Computing wheat nitrogen requirements from grain yield and protein maps

Authors: Long, Daniel; ENGEL, RICHARD - Montana State University

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 7/15/2010
Publication Date: 2/2/2011
Citation: Long, D.S., Engel, R. 2011. Computing wheat nitrogen requirements from grain yield and protein maps. In: Clay, D.E., Shanahan, J.F., editors. GIS applications in agriculture. 2:321-335.

Interpretive Summary: Combine-mounted yield monitors and grain quality sensors give farmers the ability to create maps of grain yield and grain protein during harvesting. This chapter illustrates how these maps may be used for evaluating whether water or nitrogen (N) was limited for yield. The off-the-shelf, mapping software Surfer is used to create yield and protein maps, and then calculate maps of critically low protein, N removed in grain, and N management zones. The protein content of grain was used to assess where grain yield was lost, due to inadequate N fertility, within an irrigated field in northern Montana. Where N was adequate (protein greater than 13.2%), variable-rate N management could be based upon replacing N at the rate at which it had been removed in the previous grain crop. Where it was deficient (protein less than 13.2%), N management was based upon university fertilizer recommendations that involve yield potentials and soil nitrate-N test values.

Technical Abstract: Optical protein sensors and mass-flow yield monitors provide the opportunity to continuously measure grain quality and quantity during harvesting. This chapter illustrates how yield monitor and grain protein measurements may provide useful post-harvest information for evaluating water or nitrogen (N) limitations in wheat. The surface mapping software Surfer is used to create yield and protein maps that share a common grid, and then calculate maps of critically low protein, N removed in grain, and N management zones. Analysis of a critical spring wheat protein level provided site-specific information needed to assess where N had been adequate or deficient within an irrigated northern Montana production field. Where N was adequate (=132 g of protein kg^1 of grain), variable-rate N management could be based upon replacing N at the rate at which it was removed in grain. Where it was deficient (<132 g kg^1), N management was based upon university recommendations that involve yield potentials and soil nitrate-N test values.