Why Plant Cover Crops?
By Katie Nichols, Auburn University January 15, 2016
AUBURN, Alabama–Farmers are the ultimate stewards of the land. For years, farmers have been looking for ways to improve soil quality, increase productivity and build erosion control. Cover crops are widely used to benefit the upcoming crop as well as improving the soil.
Alabama Cooperative Extension Specialist Dr. Dennis Delaney said cover crops are important for maintaining soil fertility and quality.
“Cover crops do several things,” Delaney said. “They help scavenge soil nutrients lost through leaching and are able to slowly release nutrients to the following cash crop throughout the growing season.”
Selecting the right cover crops can improve yields, soil and water conservation and quality, and producer profitability. Cover crops can protect the soil, feed soil ecosystems, increase soil organic matter, and supply nutrients to subsequent crops.
Benefits of Cover Crops
Legumes are nitrogen-fixing, meaning the nitrogen produced through the plant becomes available to following crops as plant residue breaks down. Unused nutrients from the previous crop are taken up by the cover crop and slowly released during the next growing season.
Pest pressures are often subdued by the growth of cover crops. Thick plant residues on the soil surface suppress weed growth, while other crops produce chemicals that inhibit the growth of weed seedlings. Others are known to deter nematodes and diseases by repelling, confusing or starving them.
In addition to nutrient placement, soil fertility and pest suppressants, cover crops can also make an economic difference in a farming operation. Properly managed cover crops can reduce production costs and risks. Nitrogen production and effective nutrient use can reduce costs of pesticides and application. Reduction of erosion and soil compaction means less land preparation and tillage expense, and by suppressing pests, cover crops can reduce costs of pesticides and application.
Choosing the Right Cover Crops
Many cover crops perform well in Alabama cropping systems. In order to choose the crop best suited for your system, consider the time frame between cash crops and what the crop needs to provide.
Delaney said first and foremost it is important to determine which cash crop will follow the cover crop.
“Work backwards from the cash crop you plan to plant,” he said. “Choose a cover that can be terminated in time to plant a cash crop; and be sure to plant a crop that minimizes the risk of sharing soil diseases.”
For Nitrogen: Plant a legume cover crop. Some cereals, especially rye, are good at scavenging unused nitrogen from a previous crop. Buckwheat, mustards, radish and rye can scavenge unused phosphorous and potassium from deep in the soil and move it closer to the surface.
Weed Control: Covers that produce a lot of biomass can help. Rye, black oat, sorghum-sudangrass, sunn hemp, iron clay cowpea, radish and buckwheat can smother weed seedlings. Some of these produce chemicals that can affect crop germination and growth.
Break up Soil Compaction: Crops with deep taproots, like tillage radish or canola, can break through a compacted layer.
Nematode Suppression/Beneficial Insects: Certain varieties of some cover crops, like lupin, sunn hemp, velvet bean, sorghum-sudangrass, black oats and some brassicas, repel and starve pest nematodes and keep them in check. Others, like hairy vetch, lupin, sunflower and buckwheat, attract beneficial insects that pollinate crops and eat pests.
Many cover crops can provide quality forage and grazing early and still recover to benefit soil systems. Careful management is needed to ensure payback from planting a cover crop. Good quality seed should be planted at the recommended rate and depth. Planting dates are also critical for good stands and growth.
Buckwheat as cover crop image by USDA NRCS South Dakota.