Legume cover crops and nutrient cycling in tropical fruit tree production

Legume cover crops have various important effects on nutrient cycling in tropical fruit tree production: they (i) fix atmospheric N2 and may amend the soil and trees with N, (ii) recycle nutrients, and (iii) affect soil nutrient availability. Aboveground N accumulation usually is very large in legume cover crops as seen from Pueraria phaseoloides being 8 to 14 times higher than in intercropped fruit trees. Biomass production and N turnover will often exceed these values. Nutrient cycling may be significantly enhanced by the cover, leading to less nutrient leaching and higher nutrient contents in the topsoil, such as K. The amount of biological N fixation is an important factor for the N cycling. As a result, total soil N contents may often increase and N availability is enhanced. For nutrients other than N which cannot be supplied by the legume from external sources like P, the cover crop may induce nutrient competition resulting in lower tree nutrition.