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TROPICAL SOIL MANAGEMENT

Sequential Cropping as a Function of Water in a Seasonal Tropical Region

Dep. of Agricultural Engineering, Univ. of Costa Rica, San José, Costa Rica

ricardo.radulovich{at}undp.org

In the seasonal (wet–dry) tropics, yields of rainfed staple crops are usually low and variable. However, our simulations have indicated that rainfall could be used more efficiently, increasing the length of the rainfed cropping season, the number of crops grown, and their yields, while decreasing yield variability and risk. To evaluate these predictions, cropping schemes with two or three annual rainfed crops grown in sequence were field-tested. Irrigated plantings were subsequently added to evaluate year-round cropping. Work was conducted in Costa Rica during 4 yr at one site and 1 yr at a second site. Both sites have a half-year-long, bimodal rainy season, and have deep soils with high water-holding capacity. The first crop of each year was planted early using preseason rains, and the last was planted to mature after the rainy season to maximize depletion of available soil water. Rainfed cropping sequences averaged 255 d long, which is from 50 to 100 d longer than local practices. Adding an irrigated planting during the dry season brought the mean length of the cropping season up to 346 d. Of 115 plantings, only 7 had low yields; all others had medium or high yields. Adding an irrigated crop increased yield potential of a year-round cropping season composed of two or more plantings. All low yields were attributed here to extended water excess conditions. However, water excess effects do not remain after the rainy season, nor into the next rainy season.

Abbreviations: AQUA, Agricultural Query and Analysis, a water balance model • CATIE, Tropical Agronomy Center for Research and Teaching, Turrialba, Costa Rica • CIAT, International Center for Tropical Agriculture, Cali, Colombia • FAO, Food and Agriculture Organization of the United Nations