Production of rape (Brassica napus L.) on soils amended with leguminous tree prunings : yield responses in relation to the chemical composition of the tree prunings

Abstract

Leguminous tree leaf litter has potential as a nutrient source for smallholder vegetable production systems. However, quality of the leaf litter influences yield responses by the crops grown. Comparative yield responses of rape (Brassica napus L.) to legume prunings of different chemical composition were evaluated in a three block randomized complete block design (RCBD) field experiment. Prunings of Leucaena leucocephala, Calliandra calothyrsus, Acacia angustissima and Acacia karoo were applied to the soil at 5 t ha-1. Two controls, 0 N and mineral N applied at 150 kg N ha-1, were used. Total biomass, leaf number and size, and area were measured over a 9 week period after transplanting. The mean total biomass yields following amelioration with the various prunings ranged from 2.56 to 11.12 t DM ha-1. The mean saleable leaf harvests ha-1 were 10.04, 7.56, 5.02, 3.00, 1.28 and 0.86 t for 150 N, L. leucocephala, A. angustissima, C. calothyrsus, A. karoo and 0 N, respectively. These results were corroborated by the resource quality of the respective organic ameliorants. The results indicated that biomass transfer technology could be used as an alternative to mineral fertilizers for vegetable production and that yields were dependent on resource quality of prunings.