N uptake effects on N loss in tile drainage as estimated by RZWQM

Authors: Malone, Robert - Rob; Ma, Liwang

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 10/16/2007
Publication Date: 8/27/2008
Citation: Malone, R.W., Ma, L. 2008. N uptake effects on N loss in tile drainage as estimated by RZWQM. In: Ma, L., Bruulsema, T., Ahuja, L., editors. New Advances in Understanding and Quantification of Plant N Uptake. Boca Raton, FL. CRC Press. p. 259-275.

Interpretive Summary: The dual goals of meeting food demand while protecting the environment from excess reactive nitrogen may be one of our greatest ecological challenges. Little if any research is available, however, that addresses the effect of nitrogen (N) uptake by crops on N loss in tile drains. Therefore we quantify the effect of N uptake by a corn-soybean rotation on N loss in tile drainage (and other N budget components) using the root zone water quality model (RZWQM). An equation was developed that estimated the average two year N loss in tile drainage decreased from 38 to 19 kg N/ha with soil derived N uptake during corn years (total N uptake-application) of 50 to 110 kg N/ha. With high compared to low N uptake, the average two year N loss in tile drains at an application rate of 150 kg N/ha was 30% less (-9 kg N/ha) for 4% higher (+22 kg N/ha) N uptake by crops. The results presented clearly indicate that N uptake significantly affects N loss in tile drainage and that seemingly small errors in estimating crop N uptake can lead to more substantial errors in estimating N loss to the environment. Although not explicit, the results imply that conservation practices that maintain high crop production (high N uptake) contribute to reduced N loss in tile drains. This research will help model developers, model users, and agricultural scientists understand the importance of accurate estimates of N uptake by crops to accurate estimates of water quality and help them to design more effective systems that maintain crop production while protecting the environment.

Technical Abstract: The dual goals of meeting food demand while protecting the environment from excess reactive nitrogen may be one of our greatest ecological challenges. Therefore we quantify the effect of N uptake by a corn-soybean rotation on N loss in tile drainage (and other N budget components) using the agricultural systems model RZWQM. A regression equation was developed that described 96% of variation in RZWQM estimated N loss in tile drainage for corn-soybean rotations using the variables precipitation and RZWQM estimated soil derived N uptake (total N uptake - fixation - application). The regression equation estimated that the average two year N loss in tile drainage decreased from 38 to 19 kg N/ha with soil derived N uptake during corn years (total N uptake-application) of 50 to 110 kg N/ha. With high compared to low N uptake, the average two year N loss in tile drains at an application rate of 150 kg N/ha was 30% less (-9 kg N/ha) for 4% higher (+22 kg N/ha) N uptake by crops. Additional N loss to the environment for the low N uptake scenario included +8 kg N/ha more denitrification and +15 kg N/ha more deep seepage. The results presented clearly indicate that N uptake significantly affects N loss in tile drainage and that seemingly small errors in estimating crop N uptake can lead to more substantial errors in estimating N loss to the environment. Although not explicit, the results imply that conservation practices that maintain high crop production (high N uptake) contribute to reduced N loss in tile drains.