Intermediate maturing soybean produce multiple benefits at 1:2 maize: soybean planting density

Open Access Journal; Published online: 15 Aug 2018A study was conducted to identify the most suitable intercropping arrangement in smallholder farms in Western Kenya. Biomass and N (nitrogen)-accumulation, N2 fixation and grain yield of maize and soybeans grown as intercrops at three planting densities were assessed. The study was conducted in four seasons. Three soybean varieties, Namsoy 4m, SC Squire and TGx1987-18F, were used in the experiment. Maize: soybean planting densities 1:1 (D1), 1:2 (D2), 1:3 (D3) as well as sole soybean (SS) and sole maize (SM) were tested. Higher biomass, N-accumulation, and N-fixed in the order 3.8 Mg ha-1, 260 kg ha-1 and 161 kg ha-1 respectively, were recorded in D3 with long maturing variety TGx1987-18F. Conversely, higher soybean grain yield < 2.4 Mg ha-1 was achieved by intermediate maturing SC Squire in D3. The highest maize yield in the intercrop was obtained in D1. N balance calculations indicated that planting TGx1987-18F resulted in an addition of 6 to 67 kg N ha-1, while SC Squire and Namsoy 4 m removed 3 to 89 kg N ha-1 when soybean grain was removed from the field. The differences in N balances between the intercrops depended on the N-fixed and the amount of N in harvested soybean and maize grain. Greater land equivalent ratio < 1.75 were obtained with SC Squire and Namsoy 4m in D2. We concluded that intermediate maturing soybean have multiple benefits for farmers in Western Kenya at 1:2 maize: soybean planting density provided that the practice is accompanied with good soil and crop management practices

Poor farmers - poor yields: socio-economic, soil fertility and crop management indicators affecting climbing bean productivity in northern Rwanda

Climbing bean is the key staple legume crop in the highlands of East and Central Africa. We assessed the impact of interactions between soil fertility characteristics, crop management and socio-economic factors, such as household resource endowment and gender of the farmer, on climbing bean productivity and yield responses to basal P fertiliser in northern Rwanda. Through a combination of detailed characterisations of 12 farms and on-farm demonstration trials at 110 sites, we evaluated variability in grain yields and responses to fertiliser. Grain yields varied between 0.14 and 6.9 t ha−1 with an overall average of 1.69 t ha−1. Household resource endowment and gender of the farmer was strongly associated with climbing bean yield, even though these were partly confounded with Sector. Poorer households and women farmers achieved lower yields than wealthier households and male farmers. Household resource endowment and gender were likely to act as proxies for a range of agronomic and crop management factors that determine crop productivity, such as soil fertility, current and past access to organic manure and mineral fertiliser, access to sufficient quality staking material, ability to conduct crop management operation on time, but we found evidence for only some of these relationships. Poorer households and female farmers grew beans on soils with poorer soil fertility. Moreover, poorer households had a lower density of stakes, while stake density was strongly correlated with yield. Diammonium phosphate (DAP) fertiliser application led to a substantial increase in the average grain yield (0.66 t ha−1), but a large variability in responses implied that its use would be economically worthwhile for roughly half of the farmers. For the sake of targeting agricultural innovations to those households that are most likely to adopt, the Ubudehe household typology – a Rwandan government system of wealth categorisation – could be a useful and easily available tool to structure rural households within regions of Rwanda that are relatively uniform in agro-ecology

Nutrients limiting soybean (glycine max l) growth in acrisols and ferralsols of western Kenya

Low soybean yields in western Kenya have been attributed to low soil fertility despite much work done on nitrogen (N) and phosphorus (P) nutrition leading to suspicion of other nutrient limitations. To investigate this, a nutrient omission trial was set up in the greenhouse at the University of Eldoret-Kenya to diagnose the nutrients limiting soybean production in Acrisols from Masaba central and Butere sub-Counties, and Ferralsols from Kakamega (Shikhulu and Khwisero sub-locations) and Butula sub-Counties and to assess the effect of liming on soil pH and soybean growth. The experiment was laid out in a completely randomized design with ten treatments viz; positive control (complete), negative control (distilled water), complete with lime, complete with N, minus macronutrients P, potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S) and with, micro-nutrients boron (B), molybdenum (Mo), manganese (Mn), copper (Cu) and zinc (Zn) omitted. Visual deficiency symptoms observed included interveinal leaf yellowing in Mg omission and N addition and dark green leaves in P omission. Nutrients omission resulted in their significantly low concentration in plant tissues than the complete treatment. Significantly (P≤ 0.05) lower shoot dry weights (SDWs) than the complete treatment were obtained in different treatments; omission of K and Mg in Masaba and Shikhulu, Mg in Khwisero, K in Butere and, P, Mg and K in Butula. Nitrogen significantly improved SDWs in soils from Kakamega and Butula. Liming significantly raised soil pH by 9, 13 and 11% from 4.65, 4.91 and 4.99 in soils from Masaba, Butere and Butula respectively and soybean SDWs in soils from Butere. The results show that, poor soybean growth was due to K, Mg and P limitation and low pH in some soils. The results also signify necessity of application of small quantities of N for initial soybean use

Shoot water content and reference evapotranspiration for determination of crop evapotranspiration

Determination of water requirement for crops in resource limited areas is challenging, yet worsened by the common assumption that all crop varieties within a species have similar water requirements. The objective of the study was to indirectly determine crop evapotranspiration of soybean varieties, using reference evapotranspiration and shoot water content under tillage and no tillage cultivation. The treatments were no tillage and conventional tillage as main plots, and soybean varieties Nyala, SB19, and SB20 as sub-plots, replicated three times. Crop evapotranspiration (ETC) and crop coefficient (KC) were different among varieties, and increased during growth period. SB20 had the highest KC (0.8437 at 87 days after planting - DAP); followed by SB19 (0.7888 at 70 DAP), and Nyala (0.7026 at 66 DAP). Conversely,water use efficiency (WUE) was 0.58 in SB19, 0.52 in Nyala, and 0.47 in SB20.Validation of the calculated ETC using a crop production function showed a correlation of r = 0.97 between the observed and predicted yields of the three varieties. Furthermore, the normalised root mean square error (NRMSE) and the index of agreement (d) were 0.14 and 0.87, respectively indicating accurate fit. Calculated crop coefficient strongly correlated with observed shoot water content of Nyala (R2 = 1), SB19 (R2 = 1), and SB20 (R2 = 1)

Dilemma of nitrogen management for future food security in sub-Saharan Africa – a review

Article purchased; Published online: 13 July 2017Food security entails having sufficient, safe, and nutritious food to meet dietary needs. The need to optimise nitrogen (N) use for nutrition security while minimising environmental risks in sub-Saharan Africa (SSA) is overdue. Challenges related to managing N use in SSA can be associated with both insufficient use and excessive loss, and thus the continent must address the ‘too little’ and ‘too much’ paradox. Too little N is used in food production (80% of countries have N deficiencies), which has led to chronic food insecurity and malnutrition. Conversely, too much N load in water bodies due mainly to soil erosion, leaching, limited N recovery from wastewater, and atmospheric deposition contributes to eutrophication (152 Gg N year–1 in Lake Victoria, East Africa). Limited research has been conducted to improve N use for food production and adoption remains low, mainly because farming is generally practiced by resource-poor smallholder farmers. In addition, little has been done to effectively address the ‘too much’ issues, as a consequence of limited research capacity. This research gap must be addressed, and supportive policies operationalised, to maximise N benefits, while also minimising pollution. Innovation platforms involving key stakeholders are required to address N use efficiency along the food supply chain in SSA, as well as other world regions with similar challenges

Soyabean response to rhizobium inoculation across sub-Saharan Africa: Patterns of variation and the role of promiscuity

Article purchased; Published online: 7 Sept 2017Improving bacterial nitrogen fixation in grain legumes is central to sustainable intensification of agriculture in sub-Saharan Africa. In the case of soyabean, two main approaches have been pursued: first, promiscuous varieties were developed to form effective symbiosis with locally abundant nitrogen fixing bacteria. Second, inoculation with elite bacterial strains is being promoted. Analyses of the success of these approaches in tropical smallholder systems are scarce. It is unclear how current promiscuous and non-promiscuous soyabean varieties perform in inoculated and uninoculated fields, and the extent of variation in inoculation response across regions and environmental conditions remains to be determined. We present an analysis of on-farm yields and inoculation responses across ten countries in Sub Saharan Africa, including both promiscuous and non-promiscuous varieties. By combining data from a core set of replicated on-farm trials with that from a large number of farmer-managed try-outs, we study the potential for inoculation to increase yields in both variety types and evaluate the magnitude and variability of response. Average yields were estimated to be 1343 and 1227 kg/ha with and without inoculation respectively. Inoculation response varied widely between trials and locations, with no clear spatial patterns at larger scales and without evidence that this variation could be explained by yield constraints or environmental conditions. On average, specific varieties had similar uninoculated yields, while responding more strongly to inoculation. Side-by side comparisons revealed that stronger responses were observed at sites where promiscuous varieties had superior uninoculated yields, suggesting the availability of compatible, effective bacteria as a yield limiting factor and as a determinant of the magnitude of inoculation response