Chapter 29

Cover Cropping in Vineyards

Types of Cover Crops

Many types of plants can be used as cover crops. Grasses (including cereals) and legumes and are the most extensively used, but there is increasing interest in brassicas (such as rape, mustard, and forage radish) and continued interest in others, such as buckwheat. Some of the most important types of cover crops are discussed below. Choosing a cover crop depends largely upon the objectives in the overall vineyard management plan.

Grasses

Grass cover crops produce high biomass and dense fibrous root systems preventing soil erosion. Grasses are higher in carbon than legume cover crops. Because of their high carbon content, grasses break down more slowly than legumes, resulting in longer-lasting residue. As grasses mature, the carbon-tonitrogen ratio (C:N) increases. This has two tangible results: The higher carbon residue is harder for soil microbes to break down, so the process takes longer, and the nutrients contained in the cover crop residue usually are less available to the grapevines.

Legumes

Legumes are broad-leaved, annual or perennial species known for their ability to fix atmospheric nitrogen (inert gas) into usable forms. Nodules on the roots are the “factories” that house nitrogen-fixing bacteria (Rhizobium spp.) that form a symbiotic relationship with legume roots. Nitrogen accumulations by leguminous cover crops range from 40 to 200 pounds (18 to 90 kg) of nitrogen per acre. The portion of green-manure nitrogen available to grapevines is usually about 40 to 60 percent of the total amount contained in the legume. If growing legumes it is better to incorporate them into the soil when they are blooming to get the maximum addition of nitrogen.

Brassicas

Brassicas used as cover crops include mustard, rapeseed, and forage radish. They are increasingly used as winter or rotational cover crops in vegetable and specialty crop production, such as potatoes and tree fruits.

Buckwheat

Buckwheat is a summer annual that is easily killed by frost. It will grow better than many other cover crops on low-fertility soils.

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