CHANGES IN THE AMOUNT OF NITROGEN AND PHOSPHORUS IN THE SOIL BETWEEN FALL AND SPRING SAMPLING

Abstract

Soils were sampled to 120-cm depths in the fall and again in the spring to determine the NO 3 N, NH 4 N and NaHCO 3 extractable P content. The change in nutrient content of the soil between fall and spring was measured and related to the fall sampling values and to climatic conditions between samplings. The samples were taken for each 10 yr at several sites on different soil types. The average of all sites showed little change in the P content of the soil from fall to spring. There was some increase in NO 3 -N, particularly in the 0- to 60-cm depth but there was a larger decrease in NH 4 -N, resulting in a net decrease of N (NO 3 -N + NH 4 -N) or total available mineral nitrogen from fall to spring. The amount of change in NO 3 -N, NH 4 -N and the combination of these two (N) was inversely related to the amount of that form of nitrogen present in the soil in the fall. Weather also affected the amount of change. Consideration of the amount of nitrogen present in the fall and the weather from fall to spring will improve the accuracy of predicting the amount that will be present at seeding time.