Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands - II. Maize yields and nutrient uptake

The effects of Leucaena leucocephala and L. pallida prunings and cattle man ure on maize nutrient uptake and yield were investigated in a hedgerow inte rcropping trial in the Ethiopian highlands. Hedgerow intercropping (also ca lled alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges a re pruned periodically during the cropping period and the prunings are adde d to the soil as green manure. For each leucaena species, the experiment ha d 16 treatments resulting from a factorial combination of four levels of le ucaena leaf prunings (no prunings applied; first prunings applied; first an d second prunings applied: first, second and third prunings applied), two l evels of air-dried cattle manure (0 and 3 t dry matter ha(-1)) and two leve ls of N fertilizer (0 and 40 kg N ha(-1) as urea). Uptake of N, P and K inc reased significantly with application of the three nutrient sources, but up take of Ca and Mg either did not respond or decreased with application of p runings and manure. All the three factors increased maize grain and stover yields significantly, usually with no significant interactions between the factors. At least two applications of prunings were required to significant ly increase nutrient uptake and maize yield. Maize in the: row closest to t he hedge did not respond to these nutrient inputs. It is concluded that hed gerow intercropping, with or without manure application, can increase crop yields moderately (to 2-3 t ha(-1) maize grain yields) in the highlands, bu t P. Ca and Mg may have to be supplied from external sources if they are de ficient in the soil. Additional N is still required for higher yields (>4 t ha(-1) maize grain yields). However, quantification of the competition eff ects of the trees is also required to confirm these results.