|Boyd, Nathan -|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 8, 2011
Publication Date: May 1, 2012
Citation: Brennan, E.B., Boyd, N.S. 2012. Winter cover crop seeding rate and variety effects during 8 years of organic vegetables 1. Cover crop biomass production. Agronomy Journal. 104:684-698. Interpretive Summary: Winter cover crops can in vegetable systems and improve soil quality. Cover crop biomass production of rye, legume-rye mixture, and mustard was determined during the first 8 yr of the Salinas Organic Cropping Systems trial focused on high-value crops in Salinas, CA. Cover crops were planted at standard 1x and 3x seeding rates, and were followed by vegetables annually. Shoot biomass in metric tons per hectare was lower in mustard (5.6), than in the rye (7) and legume-rye (7). Seeding rate increased cover crop through most of the season. Legumes contributed about a quarter of the shoot biomass of the legume-rye mixture. Differences in early season weather pattern explained why legume biomass varied by year. Rye and mustard were more cost-effective sources of cover crop biomass because they have lower seed costs.
Technical Abstract: Long-term research on cover crops (CC) is needed to help farmers design optimal rotations. Winter CC shoot dry matter (DM) of rye (Secale cereale L.), legume-rye, and mustard mixtures was determined in December, January, and February or March during the first 8 yr of the Salinas Organic Cropping Systems (SOCS) trial focused on high-value crops in Salinas, CA. By seed weight, legume-rye included 10% rye, 35% Vicia faba L., 25% Pisum sativum L., 15% V. sativa L., and 15% V. benghalensis L.; mustard included 61% Sinapsis alba L., and 39% Brassica juncea L. (Czern.). Cover crops were planted at standard (1x) and 3x seeding rates (SR); 1x SR were 90 (rye), 11 (mustard), and 140 (legume-rye) kg ha-1. Vegetables followed CC annually. Cover crop population densities ranged from 131 to 854 plants m-2 and varied by CC, SR and yr. Cover crop, SR, and yr, affected DM production, however, the effects varied across the season and interactions occurred. Averaged across yr, DM was greater in rye and legume-rye (7 Mg ha-1) than mustard (5.6 Mg ha-1), and increased with SR through January. Legumes contributed 27% of final legume-rye DM. Differences in early-season GDD explained CC x yr interactions for CC DM, and why legume DM varied by yr. We conclude that rye and legume-rye maximize organic matter (OM) inputs, but rye and mustard are more cost-effective OM sources. The practical implications and value of these long-term results for high-value, high-input, tillage-intensive vegetable systems are discussed.