Cover Crops as Nitrogen Source for Organic Farming in Southwest Europe

摘要

The environmental concern with the use of inorganic nitrogen fertilizers and the increasing energy and fertilizer costs renew the importance of the search for sustainable nitrogen sources. Cover crops can be used as a nitrogen source for the following crops as a substitute for inorganic nitrogen fertilizers. The fertilizer replacement value for a following crop by different annual cover crops was evaluated in a field experiment at the Agriculture School of Viseu (Portugal) in two years from 2007 to 2009. In this study, measurements were made of dry matter yield, N content of herbage and N uptake (in aerial biomass) of nine winter annual cover crops: six annual forage legumes, Trifolium michelianum (balansa clover), Trifolium incarnatum (crimson clover), Trifolium glanduliferum (gland clover), Trifolium vesiculosum (arrowleaf clover), Ornithopus sativus (French serradella) and Lupinus luteus (yellow lupine); one grass Lolium multiflorum (westerworld ryegrass); one mixture (ryegrass with balansa clover) and one control treatment (semi-natural vegetation). Analyses of variance revealed no significant differences for DM yield but significant differences for N content and for N uptake. Lupine was responsible for the highest N content (31.7 g kg~(-1)) and N uptake (174.4 kg N ha~(-1)). The treatment that had the lowest N content and N uptake was the ryegrass, 14.7 g kg~(-1) and 75.7 kg ha~(-1), respectively, though the results obtained for ryegrass are not significantly different from those found for the control semi-natural vegetation (N content 19.5 g kg~(-1) and N uptake 91 4 kg ha~(-1)). These results suggest that annual legumes have a great potential as a nitrogen source for the following spring or summer crop, and this potential depends essentially on the type of cover crops used, and their N content when used for green manuring.