A soil test for nitrogen availability in the northeastern United States

Abstract

A soil test for nitrogen availabilty to corn (Zea mays, L) has gained wide acceptance in the northeast region of the United States. The test involves sampling the surface 30 cm of soil during the early part of the growing season. The N0₃‐N present at that time is correlated with the probability of obtaining a yield increase by using sidedress nitrogen fertilizer. The test has been evaluated in 272 yr‐site N response experiments in Vermont, Pennsylvania, Connecticut, New York, and New Hampshire. The various states in the region that are now offering a N soil test (Vermont, Pennsylvania, Connecticut, and Maine) have different methods of making recommendations based on soil‐test levels. However, 20 to 30 mg NO₃‐N/kg soil is about the critical range above which there is a low probability of obtaining yield increases due to sidedress fertilizer N. Therefore, no additional N fertilizer is recommended. A major problem, which is slowing widespread utilization of this test is that the soil must be sampled at a different time of the year than the routine soil tests which are usually sampled in either the fall or prior to the growing season in the spring. Other critical issues include the deeper sampling and rapid drying needed as well as the rapid turnaround time required to get the samples to the laboratory, through the laboratory, and back to the farmer. There is only a limited “window”; of time available between soil sampling and the period for timely fertilizer N sidedressing. Various states are using different innovative programs to help introduce farmers to the test and to speed total turnaround time.