Effect of annual self-reseeding legumes on subsequent crops in organic rotation programme

Summary

Soil fertility management is a critical issue in organic agriculture, and nitrogen supply is the most important aspect, especially in the Mediterranean region. Biological nitrogen fixation by legumes seems to be a successful strategy in that nitrogen-fixing legumes can provide most of the nitrogen used in Mediterranean agriculture in a form not readily leached. According to Pimentel et al., 1992, in the U.S., an estimated $50 billion worth of nitrogen is provided by biological N fixation. Thus, the inputs of nitrogen into Mediterranean agricultural systems by biological fixation in nodulated legumes are fundamental to obtain sustainable and economic production.
This study aimed at evaluating the impact of annual self-reseeding legumes on subsequent crops performances in a rotation programme in organic farming.
15 cultivars of annual self-reseeding legumes belonging to the genera Trifolium, Medicago, Ornithopus and Biserrula were grown over two cropping cycles as green manures followed by lettuce and corn.
All legume treatments had significant positive effects on both subsequent crops.. In fact, marketable yield of lettuce increased an average of 55% over the control and yield of maize grain was an average of 15% over the control. Medicago sphaerocarpa cv Orion, Trifolium subterraneum cv York, T. glanduliferum cv Prima, and T. spumosum cv WCT36 gave the best results with both crops.