Browsing by Author "Timmer, V.R."

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Competition between maize and pigeonpea in semi-arid Tanzania: effect on yields And nutrition of crops
(Elservier, 2009) Kimaro, A.A; Timmer, V.R.; Chamshama, S.A.O; Ngaga, Y.N; Kimaro, D.A
Productivity of maize–pigeonpea cropping systems is dependent on facilitative and competitive interactive effects on resource availability. Controlling these interactions may benefit farmers through increased productivity associated with optimized crop yields. Previous research on maize–pigeonpea culture in Sub-Saharan Africa has focused on yield and soil fertility, but provided inadequate information on the mechanisms of possible interspecific competition. We employed a factorial field experiment to examine yield and nutritional responses of maize and pigeonpea to cropping systems (sole maize, intercropping, and improved fallow), N and P fertilizer additions, and cattle manure additions in Dodoma, Tanzania. The study objectives were to assess competition between crops and to determine how manure or fertilizer inputs may mitigate such interactions to improve yields. Intercropping enhanced maize yield over sole maize only when fertilized, reflecting probable nutrient competition. Improved fallows alone or with fertilizers (1.2–1.6 Mg ha 1 ) increased maize yields over sole maize (0.6 Mg ha 1 ). These increases were attributed to pigeonpea facilitation through soil nutrient replenishment, reduced competition associated with sequential cropping arrangements, and added nutrients from fertilization. Combined fertilizer and manure applications also improved maize and pigeonpea yields. Plant nutrient diagnosis indicated primary and secondary P and Ca deficiencies, respectively associated with P-fixation and leaching of cations due to high soil acidity and exchangeable Al. Maize competed strongly in mixture suppressing biomass and grain yields of the unfertilized pigeonpea by 60% and 33%, respectively due to limited soil nutrients and/or moisture. These yield reductions suggest that the intercropped pigeonpea did not recover from competition after maize harvesting that reduced competition. Optimizing yields of both maize and pigeonpea would require the addition of prescribed fertilizer when intercropped, but applications can be reduced by half under the improved fallow system due to alleviating interspecific competition.
Differential response to tree fallows in rotational woodlot systems In semi-arid Tanzania: post-fallow maize yield, nutrient uptake, And soil nutrients
(elservier, 2008) Kimaro, A.A.; Timmer, V.R.; Chamshama, S.A.O.; Mugasha, A.G.; Kimaro, D.A.
Agroforestry tree species producing high quality litter may enhance post-fallow soil nutrient availability and crop yields through mineralization of soil organic matter and green manure. A split-plot field experiment was used to evaluate maize yield and soil N and P status after fallowing indigenous and exotic tree species of contrasting litter quality. Responses were compared with recommended inorganic fertilizer use. The objective was to assess efficacy of 5-year tree fallows in improving soil productivity to screen species for increased crop yield under rotational woodlot culture, an agroforestry system mainly used for on-farm fuelwood production in semi-arid Tanzania. Post- fallow maize yield and soil nutrients differed significantly among tree fallows. Low C:N and L:N ratios enhanced nutrient release from slash. Acacia polyacantha (indigenous) and Gliricidia sepium fallows doubled maize yield compared to the natural fallow probably due to high soil N and P levels resulting from net release by high quality foliage. First season maize yield was similar to that from combined N and P fertilizers indicating high capacity of the fallows to improve crop yields and reduce fertilizer inputs usually unaffordable to small-scale farmers. Comparatively low maize yield and soil N and P levels after exotic Acacia crassicarpa and Acacia mangium fallows were attributed to net N immobilization by poor quality litter during growing seasons. This study suggests that rotational woodlot systems utilizing tree species with high litter quality can improve both post-fallow maize yield and soil fertility as well as produce sufficient fuelwood. In this aspect, A. polyacantha would be the most appropriate species.