Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2000
Publication Date: N/A
Interpretive Summary: Nitrogen, in water as the nitrate ion, can contaminate ground and surface water if it is present in quantity. Furrow irrigation often leaches nitrate-nitrogen toward ground water, threatening its quality and reducing the efficiency with which fertilizer N is used by crops. This research seeks corn production systems to concurrently manage both furrow irrigation and applied N fertilizers to increase N use efficiency, minimize the nitrate-nitrogen remaining in soil profiles at harvest, and protect water quality. For two years in southern Idaho, we evaluated the effects of N placement, row spacing, and furrow irrigation water positioning (applying water to the same or alternate side of the row with successive irrigations) on N uptake in corn silage and soil profile nitrate-nitrogen. Every second furrow was used to irrigate the silage nine times in 1988 and seven in 1989. Two-year average N uptake was 15% greater from wider rather than narrower rows where we irrigated alternating sides of the row with successive irrigations. Where irrigating the same furrow all season, N uptake in silage from banded plots was equal to that from broadcast plots the first year but was 21% greater the second. To improve N management under furrow irrigation and protect groundwater quality, we conclude that N fertilizer should be placed separate from irrigation water to allow the applied N to be used efficiently by the growing corn, reduce the nitrate-nitrogen remaining in soil profiles at season's end, and minimize the potential for nitrate-nitrogen to contaminate groundwater.
Technical Abstract: N management under furrow irrigation is difficult because nitrate-nitrogen is frequently leached to groundwater. Banding and sidedressing N fertilizer on a non-irrigated side of a row of corn (Zea mays L.) might increase N uptake and minimize nitrate leaching potential by reducing the nitrate-nitrogen in soil profiles at harvest, thereby protecting water quality. For two years in the field, we evaluated two N placements (broadcast vs. banded), two row spacings (0.76-m vs. a modified 0.56-m), and two ways of positioning irrigation water (applying water to the same side or alternating sides of the row with successive irrigations) for their effects on N uptake in corn silage and soil profile nitrate-nitrogen (to the 0.9-m depth). In southern Idaho, we grew field corn in Portneuf silt loam. Where irrigating alternating sides of the row, two-year average N uptake from 0.76-m rows was 15% greater than from 0.56-m rows. Where irrigating the same furrow all season, N uptake from banding equaled that from broadcasting the first year but was 21% greater (P<0.001) the second. Applying water to the same furrow decreased profile N by about 170 kg/ha under 0.76-m rows by season's end in 1988. Our findings suggest that corn in 0.76-m rows should be fertilized by banding N into every second furrow and irrigated season-long using the remaining, non-fertilized furrows because those practices maintained or increased N uptake in silage and minimized residual nitrate-nitrogen in 0.9-m soil profiles at season's end.