Kenneth G. Cassman

Crop Ecology: Strategies and tactics for rainfed agriculture

Most agriculture is practiced under rainfed conditions with varying supplies of water. Farming strategies and tactics divide roughly into those dealing with too much water and those for coping with too little. A discussion of the large diversity of methods that has been developed for rainfed conditions reveals critical relations between production and water supply. We begin with comments on the management of farming in wet regions where hazards and management practices to counter them are rather different from those in dry regions. Chapter 14 examines the principles of irrigation as a separate topic. Agriculture in wet regions Rainfed agriculture in humid regions would seem blessed with a free good in its generous water supply. But that supply is seldom ideal, varying from excess to transient deficiency. Excess supply leading to surface flooding and saturated soils is a major problem that generally requires drainage works (Section 12.6) but new biological solutions are being found to some problems. A successful example of combating flooding damage of rice, a major problem in many areas of southeast Asia, is presented in Box 13.1. Water erosion (Section 12.7) and nutrient loss are also greater concerns with abundant rainfall than in drier regions. Leaching of N was considered in Section 8.4.3. Because vegetative cover serves to control erosion and nutrient losses, many sloping sites are maintained in pasture. Many low lying sites also remain in pasture because cold, wet soil and poor drainage combine to make them unsuited to cropping.