The combined effect of mixed planting and spacing on the growth performance of cordia africana
1999
Mihretu, M.
Changes in soil chemical properties under scattered Croton macrostachyus trees were studied in the traditional agroforestry system in northwestern Ethiopia. Two cultivated farmers fields were selected on the basis of their uniformity and possession of several Croton trees. In each field, three adjacent Croton trees having approximately the dame sizes and age, and growing side by side were selected. Soil samples were taken from under the three trees at 50, 150, 300 and 800 cm (control) away from the tree base at the depth of 0-15 and 15-30 cm in four directions. Mean soil Corg content was low at both sites. The contents of CEC (P< 0.05), Mg++ (P< 0.01), were significantly influenced by distance at both soil depths. Differences in Corg (P< 0.001) and K+ (P< 0.001) contents were significant only in the topsoil. A decreasing trend was found for mean values of all parameters except nitrogen with increasing distance from the tree base at both depths. The decline in topsoil chemical properties was evident up to 300 cm away from the tree base, indicating the potential influence area of the tree. According to this study, some nutrient-conserving mechanisms have been postulated for this particular system against the high rates of organic matter decomposition, leaching and erosion losses. The living biomass of the system (i.e., the tree) acts as a buffer or a major storage for essential nutrients and releases them slowly to increase the nutrient efficiency of the system. However, in light of the findings of this study many of the above conclusions are subjected to further verification.
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