Stone bunds for soil conservation in the northern Ethiopian highlands: impacts on soil fertility and crop yield.

摘要

In the Ethiopian highlands, large-scale stone bund building programs are implemented to curb severe soil erosion. Development of soil fertility gradients is often mentioned as the major drawback of stone bund implementation, as it would result in a dramatic lowering of crop yield. Therefore, the objectives of this study are to assess soil fertility gradients on progressive terraces and their influence on crop yield, in order to evaluate the long-term sustainability of stone bunds in the Ethiopian Highlands. The study was performed near Hagere Selam, Tigray and comprises (i) measurement of Pav, Ntot and Corg along the slope on 20 representative plots and (ii) crop response measurement on 143 plots. Results indicate that levels of Pav, Ntot and Corg in the plough layer are highly variable between plots and mainly determined by small-scale soil and environmental features, plot history and management. After correcting for this "plot effect" a significant relationship (p0.01) was found between the position in the plot relative to the stone bund and levels of Pav and Ntot, which are higher near the lower stone bund, especially on limestone parent material. For Corg and on basalt-derived soils in general no significant relationship was found. Although soil fertility gradients are present, they are not problematic and can be compensated by adapted soil management. Only in areas where a Calcaric or Calcic horizon is present at shallow depth, care should be taken. Crop Yields increased by 7% compared to the situation without stone bunds, if a land occupation of 8% by the structures is accounted for. Yield increased from 632 to 683 kg ha-1 for cereals, from 501 to 556 kg ha-1 (11%) for Eragrostis tef and from 335 to 351 kg ha-1 for Cicer arietinum. No negative effects reducing stone-bund sustainability were found in this study. Soil erosion on the other hand, poses a major threat to agricultural productivity. Stone bund implementation therefore is of vital importance in fighting desertification and establishing sustainable agriculture in the Ethiopian highlands..