|SMITH, RICHARD - University Of California - Cooperative Extension Service|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2017
Publication Date: 9/7/2017
Citation: Brennan, E.B., Smith, R.F. 2017. Cover crop frequency and compost effects on a legume-rye cover crop during 8 years of organic vegetables. Agronomy Journal. 109:2199-2213.
Interpretive Summary: Cover crops, and compost from municipal yard waste, are the most important organic matter input used by organic vegetable farms that produce high-value organic vegetable crops. However the long-term effects of these common inputs in tillage-intensive vegetable rotations are not well understood. This study evaluated how cover crop frequency and compost affected soil nitrates and soil carbon, and overall cover crop performance during the first 8-years of a long-term systems study in Salinas, California. The cover crop was a mixture of rye and legumes including vetches, faba bean, and pea. Lettuce and broccoli were the main cash crops grown in the rotation. Compost was the main factor affecting soil organic matter changes and increased with compost input. Cover crop frequency (i.e., every year versus every 4-years) was the main factor affecting soil nitrate levels and increased with frequent cover cropping. While cover crop frequency and compost has some impact on the growth of the cover crops mixture, these effects were relatively subtle.
Technical Abstract: Organic matter inputs from compost or cover crops (CC) are important to maintain or improve soil quality, but their impact in high-value vegetable production systems are not well understood. Therefore, we evaluated the effects of CC frequency (every winter versus every 4th winter) and yard-waste compost (0 versus 15.2 Mg dry matter ha-1 annually) on the performance of a legume-rye CC in three systems during years 4 and 8 of the Salinas Organic Cropping Systems experiment in Salinas, CA. Other inputs during the 8-years of commercial-scale vegetable production did not vary between systems. The CC were planted at a high seeding rate (420 kg ha-1) and we measured soil organic C (SOC), soil NO3, CC population density, and CC shoot biomass (production, N accumulation, N concentration, and C:N ratio). At the beginning of Year 4, the two systems receiving compost had higher SOC, and the system with frequent CC had higher soil NO3. Total CC biomass production and N accumulation did not differ between systems, although legumes tended to be more productive in the systems that were cover cropped infrequently, regardless of compost. Rye and total CC residue were generally higher quality 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 CC frequency and compost have relatively subtle effects on legume-rye growth in organic vegetable production.