Land health surveillance: an evidence-based approach to land ecosystem management - illustrated with a case study in the West Africa Sahel. Summary for decision makers

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 of fallow types in terms of N P and 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 K trials were carried out with maize grown after the fallow types. Parameters studied were grain yield uptake of N P and K and nutrient use efficiency. The effects of fertiliser were much stronger than the effects of fallow types. There was 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 pThe best fallow type for soil fertility improvement was Acacia julifera suggesting 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.

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