Intercropping and crop rotation are alternative strategies applied in multiple cropping, the growing of two or more crops in the same piece of land. Both cropping systems have resulted to increased farm production and profitability per unit land area in selected crops.
Intercropping is the growing of two or more crops together in proximity on the same land. As a result, two or more crops are managed at the same time. It differs from crop rotation in which two or more crops are grown one after the other. There are at least four types of intercropping according to spatial arrangement (Sullivan, 2003).
Row intercropping is the growing of two or more crops at the same time with at least one crop planted in rows. In farms grown to perennial crops, annual crops like corn, rice and pineapple are commonly grown as intercrop between the rows of the main crop. This strategy is an efficient way of maximizing the use of farm land by utilizing vacant spaces while at the same time suppressing the growth of weeds during the juvenile stage of the main crop.
In many coconut farms, durian and mangosteen are grown at the center of four coconut hills, becoming a filler crop in a quincunx planting arrangement. Banana, papaya, coffee and cacao are commonly grown also in multiple rows. These plants are grown as sole intercrop or mixed with others, either perennial or annual crops. Soursop or guyabano, because of its tolerance to partial shade, is likewise a promising intercrop.
With annuals, the component crops are planted at the same time or the other crop(s) are planted during the juvenile stage of growth (before flowering) of the first crop. In India, pigeon pea is traditionally planted with sorghum. The pigeon pea starts flowering after the sorghum plants are harvested. In the United States, velvet bean or cowpea is planted in standing corn at the last corn cultivation. When the corn plants mature, the corn stalks become natural trellis for the beans or peas. Both the corn and the intercrop are harvested together.
Strip intercropping is the growing of two or more crops together in strips wide enough to allow separate production of crops using mechanical implements, but close enough for the crops to interact. Examples of successful strip intercropping practices in the United States are: alternating strips of wheat, corn and soybean 6 rows wide each; oat, corn and soybean; and 6 rows of corn with 12 rows of soybean.
Mixed intercropping or mixed cropping is the growing of two or more crops at the same time with no distinct row arrangement.
Examples of mixed intercropping of annual crops are the practice of growing corn, bean and squash in Central America and forage sorghum with silage corn in Oregon. In Canada, research showed increased production per land area by growing together soybean and corn for silage in the same rows. The result showed that corn grown at 16,000 seeding rate per acre (equivalent to 67% of the sole corn rate) together with soybean at seeding rate of 135,000 per acre (equivalent to 67% of the sole bean rate) within the same rows gave the highest profit. Fertilizer was applied at the rate of 53 lbs of N per acre.
Relay intercropping or relay cropping is a system in which a second crop is planted into an existing crop when it has flowered (reproductive stage) but before harvesting. There is thus a minimum temporal overlap of two or more crops. The relay crop should be fairly tolerant to shade and trampling. Examples of relay crops are cassava, cotton, sweet potato and sesban with corn; chickpea, lentil and wheat with upland rice.
In crop rotation or sequential cropping, two or more crops are grown one after the other in the same piece of land. It is advantageous that the succeeding crop belongs to a family different from that of the previous crop. The period of crop rotation may be for two to three years or longer. Farm income significantly increased by alternating lowland rice with high-value crops like garlic, onion, melons, bell pepper and other vegetables.
An example of cropping pattern applying crop rotation with multiple number of crops is corn- soybean- corn- alfalfa and sweet corn- tubers- squash- rootcrops- tomato- peas- Brassicas (http://attra.ncat.org/intern_handbook/pdf/crop_rotation.pdf).
In addition to increased crop yields and profit, the following are the advantages of crop rotation over monoculture, the continuous growing of a single crop (click to read the possible adverse effect of Cash Crop Farming due to monocropping) :
1. Better control of weeds. Crop rotation is intended to break the life cycle and suppress the growth of weeds. The sequential planting of different crops may check the development of any weed species and reduce weed growth especially if cover crops or green manures (click to read Cover Crops in Tropical Crop Farming) and tall-growing row crops are used as component rotation crops.
2. Better control of pests and diseases. Some pests and causal organisms of plant diseases are host specific. They attack certain crop species or those belonging to the same family but not others. For example, the problem with rice stem borer will continue if rice is not rotated with other crops of a different family. This is because food will be always available to the pest. However, if legume is planted as the next crop, then corn, beans and bulbs, the build up of the pest will be disrupted because they will be deprived of food.
3. Improved soil structure and organic matter content. The alternate planting of deep and shallow rooted plants will break up the soil and reduce the effects of plow pan. The planting of soybean, other grain legumes, sweet potato and vegetables will return sufficient quantities of plant residues to the soil as their leaves drop on the ground or body parts are left on the field after harvest, instead of being burned as is commonly practiced with sugarcane. Green manures will add significant amounts of organic matter.
4. Improved soil fertility. The continuous growing of a single crop will result to the depletion of certain soil nutrients. With crop rotation, soil fertility will be promoted through alternate planting of crops having different nutrient needs. This will prevent the depletion of any one essential element present in the soil. Leguminous plants, because of their ability to accumulate nitrogen by fixing it from the air in association with Rhizobium bacteria, will improve soil fertility.
Abellanosa, A.L. and H.M. Pava. 1987. An Introduction to Crop Science. CMU, Musuan, Bukidnon: Publications Office. pp. 127-147.Gupta, P.C. and J.C. O’Toole. 1986. Upland rice: a global perspective. Los Baños, Laguna, Phils.: IRRI. Retrieved October 5, 2010 from http://books.google.com.ph/books?id=DlRlYq5u-J8C&pg=PA89&lpg=PA89&dq=relay+cropping&source=bl&ots=HcupyZWlif&sig= vvQF6h2avqjBd9iwAHN1vdbT6sk&hl=tl&ei=kQarTI-5L5CiuQO3u7SeBw&sa=X&oi=book_result&ct=result&resnum= 4&ved=0CCgQ6AEwAzgK#v=onepage&q=relay%20cropping&f=false.