Overall, however, Malone notes, "The model underestimates the benefit of cover crops in reducing nitrate discharge, because the nitrate losses simulated by the RZWQM
were about 30 percent less than field observations in Iowa.
RZWQM might show that a farmer should not apply all the nitrogen fertilizer at planting time, but instead apply it in two or three split applications.
Rojas says, "The scope of science RZWQM covers is just mind boggling.
Last summer, ARS agricultural engineer Hamid Farahani ran RZWQM to simulate no-till dryland corn production in eastern Colorado.
Buchleiter, an agricultural engineer in the ARS Water Management Research Unit at Fort Collins, tested RZWQM using data from a commercial farm in eastern Colorado.
In Missouri, ARS scientists evaluated RZWQM to see how accurately it could predict crop yields, surface water runoff, and chemical movement through the soil profile.
Other sites where RZWQM is being run through its paces include Tifton, Georgia; Guelph, Ontario, Canada; Lisbon, Portugal; and Bonn, Germany.