 kg N ha−1). Legume seeds were inoculated and sown after wheat harvest each year, grown from June to August, and terminated in early September. Wheat was then sown with or without preplant tillage and grown to maturity. Grain yield, N concentration, and N accumulated in grain were analyzed to define N treatment, tillage system, and year effects. The amount and distribution of precipitation during 2008 to 2012 varied from 53 to 92% and 63 to 160% of the long‐term averages for wheat (688 mm) and legume (162 mm) phases. Tillage effects were nonsignificant (P < 0.76), but N treatment × year interactions were significant for grain yield, N concentration, and N accumulated in grain (P < 0.01). The legumes resulted in some single‐year increases in grain yield, but the overall yield response was inconsistent. The legume treatments reduced N concentration in wheat grain compared with the unfertilized control. These results show that neither legume was an effective short‐term (≤4‐yr) N source for systems of continuous wheat production in the SGP.

Effects of Legume-Enriched Diet on Cardiometabolic Risk Factors among Individuals at Risk for Diabetes: A Crossover Study

Aims: First-degree relatives of patients with diabetes are at high risk for chronic diseases, including type 2 diabetes and obesity. Our purpose was to determine the effects of consuming 4 servings of legumes per week on lipid profiles, glycemic indices, and blood pressure of participants with family history of diabetes over 6 weeks of intervention.Methods: A total of 26 first-degree relatives of patients with diabetes (14 women and 12 men) participated in this randomized crossover clinical trial study. Participants were randomly assigned to a legume-enriched diet or habitual diet for 6 weeks. Paired t test and repeated measures analysis of variance were used to compare data for the 2 experimental diets.Results: The mean ± SE of legumes intake during the legume phase was 111.12 ± 10.53 g/day that was significantly higher (p < 0.001) than the amounts of legumes during habitual diet (50.73 ± 7.10 g/d). Percentage changes for cardiovascular disease risk factors did not change significantly following 6 weeks of legume consumption.Conclusions: Consumption of 4 servings of legumes per week had no significant effect on anthropometric measurements, glycemic indices, and lipid profiles of participants with family history of diabetes, though it could reduce systolic and diastolic blood pressure at a marginally significant level.

Response of soil nitrous oxide flux to nitrogen fertiliser application and legume rotation in a semi-arid climate, identified by smoothing spline models

Although large areas of semi-arid land are extensively cropped, few studies have investigated the effect of nitrogen (N) fertiliser on nitrous oxide (N2O) emissions in these regions (Galbally et al. 2010). These emissions need to be measured in order to estimate N losses and calculate national greenhouse gas inventories. We examined the effect of different agronomic management practices applied to wheat (Triticum aestivum) grown on an alkaline Vertosol in south-eastern Australia on N2O emissions. In 2007, N2O emissions were measured over 12 months, during which N fertiliser (urea) was applied at sowing or N fertiliser plus supplementary irrigation (50 mm) was applied during the vegetative stage and compared with a treatment of no N fertiliser or irrigation. In a second experiment (2008), the effect of source of N on N2O emissions was examined. Wheat was grown on plots where either a pulse (field peas, Pisum sativum) or pasture legume (barrel medic, Medicago truncatula) crop had been sown in the previous season compared with a non-legume crop (canola, Brassica napus). To account for the N supplied by the legume phase, N fertiliser (50 kg N ha–1 as urea) was applied only to the wheat in the plots previously sown to canola. Fluxes of N2O were measured on a sub-daily basis (up to 16 measurements per chamber) by using automated chamber enclosures and a tuneable diode laser, and treatment differences were evaluated by a linear mixed model including cubic smoothing splines. Fluxes were low and highly variable, ranging from –3 to 28 ng N2O-N m–2 s–1. The application of N fertiliser at sowing increased N2O emissions for ~2 months after the fertiliser was applied. Applying irrigation (50 mm) during the vegetative growth stage produced a temporary (~1-week) but non-significant increase in N2O emissions compared with plots that received N fertiliser at sowing but were not irrigated. Including a legume in the rotation significantly increased soil inorganic N at sowing of the following wheat crop by 38 kg N ha–1 (field peas) or 57 kg ha–1 (barrel medic) compared with a canola crop. However, N2O emissions were greater in wheat plots where N fertiliser was applied than where wheat was sown into legume plots where no N fertiliser was applied. Over the 2 years of the field study, N2O emissions attributed to fertiliser ranged from 41 to 111 g N2O-N ha–1, and averaged of 75 g N2O-N ha–1 or 0.15% of the applied N fertiliser. Our findings confirm that the proportion of N fertiliser emitted as N2O from rainfed grain crops grown in Australian semi-arid regions is less than the international average of 1.0%.

Assessing agronomic and environmental implications of different N fertilisation strategies in subtropical grain cropping systems on Oxisols

A multi-season 15N tracer recovery experiment was conducted on an Oxisol cropped with wheat, maize and sorghum to compare crop N recoveries of different fertilisation strategies and determine the main pathways of N losses that limit N recovery in these agroecosystems. In the wheat and maize seasons, 15N-labelled fertiliser was applied as conventional urea (CONV) and urea coated with a nitrification inhibitor (DMPP). In sorghum, the fate of 15N-labelled urea was monitored in this crop following a legume ley pasture (L70) or a grass ley pasture (G100). The fertiliser N applied to sorghum in the legume-cereal rotation was reduced (70 kg N ha−1) compared to the grass-cereal (100 kg N ha−1) to assess the availability of the N residual from the legume ley pasture. Average crop N recoveries were 73 % (CONV) and 77 % (DMPP) in wheat and 50 % (CONV) and 51 % (DMPP) in maize, while in sorghum were 71 % (L70) and 53 % (G100). Data gathered in this study indicate that the intrinsic physical and chemical conditions of Oxisols can be extremely effective in limiting N losses via deep leaching or denitrification. Elevated crop 15N recoveries can be therefore obtained in subtropical Oxisols using conventional urea while in these agroecosystems DMPP urea has no significant scope to increase fertiliser N recovery in the crop. Overall, introducing a legume phase to limit the fertiliser N requirements of the following cereal crop proved to be the most effective strategy to reduce N losses and increase fertiliser N recovery.

Over-Drilling New Zealand Tussock Rangeland with or without a Previous Legume Phase

A nineteen year trial at Lake Tekapo compared the longer term trends of over-drilling legume and grasses into either previous undeveloped tussock country or following a previous legume phase. Tall oat grass (from summer sowing) and cocksfoot (from spring sowing) were the most successful of the sown grasses. They remained a low proportion of the swards but greater with prior herbicide treatment, sown with an experimental drill giving partial cultivation and with starter nitrogen fertiliser. Perennial lupin became the main species in the previous undeveloped block and was increasing in the previous developed block. The analysis stage considered the inclusion of covariates for contoured location responses as well as treatment effects in such multi-plot field trials on uneven ground.

Changes in soil P pools during legume residue decomposition

In rotations, cereals after legumes often have higher P uptake than after cereals, and it has been suggested that legume residues may play an important role in this effect by mobilising soil P in the legume phase and by the P added with the residues. However, little is known about the changes in P pools during legume residue decomposition. Residues from faba bean, white lupin or chickpea (shoots or roots) with varying P concentrations were added to a loamy sand soil with a low available P concentration, and the concentration of various soil P pools were assessed by soil P fractionation on days 0, 14, 28 and 56. Residue addition significantly increased cumulative respiration which was positively correlated with amount of C added with residues (r = 0.54, p < 0.05), and negatively correlated with the C/P ratio (r = −0.58, p < 0.05). The size of the P pools changed over time and was affected by both residue P concentration and plant part (root or shoot). In the first two weeks, microbial P increased and resin P and NaHCO3–Pi decreased with low-P residues (0.6–1.8 mg kg−1) while the reverse was true for high-P residues (6.5–8.3 mg kg−1). In medium-P residues (2.9–3.3 mg kg−1), there was a balance between mineralisation and immobilisation. Decreases of NaOH–Po occurred earlier with low-P and medium-P residues (d0 to d14) than with high-P residues (d14–d28). The increase in residual P with all residues indicated that part of mineralised P was converted into stable P within 14d; but later (d28–d56), the concentration of residual P strongly decreased. In the period from d28 to d56, there was an increase in NaOH–Po and HCl–P with all residues, indicating net conversion of P into stable organic and inorganic P. Changes in P pools between roots and shoots occurred mainly in the initial phase. The concentration of NaOH–Po increased from d0 to d14, but then decreased from d14 to d28 with addition of shoot residues whereas the reverse was found with roots. These changes were generally more pronounced in low-P than in medium-P residues. This study demonstrates that changes and transformations in soil P pools over time were dependant on residue P concentration and plant part.

Effects of Tillage on Forage Legumes Growth and Subsequent Dry Matter Yields of Corn Planted for Livestock Feeding

Two field experiments were conducted to find a simple tillage method to introduce centro (Centrosema pubescens Benth.) and calopo (Calopogonium mucunoides Desv.) on native grasslands and to find out the effects of the tillage and legume phase on the growth of subsequent corn planted for livestock feeding. A 4 x 3 factorial experiment in a randomized complete block design was conducted with three replications. The first factor was the methods of tillage viz. undisturbed, cutting followed two weeks afterwards by glyphosate application at 3.0 kg ha -1 active ingredients (a.i.), burning which was cutting followed after two weeks by burning and conventional tillage. The second factor consisted of three treatments viz. introducing centro, calopo and no legume introduction. After one year, using the same plots and design that had been used in Experiment 1, the Experiment 2 was conducted, by planting corn for cattle feeding. Cutting the native grasses followed two weeks afterwards by glyphosate application was superior compared to other methods of tillage for the growth of legumes. Combining these treatments with legume inclusion resulted in 300% increase in dry matter of corn planted

STRATEGIC PHOSPHORUS APPLICATION IN LEGUME-CEREAL ROTATIONS INCREASES LAND PRODUCTIVITY AND PROFITABILITY IN WESTERN KENYA

SUMMARYMany food production systems in sub-Saharan Africa are constrained by phosphorus (P). We hypothesized that within legume-cereal rotation systems: targeting P to the legume phase leads to higher system productivity, and that use of grain legumes leads to better economic returns than use of herbaceous legumes. Four P application regimes: (i) no P, (ii) P applied every season, (iii) P applied in season 1 only and (iv) P applied in season 2 only were tested for four seasons in three cropping systems (continuous maize, mucuna-maize rotation and soybean-maize rotation) in a split plot experiment set up in Nyabeda, western Kenya. Treatments where P was applied were better than no P treatments. While continuous cereal systems showed the need for application of P every second season, rotation systems involving mucuna and soyabean indicated that application in one out of three seasons could be sufficient. Nitrogen fertilizer equivalence was 52 to &gt;90 kg N ha−1for soyabean and 37 to &gt;90 kg N ha−1for mucuna, depending on P fertilization and season. Analysis of marginal rates of return (MRR) showed that soybean-maize rotation with one application of P was the most economically viable option, with an MRR of at least 147% compared to other non-dominated options.

Productivity and residual benefits of grain legumes to sorghum under semi-arid conditions in south-western Zimbabwe: Unravelling the effects of water and nitrogen using a simulation model

The APSIM model was used to assess the impact of legumes on sorghum grown in rotation in a nutrient-limited system under dry conditions in south-western Zimbabwe. An experiment was conducted at Lucydale, Matopos Research Station, between 2002 and 2005. The model was used to simulate soil and plant responses in the experiment. Sequences of cowpea ( Vigna unguiculata), pigeonpea ( Cajanus cajan), groundnut ( Arachis hypogaea) and sorghum ( Sorghum bicolor) were used in the rotations. Legumes accumulated up to 130 kg of N ha −1 which was potentially available for uptake by sorghum in the following season. The APSIM model predicted total biomass, grain and N yields of the legume phase within the experimental error and performed well in predicting sorghum yield and N supplied in the rotation after cowpea and groundnut. The model generally under-predicted sorghum total biomass and grain yield after pigeonpea. Observed patterns of crop water use, evaporative losses during the dry season and re-charge of soil profile at the start of the rainy season were generally well predicted by the model. An assessment of output on sorghum N and water stresses in the rotation indicated that the legume–cereal rotation is more driven by soil nitrogen availability than water availability even under semi-arid conditions. Further legume–cereal rotation analysis using the model will assist in the understanding of other processes in the rotations in dry environments.

Hydrogen emission from nodulated soybeans [Glycine max (L.) Merr.] and consequences for the productivity of a subsequent maize (Zea mays L.) crop

Hydrogen (H2) is a by-product of the symbiotic nitrogen fixation (N2 fixation) between legumes and root-nodule bacteria (rhizobia). Some rhizobial strains have an uptake hydrogenase enzyme (commonly referred to as Hup+) that recycles H2 within the nodules. Other rhizobia, described as Hup−, do not have the enzyme and the H2 produced diffuses from the nodules into the soil where it is consumed by microorganisms. The effect of this phenomenon on the soil biota and on the soil itself, and consequent stimulation of plant growth, has been demonstrated previously. Soybeans [Glycine max (L.) Merr.] cv. Leichhardt, inoculated with either a Hup+ strain (CB1809) or one of two Hup− strains (USDA442 or USDA16) of Bradyrhizobium japonicum and uninoculated soybeans, plus a non-legume control [capsicum (Capsicum annuum L.)] were grown in the field at Ayr, North Queensland, Australia. The objectives were to examine (1) relationships between N2 fixation and H2 emission, and (2) the influence H2-induced changes in soil might have during the legume phase and/or on the performance of a following crop. Strains CB1809 and USDA442 were highly effective in N2 fixation (“good” fixers); USDA16 was partly effective (“poor” fixer). The soil had a large but non-uniformly distributed naturalised population of B. japonicum and most uninoculated control plants formed nodules that fixed some N2. These naturalised strains were classified as “poor fixers” of N2 and were Hup+. H2 emissions from nodules were assessed for all treatments when the soybean crop was 62 days old. Other parameters of symbiotic N2 fixation and plant productivity were measured when the crop was 62 and 96 days old and at crop maturity. Immediately after final harvest, the land was sown to a crop of maize (Zea mays L.) in order to determine the consequences of H2 emission from the soybean crop on maize growth. It was estimated that soybeans inoculated with USDA442, the highly effective Hup– strain of B. japonicum, fixed 117 kg shoot N/ha (or about 195 kg total N/ha if the fixed N associated with roots and nodules was taken into account), and contributed about 215,000 l H2 gas per hectare to the ecosystem over the life of the crop. The volume of H2 evolved from soybeans nodulated by the Hup+ strain CB1809 was only 6% of that emitted by the USDA442 treatment, but there was no indication that soybean inoculated with USDA442 benefited from the additional H2 input. The shoot biomass, grain yield, and amounts of N fixed (105 kg shoot N/ha, 175 kg total N/ha) by the CB1809 treatment were little less than for USDA442 plants. Three days after the soybean crop was harvested, the plots were over-sown with maize along the same row lines in which the soybeans had grown. This procedure exposed the maize roots to whatever influence soybean H2 emission might have had on the soil and/or the soil microflora immediately surrounding soybean nodules. The evidence for a positive effect of soybean H2 emission on maize production was equivocal. While the consistent differences between those pre-treatments that emitted H2 and those that did not indicated a trend, only one difference (out of the 12 parameters of maize productivity that were measured) was statistically significant at P < 0.05. The findings need substantiation by further investigation.

Alternate wet - dry regime during fallow failed to improve nitrogen release from added legume residues in legume - wheat rotations on a Vertisol

Forage and grain legumes are integral components of sustainable crop rotations and farming systems in semiarid subtropical agricultural systems of northern Australia. The sustainability of these farming systems largely depends on the contribution of legumes to the nitrogen (N) requirement of non-legume crops. The potential legume contribution to a succeeding wheat crop was measured in a Vertisol for 17 weeks under optimum moisture (–0.006 to –0.05 MPa) or alternate wet–dry moisture regime (–0.006 to –1.2 MPa) with or without plant residue additions (4 t/ha equivalent) following the legume phase in a glasshouse experiment. The N release from the residues followed first order kinetics. Both the N release rate and net N mineralised were positively correlated with the N concentration and negatively but log-linearly correlated with carbon and N ratios of tops and roots residues. The net N mineralised and N mineralisation potentials (N0) were not significantly affected by different moisture regimes. The proportions of net N mineralised from the annual medics, chickpea and lucerne residues were 30, 52, and 64%, respectively. The amount of nitrate N accumulated in the field during the fallow periods from 1989–98 was not related to the amount of rainfall during these periods, and most likely limited by the amount of labile or mineralisable N. Its positive correlation with N0 values showed that even during the relatively dry fallows (≥250 mm) in this semiarid subtropical environment, soils growing legumes could mineralise enough N to make a significant N contribution to the following crop in legume–cereal rotations.

Barley–legumes rotations for semi-arid areas of Lebanon

In arid and semi-arid areas of West Asia and North Africa, including the northern Bekaa Valley of Lebanon, farmers have been increasingly practicing continuous barley cultivation. The objectives of the study were to (1) determine whether barley monoculture is unsustainable 1 1 Defined in this study as having a marked yield decline over years. , (2) ascertain if barley and total dry matter yields can be increased and sustained by including a legume crop in the rotation, and (3) determine which barley–legume rotations are more productive. The trial was set up in a randomised complete block design with two replicates under rain-fed conditions in 1994–1995 at the Agricultural Research and Educational Center (33°56′ N, 36°5′ E, 995 m above sea level). Eight two-phase barley-based rotations were compared: barley in rotation with barley, lentil, common vetch, bitter vetch, common vetch for grazing, medics for grazing, common vetch for hay, and common vetch with barley for hay. Seed and straw were harvested from barley and legumes in the first four rotations. Relative to the trial mean, seed and straw yield under barley monoculture slumped in 1997–1998 and did not recover since then. Infestation of wild barley was a cause of this yield decline. Barley–legume rotations yielded 44–80% more barley grain and 27–53% more barley straw than the barley monoculture over the 6 years (1995–1996 to 2000–2001). Furthermore, in the legume phase, common and bitter vetch gave higher seed yield than barley monoculture. Thus, all barley–legume rotations, except barley–medics, yielded more total dry matter than barley monoculture on the basis of per rotation cycle. Among the barley–legume rotations, the barley-common vetch for seed rotation gave the highest and most stable dry matter yield. In conclusion, barley monoculture was unsustainable, but barley yields could be increased and sustained by including legumes in the rotation. Farmers in semi-arid areas of Lebanon should discontinue practicing barley monoculture and adopt a barley–legume, such as common vetch, rotation.

Sustainability of New Zealand high‐country pastures under contrasting development inputs. 7. Environmental gradients, plant species selection, and diversity

The change in plant species relative abundance under different fertiliser and management inputs over 19 years is reported for two grazed multiple‐species trials on a Pukaki/Tekapo high‐country soil. One trial was 30 combinations of 5 superphosphate rates (0–500 kg ha‐1 yr‐1) × 3 stocking rates × 2 stocking methods, and the second was 31 combinations of S, P (0–100 kg ha‐1 yr‐1), and micronutrient fertilisers. Both were overdrilled with a 25‐species pasture mixture. There was rapid initial separation in relative abundance of species, principally according to fertiliser level. Main features were Hieracium pilosella remaining dominant in the absence of fertiliser; the initial success of Trifolium hybridum; the dominance and long‐term persistence of Lupinus polyphyllus at low fertiliser inputs; the transition to Dactylis glomerata dominance at high fertiliser inputs following a legume phase, in the middle years; the slow vegetative increase of Trifolium ambiguum to become dominant in most of the moderate and high fertiliser treatments in the second decade; and the increase of Bromus tectorum in later years. Species distributions were predominately determined by P fertiliser rates, or P by S fertiliser interactions. The effects of different grazing managements on late spring pasture composition were small during the first decade but increased over time, with the principal changes under moderate to high rate set‐stocking. Diversity considerations showed that the number of vascular plants in a plot (n), or their proportional distribution in biomass (k diversity), gave only a weak and inconsistent correlation with secondary production (mean sheep carrying capacity), or its stability (CV of annual grazing capacity), after fertiliser and grazing management treatment effects were considered. The only significant trend was in one trial where production tended to be inversely related to the number of plant species (2.2% decrease per species).

Using legumes to enhance nitrogen fertility and improve soil condition in cotton cropping systems

Many Australian cotton growers now include legumes in their cropping system. Three experiments were conducted between 1994 and 1997 to evaluate the rotational effects of winter or summer legume crops grown either for grain or green manuring on following cotton (Gossypium hirsutum L.). Non-legume rotation crops, wheat (Triticum aestivum) and cotton, were included for comparison. Net nitrogen (N) balances, which included estimates of N associated with the nodulated roots, were calculated for the legume phase of each cropping sequence. Faba bean (Vicia faba — winter) fixed 135–244 kg N ha−1 and soybean (Glycine max — summer) fixed 453–488 kg N ha−1 and contributed up to 155 and 280 kg fixed N ha−1, respectively, to the soil after seed harvest. Green-manured field pea (Pisum sativum — winter) and lablab (Lablab purpureus — summer) fixed 123–209 and 181–240 kg N ha−1, respectively, before the crops were slashed and incorporated into the topsoil. In a separate experiment, the loss of N from 15N-labelled legume residues during the fallow between legume cropping and cotton sowing (5–6 months following summer crops and 9 months after winter crops) was between 9 and 40% of 15N added; in comparison, the loss of 15N fertilizer (urea) applied to the non-legume plots averaged 85% of 15N added. Little legume-derived 15N was lost from the system during the growth of the subsequent cotton crop. The improved N fertility of the legume-based systems was demonstrated by enhanced N uptake and lint yield of cotton. The economic optimum N fertilizer application rate was determined from the fitted N response curve observed following the application of N fertilizer at rates between 0 and 200 kg N ha−1 (as anhydrous ammonia). Averaged over the three experiments, cotton following non-legume rotation crops required the application of 179 kg N ha−1, whilst following the grain- and green-manured legume systems required only 90 and 52 kg N ha−1, respectively. In addition to improvements in N availability, soil strength was generally lower following most legume crops than non-legume rotation crops. Penetrometer resistance during the growth of the subsequent cotton crop increased in the order faba bean, lablab, field pea, wheat, cotton, and soybean. It is speculated that reduced soil strength contributed to improvement in lint yields of the following cotton crops by facilitating the development of better root systems.

The fate of biologically fixed nitrogen in legume-based dryland farming systems: a review

The fate of biologically fixed nitrogen in legume-based dryland farming systems: a review