Potato yields as related to nitrate levels in petioles and soils

Abstract

The effects of various rates and times of nitrogen application on the yield of potatoes were determined in field experiments in Michigan. Both irrigated and non-irrigated trials were conducted with Katahdin, Russet Burbank, or Sebago varieties. Petioles were sampled for nitrate determinations one or more times during the growing season on each experiment, and the nitrate level in the soil was also followed throughout the season on Kent sandy loam.

Nitrate levels in plant petioles tended to be high when the plants were young (4 tto 6 weeks) and then decreased rapidly as the plants matured. At any sampling date, differences in nitrate content between treatments could be measured and a critical nitrate level established for that sampling date. However, nitrate in petioles decreased so rapidly during the season that no valid interpretation of these levels could be made unless the age of the plants was precisely known. In the soil, nitrate levels tended to be more stable, although they also tended to decrease as the season progressed. Neverthehless, soil nitrate level may be a more stable criterion of nitrogen needs during the growing season than the nitrate content of petioles. Critical nitrate levels in soil need to be more firmly established, and movement of nitrate into the subsoil under irrigation more completely characterized. Preliminary data suggest that supplemental nitrogen fertilizers should be applied if soil nitrate falls below 20 ppm N before the end of July (10 to 12 weeks after plant emergence).