Regenerative Agriculture: Cover crops for soil health and carbon sequestration

Before I became sidetracked by Timorasso, and, before that, by Emergent Spanish Wine Regions, etc., etc., I had begun a series on Regenerative Agriculture and published posts on: what it is and its positioning within the body of farming practices; the main land-management objectives (soil health and carbon sequestration) of the approach; a primer on soils composition; the then-brand-new Regenerative Organic Certification; and the use of Biochar as one of the tools to aid in the attainment of approach objectives. With this post I continue the journey.

"A cover crop is a crop you grow for the soil, instead of for your plate. The practice of growing specific crops just for fertilizing and building the soil dates back to the Roman Empire" (Organic Growers School). UCANR defines a cover crop as any non-harvested vegetation grown between vineyard rows (and, in some cases, under the vines). Cover crops were used in California since the early 1900s but were mostly abandoned during the late 1940s and early 1950s when conventional agriculture became dependent on synthetic fertilizers for enhancement of soil fertility. There was a resurgence of cover-cropping in the 80s and 90s, thanks largely to a growing interest in sustainable agriculture (UCANR).

Cover-cropping is an important component of the Regenerative Agriculture system, with its application having a "direct impact on the health of vines and the surrounding ecosystem." One of the areas where cover cropping plays a role is in the fight against soil erosion. Soil erosion involves "movement of soil particles from one area to another: by wind, in arid areas; by water movement in areas with more rainfall. "Surface runoff, and resulting soil erosion, are the principal means by which fertilizers, sediments, and pesticide residues reach surface water." Sandy soils are most prone to erosion because they do not aggregate well due to a lack of clay minerals or other colloids that facilitate soil-particle adhesion. The harm-minimization strategies that can be employed here include cover crops to avoid direct raindrop strikes on bare surfaces as well as to slow the movement of water in the vineyard. 

The benefits, and potential drawbacks, of cover-cropping are presented in the tables following.

Table 1. Benefits of growing cover crops

Benefit	Description
Improve soil structure	Glue-like substances produced by roots and associated soil organisms bind soil particles together, ameliorating soil structure and water infiltration Mechanical action of cover-crop roots loosen the soil up to 60 inches depth, reducing its compaction and improving the penetration of air and water
Improve mineral fertility	Decomposition increases soil nitrogen and soil cation exchange capability Legumes contribute to nitrogen-enrichment of the soil by symbiotic fixation of its atmospheric form Can prevent the leaching of some soil nitrate to ground water during the wet winter months by taking up and storing excess soil nitrogen
Improve soil botanical activity and organic matter content	Rapidly and intensely stimulate the biological activity of the soil during their growth and, especially, after decomposition The quantity of formed humus allows maintenance of the soil organic content Roots add organic matter and create pores in the soil as they die
Protect against erosion and runoff	Protects the soil surface from the impact of soil-dispersing raindrops Grasses reduce erosion by improving water penetration and by slowing the movement of water downslope
Provide habitat for beneficial insects and predators	Some crops attract beneficial insects and arthropods which contribute to the control of harmful insects and mites
Pest management	Some weeds may be suppressed by use of appropriate cover-crop species and cultural practices Some crops act against Root-Knot and Pratylenchus nematodes
Influence grapevine growth	Compete with the vines for water and nutrients Provide additional nitrogen for vine development
Aesthetics

Table 2. Potential drawbacks associated with growing cover crops

Potential Drawbacks	Description
Demand for water	Cover crops often compete with the vines for soil moisture
Compete with vines for nutrients	Winter annual grasses require large quantities of nitrogen and, if allowed to mature, can delay nitrogen availability to the vines and reduce vigor      - Can be used to advantage in vineyards with excessive vigor      - Adding legume to the mix can offset the demand for nitrogen      - Adding fertilizer to the cover crop can offset its demand for nitrogen
Pest problems may arise from cover cropping	Flower thrips may move to the vines as cover crops mature in the spring or after they are mowed Some cover crops may themselves become weeds if they reseed and grow in an undesirable manner Buildup of vertebrate pests (gophers and voles) can be especially damaging to young vines Nematode populations may increase in cover-cropped vineyards
Threat of frost in early spring	Cover crops reduce the amount of solar radiation reaching the soil during daylight hours and can reduce temperatures on cold, clear nights Duration f lower temperatures may be longer in cover-cropped vineyards
Increased cost	Cover cropping costs more in real terms Requires more attention

The benefits and shortcomings listed above are not characteristic of cover crops as a class; rather they may exist to a greater or lesser extent depending on the species or seasonal characteristic of the cover crop. The different views of cover crops are detailed in the chart immediately following and specific selection criteria in the second chart.

Compiled from UCANR

The method of tilling the cover crops is the obvious next discussion step and I will take that up in a follow-up post.

©Wine -- Mise en abyme