EFFECT OF PLANT-POPULATION AND HARVEST TIMING ON YIELD AND CHIPPING QUALITY OF ATLANTIC AND NORCHIP POTATOES AT 2 IOWA LOCATIONS

The effect of plant population and harvest timing on potato yield and chipping quality was studied at two Iowa locations during 1986, 1987, and 1988. Evaluations were conducted in eastern Iowa near Muscatine and in western Iowa at Whiting. The cultivars Atlantic and Norchip were planted at in-row spacings of 15, 31, and 46 cm and were harvested approximately 12, 14, and 16 weeks after planting. Delaying harvest until 14 or 16 weeks after planting resulted in greater yields and better specific gravities for both cultivars. At Muscatine, chip color was not significantly affected by harvest date, but at Whiting, each successive harvest produced lighter-colored chips. Greater seed piece populations increased both Atlantic and Norchip yields. Greater planting populations also caused a small increase in specific gravity. Seed spacing did not significantly affect chip color. In comparison with Norchip, Atlantic produced tubers with higher specific gravities throughout the season and greater total yields on the final harvest date. Atlantic did, however, show susceptibility to hollow heart. The incidence of hollow heart was reduced by close seed spacing.