Browsing by Author "Wanjohi, Kinyua Michael"

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    Agro-economics of cereal-legume innovations and their influence on farmer household decision making and knowledge in Babati, Tanzania
    (Kenyatta University, 2024-10) Wanjohi, Kinyua Michael
    The robust linkage between soil fertility, food security and smallholder farmer economies unveil the need for developing agronomic innovations that improve soil fertility while ensuring climate resilience of smallholder systems. Introduced innovations should not only be targeted to achieve holistic improvement in cereal-legume productivity but also boost farmer knowledge without compromising the existing gender relations. For this reason, a study was conducted in Babati District of Tanzania guided by the following objectives, to: i) assess the economics of improved cropping systems in Gallapo, Sabilo and Riroda villages of Babati, ii) examine the effect of different cropping systems on biological nitrogen fixation of intercropped legumes, iii) evaluate how different cropping systems influence crop physiological characteristics and soil physical-chemical properties, iv) assess the influence of farmer gender on agricultural-based decisions making involving implementation of improved cropping systems, and v) examine how different socio-economic factors affect farmer knowledge on implementing improved cropping systems. Experimental trials were established to address objectives 1, 2 and 3 while household surveys addressed objectives 4 and 5. Six on-farm trials were set in randomized complete block design replicated three times. Eight treatments were laid on 5 m × 7 m plots comprising different intercropping options under uniform N (50 kg ha-1) and P (20 kg ha-1) fertilization regime. Cropping systems tested were a business-as-usual and an improved maize-legume system with and without de-topping, sole maize, Mbili-Mbili, doubled-up legume and maize (vertical leaf architecture) intercropped with pigeon pea. Probability proportionate to size sampling was conducted during enrollment of farmers for participatory technology testing. Results indicated that maize equivalent yields of between 2.0 t ha-1 in sole maize and maize-pigeon pea with no de-topping in 2019 to 12.2 t ha-1 in doubled-up legume in 2021 season. Mbili-Mbili was stable across seasons and earned more net benefits (US$ 150; p≤0.01) and highest value cost ratio (8.1; p≤0.001) than other intercropping options. Biological nitrogen fixation indicated pigeon pea to fix between 23–120 kg N ha-1 depending on site and season. Doubled-up legume had significantly higher and earlier pigeon pea branch and flower development than treatments under maize-pigeon pea system. Male household heads made 50-73% of decisions relating to Mbili-Mbili and 37-66% for doubled-up legume. Decisions on control of incomes were dominated by male household heads (42%), joint decision by male household heads + female spouses (29.5%), female spouses (22.2%) and other household members (7%). Four independent factors i.e., technical, functional, application, and soil fertility had a positive association explaining 71% of variation in farmer knowledge on Mbili-Mbili and 76.5% for doubled-up legume. The most significant socio-demographical drivers of farmer knowledge were age and gender of farmer, household size, distance of plot from homestead, type of farmer engagement, and years of farming experience. In conclusion, Mbili-Mbili is a cropping system with a potential for increasing productivity and climate resilience of smallholder farmers in areas characterized by similar agro-ecological conditions as Babati. However, cheaper mechanization strategy is needed to reduce labor demands which this study identified as the main disincentive for its adoption by farmers
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    Tillage, Crop Residue and Inorganic Nitrogen Effects on Crop Yields, Soil Carbon and Nitrogen in Kirimari Ward in Embu County, Kenya
    (Kenyatta University, 2019-06) Wanjohi, Kinyua Michael
    Integration of crop residues, inorganic N and appropriate tillage system is an important strategy for improving soil fertility, enhancing crop yields and reducing food insecurity. Such integration under zero tillage systems could enhance soil structural development and nutrient management hence mitigating against soil impoverishment through nitrogen and carbon losses. Crop residues combined with inorganic N in zero tillage results to a controlled immobilization-mineralization process which could avert nitrogen leaching while concurrently improving carbon stock within the macroaggregates relative to conventional tillage systems. However, despite zero tillage being promoted as a promising nutrient management strategy, there is little documentation on the effects of applying stover residues and inorganic N on maize yields, soil mineral N, carbon and aggregate fractions in Embu. The objectives of the study were to; (i) assess the effects of applying different rates of residue and inorganic N on maize productivity in conventional relative to zero tillage systems, (ii) examine the effects of applying different levels of residue, inorganic N and tillage on soil mineral N and (iii) assess the effects of residues, inorganic N and tillage on organic and active carbon fractions and soil aggregation. An on-station trial was set in a randomized complete block design replicated three times. The test crop was maize. Six treatments were laid in 6 × 4.5 m plots comprising of combinations of different rates of maize stover residues (0, 3 and 5 tons ha-1) and N in form of urea (0, 80, 120 kg ha-1) in conventional and zero tillage systems. The key variables assessed were; grain and stover yields, nitrate-N and ammonium-N concentration sampled at four depths (0-10, 10-30, 30-60 and 60-90 cm) during sowing, 8th leaf, 10th leaf and dent stage, soil carbon and aggregate fractionation at four depths at the end of the season. Analysis of variance was done using GenStat 14th edition, means separated using least significant difference (p≤0.05) and orthogonal contrasts between treatments run using R environment. Application of inorganic N as the only nutrient input resulted to higher (p≤0.01) grain yield than the control. Application of inorganic N as the only nutrient input increased (p≤0.02) phosphorus accumulation in maize grain in conventional system compared to the control. At 0-5 cm depth, application of similar (3 tons and 80 kg N ha-1) input rates increased macroaggregates yield in zero tillage system by 28.1% over that of conventional tillage system. Averaged over the different depths, incorporating 3 tons ha-1 residues caused 18.2 and 11.2% higher active and organic carbon, respectively, compared to surface residue application. Applying 5 tons of residues and 80 kg N ha-1 under zero tillage system has an increased potential of enhancing maize grain yield to similar levels as conventional systems. Besides, increasing the application period of 5 t ha-1 of residues with appropriate N rates could improve soil nutrient replenishment potential through macroaggregate build-up in the study area.