Cassava-legume intercrop: I. Effects of relative planting dates of legumes on cassava productivity

ABSTRACT

Cassava is a long duration crop which grows slowly during the early stages hence incorporation of early maturing crops may improve resource use efficiency and hence crop productivity in cassava-based cropping systems. We conducted field experiments in clay and loamy sand soils, in two consecutive seasons, to assess the response of cassava productivity to relative planting dates of 3 legume species (Bambara groundnut, chickpea and cowpea) in a cassava-legume intercrop. Root yield, determined at 10 months after planting, was greater at 4 weeks after cassava (1.7 kg plant^–1) compared to when legumes were planted same time (1.2 kg plant^–1) and 2 weeks after cassava (0.7 kg plant^–1), and intercropping decreased cassava root yield by 40% (cowpea) and 26% (chickpea) in season I in the clay soils. Neither relative planting dates of legumes nor cropping systems affected root yield in both seasons in the loamy sand soils. Intercropping increased LER in season I by 25% to 65% in clay, and 45% to 101% in loamy sand soils. Although cassava root yield was highest with a 4 week-delay in sowing the legumes and LER greatest in cassava-cowpea intercrop, we propose further studies before making any definite recommendations.     

Growth,yield and water use efficiency of chickpea (Cicer arietinum): response to biochar and phosphorus fertilizer application

Field experiments were conducted during summer (2013/2014) and winter (2014) in two different soil types to evaluate the effect of biochar and P fertilizer application on growth, yield, and water use efficiency of chickpea. Soil types include Rhodic Ferralsols (clay) in Thohoyandou and Leptic Cambisols (loamy sand) in Nelspruit, South Africa. Treatments consisted of a factorial combination of four biochar levels (0, 5, 10 and 20 t ha^?1) and two phosphorus fertilizer levels (0 and 90 kg ha^?1) arranged in a randomized complete block design and replicated three times. Biochar application at 5 t ha^?1 significantly increased biomass, grain yield and water use efficiency of biomass production (WUE_b) in the clay soil compared to 10 and 20 t ha^?1. However, the increase was attributed to the addition of P fertilizer. Biochar application had no effect on yield components in the loamy sand soil, but P fertilizer addition increased number of seeds/pod in the loamy sand soil and number of pods/plant in the clay soil. Biochar and P fertilizer application on growth and yield of chickpea varied in soil types and seasons, as the effect was more prominent in the clay soil than the loamy sand soil during the summer sowing.     

Evaluating N2 fixation by food grain legumes in farmers’ fields in three agro-ecological zones of Zambia, using 15N natural abundance

A survey of N₂ fixation in farmers’ fields of Northern (>1,000 mm rainfall), Central (800–1,000 mm rainfall), and Southern (<800 mm rainfall) Zambia revealed some significant differences in plant growth and symbiotic performance of different food grain legumes. Of the three grain legumes (i.e., Bambara groundnut (Vigna subterranea L. Verdc.), cowpea (Vigna unguiculata L. Walp.), and groundnut (Arachis hypogaea L.)) grown in Southern Zambia, cowpea showed greater shoot biomass and significantly lower shoot δ¹⁵N values than groundnut and Bambara groundnut. The lower shoot δ¹⁵N resulted in greater %Ndfa (59%) in shoots and higher amounts of N-fixed, whether per square meters (6,394.0 mg N), per plant (650.8 mg N), or per hectare (63.9 kg N) relative to groundnut and Bambara groundnut, even though the number of cowpea plants per square meter was significantly lower than that of groundnut or Bambara groundnut. Although the shoot δ¹⁵N values of cowpea, Bambara groundnut and common bean (Phaseolus vulgaris L.) were significantly lower than those of groundnut in Central Zambia and their %Ndfa values, therefore, greater, the higher number of groundnut plants per square meter resulted in significantly greater shoot N content, as well as N-fixed per square meter and per hectare relative to the other species. Despite having similar plant density as cowpea in Central Zambia, common bean could fix only 6.0 kg N ha⁻¹ compared with 35.4 kg N ha⁻¹ by cowpea. In Northern Zambia, Bambara groundnut showed the lowest mean shoot δ¹⁵N value (0.54 ± 0.3‰), followed by groundnut (1.59 ± 1.0‰), and then common bean (the three grain legumes grown in that region). As a result, %Ndfa and N-fixed were significantly greater in groundnut (69.7% and 566.0 mg N per plant) and Bambara groundnut (62.9% and 440.1 mg N per plant) than in common bean (2.6% and 2.4 mg N per plant). In Northern Zambia, groundnut, Bambara groundnut and common bean fixed 78.7, 67.6, and 0.9 kg N ha⁻¹, respectively, even though the plant density per square meter of common bean (which fixed the lowest amount of N per hectare) was twice that of groundnut and Bambara groundnut. A species × site analysis showed that cowpea fixed relatively greater amounts of N per plant, per square meter, and per hectare in Southern than Central Zambia. Bambara groundnut and common bean also had significantly lower δ¹⁵N values and higher %Ndfa in Central than Northern Zambia.     

A study of some tillage practices for sustainable crop production in India

Soil tilth has been defined in terms of a ‘Physical Index’ based on the product of the ratings of eight physical properties — soil depth, bulk density, available water storage capacity, cumulative infiltration or apparent hydraulic conductivity, aggregation or organic matter, non-capillary pore space, water table depth and slope. The Physical Index and a tillage guide were used to identify the tillage requirements of different soils varying in texture from loamy sand to clay in the semi-arid tropics. The physical index was 0.389 for a loamy sand, 0.518 for a black clay loam and 0.540 for a red sandy loam soil and the cumulative rating indices in summer and winter seasons were 45 and 44 for loamy sand, 52 and 51 for red sandy loam and 54 and 52 for black clay loam soils, respectively. The compaction of the loamy sand by eight passes of a 490 kg tractor-driven roller (0.75 m diameter and 1.00 m length) increased the physical index to 0.658 and chiselling of the red sandy loam and black clay loam increased the physical indices to 0.686 and 0.729, respectively. The grain yields of rainfed pearl millet and guar and irrigated pearl millet, wheat and barley increased significantly over the control (no compaction) yields by compaction.

The chiselling of the soils varying in texture from loamy sand to clay at 50 to 120-cm intervals up to 30–40 cm depth, depending upon the row spacing of seedlines and depth of the high mechanical impedance layer, increased the grain yields of rainfed and irrigated maize on alluvial loamy sand, rainfed maize on alluvial sandy loam and red sandy loam, rainfed sorghum on red sandy loam and black clay loam, irrigated sorghum on black clay loam and rainfed black gram on red sandy loam, pod yield of rainfed groundnut, tuber yield of irrigated tapioca and fresh fruit yield of rainfed tomato on red sandy loam and sugarcane yield on black clay soil, significantly over the yields of no-chiselling systems of tillage such as disc harrow and country plough.     

Nitrogen Fixation and N-Balance Studies on Bambara Groundnut (Vigna subterranea L. Verdc) Landraces Grown on Tropical Acidic Soils of Malaysia

Bambara groundnut has great potential as an alternative crop for improving food security in its production regions and beyond. A field experiment was conducted at the Field Research Centre of the Crops for the Future to obtain information on the nitrogen (N) fixation and N balance of Bambara groundnut landraces on tropical acidic soils of Malaysia. Treatments consisted of three Bambara groundnut landraces (Ex-Sokoto, Kaaro, and NN-1) laid out in a randomized complete block design replicated three times. Results obtained revealed that Ex-Sokoto landrace was greater in yield and N fixation, whereas N balance (-haulm) was greater in NN-1 landrace. The results revealed grain yield of 703–2256 kg ha^?1 and N fixation from 32–81 kg ha^?1 and suggest that Bambara groundnut could be integrated into a cereal-based cropping system. Ex-Sokoto landrace appeared to be the most promising for yield and N fixation under Malaysian acidic soil conditions.     

Nitrogen dynamics in tropical soils of Mali,West Africa

Soil samples were collected from a loamy sand and a clayey soil near Cinzana, Mali, for the purpose of documenting the seasonal dynamics of soil inorganic N after 9 years under five crop-management systems. The cropping systems were: continuous grain sorghum (Sorghum bicolor) or millet (Pennisetum glaucum) without residue return, continuous grain with stalk residue returned to the field every second year, grain in rotation with cowpea (Vigna unguiculata), and grain in rotation with the green manure crops, sesbania (Sesbania rostrata) and dolichos (Dolichos lablab). A sharp increase in soil N was observed early in the rainy season in both soils. Extractable N concentration in loamy sand and clayey soils, respectively, peaked between 15–22 kg and 33–51 kg N ha^–1 in the upper 10 cm of soil. In the clayey soil, the higher soil N concentrations associated with the early season flush lasted 8 weeks after the onset of rain. Nitrogen addition through rotational crops and crop residue was low. Significant improvement of cereal grain yield may not be possible solely by rotation with sesbania and dolichos green manure or cowpea without additional nutrient input. Earlier cereal planting, where feasible, is recommended to improve synchrony of soil N mineralization and crop demand.     

Growth,P uptake in grain legumes and changes in rhizosphere soil P pools

In soils with low P availability, several legumes have been shown to mobilise less labile P pools and a greater capacity to take up P than cereals. But there is little information about the size of various soil P pools in the rhizosphere of legumes in soil fertilised with P although P fertiliser is often added to legumes to improve N₂ fixation. The aim of this study was to compare the growth, P uptake and the changes in rhizosphere soil P pools in five grain legumes in a soil with added P. Nodulated chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), white lupin (Lupinus albus L.), yellow lupin (Lupinus luteus L.) and narrow-leafed lupin (Lupinus angustifolius L.) were grown in a loamy sand soil low in available P to which 80 mg P kg⁻¹ was added and harvested at flowering and maturity. At maturity, growth and P uptake decreased in the following order: faba bean > chickpea > narrow-leafed lupin > yellow lupin > white lupin. Compared to the unplanted soil, the depletion of labile P pools (resin P and NaHCO₃-P inorganic) was greatest in the rhizosphere of faba bean (54% and 39%). Of the less labile P pools, NaOH-P inorganic was depleted in the rhizosphere of faba bean while NaOH-P organic and residual P were most strongly depleted in the rhizosphere of white lupin. The results suggest that even in the presence of labile P, less labile P pools may be depleted in the rhizosphere of some legumes.     

Effect of biochar and phosphorus fertilizer application on soil fertility: soil physical and chemical properties

This study evaluated the effect of biochar and phosphorus fertilizer application on selected soil physical and chemical properties in two contrasting soil types: Rhodic Ferralsols (clay) in Thohoyandou and Leptic Cambisols (loamy sand) in Nelspruit, South Africa. Field experiments were conducted in summer and winter. Treatments consisted of a factorial combination of four biochar levels (0, 5, 10 and 20 t ha^?1) and two phosphorus fertilizer levels (0 and 90 kg ha^?1) arranged in a randomized complete block design with three replicates. Chickpea was the test crop. Soil bulk density, aggregate stability, porosity, total C, total N, C:N ratio, K and Mg were determined. Biochar (10 t ha^?1) and phosphorus increased bulk density and decreased porosity at 0–5 and 15–20 cm soil depth on a loamy sand soil in both seasons. The interaction between biochar and phosphorus increased total C and total N on a clay soil in the summer sowing. However, in the loamy sand soil, biochar (10 t ha^?1) increased total C, C:N ratio, K and Mg in the summer sowing. The effect of biochar was more evident in the loamy sand soil than the clay soil suggesting that the influence of biochar may be soil-specific.     

EFFECTS OF CARBONIZED CHICKEN MANURE ON THE GROWTH,NODULATION, YIELD,NITROGEN AND PHOSPHORUS CONTENTS OF FOUR GRAIN LEGUMES

The effects of carbonized chicken manure (CCM) on the growth, nodulation, yield, nitrogen (N) and phosphorus (P) contents of four grain legumes (soybean, cowpea, common bean and adzuki bean) were evaluated in a greenhouse experiment. Carbonized chicken manure produced from chicken manure dried in a furnace at 450°C was used in this experiment. The manure was incorporated into the sandy loam soil of each grain legume at two rates (0 kg N ha^?1 and 100 kg N ha^?1) three weeks before sowing. Growth, nodulation and total biomass N and P were evaluated at peak flowering stage of growth. The CCM showed positive effects on nodule number and weight of soybean and cowpea while it depressed nodule number in adzuki bean. Biomass total N content of soybean and cowpea increased with CCM supply while it decreased in adzuki bean. Biomass and seed total P content of soybean, cowpea and adzuki bean all increased in response to CCM application. Soybean and cowpea seed yields increased by 27% and 43% respectively in response to CCM supply. There was a strong positive correlation between seed P content and seed yield of soybean which indicates the importance of elemental P to soybean seed yield. No such phenomenon was observed in adzuki bean. A strong positive correlation was also observed between seed total N content and seed yield of the grain legumes. The results indicate that although common bean had the highest biomass total P content at peak flowering stage both vegetative and reproductive growth were poor due to the unsuitably high day/night temperatures in the greenhouse. Application of CCM slightly depressed yield of adzuki bean due to the reduction in the number of pods per pot and the 100 seed weight. This study shows that CCM is a good source of N and P for the growth, nodulation and yield of some grain legumes particularly soybean and cowpea.     

The establishment of winter wheat root system architecture in field soils: The effect of soil type on root development in a temperate climate

Winter wheat (Triticum aestivum L.) is an important cereal crop in the temperate climates of western Europe. Root system architecture is a significant contributor to resource capture and plant resilience. However, the impact of soil type on root system architecture (RSA) in field structured soils is yet to be fully assessed. This work studied the development of root growth using deep cultivation (250 mm) during the tillering phase stage (Zadock stage 25) of winter wheat across three soil types. The three sites of contrasting soil types covered a geographical area in the UK and Ireland in October 2018. Root samples were analysed using two methods: X-ray computed tomography (CT) which provides 3D images of the undisturbed roots in the soil, and a WinRHIZO^™ scanner used to generate 2D images of washed roots and to measure further root parameters. Important negative relationships existed between soil bulk density and root properties (root length density, root volume, surface area and length) across the three sites. The results revealed that despite reduced root growth, the clay (Southoe) site had a significantly higher crop yield irrespective of root depth. The loamy sand (Harper Adams) site had significantly higher root volume, surface area and root length density compared with the other sites. However, a reduction in grain yield of 2.42 Mt ha⁻¹ was incurred compared with the clay site and 1.6 Mt ha⁻¹ compared with the clay loam site. The significantly higher rooting characteristics found in the loamy sand site were a result of the significantly lower soil bulk density compared with the other two sites. The loamy sand site had a lower soil bulk density, but no significant difference in macroporosity between sites (p > 0.05). This suggests that soil type and structure directly influence crop yield to greater extent than root parameters, but the interactions between both need simultaneous assessment in field sites.     

Effect of water stress and nickel application on yield components and agronomic characteristics of canola grown on two calcareous soils

A greenhouse experiment (5 × 2 × 2 factorial arranged in randomized-complete-design with three replicates) was conducted to assess the combined effects of nickel (Ni) and drought stress on growth and yield parameters of canola (Brassica napus L. var. Talaye) grown on two calcareous soils of loamy and sandy clay textures. Treatments consisted of five Ni levels (0, 0.05, 0.1, 0.5 and 1 mg Ni kg^?1 soil) and two levels of water status 100% and 60% field capacity (FC and 0.6FC, respectively). Growth parameters and yield components of plants decreased at drought-stress conditions. Almost all of the studied growth/yield parameters of canola grown on loamy soil were significantly more than those of the sandy clay soil, probably due to the increased capability of loamy soil for supplying the plant water/nutrient requirements. Nickel could positively affect some of the mean growth and yield parameters (e.g., grain yield) over both of the water status conditions. Nevertheless, some of the traits not only increased by Ni fertilization but also decreased compared to that of the control. The positive responses of canola was observed with higher amounts of applied Ni in the sandy clay soil than in loamy soil, e.g., the maximum grain yields of canola grown on loamy and sandy clay soils were obtained with applications of 0.5 and 1 mg Ni kg^?1, respectively. Generally, results demonstrated that Ni could not mitigate the negative effects of drought stress on canola growth or yield components.     

Decomposability of organic matter in particle size fractions from field soils with straw incorporation

Soils from two field experiments on straw disposal were fractionated according to particle size using ultrasonic dispersion and gravity-sedimentation in water. Samples of whole soils, clay. silt and sand-size fractions were held for 49 days at 20°C and the CO₂ evolution measured on 14 dates by gas chromatography.Recovery of soil solids. C and N was 99, 98 and 93%, respectively. Most of the soil C and N was in the clay (<2μm). (loamy sand, 50% C and 56% N; sandy loam. 65% C and 68% N), the silt (2–20 μm) having smaller proportions (loamy sand, 41% C and 38% N; sandy loam. 29% C and 27% N). The sand fraction (20–6000 μm) accounted for 4–7% of the organic matter, and 1–2% of the C was water soluble. Straw incorporation generally increased the C and N content of whole soils and size fractions.The decomposition rate constants were higher for the sandy loam than for the loamy sand soil. For both soils, the decomposability of the organic matter decreased in the order: sand > clay ⩾ whole soil > silt. Straw incorporation increased the decomposition rate of whole soil and sand organic matter. whereas the effect of straw on clay and silt respiration was small.Between 58 and 73% of the respiration was from clay, 21–25% from silt and 6–19% from the sand size fraction.     

Nitrogen availability to grain sorghum from organic and inorganic sources on sandy and clayey soil surfaces in a greenhouse pot study

In a greenhouse pot study, we examined the availability of N to grain sorghum from organic and inorganic N sources. The treatments were¹⁵N-labeled clover residues, wheat residues, and fertilizer placed on a sandy clay loam and loamy sand soil surface for an 8-week period. Soil aggregates formed under each soil texture were measured after 8 weeks for each treatment. Significantly greater ¹⁵N was taken up and recovered by grain sorghum in sandy clay loam pots compared with loamy sand pots. Greater ¹⁵N recovery was consistently observed with the inorganic source than the organic sources regardless of soil texture or time. Microbial biomass C and N were significantly greater for sandy clay loam soil compared with the loamy sand. Microbial biomass ¹⁵N was also significantly greater in the sandy clay loam treatment compared to the loamy sand. The fertilizer treatment initially had the greatest pool of microbial biomass ¹⁵N but decreased with time. The crop residue treatments generally had less microbial biomass ¹⁵N with time. The crop residues and soil texture had a significant effect on the water-stable aggregates formed after 8 weeks of treatments. Significantly greater water-stable aggregates were formed in the sandy clay loam than the loamy sand. Approximately 20% greater water-stable aggregates were formed under the crop residue treatments compared to the fertilizer only treatment. Soil texture seemed to be one of the most important factors affecting the availability of N from organic or inorganic N sources in these soils.Contribution from the MissouriAgricultural Experiment Station, Journal Series No.12131     

Grain legumes differ in nitrogen accumulation and remobilisation during seed filling

In grain legumes, the N requirements of growing seeds are generally greater than biological nitrogen fixation (BNF) and soil N uptake during seed filling, so that the N previously accumulated in the vegetative tissues needs to be redistributed in order to provide N to the seeds. Chickpea, field bean, pea, and white lupin were harvested at flowering and maturity to compare the relative contribution of BNF, soil N uptake, and N remobilisation to seed N. From flowering to maturity, shoot dry weight increased in all crops by approximately 50%, root did not appreciably change, and nodule decreased by 18%. The amount of plant N increased in all crops, however in field bean (17?g?m^?2) it was about twice that in chickpea, pea, and lupin. The increase was entirely due to seeds, whose N content at maturity was 26?g?m^?2 in field bean and 16?g?m^?2 in chickpea, pea, and lupin. The seed N content at maturity was higher than total N accumulation during grain filling in all crops, and endogenous N previously accumulated in vegetative parts was remobilised to fulfil the N demand of filling seeds. Nitrogen remobilisation ranged from 7?g?m^?2 in chickpea to 9?g?m^?2 in field bean, and was crucial in providing N to the seeds of chickpea, pea, and lupin (half of seed N content) but it was less important in field bean (one-third). All the vegetative organs of the plants underwent N remobilisation: shoots contributed to the N supply of seeds from 58% to 85%, roots from 11% to 37%, and nodules less than 8%. Improving grain legume yield requires either reduced N remobilisation or enhanced N supply, thus, a useful strategy is to select cultivars with high post-anthesis N₂ fixation or add mineral N at flowering.     

Grain legume pre-crops and their residues affect the growth, P uptake and size of P pools in the rhizosphere of the following wheat

Legumes have been shown to increase P uptake of the following cereal, but the underlying mechanisms are unclear. The aim of this study was to compare the effect of legume pre-crops and their residues on the growth, P uptake and size of soil P pools in the rhizosphere of the following wheat. Three grain legumes (faba bean, chickpea and white lupin) were grown until maturity in loamy sand soil with low P availability to which 80?mg P kg^?1 was supplied. This pre-crop soil was then amended with legume residues or left un-amended and planted with wheat. The growth, P uptake and concentrations of P pools in the rhizosphere of the following wheat were measured 6?weeks after sowing. In a separate experiment, residue decomposition was measured over 42?days by determining soil CO₂ release as well as available N and P. Decomposition rates were highest for chickpea residues and lowest for wheat residues. P release was greatest from white lupin residues and N release was greatest from faba bean residues, while wheat residues resulted in net N and P immobilisation. The growth of the following wheat was greater in legume pre-crop soil without residue than in soils with residue addition, while the reverse was true for plant P concentration. Among the legumes, faba bean had the strongest effect on growth, P uptake and concentrations of the rhizosphere P pools of the following wheat. Regardless of the pre-crop and residue treatment, wheat depleted the less labile pools residual P as well as NaOH-Pi and Po, with a stronger depletion of the organic pool. We conclude that although P in the added residues may become available during decomposition, the presence of the residues in the soil had a negative effect on the growth of the following wheat. Further, pre-crops or their residues had little effect on the size of P pools in the rhizosphere of wheat.     

Ontogenic variation in nitrogen fixation and accumulation of nitrogen in mungbean,blackgram, cowpea,and groundnut

Ontogenic variations in N₂ fixation and accumulation of N by the mungbean (Vigna radiata L. Wilczek), blackgram (Vigna mungo L. Hepper), cowpea (Vigna unguiculata L. Walp.), and groundnut (Arachis hypogaea L.) were studied by a ¹⁵N-dilution technique. Pots filled with 7 kg of red yellow podzolic soil were used. Samples were taken 20, 40, 60, and 80 days after emergence which approximately corresponded to preflowering, flowering, early/mid-pod filling and late pod filling stages, respectively. During early growth (up to 40 days after emergence), the carryover of seed N accounted for a considerable fraction of the total plant N in the legumes, the highest being in the groundnut. With a correction for carryover, the groundnut derived over 45% of its N content from the atmosphere 20 days after emergence whereas the corresponding figures were 33% for the blackgram and about 28% for the cowpea and mungbean. Between flowering and early pod fill, there was a rapid increase in N₂ fixation in all legumes except in groundnut which showed highest fixation from 60 to 80 days after emergence. In the mungbean, N₂ fixation and uptake of soil N were insignificant 60 days after emergence while in other legumes these processes continued beyond this time. All legumes derived about 90% of their N from atmosphere by 80 days after emergence. However, due to considerable interspecific differences in total N yield the final amount of N₂ fixed showed an appreciable variation among legumes. It was highest in the groundnut (443 mg N plant^-1) followed by the cowpea (385), blackgram (273), and mungbean (145), respectively. The groundnut maintained nodules until the late pod filling stage while in other legumes, nodules senesced progressively following the mid-pod filling stage. During pod filling there was a net mobilization of N from vegetative tissues to developing pods in the mungbean, which amounted to about 20% of N in seeds. This mobilization was not evident in other legumes.     

Rock phosphate-enriched organic fertilizer with phosphate-solubilizing microorganisms improves nodulation,growth, and yield of legumes

ABSTRACT

Phosphorus availability from rock phosphate (RP) can be increased via composting with organic fertilizer and phosphate-solubilizing microorganisms (PSMs) in the soil. Incubation and pot experiments were conducted to investigate the comparative efficacy of RP-enriched organic fertilizer with PSMs vs. diammonium phosphate (DAP) as a control to enhance the production of legumes. In incubation studies, RP-enriched organic fertilizer with PSM₂ significantly increased soil aggregate stability (37%) and P-release (2.35 folds) as compared to control, whereas, in pot study, the number and dry weight of nodules plant^?1, shoot length, number of pods plant^?1, and grain yield of chickpea increased by 23%, 13%, 17%, 15%, and 15% with RP-enriched organic fertilizer + PSM₂ compared to control. Similarly, nitrogen and phosphorus contents in straw (11 and 42% respectively) and grains (11 and 13% respectively) and protein contents (16%) of chickpea were also increased. A similar trend was observed regarding the growth and yield parameters of lentil. The use of RP-enriched organic fertilizer with PSM could produce results similar to that of DAP for the optimum production of legumes.     

Survey of Underutilized Grain Legume Production Systems in the Southwest Agricultural Zone of Nigeria

ABSTRACT

A socio-economic survey of production systems was carried out in four out of the eight states that make up the southwest agricultural zone of Nigeria. A total of 157 minor grain legume farmers selected by multi-stage sampling were interviewed using structured questionnaires. The study shows that lima bean, pigeon pea, African yam bean, and bambara groundnut are the prominent minor grain legumes grown on less than 10% of the total cultivated land area. The minor grain legumes are grown on an average land size ranging from 0.2 to 0.4ha and predominantly in mixture with crops like cassava, maize, yam, sorghum, cocoyam, etc. The use of modern inputs like herbicides, pesticides, fertilizers, and improved varieties is uncommon in minor legume production systems. The cultivation of these legumes is more popular among the older members of the farming communities, about 78% of which are above 40 years of age. The average yield of the legumes on farms is considerably low, estimated at 271kg/ha, 265kg/ha, 174kg/ha, and 275kg/ha for lima bean, pigeon pea, African yambean, and bambara groundnut, respectively. Major constraints identified by the farmers include low market demand, inadequate seed supply, high cost of labour, and low yield. Research work is therefore needed in agronomy and breeding for improved yield and utilization for expanded market and, consequently, increased production.     

Symbiotic and genomic diversity of ‘cowpea’ bradyrhizobia from soils in Botswana and South Africa

Strain CB756 is usually an effective competitor against indigenous bradyrhizobia for nodulation of peanut in South Africa. Recently, inoculation of peanut and cowpea with CB756 in loamy sand soils of Botswana or a sandy clay loam in South Africa proved unsuccessful, achieving <2% nodule occupancy. A survey of ‘cowpea’ bradyrhizobia from five soils in Botswana and one in South Africa showed that many were effective in ability to fix N₂ on peanut and cowpea. However, 15 isolates from Good Hope, Botswana were all effective on cowpea but ineffective on peanut, three failing to nodulate the latter. Selected cowpea isolates were significantly more competitive than CB756 for nodulation of cowpea in Leonard jars, but four were unsuccessful when inoculated at Roodeplaat, South Africa. When strain CB756 and two isolates were inoculated in pots containing Roodeplaat soil, at a 4:1 inoculant to soil bradyrhizobia ratio, their average nodule occupancy was 8% on cowpea compared to 40% on peanut. Significant differences in strain nodule occupancy were not detected on either cowpea or peanut. In contrast, nodule occupancy in loamy sand from Good Hope, Botswana, inoculated at a 40:1 inoculant to soil bradyrhizobia ratio, was 22.4% on cowpea and only 6.8% on peanut. In Good Hope soil, strain CB756 was the weakest competitor on cowpea but strain differences were insignificant on peanut. Whereas the Good Hope soil population was effective on cowpea, it was ineffective on peanut. DNA fingerprinting showed that isolates from Gaborone, Francistown and Roodeplaat contained several different genotypes, whereas those from Good Hope, Rasesa and Maun were more homogeneous. The dominance at Good Hope of genotypes effective on cowpea but ineffective on peanut emphasises the value of assessing the symbiotic capabilities and structures of indigenous populations.     

Effects of rice husk biochar on selected soil properties and nitrate leaching in loamy sand and clay soil

Biochar is a product of pyrolysis of biomass in the absence of oxygen and has a high potential to sequester carbon into more stable soil organic carbon (OC). Despite the large number of studies on biochar and soil properties, few studies have investigated the effects of biochar in contrasting soils. The current research was conducted to evaluate the effects of different biochar levels (0 (as control), 1% and 3%) on several soil physiochemical properties and nitrate leaching in two soil types (loamy sand and clay) under greenhouse conditions and wet-dry cycles. The experiment was performed using a randomized design with three levels of biochar produced from rice husks at 500 °C in three replications. Cation exchange capacity increased significantly, by 20% and 30% in 1% and 3% biochar-amended loamy sand soil, respectively, and increases were 9% and 19% in 1% and 3% biochar-amended clay soil, respectively. Loamy sand soil did not show improvement in aggregate indices, including mean weight diameter, geometric mean diameter, water stable aggregates and fractal dimension, which was contrary to the results for the clay soil. Rice husk biochar application at the both rates decreased nitrate leaching in the clay soil more than in the loamy sand. Our study highlights the importance of soil type in determining the value of biochar as a soil amendment to improve soil properties, particularly soil aggregation and reduced nitrate leaching. The benefits of the biochar in the clay soil were greater than in the loamy sand soil.