NITROGEN ADDITIONS AND LOSSES TO DRAINAGE IN ORCHARD-TYPE IRRIGATED LYSIMETERS

Abstract

Controlled fertilizer nitrogen (N) inputs and releases to drainage waters were recorded for 9 yr in orchard-type lysimeters. Irrigations were varied year by year from about 37 to 100% of the maximum for the area. One apple tree per lysimeter was the test crop. Large amounts of drainage resulting from the highest levels of irrigation carried the largest amounts of nitrate [Formula: see text] to groundwater but when irrigation was less than 75% of maximum much smaller annual amounts appeared in drainage, mostly because drainage was small. Year 1 of drainage, although light, carried substantial amounts of [Formula: see text] out of the lysimeters probably reflecting mineralized native organic N plus applied N. The largest single influence on the retention of N was the presence of a cover crop. In 9 yr, 40 – 45% of applied N reappeared in drainage waters under grass while 88 – 115% of applied N reappeared under bare soil. The quantities of applied N (N1 = 162 kg N ha−1; N2 = 324 kg N ha−1) had less influence than the cover crop. The importance of measuring and sampling every drainage event because of wide ranges of [Formula: see text] concentrations is emphasized. Averaging could be misleading. The potential impact of [Formula: see text] releases to the aquatic environment of the watershed is discussed briefly. Key words: Nitrogen losses, lysimeters, irrigation, watershed, nitrate