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Abstract
Yields, water use efficiency, and nitrogen use efficiency for field corn, Irish potato, sweet corn, sweet potato, and soybean were evaluated on a highly weathered Oxisol subjected to three levels of simulated erosion and three levels of nutrient replenishment. Simulated erosion reduced crop yields, water use efficiency (WUE) and nitrogen use efficiency (NUE); the reductions were particulary severe with the highest erosion level. Elevating nutrient levels in the eroded soil generally improved crop yields, WUE, and NUE. However, the improvement was only partial at the highest erosion level. This, and direct observations of crop roots, indicated that soil physical constraints exacerbated nutritional constraints. In addition, erosion reduces the level of beneficial microorganisms in the soil. All these conditions must be improved for full recovery of productivity and rehabilitation of eroded Oxisols. Inefficient use of water and nutrient inputs can be detrimental to rainfed agriculture, especially as the dryland farming practiced by millions of resource-poor farmers of the tropics.
ACKNOWLEDGMENTS
This work was supported by Hatch funds and Grant No. 91-34135-6177, Section 406, Food for Peace Act (USDA Cooperative State Research Service). Journal Series 4489 of the University of Hawaii College of Tropical Agriculture and Human Resources. I am grateful to the many colleagues, students, and associates who assisted in the course of this field-intensive research. The contributions of E.W. Dangler and R.S. Yost are particularly acknowledged.