- Author: Yoni Cooperman
- Contributor: Jordon Wade
A variety of cover crops exist, way too many to be fully covered in this blog post. Generally speaking, cover crops tend to be grasses or legumes, and many growers utilize mixes to achieve targeted results. Legumes can be a source of N fertilization, though they can also contribute to N pollution if N levels exceed crop needs. Grasses have the potential to hold on to excess soil N and limit losses through nitrate leaching. Mixes of multiple cover crop types with different uses are used to maximize inputs of organic matter in hopes of building soil carbon.
While cover crops can have many potential benefits, like any other management decision tradeoffs are involved. While competition for soil water and nutrients can be used to control vigor, under certain conditions this can be harmful for vine development. Another possible downside to using cover crops, their potential to increase the production of greenhouse gas emissions, was the focus of our study conducted in a three year old Merlot vineyard in Lodi, CA. The vineyard soil is classified as a Devries sandy loam.
In our two year study, we compared rates of greenhouse gas (GHG) emissions from vineyard alleyway soil grown under three different cover crop mixes: a legume mix, a “soil builder” mix, and a ryegrass treatment all planted at 100 lbs/ac.
These three treatments were chosen to represent three reasons growers might utilize cover crops in a vineyard. The legume mix was chosen to be a “green manure” and increase soil nitrogen. The “soil builder” mix was meant to maximize plant biomass and increase soil organic matter. The ryegrass was chosen as a “catch crop” that can take up large amounts of soil N, limiting N losses through nitrate leaching.
After our two year monitoring period, we found that cover crops had little effect on soil N2O emissions, while they increased soil CO2 emissions. While CO2 emissions were higher when cover crops were used, there were no differences between the different cover crop types. These findings suggest that during drought years, growers are free to choose the cover crop mixes they think will best serve their needs, without being overly concerned about excess N2O emissions stimulated by cover cropping. However, the legume mix did result in higher levels of soil N and the ryegrass treatment did decrease leachable soil nitrate. It is unclear if the "soil builder" mix resulted in increased soil organic matter, although that is to be expected, considering it takes several years to substantially increase soil organic matter content.
For more information about utilizing cover crops visit the Solutions Center for Nutrient Management page on cover crops.