Managing Your Cover Crop Now to Prevent Frost Injury, Soil Water Loss

Hi Fodder Followers! Spring has sprung! And as many of you know, cover crops provide a wealth of benefits for foothill farms- having some type of "cover" is essential to prevent soil erosion on our foothill slopes as we discussed in the last post.

The most important thing to consider NOW about your cover crop is managing it in a timely manner-either by disking it in or mowing it down (made difficult with wet soils, I know)-as soon as possible.  

Why the rush? You might ask. When budbreak occurs in our trees and vines, it signals the time when our crops become

vulnerable to frost damage-especially a concern in early budbreak years such as this.  Frost is mediated by "ice nucleating bacteria", many of which live on cover crop plants.  If these bacteria are present (that is, if the cover crop on which they live is present), frost can form at temperatures greater than what would normally occur, a phenomenon known as "supercooling", and with frost, one or two degrees can make all the difference. UC Berkeley Plant Pathologist Steve Lindow, who received his PhD way back when from my Alma mater, UW Wisconsin-Madison (Go Badgers!), has been doing studies for years on the microbial communities that inhabit the surface of plants, especially ice nucleating bacteria. His latest work with Glenn McGourty, my colleague in Mendocino/Lake counties (check out the cool new article about Glenn in the link!), is looking at copper sprays or sprays of competing bacteria to reduce the ice nucleating bacteria population on vines. A high cover crop can cool the air 2-4°; a high cover crop with poor air drainage can cool the air 6-8°!  

Budbreak is also the time our crops will start to utilize that precious soil moisture we've been receiving, but cover crops compete for the crop for that soil plant available water.  How much do they compete? The answer is: A LOT! My colleague Mark Battany, Viticulture

Water content in soil with and without a cover crop. Courtesy of Mark Battany, UCCE San Luis Obispo/Santa Barbera Counties.

Advisor for San Luis Obispo/Santa Barbera counties, shared this graph on soil water content measured in a vineyard with and without a cover crop (thank you Mark!). As you can see, in Mark's study, by April the cover cropped soil water content took a big dive-a measured difference of 68 gallons per vine less water in the soil because the cover crop used it instead of the grape crop!

The solution? Disk in or mow down that cover once you have budbreak in your crop...which has already occurred in our tree crops and is happening right about now in many grape varieties.  If you've planned for what you want out of your

cover crop then the decision to mow or disk will have already been made. To get nitrogen from your cover crop, use a leguminous cover and disk it in at flowering (or crop budbreak).  You can use a cool machine like this Muratori seeder/rotary tiller that Leslie Hurst demonstrated for us during my cover crop  meeting in fall 2014. Or you can flail it and then disk it in.

If you've chosen a grassy cover crop then you will likely be mowing it down as soon as the soil dries down enough to get in and do tractor work.

See my website handouts from my cover crop meeting for more information on choosing and managing a cover crop.