Subsurface Drip Nitrogen Fertigation of Corn.

The efficient management of nitrogen (N) fertilizer and irrigation is of utmost importance. This project was conducted to determine if yield and efficiency of N fertilization in corn could be improved by applying N at later developmental stages through a subsurface drip irrigation (SDI) system. Experiments in 2014 and 2015 compared a Preplant Surface application that injected fertilizer in bands below the residue at planting, to four versions of SDI fertigation that differed in timing and total amount of N applied. The SDI Sidedress treatment concluded at tassel stage (VT). The SDI Maximum treatment supplied an additional 40 pounds of N acre^-1 through blister stage (R2). The SDI Sensor treatment received N fertigations after V10 stage only if the ratio of the SPAD (chlorophyll) meter readings from the SDI Sensor plot to the Reference plot was less than 95%. The Reference treatment received both the surface band injections and all SDI fertigations for total seasonal N application that exceeded crop N requirements. The Reference treatment produced up to 32 bushels acre^-1 more grain than the Preplant Surface treatment, but averaged only 0.7 bushels of grain pound^-1 of N fertilizer. The SDI Maximum treatment averaged slightly less grain yield than the reference treatment, but produced 1.15 bushels of grain pound^-1 of N fertilizer. The SDI Sidedress and SDI Sensor treatments resulted in 16 bushels acre^-1 more than the Preplant Surface treatment. The SDI Sidedress treatment used N fertilizer most efficiently, producing 1.3 bushels of grain pound^-1 of N fertilizer. Applying N into the reproductive stages of corn increased yield, but N fertilizer was used most efficiently when N applications were completed by VT. The use of the SPAD sensor to determine later N applications reduced fertilizer input but resulted in fertilizer use efficiency similar to the SDI Maximum treatment.