|Resource Management for Upland Areas in Southeast Asia - An Information Kit (IIRR, 1995, 207 p.)|
|3. Soil and water conservation approaches|
Considering its widespread adoption, crop rotation is arguably the most important crop management practice in Southeast Asia. Various crop species are grown in sequence, one after another, in the same part of the farm or field. These cropping patterns can vary from year to year; but they are designed to achieve a common result: better soil physical and nutrient composition.
Each crop places a different demand on the soil in which it is grown. Likewise, each crop leaves some amount of beneficial residue or performs some action on the physical structure of the soil. A good crop rotation takes into account each crop's characteristics-what it takes and gives back to the soil-so that the net effect is improved soil.
In agroforestry systems, the perennial crop component can be changed after a number of years. This would be considered one rotation. The agricultural crop component can follow a shorter rotation period, usually less than one year. Agroforestry requires a longer-term approach to rotations, involving a wider variety of crops, each with a unique production cycle.
A typical crop rotation is rice-mungbean-corn-cowpea. Since legume crops increase soil nitrogen, mungbean (Vigna sinensis) is planted after rice (Oryza sativa), to replenish some of the nitrogen and other nutrients taken by the rice. Likewise, cowpea (Vigna radiata), with its nitrogen-fixing ability and positive effects on soil, can be grown after corn (Zea mays), which places relatively high demands on the soil.
Very effective in improving soil fertility.
Reduces nutrient drain.
Helps sustain crop production.
Diversifies crop production.
Helps controls pests and diseases.
May be difficult where input supplies are poor.
Less applicable for long-term crops.
May require a farmer to plant a crop which is not the highest priority.
Demands more skills of the farmers.
Factors affecting adoption
While nutrient supplements are still required, crop rotation
lends itself to sustained crop production.
Crop rotation can be designed to work well in poor soil conditions.
Can produce increased income in the long run, but may yield
lower income in the short run.
Can supply a varied diet.
Short-term tenure discourages conservation objectives.
Can have a high labor demand-a problem especially in areas with seasonal migrations.
Precludes intensive crop production in the offseason.