Cover Crop Frequency and Compost Effects on a Legume-Rye Cover Crop During Eight Years of Organic Vegetables

The long-term impacts of adding organic matter to the soil using cover crops (CC) and compost are poorly understood in high-value, tillage-intensive vegetable systems. Therefore, we evaluated the effects of CC frequency (annually vs. every fourth winter) and yard-waste compost (0 vs. 15.2 Mg dry matter ha(-1) annually) on the performance of a legume-rye (Secale cereale L.) CC in three systems during Years 4 and 8 of the Salinas Organic Cropping Systems experiment in Salinas, CA. Other inputs during the 8 yr of commercial-scale vegetable production were identical across systems. The CC were planted at 420 kg ha(-1) and we measured soil organic carbon (SOC), soil NO3, CC population density, and CC shoots (biomass, N accumulation, N concentration, and C/N). At the beginning of Year 4, the systems receiving compost had higher SOC, and by Year 8 the system with frequent CC had higher soil NO3. Total CC biomass and N accumulation did not differ markedly between systems, although legumes were less variable and somewhat more productive in the systems with infrequent CC, regardless of compost. Rye and total CC residue were generally higher quality (lower C/N) in the system with frequent CC. Despite large differences in rainfall between years (234 vs. 123 mm), CC performance was relatively stable across years, although the percentage of legume biomass declined more during the drier year. We conclude that cover cropping frequency and compost have relatively subtle effects on legume-rye growth in intensive, high-value, organic vegetable production.