YIELD AND NITROGEN RECOVERY OF RAPE (BRASSICA NAPUS L.) IN RESPONSE TO APPLICATION OF LEGUMINOUS LEAF LITTER AND SUPPLEMENTAL INORGANIC NITROGEN

Abstract

SUMMARYThe short term nutrient supply of Leucaena leucocephala, Calliandra calothyrsus, Acacia angustissima and Acacia karoo prunings with or without supplemental inorganic nitrogen were tested using rape (Brassica napus L.) in a field trial. Prunings were applied at a rate of 5 t ha−1 to soil, alone or with supplemental N at 37.5 kg N ha−1 (¼ of recommended N). The respective decomposition and N release constants of the prunings were 9.15 and 9.70% for L. leucocephala; 6.15 and 6.40 for A. angustissima; 4.50 and 4.90 for C. calothyrsus; and 2.20 and 2.10 for A. karoo. These constants were best described by the (lignin+polyphenol)-to-nitrogen ratio of the prunings. Total biomass over the two seasons ranged from 1.40 to 17.28 t DM ha−1 and total growth rates ranged from 2.34–26.70 g plant−1 week−1. The cumulative N recovery at week 9 ranged from 21.1–66.1 %. Legume tree leaves can be used as a source of N for vegetable production. Farmers who use high tannin leaf litter are recommended to supplement with mineral N in order to assure adequate N availability during plant growth.