Submitted to: American Society of Agri Engineers Special Meetings and Conferences Papers
Publication Type: Proceedings
Publication Acceptance Date: May 10, 1996
Publication Date: N/A
Estimates of evapotranspiration are important to all aspects of agriculture. Water use by crops provides a means of comparing different practices for their water use efficiency, the potential impact of cropping patterns on nonpoint source pollution, and the effectiveness of conservation measures on water use. There is little information on the seasonal comparison of different evapotranspiration equations over different rotations and tillage practices. A study was conducted in the Walnut Creek watershed south of Ames, Iowa, on six farmer-operated fields to evaluate the seasonal water use from a corn-soybean rotation with ridge-tillage, chisel-plow, and no-till. Bowen ratio equipment was installed in each field from planting until maturity. Surface infrared thermometers (60 deg fov) were positioned to view the surface. Water used was affected by the tillage practice in the early season with the lowest water use in the no-till practices. Evaporative fraction ranged from 0.3 in the first 20 days after planting to over 0.9 during full vegetative cover. Use of different evapotranspiration equations requires accurate estimates of both aerodynamic and canopy resistance.