Chapter 16

The Use of Cover Crops to Manage Soil

Cover Crops: Monocultures or Mixes

Growers have the option of either planting a single species cover crop, referred to as a monoculture, or planting a mixture of various cover crop species, known as “polyculture” by some. Whether to grow a monoculture or a mixture of cover crop species depends largely upon the objectives in the overall soil management plan.

Cover Crops Monocultures

Monoculture cover crops (single species) are often used to achieve specific goals in diverse cropping systems. Single species of cover crops are often planted if operational constraints limit selection to a single species or when the species has a history of proven performance (Figure 16.13). Grass species are desirable for their vigorous growth and persistent residues that decay slowly and provide substantial soil cover. Legumes are specifically utilized for their ability to fix atmospheric nitrogen in the nodules of the roots.

Cover Crop Mixes

Mixing of cover crop species, also known as polycultures, has been used to obtain the benefits of grasses, legumes, brassicas, and forbs cover crops (Figure 16.14). The theory behind multispecies cover crop mixtures is that at least one or a few species will thrive every year and improve soil properties. The success of a cover crop mixture depends on each species in the mix providing the desired services in the appropriate balance with other species in the mix. Achieving this balance can be difficult because certain species are highly competitive, causing the desired services of the less competitive species to go unrealized.

Grain-Legume Combinations

Some popular combinations include hairy vetch, crimson clover, or red clover plus winter rye or cereal rye in cold-winter areas, or bell beans plus oats in milder-winter areas. A legume–grass combination offers several benefits. Legumes and grasses grown together balance the carbon-to-nitrogen ratio in the soil after plow-down. The legumes, rich in nitrogen, break down quickly, while the carbon-rich grasses take longer to decompose. Growing the two together makes nitrogen available to help break down the grass residue and reduces the amount of time that must elapse before a subsequent cash crop can be planted. In no-till or strip-till systems, the grain also provides a longer lasting residue than a monoculture legume that helps suppress weeds and well as protect the soil.

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