Soil and Environmental Factors Affecting Internal N Efficiency of Maize.

The inverse of internal N efficiency (IE), N needed per quantity of grain produced, is used in yield-goal based N recommendations to determine the target quantity of N needed to attain a chosen maize yield. Often the value of IE is considered static, irrespective of environment. Evaluation of 47 site-years of data across the U.S. Corn Belt demonstrated variation in IE at the economically optimum N rate (IE_E). IE_E ranged from 38 to 73 kg grain dry matter per kg plant N with a mean and standard deviation of 54 and 7 kg grain kg^-1 N. A linear model based on soil properties determinable at planting (texture, organic matter, and pH) explained only 16% of the variation in IE_E. Just prior to sidedress at growth stage V9, 38% of the variation in IE_E was explained by soil texture, soil nitrate-N, and NDVI. Considering all variables at the end of the season, including soil, weather, and crop parameters, only about 60% of the variation in IE_E was explained by linear models. Unpredictable variation in IE_E introduces meaningful variation in yield-goal based N recommendations.