Cover crops (also written in single word, i.e. covercrops) are plants grown or managed primarily to prevent the soil from being eroded by wind and water. They are distinct from the ornamental groundcovers in landscaping which are primarily chosen for their aesthetic effects.
Cover crops can be either annual, biennial, or perennial plants. They are grown as a sole crop or mixed. In addition to their usage for erosion control, they help regulate soil temperature, suppress weed growth, reduce pests and diseases, minimize loss of water from the ground through evaporation, enhance soil fertility, add organic matter to the soil, improve soil aeration, and promote high water infiltration.
Several terms are used to describe various types of cover crops which are grown for special purposes.
Green Manures are plants that are incorporated with the soil by plowing and other means of cultivation while they are still green or soon after the flowering stage, for the main purpose of soil improvement. Common examples are the grain legumes cowpea (Vigna unguiculata) and mungbean (Vigna radiata) after rice. Green manures are capable of adding organic matter to the soil comparable to 9 to 13 tons per acre (22.24 to 32.12 tons per hectare) of farm manure or 1.8 to 2.2 tons of dry matter per acre (4.45 to 5.44 tons per hectare) (Sullivan, 2003). Leguminous plants improve soil fertility.
Catch Crops are cover crops which are grown after harvest of a main crop to utilize residual resources like soil moisture and fertilizers and to reduce nutrient leaching. Both cowpea and mungbean become catch crops if they are allowed to mature and harvested for pods. Other common catch crops after rice are melons, garlic, tomato and many vegetables. These also include those short maturing crops which are planted between two main crop seasons.
Living Mulches are those grown and maintained alive simultaneously with any cash crop, primarily to prevent rapid loss of water from the soil through evaporation. Examples are grass plants like Bermuda grass (Cynodon dactylon) and carabao grass (Paspalum conjugatum) under coconut (Cocos nucifera), oil palm (Elaeis guineensis) and in many orchards and vineyards. For rapid establishment of living mulches, leguminous vine plants are seeded.
Pasture and Forage Crop are those grown to be used as feed to livestock through pasturage, soilage, silage or haying. These can be either grass alone, leguminous crops, or mixed grass-legume crops. These crops are ideal in mixed crop-livestock integrated farming system ( click to read how livestock integration benefited mango ). Common pasture crops in perennial crop farms integrated with ruminant animals are Bermuda grass, carabao grass, stargrass (Cynodon plectostachyus) and many leguminous vines.
The growing of cover crops in orchards and other perennial crop farms has obvious advantages to the farmers. Leguminous perennial plants, mostly vines, are favored in farms grown to perennial, tropical cash crops like coconut, oil palm, cashew (Anacardium occidentale), durian (Durio zibethinus), mango (Mangifera indica), mangosteen (Garcinia mangostana), pummelo (Citrus maxima) and soursop (Annona muricata).
Fast growing vines can easily cover the spaces between crop plants and kill weeds, including cogon (Imperata cylindrica), by depriving them of sunlight. The shading of the soil will prevent the germination of weed seeds. Leguminous plants are also good sources of feed for ruminant animals. Being high in nitogen content, they are excellent substitute to manure. Manure is mixed with carbonaceous substrates in organic fertilizer production through vermicomposting or with the use of Trichoderma as compost fungus activator (CFA).
Legumes are capable of fixing nitrogen from the air through a symbiotic association, called mutualism, with Rhizobium bacteria. The amount of nitrogen that leguminous cover crops accumulate range between 40 to 200 lbs per acre (44.83 to 224.17 kg per hectare). About 40 to 60 percent of this nitrogen will become available to a following crop if the cover crop is used as a green manure (Sullivan, 2003).
Common examples of tropical, leguminous cover crops are pinto peanut or creeping peanut (Arachis pintoi), calopo (Calopogonium muconoides), centro (Centrosema pubescens), kudzu (Pueraria phaseoloides), siratro (Macroptilium atropurpureum) and stylo (Stylosanthes guianensis). All are perennial plants and, with the exception of pinto peanut, vines. Seeds of these vine plants can be broadcasted or sown in furrows at the rate of 15-20 kg per hectare.
The pinto peanut is also popular as an ornamental crop. It is commonly used as a groundcover in landscaping. It has stolons which produce roots and shoots at the nodes and can be easily propagated from stem cuttings. A close relative, the rhizoma perennial peanut (Arachis glabrata), is popular in the US. As of 2008, more than 26,000 acres (10,522 ha) have been planted to the ‘Florigraze’ and ‘Arbrook’ cultivars of the rhizoma peanut in Florida, Georgia and Alabama. These were sold mostly for hay at prices comparable to alfalfa (NRCS, 2008).
Coconut Committee. 1983. The Philippines recommends for coconut. Los Baños, Laguna: PCARRD. 89 p. (PCARRD Technical Bulletin No. 2A).
Committee on Forage and Pasture Crops. 2001. The Philippines recommends for forage and pasture crops. Los Baños, Laguna: PCARRD-DOST and Agrikulturang MakaMASA- Livestock Program- DA. 93 p. (Philippines Recommends Series No. 12-B).
Natural Resources Conservation Service (NRCS). 2008. Rhizoma perennial peanut- the perennial peanut for urban conservation in Florida. Retrieved October 3, 2010 from http://www.plant-materials.nrcs.usda.gov/pubs/flpmsfo8065.pdf.
Sullivan, P. 2003. Overview of cover crops and green manures. Retrieved October 2, 2010 from http://attra.ncat.org/attra-pub/covercrop.html.
(Ben G. Bareja. 2010)