POTATO RESPONSE TO SPLIT NITROGEN TIMING WITH VARYING AMOUNTS OF EXCESSIVE IRRIGATION

Irrigation and nitrogen management are two of the most important facto rs affecting production efficiency and environmental quality in potato cropping systems. Field studies were conducted in 1990 and 1991 to de termine the interactive effects of irrigation amount and N timing on p otato yield, quality and nitrate leaching potential. Sprinkler irrigat ion was applied at approximately 1.0, 1.2 or 1.4 times estimated evapo transpiration (ET) to Russet Burbank potatoes grown on a silt loam soi l. Following tuber initiation, a total of 132 kg N/ha was applied thro ugh the irrigation system to N treatment subplots using either six wee kly 22 kg N/ha applications or 3 biweekly 44 kg N/ha applications. Exc essive irrigation reduced root zone and petiole NO3-N concentrations d uring substantial portions of the tuber bulking period. Biweekly 44 kg N/ha applications in 1991 produced higher and more consistent early-s eason root zone NO3-N concentrations in the 1.2 and 1.4 ET plots than did the weekly 22 kg N/ha applications. Late-season tuber dry weight, total plant dry weight and plant N uptake were not affected by irrigat ion rate or N timing. However, excessive irrigation reduced U.S. No. 1 yield and yield of tubers > 284 g in both 1990 and 1991 and reduced t otal yield in 1990. Biweekly N applications produced higher U.S. No. 1 yields than weekly N applications at all irrigation levels. Excessive irrigation also reduced NO3-N remaining in the top 60 cm of soil at t he end of the growing season. These results show that irrigating at op timal rates and applying split N at two week intervals on a silt loam soil can maximize Russet Burbank yield and quality while minimizing NO 3-N losses.