DECREASING RICE AND COWPEA YIELDS IN ALLEY CROPPING ON A HIGHLY WEATHERED OXISOL IN WEST SUMATRA, INDONESIA

A hedgerow intercropping study was conducted for 7 years in West Sumat ra, Indonesia on an acid and highly Al-saturated (72%) soil to determi ne growth and yield responses of tree hedgerows and upland rice and co wpea intercrops. Three tree species, Paraserianthes falcataria, Callia ndra calothyrsus, and Gliricidia sepium, and a no tree control were pl anted at three lime rates of zero, 375 kg ha(-1), and liming to 25% Al +H saturation. Annual fertilizer inputs of 20 kg P and 50 kg K ha(-1) were kept low to approximate low input farming systems. The trees were pruned 4 to 6 times per year and prunings applied to the intercrops. Paraserianthes and Calliandra grew vigorously, while Giricidia grew po orly and was replaced after four years with Flemingia macrophylla. Hed gerow growth and yields were reported in a previous paper [Evensen et al., 1994]. Rice and cowpea yields initially increased with lime and P araserianthes pruning application, but yields and soil cations (Ca, Mg , and K) declined until fertilizer inputs were increased after four ye ars. Thereafter, crop yields increased and soil cations returned to or iginal levels. Soil C and N were maintained over the 7 years on plots with trees. These results indicate little build-up of nutrient cations due to recycling by the trees and suggest that successful alley farmi ng on such highly weathered soils requires maintenance of soil fertili ty with external inputs.