Amount Of Biological Nitrogen Fixation Research Articles

Effects of management practices on legume productivity in smallholder farming systems in sub‐Saharan Africa

AbstractLegumes play a key role in food and nutrition security, providing livestock feed and contributing to soil fertility, in mixed smallholder farms in sub‐Saharan Africa (SSA). The environmental conditions under which smallholder farming is practiced are highly heterogeneous with large differences in management practices among farms resulting in variable legume productivity. A meta‐analysis based on 128 publications was conducted to quantify the effects of intercropping, inoculation with rhizobia, minimum tillage and phosphorus application on legume grain and biomass yield and the amount of biological nitrogen fixation in a range of SSA contexts. To further explain the heterogeneity in the results, legume species, type of inoculant, P‐application rate, altitude, rainfall, soil characteristics and non‐legume companion crops were used as moderators. Intercropping as compared to sole cropping reduced legume biomass and grain yields to varying extents, although the total land equivalent ratio for the sum of the intercrops was higher than 1 (1.2–1.9) in all cases. Expressed as the relative land equivalent ratio (rLER) intercropping affected pigeonpea grain yield the least (rLER 0.9) and faba bean the most (rLER 0.3). The non‐legume companion crops explained some of the heterogeneity where maize and sorghum significantly reduced the legume yields. Inoculation and P application increased legume grain and biomass yield and moderators such as legume species, type of inoculant, soil organic carbon and soil pH further explained the different effects of the management practices on legume productivity. Minimum tillage had no effect on legume productivity, although less data were available than for the other practices. We conclude that intercropping with legumes improves overall productivity and that application of P fertilizer and inoculants increase legume grain and biomass yield. The effect varies with crop species, soil type and other environmental conditions, and this needs to be factored into tailored recommendations supporting decision making in smallholder farming.

The amount, but not the proportion, of N2 fixation and transfers to neighboring plants varies across grassland soils

ABSTRACT Biological nitrogen fixation (BNF) is an important nitrogen source for both N2-fixers and their neighboring plants in natural and managed ecosystems. Biological N fixation can vary considerably depending on soil conditions, yet there is a lack of knowledge on the impact of varying soils on the contribution of N from N2-fixers in mixed swards. In this study, the amount and proportion of BNF from red clover were assessed using three grassland soils. Three soil samples, Hallsworth (HH), Crediton (CN), and Halstow (HW) series, were collected from three grassland sites in Devon, UK. A pot experiment with 15N natural abundance was conducted to estimate BNF from red clover, and the proportion of N transferred from red clover to the non-N2 fixing grass in a grass-clover system. The results showed that BNF in red clover sourced from atmosphere in the HH soil was 2.92 mg N plant−1, which was significantly lower than that of the CN (6.18 mg N plant−1) and HW (8.01 mg N plant−1) soils. Nitrogen in grass sourced from BNF via belowground was 0.46 mg N plant−1 in the HH soil, which was significantly greater than that in CN and HW soils. However, proportionally there were no significant differences in the percentage N content of both red clover and grass sourced from BNF via belowground among soils, at 65%, 67%, 65% and 35%, 27%, 31% in HH, CN, and HW, respectively. Our observations indicate that the amount of BNF by red clover varies among grassland soils, as does the amount of N sourced from BNF that is transferred to neighboring plants, which is linked to biomass production. Proportionally there was no difference among soils in N sourced from BNF in both the red clover plants and transferred to neighboring plants.

Evaluation of the field performance, nitrogen fixation efficiency and competitive ability of pea landraces grown under organic and conventional farming systems

ABSTRACTIn the present study, three pea Greek landraces Schinousa (AUASCHIN001), Andros (AUAANDRO001), and Amorgos (AUAAMORG001), and the commercial variety Onward were grown following either conventional or organic farming practices. The main objective of the study was to assess the suitability of these three landraces for organic cultivation as compared with a standard commercial variety. The total fresh pod yield produced by AUASCHIN001 and AUAAMORG001 was significantly lower than that obtained from ‘Onward’ and AUAANDRO001. Furthermore, the three landraces exhibited a higher competition to weeds than the commercial variety. Under organic farming conditions, AUASCHIN001 and AUAAMORG001 produced appreciably less shoot biomass than ‘Onward’ and this resulted in commensurate decreases in the total amount of BNF (biological nitrogen fixation) in their plant tissues, although the percentage of nitrogen (N) fixed from the atmosphere was significantly lower in ‘Onward’. AUAANDRO001 rendered the highest amounts of BNF in the organic farming systems, which was similar to that produced by ‘Onward’ in the conventional system. These results indicate that the tested landraces and especially AUAANDRO001 are more adaptable to low soil N levels and high weed competition, and thus they are more suitable for organic cultivation than ‘Onward’ which performs best in conventional cropping systems.

Vetch-rye biculture is a sustainable alternative for enhanced nitrogen availability and low leaching losses in a no-till cover crop system

The reliance of current farming systems on synthetic fertilizers caused concerns about their sustainability, and alternatives to supply nitrogen through biological processes have to be adapted to practical conditions. The present study compared a pure legume and legume-grass biculture as cover crops for sorghum in their supply of nitrogen (N) to the cash crop and their N leaching losses during fallow. A three-year field experiment under no-till with sorghum (Sorghum bicolor Moench.) as main crop and cover crop treatments (C- control=bare fallow; R-rye Secale cereale L.; V-vetch Vicia villosa sp dasycarpa; VR-vetch-rye biculture) was established with a completely randomized block design (four replicates) in semiarid central Argentina. Aerial biomass (AB) and N contents were determined for all crops. Soil moisture to 1m and nitrate-N to 0.60m depth were determined. Water use- and nitrogen use efficiencies (WUE and NUE) were calculated and biological nitrogen fixation (BNF) estimated. BNF depended on nitrate-N contents of the soils; highest values (11 and 10g BNFm−2 for V and VR respectively) were reached at 1.3gNm−2. Sorghum responded to higher N availability with an average of +299 and +512gABm−2 for V and VR compared to C, with higher WUE. The relationship between WUE and nitrate-N was positive with an optimum of 0.048gNm−2mm −1 where WUE reached a maximum of 4.9gABm−2mm−1. Potential N losses by leaching were highest in control, while all cover crop treatments had lower losses. Our results support the hypothesis that a legume-grass biculture was more efficient in the trade-off between nitrogen provision to the cash crop and prevention of N losses by leaching. Although the amount of BNF was lower in the biculture than in pure vetch, it covered sorghum N requirements with less potential leaching losses even in high rainfall fallows.

Arboreal Legume Litter Nutrient Contribution to a Tropical Silvopasture

Legumes contribute to pasture sustainability through symbiotic N2 fixation, which may increase primary productivity and animal performance in low‐input systems. Litterfall is the main way of cycling nutrients from tree legumes. We quantified gliricidia [Gliricidia sepium (Jacq.) Kunth ex Walp.] and sabiá (Mimosa caesalpiniifolia Benth) litter deposition, along two 336‐d cycles, in a signalgrass (Brachiaria decumbens Stapf.) pasture. Litterfall was produced throughout the year but concentrated in the dry season. Sabiá produced slightly greater (P < 0.0001) litterfall amounts in the two cycles (10,790 kg ha−1) than gliricidia (10,420 kg ha−1) but the overall average N concentration of gliricidia (21.5 g kg−1) was greater than that of sabiá (18.8 g kg−1). Nitrogen amounts cycled through the litter were greater for gliricidia in both cycles (105 and 109 kg N ha−1) than for sabiá (87 and 98 kg N ha−1). The proportions of litter N that were derived from the atmosphere by symbiotic fixation were similar (P ≥ 0.05) in both species (55%) and varied little along the two cycles. Lignin concentration, which influences decomposition, was similar in both species, averaging 238 and 214 g kg−1 in the two cycles for gliricidia and 233 and 246 g kg−1 for sabiá. Greater N concentration, lower C/N ratio and lower lignin concentration indicate that gliricidia litter may have a faster cycling rate than sabiá litter. Sabiá could be a more promising species for soil cover and protection because of its slower litter decomposition rate.Core Ideas Litter deposition was an important pathway of N return in warm‐climate silvopasture systems. Tree legumes added significant amounts of biological nitrogen fixation to silvopasture systems. Gliricidia litter presented better quality than Mimosa litter. Proportion of litter N derived from atmosphere was significant.

Proteomics and Metabolomics: Two Emerging Areas for Legume Improvement.

The crop legumes such as chickpea, common bean, cowpea, peanut, pigeonpea, soybean, etc. are important sources of nutrition and contribute to a significant amount of biological nitrogen fixation (>20 million tons of fixed nitrogen) in agriculture. However, the production of legumes is constrained due to abiotic and biotic stresses. It is therefore imperative to understand the molecular mechanisms of plant response to different stresses and identify key candidate genes regulating tolerance which can be deployed in breeding programs. The information obtained from transcriptomics has facilitated the identification of candidate genes for the given trait of interest and utilizing them in crop breeding programs to improve stress tolerance. However, the mechanisms of stress tolerance are complex due to the influence of multi-genes and post-transcriptional regulations. Furthermore, stress conditions greatly affect gene expression which in turn causes modifications in the composition of plant proteomes and metabolomes. Therefore, functional genomics involving various proteomics and metabolomics approaches have been obligatory for understanding plant stress tolerance. These approaches have also been found useful to unravel different pathways related to plant and seed development as well as symbiosis. Proteome and metabolome profiling using high-throughput based systems have been extensively applied in the model legume species, Medicago truncatula and Lotus japonicus, as well as in the model crop legume, soybean, to examine stress signaling pathways, cellular and developmental processes and nodule symbiosis. Moreover, the availability of protein reference maps as well as proteomics and metabolomics databases greatly support research and understanding of various biological processes in legumes. Protein-protein interaction techniques, particularly the yeast two-hybrid system have been advantageous for studying symbiosis and stress signaling in legumes. In this review, several studies on proteomics and metabolomics in model and crop legumes have been discussed. Additionally, applications of advanced proteomics and metabolomics approaches have also been included in this review for future applications in legume research. The integration of these “omics” approaches will greatly support the identification of accurate biomarkers in legume smart breeding programs.

Sunnhemp and millet as green manure for tropical maize production

Commonly N release from legume residues is rapid in the tropics. Legume mixtures with grasses can result in slower nutrient release from residues, better matching the N requirements of the following crop. The objectives of this study were to evaluate the effects of the green manures sunnhemp (Crotalaria juncea) and millet (Pennisetum glaucum), alone or mixed, on the performance of a subsequent maize crop with and without the application of N-fertilizer. The experiment consisted of four randomized blocks, with split plots. The plot treatments consisted of previous cultivation of sunnhemp, millet, mixed sunnhemp+millet and weeds. The subplot treatments were 90 kg N ha-1 and absence of N-fertilizer. Substantial amounts of biological nitrogen fixation (BNF) nitrogen were present in above ground parts of sunnhemp alone (173 kg ha-1) and mixed with millet (89 kg ha-1). Decay rates showed that half of the N was released 15 and 22 days from sunnhemp and sunnhemp+millet residues, respectively. The difference was attributed to temporary immobilization due to the higher C/N ratio of sunnhemp+millet. The preceding sunnhemp+millet treatment resulted in a larger maize yield than sunnhemp alone, when no N-fertilizer was applied. This effect was not observed when N-fertilizer was added. This effect may be due to a more timely N release, compared to sunnhemp and millet alone, when available N is required for maize. Nitrogen budgets showed that 15% and 10% in maize grain N was recovered from BNF for sunnhemp alone and sunnhemp+millet respectively. The recovery of N-BNF by maize was 65% higher after sunnhemp+millet than after sunnhemp monocrop.

COMPARISON OF BIOLOGICAL NITROGEN FIXATION IN FOUR PAIRS OF CONVENTIONAL AND ALTERNATIVE MIXED CROPPING FARMS WITH THREE ROTATIONAL STAGES OF PASTURE ESTABLISHMENT IN CANTERBURY, NEW ZEALAND

It is generally recognized that in order for arable farming systems to remain sustainable in the long term, they need to be productive and their soil fertility must be maintained to continue to provide viable yields with minimum detrimental effects on soil and environmental quality. The use of biological nitrogen fixation (BNF) as the main source of nitrogen (N) for crops is an important sustainable management strategy. Amounts of BNF in four pairs of conventional and organic mixed cropping farms, each with three stages of pasture establishment in Canterbury, New Zealand were compared under farmers' field conditions over a period of one year using the 15N isotope dilution technique. Composite topsoil (0–75 mm) samples were taken from all sites at the beginning and end of the trials. These were analyzed for soil pH and available nutrients according to New Zealand “MAF Quick Test” methods. In addition, at the end of the trials, soil samples at four depths (0–50, 50–100, 100–150, 150–200 mm) were taken from inside and outside the experimental plots in pastures of three different ages in one of the pairs of conventional and organic farms and analyzed for total soil N. Results obtained showed that the amounts of biologically-fixed N varied from 19 to 68 kg N ha−1 year−1. There were no significant differences between paired conventional and organic farms or between pastures of different ages. This was attributed to the large variability present and the possibility that the farms studied were at a steady state condition in terms of BNF as supported by total soil N and available soil nutrient data. The BNF was significantly correlated with clover biomass and was also affected significantly by seasons.

Balance of nitrogen and phosphorus in a paddy field of central Korea

The present study was carried out during a period of 1 y (from May 1, 1997 to April 30, 1998) in a rice cultivation area not affected by livestock farming, farmstead, and industrial complexes to investigate the balance of nutrients in rainfall, irrigation water, runoff water, and infiltration water. The soil of the experimental field belonged to the Jisan series (SiL; fine loamy, mixed mesic family of Fluventic Haplaquepts) covering on area of 5,000 m2 (100 m × 50 m). In the investigated area, the amount of rainfall was 1,095 mm during the cropping season and 415 mm during the non-cropping season (off-season). The annual rainfall was 1,510 mm. The total amount of runoff water was 1,043 mm during the cropping season and 281 mm during the off-season and the added total amount of runoff water during the two seasons was 1,324 mm. The input amounts of nitrogen and phosphorus were as follows: 217.6 kg ha-1 for nitrogen and 27.2 kg ha-1 for phosphorus from chemical fertilizer, 39.5 and 0.7 kg ha-1 y-1 from rainfall, 29.7 and 0.5 kg ha-1 from irrigation water, 1.0 and 0.2 kg ha-1 from irrigation sediments, and 34.0 and 12.3 kg ha-1 from rice straw, respectively. The amount of biological nitrogen fixation was 94.8 kg ha-1 y-1. The residual amounts of nitrogen and phosphorus in soil were 85.0 and 15.6 kg ha-1 y-1, respectively. The output amounts of nitrogen and phosphorus from different channels were as follows: 157.9 kg ha-1 y-1 for nitrogen and 4.5 kg ha-1 y-1 for phosphorus from runoff water, 3.2 and 0.9 kg ha-1 y-1 from runoff sediments, 20.3 and 0.2 kg ha-1 from infiltration water, and 111.6 and 19.2 kg ha-1 from rice plant absorption. The nitrogen losses from paddy fields were 24.0 kg ha-1 y-1 by denitrification and 44.6 kg ha-1 by ammonia volatilization. When the loss ratio was calculated based on the amount of applied chemical fertilizer, about 68.6% of nitrogen was lost by rainfall-runoff while 16.7% of phosphorus was lost. The loss ratio of nutrients by infiltration was as follows: nitrogen, 9.4% out of the amount applied; and phosphorus, 0.6%. Also, about 11% of nitrogen was lost by denitrification and about 20.5% by ammonia volatilization.