WATER AND NUTRIENT MANAGEMENT WITH DRIP IRRIGATION IN HIGHLY WEATHERED SOILS OF THE TROPICS

Laboratory studies of profile water movement from line source were conducted using one clayey Oxisol and one sandy Oxisol. Functional relationships between water application rates and vertical/horizontal advances were established. P distribution was also examined. High P concentration was observed in the vicinity of the water source, in both soils under various water application rates. A drip irrigation system was designed based on the laboratory results. For the field experiments, a randomized complete block design was chosen to compare their different fertilization techniques. All treatments but the control plot received the same total amount of fertilizer and the whole experimental area was uniformly drip irrigated. The three fertilization techniques included: fertigation (drip application of N and K, banded P); banded N, P, and K; and broadcast N, P, and K. The fertigation treatment and the banded fertilizer treatment produced the highest yield. The drip method of irrigation is feasible and may be profitable for certain crops in the tropics. However, detailed studies on drip discharge rates and irrigation and fertilizer schedules are needed in order to modify and standardize the drip system operations.