Role of Cover Crops in Conservation Planning
Rani G. Kumar, Girish K. Panicker* and Franklin O. Chukwuma Cover crops are annual, biennial or perennial small grains or legumes and grasses cultivated thickly between crops or intercropped with cash crops to develop a living mulch in order to protect and improve the soil. They are used globally in crop production to provide ground cover, sufficient biomass to turn under, and safeguard the soil. Cover crops are called “catch crops’ when they are raised for nutrients, following the primary crop. Advantages of Cover Crops The positive impacts of cover crops in the fields of soil and water conservation, environmental and ecological protection, sustainable farming systems, and agricultural and economical growth resources are multiple and outstanding. Cover crops are effective in increasing soil quality, soil tilth, and adding organic matter, soil N and humus to the soil. In aerating and loosening the soil, the rooting action of cover crops plays a large part. They prevent soil erosion, nitrogen leaching, weed problems, insect pests and plant pathogens. Cover crops considerably reduce the inputs of herbicides, and provide plant diversity and shelter to beneficial organisms. Purposes
To conserve soil and water through the use of vegetation To maintain and /or improve soil availability, quality, and soil nutrients To suppress weeds, reduce insect pests and diseases, and increase crop yield To improve soil tilth, soil organic matter, and soil structure
Five significant and effective cover crops, namely Cow pea or Southern Peas (Vigna sinensis), English Peas (Pisum sativum), Clover (Trifolium incarnatum), Hairy Vetch (Vicia villosa), and Winter Wheat (Triticum aestivum) are carefully studied here. General Criteria Applicable to all Purposes: Cover crops are useful for changing seasons. Specific crops serve the farmer in spring, fall and winter. They can be planted directly after the
2 harvest and thus encourage the growth rate of the following crops. They have the capability to control wind and water erosion. Mixtures of cover crop are very effective. In conservation tillage systems, a thick cover will suppress the weeds efficiently, better than herbicides. Crop rotation is a necessary principle to practice in cover crop production. Cover crops have to be destroyed mechanically or chemically when they start re-growing. While decomposing, they supply nutrients and organic matter to the soil. The process of allelopathy may have some negative effects on the next crops and have to be avoided by killing the cover crops early, before the next planting. Planting: Cover crops have to be planted early in the fall. Seeding rates on lb/acre basis is decided by dividing the seeds/acre by seeds/lb. They need only less than 6 - 8 weeks growing time. In the United States, cover crops planting season changes with climate and geography. They are planted immediately after the summer crops, in the northern and central regions. Usually, cover crops are raised in the southeastern states during the winter time, afterward the cash crops. A combination of winter and summer crops grown together has the power to control weeds, break up soil compaction, and improve tilth and fertility of the farmland. Cowpea (Southern Peas) a native of India, is one of the oldest crops in the world. This annual leguminous plant came to North America in the 18th century with the British colonists. As an excellent cover, edible, and a green manure, cowpea prevents soil erosion. It thrives as a summer cover crop in warm, humid areas and prefers sandy or loamy soil. Also, it is very shade tolerant, widely adapted and capable of improving the soil with its deep roots. Disking cowpeas encourages the flow of nitrogen and humus in the soil. This crop enriches the soil by fixing nitrogen, adding beneficial hydronium ions production and by lowering the soil pH. The farmer can grow cowpea in any part of the garden where he wants ground coverage and soil improvement. A southern pea cover crop has allelopathic effect and it decreases the diversity of weed species but not insect populations, suggesting this cover crop is not an alternate host for pests. It returns 2 to 3.5 tons of dried residue and 100 to 130 lbs of N per acre. English Pea, an indigenous crop of Asia, came to this country with the colonists. It is cold sensitive, gives low shade and has good traffic tolerance. This legume is very popular as an annual summer cover crop, mainly in rotation with vegetable and field crops. Peas are dormant during winter, but grow aggressively when the weather is warm. They fix nitrogen from the atmosphere, use the N to safeguard mineral nutrients from runoff, provide a part of the N requirement for the following crops and improve soil tilth by supplying residues to the soil. This cover crop returns 100 to 1,800 lbs of dried residue and 75 to 90 lbs of N per acre.
3 Crimson Clover is a successful winter annual cover crop and green manure, introduced to the United States from Europe. It prefers loams (silt and sandy) and clayey soils with good drainage, tolerates low winter temperatures (-35 F) and minimal waterlogging. It has exceptional reseeding and shade tolerance capability. Planting times for this legume are late August or early September. It is a good rely crop. Clover cover crop residues provide large amounts of N to succeeding crops. Its other advantages include suppressing weed pressure, surface water pollution and soil erosion and increasing soil organic matter. Clover is easy to plow down into the soil and it decomposes fast. It returns 2,000 to 3,000 lbs of dried residue and 100 to 150 lbs of N per acre. Hairy Vetch is a concrete winter hardy cover crop introduced from Europe. This viny annual legume grows best in sandy or loamy soils at 6 to 7 pH. Late August or early September is the suitable month to plant. It is considered a hostile companion plant for grasses. Earlier seeding can ascertain a thick vegetative mat and return over 3,000 lbs of fresh biomass per acre. Raising hairy vetch as living mulch along with cool season vegetables severely minimizes wind and water erosion, enhances soil moisture management and soil structure, and controls soil temperature. Hairy vetch is virtually shade-tolerant and more drought resistant than other vetches. If well established in fall, it survives frozen soils, remaining dormant until spring. For the benefit of maximum nitrogen fixation, and moisture conservation, Hairy vetch should be grown until May. This crop gives positive results for no-till planting but has to be clipped before flowering. It returns over 2000 lbs of dried biomass and 120 to 140 lbs of N per acre. Winter Wheat came to the US from Russia in the 19th century. It is an effective, winter-hardy, annual cover crop and soil stabilizer. Planting should be done from midSeptember to mid November (seeded at 80 to 110 pounds per acre). It is a suitable ground cover for the fall and winter and stays dormant till spring. Winter wheat adjusts well in a variety of soils due to its extensive root system. It has tremendous capability for conserving the soil, controling winter erosion and weeds, supplying organic matter to the soil, and increasing the yield. It decomposes easily when it is turned down. This winter cover returns over 2,500 lbs of dried residue per acre.
4 Crop Rotation is a good principle to follow for maintaining a productive garden. It is a planned method of raising different crops every year on the same piece of ground. Crop rotation provides the soil ample time to build up the nutrients taken away by the previous crop. This practice eliminates pest problems and plant diseases. Cover crops adjust well with several cropping patterns and vegetable rotations. An effective rotation enhances soil fertility and limits the usage of fertilizers, but the grower must be prepared well in advance with a design and a timely cropping sequence. Cover crops are rotated in warm areas during summer time as green manure crops and raised as cover crops in wet areas. In order to reduce the buildup of harmful pests and weeds, cover crops have to be rotated in sequence, the same way other cash crops are rotated. Disking and plowing speed up the process of soil organic matter breakdown and oxidization of cover crop residues. Disking the cover crops before flowering and turning under three weeks prior to planting will make time for decomposition and soil warmth. Minimal addition of fertilizer during disking will enrich the soil. Practicing no-till system has the advantage of saving large quantity of surface crop residue, labor, time, expenditure, and established beneficial insect habitat. Mulching is a positive conservation method practiced around the world. Cover crop mulches are useful for water retention, continuous weed growth prevention, soil conditioning, and reducing temperature fluctuations. They are effective in eliminating vegetable crop pests and limiting the use of pesticides. Mulching with cover crop residues paves the way to improve earliness and overall vegetable crop yields. Southern pea mulch provides season long weed control without herbicides, while promoting plant growth and fruit production.
Published by Cooperative Extension, School of Agriculture, Research, Extension, and Applied Sciences, Alcorn State University, Mississippi, in collaboration with the USDA/NRCS. Alcorn State University is deeply grateful to the USDA/NRCS for providing funds for this publication. *Corresponding author.