|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 2. Cover crop nitrogen accumulation. Agronomy Journal. 104:799-806. Interpretive Summary: Winter cover crops can improve nutrient-use efficiency in vegetable systems and improve soil quality. The nitrogen scavenging abilities and residue quality 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 nitrogen in kg per hectare was lower in rye (110) and mustard (114), than legume-rye (151). Seeding rate increased nitrogen uptake in legume-rye at the beginning of the season. Legumes contributed about a third of the shoot nitrogen of the legume-rye mixture. These results indicate that all three cover crops will be useful for scavenging nitrogen, but that the lower carbon to nitrogen ratio of mustard and the legume-rye mixture are less likely to create problems with nitrogen immobilization in subsequent vegetable crops.
Technical Abstract: Winter cover crops (CC) can improve nutrient-use efficiency in vegetable systems. Nitrogen uptake (NU), and shoot residue quality of rye (Secale cereale L.), legume-rye, and mustard 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), and were followed by vegetables annually. Final NU (kg ha-1) was lower in rye (110) and mustard (114), than legume-rye (151), and varied by yr. During December, SR increased NU in legume-rye alone. Legumes contributed 36% of final NU in legume-rye, presumably from N fixation. Nitrogen and C concentrations of CC residue varied by CC, yr, and their interactions. Nitrogen concentrations were greater in mustard and legume-rye, whereas C concentrations were greater in rye and legume-rye. Rye N concentrations declined with rye plant density. Mustard and legume-rye had lower C:N ratios than rye. We conclude that (1) all CC were effective N scavengers, (2) rye and legume-rye will maximize C inputs, (3) legume-rye will maximize N inputs, (4) rye residues may immobilize N after incorporation, and (5) additional research is needed to determine if there are economic benefits from the higher-priced legume-rye versus non-legume CC.