Cover Crop Variety
Trial in Rice, 2022


Whitney Brim-DeForest, UCCE farm advisor, Sutter, Yuba, Placer, and Sacramento counties

Previous research in California rice systems identified several benefits and challenges from cover cropping (Pettygrove and Williams, 1996). Adding nitrogen to the system is one potential benefit. Improving subsequent rice yields and long-term soil quality are examples of other benefits. Challenges may include difficulty with residue management that delays rice planting, increased greenhouse gas production in waterlogged soils, and increased management costs. Growers incur costs with cover cropping that may not be recovered with increased rice yield or reduced inputs in the short-term. For these reasons, it is important to identify cover crops that will perform well in rice production systems in order to optimize benefits

The overall purpose of this proposal is to start assembling information for California rice growers on cover crops that will survive the typically wet winters and water-logged soils found in most rice fields. If cover crops do not grow and produce sufficient biomass, they cannot confer the benefits that are typically associated with cover crops.

The Rice Cover Crop Variety trail will be conducted over two years from December 2022- December 2024. This trial is located across three sites, Butte (Rice Experiment Station) and Colusa County, and one in the Northern San Joaquin Delta region. Both the Rice Experiment Station (RES) and the Colusa site have dominantly clay soils. The site in the Northern San Joaquin, has a high organic matter soil.

A total of 10 different cover crop species and 2 Cover Crop Mixtures were trialed. The species planted in a monoculture were: 1) Purple Vetch (Vicia benghalensis L.), 2) Woolypod Vetch (Vicia villosa ssp. dasycarpa, 3) Bell Bean (Vicia faba), 4) Balansa Clover (Trifolium michelianum Savi), 5) Field Pea (Pisum sativum ssp. arvense), 6) Yellow Mustard (Brassica juncea L.), 7) Purple Top Turnip (Brassica rapa), 8) Rye (Secale cereale), 9) Oats (Avena sativa L.), and 10) Biomaster Pea (Pisum arvense). Mixture 1 was a mixture of Purple Vetch, Bell Bean, Field Pea and Rye. Mixture 2 was Purple Vetch, Balansa Clover, Field Pea, Oats, and Radish (Sp.).

Germination counts of each species, and percent cover was measured in December and January. While current findings are preliminary, during the December months, the site in Colusa County had the greatest germination and percent cover compared to the other two. At the Rice Experiment Station site, rice straw may have hindered the development of a good seed bed, while at the San Joaquin site, late planting and minimal seed incorporation may have reduced germination success. However, high rainfall and flooding at each site greatly reduced cover crop success by January overall, even at the Colusa site. Within sites, there were certain species that appeared in the beginning to be performing better than others: Rye, Turnip and Mix 2 at Colusa, and Rye, Mix 1, Oats and Woolypod vetch at the Rice Experiment Station. However, there is limited data at this time to suggest any certain outcomes.