Unexpected high decomposition of legume residues in dry season soils from tropical coffee plantations and crop lands

Crop residues are essential fertilizer source of low-input farming systems in Sub-Saharan Africa. However, crop residues provide nutrients only if they decompose in the soil. Decomposition is assumed to be very low during the dry season due to the scarcity of water, but there are few quantitative knowledge on decomposition under such conditions. Therefore, we studied the decomposition of legume residues, haricot bean (Phaseolus vulgaris L.), and pigeon pea (Cajanus cajan L. (Millps) using litterbag experiments in two coffee and two crop land agroecosystems of southern Ethiopia. The residues were surface applied and subsoil buried under irrigated and non-irrigated conditions and were then retrieved after 30-180 days. We measured mass loss, decay rate constant (k), and C and N concentrations. Results demonstrate an unexpected high decomposition in seasonal dry soils, even when the litterbags were placed on the soil surface. Interestingly, 89 % of the initial N of pigeon pea and 85 % of haricot bean were released after 150 days, on the average. Thus microbial decomposition is unexpectedly high during the dry season. This finding has implications for the effect of plant residues on the supply of mineral N to crops growing during subsequent wet season.