Decomposition and Nutrient Release Dynamics of Two Tropical Legume Cover Crops

Abstract

AbstractShifting agriculture is a main contributor to deforestation in the humid tropics. Substitution of managed fallows using cover crops is a possible alternative to natural fallow that may contribute to more sustainable farming systems via more efficient nutrient cycling. Our objective was to determine the rate of decomposition and nutrient (N, P, K, Ca, Mg) release patterns resulting from two managed fallow periods (12 or 18 mo) for Desmodium adscendens (Sw.) DC. (syn. D. ovalifolium Guillemin & Perrottet) and Pueraria phaseoloides (Roxb.) Benth. (tropical kudzu) grown on Typic and Aquic Dystropept soils at two locations in the Bolivian Amazon. Dry matter disappearance and nutrient release rates from decomposing cover crop residues were monitored using 1‐mm mesh nylon bags. The longer managed fallow (18 mo) reduced the decomposition rate of both cover crops. After 30 wk, residues remaining from 12‐mo managed fallows averaged 24% for desmodium and 16% for pueraria, whereas residues from 18‐mo managed fallows averaged 53% for desmodium and 32% for pueraria. Similar to dry matter disappearance, cover crops grown for 12 mo released nutrients faster than those grown for 18 mo. Nutrient release patterns between sites were similar. By 30 wk, nutrient percentages remaining in desmodium vs. pueraria grown for 12 mo at Site 1 were 46 vs. 17% N, 17 vs. 9% P, 4 vs. 2% K, 36 vs. 20% Ca, and 30 vs. 21% Mg. Similar proportional differences in release patterns were observed for all nutrients except Ca for 18‐mo managed fallows. These results indicate a greater potential for asynchrony between crop nutrient demand and cover crop residue nutrient release for 12‐ vs. 18‐mo managed fallows, and more so for pueraria than desmodium.