ttese rational cropping patterns could include crop improvement through crop diversification, altering crop mix and use of hybrids, use of cash crops that have secure markets, and practice of different cropping systems (double/multiple cropping, intercropping, mixed cropping, sequential cropping, ratoon cropping), and also rotation of crops.
Diversification of crops, cultivars and plot locations are most common means by which farmers attempt to stabilize agriculture income (Matlon 1991). Farm crop diversification basically refers to the diversification of crop species and the diversification of farmland ecosystems (Mengxiao 2000). ttere is, thus, a change in crops or a change of varieties, of cropping systems, as well as cropping intensities. Matlon and Fafchamps (1988) define the objectives of crop diversification as:
• to make more complete and efficient use of production factors by spreading their use across enterprises with different temporal profiles;
• to increase aggregate productivity by matching physiological requirements of crops to specific micro-environments;
• to meet domestic household consumption requirements in the context of multiple failures in both product and factor markets;
• to exploit morphological complementarities and compensatory behavior of crop components (as in the case of intercropping), and to improve and stabilize plot level productivity; and
• to improve aggregate production and reduce income risk.
In one of the Expert Consultations on Crop Diversification in the Asia-Pacific Region, it was recognized by all the country experts that crop diversification is a useful means to increase crop output under different conditions, tte commonly understood mechanism is the addition of more crops to the existing cropping systems; and it is in effect, a broadening of the base of the system, ttis method of horizontal diversification has been responsible for production increases due to high cropping intensities. One of the experts acknowledged that the system of multiple cropping has been able to increase food production potential to over 30 tons/ha with an increase of the intensity by about 400-500 percent (FAO 2000).
tte other type is vertical crop diversification which refers to the upstream and downstream activities of a particular crop or crops, ttere are tremendous opportunities for downstream activities such as minimally processed fruits, tropical fruit juices, natural food ingredients, functional food, frozen fruits, beverages and high fibre products (Yahya 2000).
In Bangladesh, the traditionally " rice-led " growth is now converted into a more diversified production base which includes several non-rice crops (Hoque 2000). ttere are programmes which promote crop diversification involving potatoes, oilseeds, pulses, spices and vegetables. A systematic arrangement of growing a variety of crops in rotation with rice has been launched and implemented. Diversified cropping systems are introduced to free upland areas in the winter season for non-rice crops; thereby, enabling the introduction of a third crop in the land under irrigated conditions (e.g., short-duration mustard or a sandwich crop of grain legume).
Meanwhile in China, attention is focused on guiding and encouraging farmers to adopt the market-oriented cropping structure using the agro-resource environment rationally. A substantial acreage has been changed to higher value and more profitable crops. Cultivation of three crops a year is widely practiced. Intercropping and multiple cropping are also extensively undertaken.
In India, the cropping patterns have occurred mainly from crops with declining demand and lower value potential to crops with an increasing demand and higher value potential (Hazra 2000). ttere is substantial diversification from coarse cereals to oilseeds, even if the current trend is a shift from coarse cereals like sorghum to superior cereals like rice and wheat.
Oil palm, rubber, cocoa and rice continued to be Malaysia's major crops (Yahya 2000). However, other crops such as coconut, tropical fruits, vegetables, flowers are also being grown. While in Nepal, to fit the variety of climatic conditions at any given time, a wide variety of crops is incorporated into the cropping system which is based on major staple food crops, but mostly rice-based cropping system in the lowlands and maize in upland areas (Sharma 2000).
Likewise in the Philippines, there are two perspectives of crop diversification. One is planting alternate crops after main crop (rice), tte other is planting one or more crops in between a perennial crop (for example, coconut). Among the sue-
cessful rice-based cropping patterns are rice-onion, rice-garlic, rice-peanut, and rice-mungbean (Espino 2000). While in the coconut-based system, the more successful are coconut + cacao, coconut + passion fruit, coconut + pineapple and many others.
In Sri Lanka, the marginal plantations of tea and rubber like the rice lands in the wet zone are diversified, tte most important crops that are cultivated in crop diversification programmes are chillies, onion, shallots, vegetables, root and tuber crops and pulses (Weerasena 2000).
Crop diversification in ttailand aimed at improving socio-economic conditions of the farmers in the rainfed and irrigated areas centers on rice as the most important crop, ttose areas not very congenial for rice production are being diverted to other crops, such as cassava, rubber, fruits and vegetable (Chainuvati 2000).
And in Vietnam, farmers in the Mekong Delta enjoy favourable conditions for practicing crop diversification integrating agriculture and the other related sectors like fisheries, forestry and livestock (Van Luat 2000). To address the annual flooding during the rainy season and droughts in dry seasons, farmers use the ditch and dike system of farming in their fields, in which the dikes are expected to be a preventive measure to avoid submergence of their crops, ttey lay pipes through the dike to take the water with silt and useful aquatic fauna and to facilitate drainage, thereby leaching decomposing matter, ttey plant many crops (with rice as main crop) on the dikes, and try to harvest the crops and fish from their fields before floods become imminent. After the floods that come during the rainy season recede, they plant their second crop. In all rice growing areas, advanced techniques of rice farming are being applied. Examples of these are the use of the row-seeding methods and the use of very short-duration rice varieties (80-90 days) with high grain quality and resistance to many pests and diseases which can yield 7-8 tons/ha.
Additionally, a number of researchers have indicated that an added advantage of intercropping is that it further improves stability at the plot level to the extent that crop mixtures yield better than sole equivalents in stress conditions, reduce the incidence and buildup of pests and diseases and manifest compensatory yield behavior due to the differences in crop structure, physiology or phenology.
On the other hand, rotation of crops spreads risks, improves soil tilth and other factors, and optimizes yields for the crops being rotated.
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