Efficient Use of Manure Nitrogen By Corn with Canopy Reflectance Guidance of Sidedress Application.

Improving nitrogen use efficiency for corn production is of environmental and economic importance. Much manure N is not efficiently used because of low predictability of organic N availability. Use of reflectance from corn canopies to determine sidedress N rates needs to be adapted to manured fields for which more in-season N mineralization is expected compared with non-manured fields. Field research is underway for irrigated corn with applications of stockpiled beef feedlot manure at 0, 15 and 30 Mg ha^-1 in 2015 and composted feedlot manure at 0, 5 and 10 Mg ha^-1 in 2014 at Mead and Brule NE, respectively. Spring N rates were 0, 30, 60, 90 and 120 kg. N per hectare. Crop canopy reflectance (CCR), leaf area index (LAI) and chlorophyll (CH) were measured from V8 to R5. Fertilizer nitrogen was sidedress applied at V12 according to the Normalized Difference Red Edge sufficiency index (SI) value with Nrate =  317 * sqrt (0.97 – SI). At Mead, N and manure application resulted in increased crop reflectance, LAI, CH, and yield; but only N had these effects at Brule in 2015. Sensor guided in-season N application increased yield, residual soil nitrate and grain N content, but N recovery, physiological use, and agronomic efficiencies were not improved compared with an sole spring inorganic N application. The fertilizer N substitution value of the manure was 2.1 and 1.1 kg of N ha^-1 per ton of manure, respectively, with 0 and 60 kg ha^-1fertilizer N applied in the spring, and therefore 22 and 12% of organic N applied in the manure which was 9.4 kg ton^-1. Active crop sensor adoption to determine in season N application in manured field seems to be an adoptable technology to improve corn yield; however to increase NUE other management practices have to be combined.