Decomposition and nitrogen use efficiency of high quality tree prunings and low quality crop residues in agroforestry systems

Abstract

Crop yields are low in agroforestry systems due to assynchrony between nutrient release by the organic materials and nutrient demand by the crop. The decomposition and N release patterns of high quality tree prunings (gliricidia and sesbania) and crop residues (pigeon pea leaves and roots, and maize slover) were studied in agroforestry systems. The experiment was arranged iii a 3 x 6 factorial, (lie high quality lcvels were: no tree pruiiings (NIP), gliricidia (Gs) and sesbania (Ss), and the crop residue levels were: no crop residues (NCR), pigeon pea leaves (Pea L), pigeon pea leaves + roots (Pea-LR), pigeon pea roots (Pea-R), and two rates of maize stover (Stover-l and Stover-2). Maize grain yield and N uptake of GsìPea-(. Gs/Pea-LR, Ss/Pea-L and Ss/Pea-LR treatments were statistically not difierent from GSI1CR and Ss/NCR during ibe two seasons. Mixtures of tree prunings with 2.5 t ha- maize stover increased maize N uptake and grain yield whereas 5 t ha’ maize stover had reduced during the wetter season. Mixtures of Pea-R, Stover-1 or Stover-2 with tree prunings depressed yields during the drier season. Stover 2 had the highest N fraction immobilized N, 15% and 35% N during the wetter and drier conditions respectively. We conclude that (1) mixing of liglì quality tree prunings with crop residues may enhance the decomposition of low quality crop residues but there is no special interaction, (2) reminemalization of N immobilized early in the season by the low quality organic materials i stimulated by well distributed rainfall