CORN YIELD RESPONSE TO IRRIGATION, PLANT POPULATION AND NITROGEN IN A COOL, HUMID CLIMATE

Abstract

Summer dry spells in some areas of southern Ontario during the last decade have increased interest in supplemental irrigation. Field studies were conducted in a 2500 heat unit area of southern Ontario on Orthic/Brunisolic Grey Brown Luvisol soils to determine the yield response of field corn (Zea mays L.) to irrigation in midsummer when combined with increased plant density and N rates. The yield responses, phenological records and soil moisture measurements are to be used in the calibration and validation of a corn yield estimation model, to be published in a subsequent paper. Two to four irrigations were applied each year using the line method when soil moisture pressure potential reached −40 to −60 kPa at 22.5 cm depth. Development stages were unaffected by irrigation. Yield increases from irrigation were directly proportional to water applied in midsummer and the intensity of dry weather. Yields increased with plant density in 4 of the 5 yr and were usually consistent over irrigation levels. Additional nitrogen above the recommended rate increased yields in 1982 and 1983, decreased yields in 1981, and resulted in no differences the other two years. In years of positive response to extra nitrogen, there was usually a greater response with irrigation and the responses were greatest at high plant density and for the longer season hybrids. Harvest indices decreased as irrigation amount increased and were exceptionally high in 1983.Key words: Corn, Zea mays L., line-source irrigation, plant population, nitrogen, harvest index