Analysis of the effects of rotational woodlots on the nutrition and yield of maize following trees in western Tanzania

Farmers in western Tanzania are establishing rotations of trees and crops in an attempt to overcome the shortage of wood, reverse deforestation of natural forests and improve soil fertility for food security enhancement. We compared fallows of Acacia crassicarpa, A. julifera, A. leptocarpa, Leucaena pallida and Senna siamea, with traditional bush fallow and continuous sole maize (Zea mays L.). The aim of the study was to analyze the effectiveness offallow types in terms of N, Pand K use by maize. Trees were intercropped with maize for the first 3 years. After 5 years, trees were harvested, wood components were removed, and leaves, twigs and grasses were incorporated into the soil. Factorial N,P,Ktrialswere carriedoutwithmaizegrown afterthefallowtypes. Parameters studiedweregrainyield,uptakeof N,PandK,and nutrient use efficiency. The effects offertiliser were much stronger than the effects offallow types. Therewas no clear effect of tree fallows on nutrient use efficiency of the following maize. Non-fertilized maize yielded more after acacia than after the other trees and natural fallow. Upon fertiliser application the influences of fallow types became weaker. Fertiliser N improved maize yields more than fertiliser P, and there was a positive NP interaction. Fertilizer K did not bring about clear effects. N recovery efficiency was improved by the application of P and vice versa. When fertilisers were applied, differences in average maize grain yields between tree fallows and natural fallow varied from 300 kg ha 1 (for A. julifera) to minus 250 kg ha 1 (for S. siamea). A yield increase of 300 kg maize grain could also be obtained by application of 10 kg fertiliser N or 8 kg fertiliser P. The best fallow type for soil fertility improvement was Acacia juliferasuggesting that this acacia is mining the soil for P and K. In conclusion, benefits of rotational woodlots seem larger in terms of wood production than in terms of soil fertility restoration. # 2006 Elsevier B.V. All rights reserved.