Nitrogen fertilization for subsurface drip-irrigated corn

Microirrigation can potentially "spoon feed" nutrients to a crop. Accuratel y supplying the crop's nitrogen (N) needs throughout the season can enhance crop yields and reduce the potential for groundwater contamination fi-om n itrates. A 2-year study (1990-1991) was conducted on a Keith silt loam soil (Aridic Argiustoll) to examine combinations of both preplant surface appli cation (30 cm band in center of furrow) and in-season fertigation of N fert ilizer for field corn (Zea mays L.) at three different levels of water appl ication (75%, 100%, and 125% of seasonal evapotranspiration) using a subsur face drip irrigation (SDI) system. The method of N application did not sign ificantly affect corn yields, apparent plant nitrogen uptake or water use e fficiency, but all three factors were generally influenced by the combined total N amount. The N uptake, or water use ef application method did have a n effect on the amount and distribution of total soil N and nitrate-N in th e soil profile following hat-vest. In both years, nearly all of the residua l nitrate-N after corn harvest was within the upper 0.3 m of the soil profi le for the treatments receiving only preplant-applied N, regardless of irri gation regime. In contrast, the nitrate-N concentrations increased with inc reasing rates of N injected by the SDI system and migrated deeper into the soil profile with increased irrigation. The results suggest that N applied with an SDI system at a depth of 40-45 cm redistributes differently in the soil profile than surface-applied preplant N banded in the furrow.