Annual self-reseeding legumes and their application into Mediterranean Organic cropping systems

Summary

Self-reseeding winter annual legumes are an essential component of the Mediterranean natural resources. This study aimed to investigate self-establishment potential, ability of biological nitrogen fixation (BNF), of seven annual self-reseeding legumes and their short–term pre-crop effect on succeeding zucchini and lettuce crops. Results are presented from field experiment in Apulia region, South of Italy, where the self-reseeding legumes were screened during two cropping cycles.
For the first cropping cycle (2005-2006) preliminary results suggested that Trifolium spp. performed better than Medicago spp. Among the seven species, five were more suitable to the site’s conditions. T. angustifolium and M. polymorpha gave the best results. T. angustifolium fixed 131.7 kg ha-1 of nitrogen (15N isotopic dilution method), produced 1976 kg ha-1 of seeds and 8.7 t ha-1 of dry matter (DM). M. radiata and M. rigidula were the less performing. During the second cropping cycle (2006-2007) results showed that Trifolium spp. self-established better than Medigaco spp. Regenerated species appeared to sustain optimum level of BNF. Again T. angustifolium was the best performing species producing the highest DM (7.7 t.ha-1) and fixing nitrogen (146.7 kg ha-) symbiotically. In contrast, M. polymorpha, was the less performing (0.3 t.ha-1 of DM and 11.5 kg ha1 of BNF) while M. rigidula and M. radiata did not regenerate. Instead, the regenerated species, used as green manure, induced positive effects on both zucchini and lettuce growth parameters. Zucchini and lettuce marketable yield were significantly increased affected by preceding legumes, respectively in average 53% and 24% over the control. T. angustifolium was the best promising species. It induced the best effect on all zucchini and lettuce parameters including crop yield (respectively 42.66 and 48 t ha-1). Given the overall performance of all species, it was determined that T. angustifolium had the greatest potential for further development in this environment.