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Background and Aims: To sustainably manage N in oil palm systems quantities of N fixed by cover legumes need to be understood. Current values are scarce, based on shoot N measures and do not include litter which releases nitrate as it decomposes. We aimed to quantify N2 fixed by legumes under oil palm systems in PNG and to determine if soil nitrate influenced dependence on N2 fixation (Ndfa). Methods: The ureide technique for estimating tropical legume Ndfa was calibrated for Calapogonium mucunoides and Pueraria phaseoloides using 15N isotope dilution, and then used to assess Ndfa for legume cover under oil palms (2 to 25 years old) in Papua New Guinea. Amounts of fixed N in above-ground legume biomass (shoot plus litter) were calculated incorporating % groundcover. Soil nitrate under the legume litter was also measured. Results: Legume Ndfa was highly negatively correlated with soil nitrate concentration but independent of palm age. Legume groundcover, shoot and litter dry matter, and quantity of fixed N were greater under oil palms less than 5 years old, decreasing under older plantations where solely C. caeruleum was present. DM and N content of litter were similar to shoots for legumes in plantations less than 6 years old. Conclusion: The calibrated ureide technique can be used, together with estimates of annual legume N accumulation, to quantify N input from legume groundcover during the life cycle of oil palm plantations and other tropical ecosystems, in order to support more sustainable management of N. [ABSTRACT FROM AUTHOR]

Soybean (Glycine max L. Merril) is among the key oil seed crops worldwide, providing several benefits from human consumption to the enhancement of soil productivity. In Uganda, legumes are cultivated on roughly 1.5 million ha, with soybean being produced on a lower production area of 150,000 ha compared to beans (925,000 ha) and groundnuts (253,000 ha). In terms of achievable yield, soybean emerges the highest at 1.2 t·ha−1 as compared to beans (0.5 t·ha−1) and groundnuts (0.7 t·ha−1). Despite the smallest production coverage area, the crop's feasible grain yield is projected at 4.6 t·ha−1 under optimal environmental conditions. The major bottleneck to the crop's production is the decreasing soil fertility, mainly caused by low nitrogen (N) but also phosphorus (P) levels in the soil. There is a high potential for supplying N from the atmosphere through biological N fixation (BNF), a natural process mediated by the symbiotic bacteria Bradyrhizobium japonicum, which requires optimum P levels for effective N fixation and increased yield. The current work reviews the present status of soybean production in Uganda, highlights its ecological requirements, importance, and constraints, and proposes the use of inoculation and P application to boost its production. [ABSTRACT FROM AUTHOR]

Aims: The improvement of biological nitrogen fixation (BNF) is beneficial to improving legume yield and soil fertility. Thus, the potential of a white-rot fungus Ceriporia lacerata HG2011 in promoting soybean BNF and yield along with the mechanisms was investigated. Methods: Fungal metabolites and the effects of C. lacerata HG2011 on rhizobial growth, chemotaxis, and biofilm formation were investigated through pure culture. Soybeans inoculated with this fungus were grown in the climatic cabinet, greenhouse, and field for measuring nodulation parameters, BNF-related enzyme activity, BNF, and yield. Results: Although C. lacerata HG2011 had no significant influence on the growth of the rhizobium Ensifer fredii S2-1, the rhizobial chemotaxis and biofilm formation were improved by this fungus broth in pure culture. C. lacerata HG2011 dwelled on the root surface, increased root tips and surface area, produced the nodulation-associated metabolites (phytohormones, flavonoids, and low-molecular-weight organic acids) and hydrolases (cellulase, pectinase, protease, and phosphatase), mobilized soil P and Fe, and stimulated the activities of plant BNF-related enzymes (nitrogenase, glutamine synthetase, and dehydrogenase). Compared with fungus-free control plants, C. lacerata HG2011 improved nodulation and increased %Ndfa by 3.61–4.64%, BNF by 29.26–40.68%, nutrients uptake (N, P, and K) by 4.38–19.60%, and mean grain yield by 10.55% in the fields. Conclusion: C. lacerata HG2011 promoted rhizobial chemotaxis as well as soybean nodulation and BNF via releasing phytohormones and improving mineral nutrition. Thus, the fungal inoculant significantly increased soybean yield in both greenhouse and fields, showing a promising application in legume cultivation. [ABSTRACT FROM AUTHOR]

Mucuna pruriens is a legume with high nitrogen (N) fixing efficiency which makes it an ideal plant for soil N inputs/enrichment in nutrient-poor ecosystems. The current study investigated how soil nutrient availability and microbe symbiosis influence the nutrient assimilation rates, growth carbon (C) cost and phytochemicals in Mucuna pruriens under greenhouse conditions. We collected soils from four sites (namely: Ashburton, Bergville, Hluhluwe and Izingolweni) in KwaZulu-Natal (KZN) province which was used as natural inoculum and growth substrate for Mucuna pruriens seeds. Mucuna pruriens established symbiotic interactions with 18 bacterial accessions from five genera which were dominated by Burkholderia, Bacillus and Paenibacillus. Hluhluwe soil-grown Mucuna pruriens had the highest concentrations of nitrogen (≈ 1.6 mmol) and phosphorus (≈ 50 mmol) as well as specific nitrogen and phosphorus absorption rate. Conversely, the specific nitrogen and phosphorus utilisation rate was highest in Izingolweni soil-grown plants. In terms of nitrogen source, Mucuna pruriens derived a significant portion (68–86%) from the atmosphere. Hluhluwe soil-grown seedlings had the lowest (0.006 mmol C g−1 DW) C cost and the highest (0.03 g day−1) relative growth rate. A total of nine phenolic acids consisting of hydroxybenzoic and hydroxycinnamic derivatives were quantified in the plants. Protocatechuic (≈ 4–11 μg g−1 DW), caffeic (≈ 3–17 μg g−1 DW), 4-coumaric (≈ 2–17 μg g−1 DW) and ferulic (≈ 2–13 μg g−1 DW) acids were the most abundant phenolic acids in Mucuna pruriens. The current findings demonstrated that Mucuna pruriens possibly establish symbiosis with different bacteria genera and synthesize different concentrations of phenolic acids when grown in grassland and savannah ecosystem nutrient-poor soils. [ABSTRACT FROM AUTHOR]

Reducing nitrogen (N) input can improve crop productivity in cereal-legume intercrops, but the impact on phosphorus (P) acquisition is unclear. A 10-year (2009–2018) field experiment was conducted to quantify how P acquisition by sugarcane (Saccharum officinarum) was affected by intercropping with soybean (Glycine max (L.) Merrill at 1:1 and 1:2) with two N inputs (300 kg ha−1 [reduced], 525 kg ha−1 [conventional]). Nitrogen was supplied only to the sugarcane crop, and soybean received no N. There was a significantly higher land-equivalent ratio of sugarcane-soybean intercropping than of the sole cropping, and the intercropping advantage was more pronounced under reduced N input which can be associated with high degree of complementary N use. Furthermore, soybean intercropping with reduced N input stimulated acid phosphomonoesterase activity and depleted organic P in the rhizosphere of sugarcane, resulting in increased sugarcane stem P concentration and system P-use efficiency. The interspecific facilitation of P acquisition could be associated with the increased symbiotic N2 fixation in soybean, soil microbial biomass and activity under reduced N input. In conclusion, soybean intercropping with reduced N input to sugarcane enhanced rhizosphere enzymatic organic P transformation and sugarcane P acquisition, which may contribute to maintaining a sustainable sugarcane production under low N supply. The findings advance our understanding of interactions between N and P cycling and provide new evidence for the value of cereal-legume intercrops in reducing fertilizer input. [ABSTRACT FROM AUTHOR]

Soybean yields in Ghana are low and stagnant in spite of the trio of recommendations: (1) improved seed, (2) rhizobium inoculant and (3) phosphorous fertilizer application being promoted by government to boost productivity. This study evaluates the response of soybean to Pro-soil biostimulant, triple super phosphate (TSP), and rhizobium inoculant in the interior savanna of Ghana. A treatment structure comprising two mainplot factors (biostimulant and conventional), and four subplots factors; TSP, inoculant, TSP+Inoculant and unamended control arranged in a split-plot design was used for this study. Apart from dry matter which increased by 42%, Pro-soil biostimulant as a stand-alone management practice did not significantly increase agronomic parameters measured in this study. Biostimulant did not have a significant effect on grain yield, nodule weight, nodule number, canopy diameter, and plant height. Application of TSP alone, and in combination with inoculant, significantly increased yield, plant dry matter, nodule weight, nodule number, and dry pod weight. Highest soybean yield was obtained from TSP + Inoculant treatment, averaging 3.6 t ha−1 compared to 1.8 t ha−1 for control. Biostimulant, TSP+Inoculant combination resulted in yields as high as 4 t ha−1. Overall, the results indicate that neither PS-Foundation biostimulant nor rhizobia inoculation can be used as stand-alone management practices to increase soybean yield. However, an integrated application of PS-Foundation biostimulant, TSP, and inoculant could double current soybean yields in Ghana. [ABSTRACT FROM AUTHOR]

Formal public sector soybean breeding in Africa spans over four decades, and it was initiated by the International Institute of Tropical Agricultural (IITA). As the demand of soybean continues to outstrip production, strategic projects such the Tropical Legume (TL) were initiated, in which the main goal was to enhance the productivity of soybean in the farmers' fields in Sub‐Saharan Africa. One of the strategies to enhance the productivity of soybean in the farmers' fields is through developing and deploying improved soybean varieties in the target countries. Through the TL I and TL II projects, a number of varieties were released in the target countries, Kenya, Nigeria, Malawi and Mozambique by employing participatory variety selection (PVS). This review provides highlights of the achievements made by IITA breeding programme and insights of what needs to be done to enhance yield improvement for soybean in Africa using demand‐driven breeding approaches. [ABSTRACT FROM AUTHOR]

Quantifying biologically fixed nitrogen (BNF) by legumes through the N natural abundance techniques requires correct determination of a so-called B value. We hypothesized that significant variations in B values exist between faba bean ( Vicia faba L.) varieties having consequences for BNF and N balance calculations. We experimentally determined B values for a range of faba bean varieties and quantified to what extent variety has an effect on B values and hence BNF quantification. Seeds of six faba bean varieties released in Ethiopia were inoculated with Rhizobium fabae strain LMG 23997-19 and grown in vermiculite with an N-free nutrient solution in a growth room until full flowering. Total N and N content of nodules, roots, and shoot components was analyzed separately to determine the weighted whole plant N fractionation during N fixation, i.e., the B value. Owing to its large seed size and high N content, a correction for seed N was carried out. We then calculated the percentage of N derived from air (%Ndfa), BNF, and N balance for faba beans grown in the field using three B value scenarios (variety specific B value corrected for seed N, variety specific B value without seed N correction, and a literature derived B value). Whole plant seed N corrected B values were significantly different ( P < 0.05) between varieties and varied between +0.5 ± 0.4 and −1.9 ± 1.4‰ suggesting a variable isotope fractionation during N fixation. The %Ndfa was significantly ( P < 0.05) different between varieties (59 ± 4.2-84 ± 4.5 %) using seed N corrected B values. BNF (218 ± 26.2-362 ± 34.7 kg N ha) was significantly ( P < 0.05) different between varieties for corrected and uncorrected B values. Soil N balance did not result in statistically significant ( P > 0.05) difference between varieties for all three B value scenarios. Use of inappropriate B values masked the difference between varieties and affected their ranking in terms of BNF, resulting from an over- to underestimation of 15 and 19 %, respectively. When applying the N natural abundance technique to compare BNF of legume accessions, we recommend determining a B value for each accession. For legumes with large seeds such as faba beans, it is moreover essential to account for seed N when determining the B value. [ABSTRACT FROM AUTHOR]

Tropical legume cover crops are important components in cropping systems because of their role in improving soil quality. Information is limited on the influence of nitrogen (N) fertilization on growth of tropical legume cover crops grown on Oxisols. A greenhouse experiment was conducted to evaluate the influence of N fertilization with or without rhizobial inoculation on growth and shoot efficiency index of 10 important tropical cover crops. Nitrogen treatment were (i) 0 mg N kg−1(control or N0), (ii) 0 mg N kg−1+ inoculation withBradyrhizobialstrains (N1), (iii) 100 mg N kg−1+ inoculation withBradyrhizobialstrains (N2), and (iv) 200 mg N kg−1of soil (N3). The N × cover crops interactions were significant for shoot dry weight, root dry weight, maximal root length, and specific root length, indicating that cover crop performance varied with varying N rates and inoculation treatments. Shoot dry weight is considered an important growth trait in cover crops and, overall, maximal shoot dry weight was produced at 100 mg N kg−1+ inoculation treatment. Based on shoot dry-weight efficiency index, cover crops were classified as efficient, moderately efficient, and inefficient in N-use efficiency. Overall, the efficient cover crops were lablab, gray velvet bean, jack bean, and black velvet bean and inefficient cover crops were pueraria, calopo, crotalaria,smooth crotalaria, and showy crotalaria.Pigeonpea was classified as moderately efficient in producing shoot dry weight. [ABSTRACT FROM AUTHOR]

Sustainable intensification of smallholder farms in Africa is highly dependent on enhancing biological nitrogen fixation (BNF). Legume diversification of maize-based systems is a core example of sustainable intensification, with the food security of millions of farm families at stake. This study highlights the constraints and opportunities associated with the adoption of legumes by smallholder farmers in southern Africa. A two-part survey of households and farm fields (n=88) was conducted in the Ekwendeni watershed of northern Malawi. Participatory research and education activities have been underway for over a decade in this region, resulting in expanded uptake of a range of legume species as intercrops and in rotation with the staple maize crop. Farmer adoption has occurred to a varying extent for soybean (Glycine max), pigeon pea (Cajanus cajan), velvet bean (Mucuna pruriens) and fish bean (Tephrosia vogelii). Farmers, working with the project valued pigeon pea and other legumes for soil fertility purposes to a greater extent than farmers not working with the project. Legumes were valued for a wide range of purposes beyond soil cover and fertility enhancement, notably for infant nutrition (at least for soybean), insect control, and vegetable and grain production for both market and home consumption. Literature values for BNF in tropical legumes range up to 170 kg N ha−1 for grain and 300 kg N ha−1 for green manure species; however, our field interviews illustrated the extent of constraints imposed by soil properties on smallholder fields in Malawi. The key edaphic constraints observed were very deficient to moderate phosphorus levels (range 4–142, average 33 mg kg−1), and moderately acid soils (range pH 5.1–7.9, average 6.2). The per farm hectarage devoted to legume production relative to maize production was also low (0.15 versus 0.35 ha), a surprising find in an area with demonstrated interest in novel legume species. Further, farmers showed a strong preference for legumes that produced edible grain, regardless of the associated nutrient removal in the harvested grain, and did not sow large areas to legume crops. These farm-level decisions act as constraints to BNF inputs in maize-based smallholder cropping systems. Overall, we found that legume productivity could be enhanced. We documented the value of policies and educational efforts that support farmers gaining access to high-quality seeds, amendments for phosphorus-deficient soils, and promotion of multipurpose legumes that build soils through leafy residues and roots, as well as providing grain for food security and sales. [ABSTRACT FROM AUTHOR]

The nitrogen difference method (NDM) for quantifying N² fixation, based on the same amount of soil N exploited by N²-fixing and non-N²-fixing plant, may not be suitable to plants with different root traits. We tested the reliability of NDM in legume-based intercropping systems by two field experiments in Northwest China. In experiment 1, faba bean (Vicia faba), pea (Pisum sativum), and soybean (Glycine max) grew solely or intercropped with maize (Zea mays) with two N application rates (0, 225 kg ha-1). The biomass of faba bean, pea, and maize was significantly increased, whereas that of soybean was decreased when intercropped than solely grown. Aggressivity analyses demonstrate greater N competition ability of faba bean and pea, but not soybean, than maize. An improved NDM (INDM) could mitigate these effects: Nfix-int = [Nleg-int + 1-x/x Nref-int - Nref-sole/x] + [soilNleg-int] + 1-x/x soilNref-int - soilNref-sole/x], where x and 1-x are planting area of legume and non-legume in the intercropping system. Compared to traditional NDM (TNDM, Nfix-int = Nleg-int - Nref-sole + [soilNleg-int - soilNref-sole]), %Ndfa (N derived from air) by INDM was decreased by 54.3% and 39.8% for faba bean, 44.7% and 5.0% for pea, but increased by 113.5% and 191.0% for soybean at the two N application rates, indicating different %Ndfa quantifications between the two methods. In experiment 2, %Ndfa of sole or intercropped faba bean was quantified by TNDM, INDM, and 15N natural abundance method (NA). The %Ndfa only by INDM correlated significantly with that from NA. Both interspecific root interactions and N loss affect %Ndfa estimation. Our results suggested that INDM could be more suitable than TNDM for quantifying %Ndfa of a N2-fixing plant in intercropping systems. [ABSTRACT FROM AUTHOR]

Legume cover crops are a potential means for overcoming N depletion in the derived savanna of West Africa. A 3-year trial was, therefore,conducted near Ibadan, southwestern Nigeria to measure the N contribution of 13 legume cover crops as compared to urea -N, using a N fertilizer replacement index for a maize test crop. Two series of trials involved the following legume cover crop species: Aeschynomene histrix, Centrosema brasilianum, Centrosema pascuorum, Chamaecrista rotundifolia, Cajanus cajan, Crotalaria verrucosa, Crotalaria ochroleuca, Lablab purpureus, Mucuna pruriens, Psophocarpus palustris, Pseudovigna argentea, Pueraria phaseoloides and Stylosanthes hamata. Trials were undertaken using a complete block design. Cover crops were planted in1994 (Series 1) and 1995 (Series 2) in separate sites and each series was subsequently slashed and planted for one season with maize (Zeamays) in 1995 and 1996. At the 50% flowering stage, N concentration of above-ground vegetation of cover crops ranged from 21 to 38 g N kg-1. Nitrogen accumulated by 4.5-month old cover crops ranged from 14 to 240 kg N ha-1, depending on species and year. Cover crops increased grain yield of the subsequent maize crop by 25-136% over the control without N application. Nitrogen uptake by themaize crop was higher following cover crops than after maize or natural grass. The N fertilizer replacement index of cover crops for maize ranged from 11 (A. histrix) to 96 kg N ha-1 (C. cajan) in Series 2. Perennial ( C. brasilianum, S. hamata, C. cajan, P. phaseoloides and C. verrucosa) and annual (C. rotundifolia, M. pruriens, C. ochroleuca and L. purpureus) species could potentially save 50 to 100 kg N ha-1 for maize crops. The cover crops accumulated more N in the wetter than in the drier year. However, the N fertilizer replacement index was higher for subsequent maize grown in the drier year. The cover crop-N recovery in maize was also higher than the urea- [ABSTRACT FROM AUTHOR]