Cover crops reduce nitrogen leaching and improve food quality in an organic potato and broccoli farming rotation

Abstract

Summer cover crops may be an effective management option for scavenging residual soil nitrogen (N) when used in conjunction with crop rotation. The objective of this study was to investigate the ability of summer cover crops to reduce N leaching and to examine the effect on the yield and food quality in an organic potato (Solanum tuberosum L.) and broccoli (Brassica oleracea L.) farming rotation system. Conventional production systems were also compared with the organic system over a two-year field research period. We examined two farm management systems (conventional and organic), three cover crop regimes (summer fallow, Japanese millet [Echinochloa esculenta A. Braun], and sorghum [Sorghum bicolor L.]), and three fertilizer application levels (no input, 50% reduction of nutrient input, and conventional input) in potato and broccoli production from 2003 to 2004. Aboveground N accumulation was 13.9 to 41 kg N ha⁻¹ in a summer cover crop of sorghum, 10.1 to 33.7 kg N ha⁻¹ in millet, and only 0.4 to 0.8 kg N ha⁻¹ in summer fallow plants after the potato harvest, although the N accumulation differed between the organic and conventional system. As the cover crop N accumulation increased, residual soil inorganic N in the top 90 cm of soil depth was reduced. Broccoli yields did not differ significantly in response to different summer cover crops or different levels of fertilizer application. However, a summer cover crop significantly reduced the nitrate (NO₃⁻) concentration in broccoli heads, and the degree of NO₃⁻ reduction was significantly affected by type and concentration of fertilizer. These results revealed that summer cover crops significantly prevented N leaching and improved broccoli food quality.