The goal of any good nitrogen (N) management program is to maximize yield and minimize inputs. For corn growers that utilize manure or other organic forms of N, using the Presidedress Soil Nitrate Test (PSNT) can be a good tool for fine tuning N needs of the crop prior to sidedressing with N.
The PSNT is a way to measure the amount of N, in the form of nitrate, which is supplied by organic materials in the soil. The procedure was developed to measure the amount of N that is naturally released, or mineralized, from the decomposition of organic materials in the soil. This test is applicable in fields where manure has been applied, following legume forage crops, or following cover crops.
Sampling for the PSNT is different than routine soil sampling. Samples are collected approximately 1 week prior to a planned sidedress application, generally when corn is 6 to 12 inches tall (V4 to V6). Samples are taken to a depth of 12 inches. Take 10 to 15 cores to represent one sample area. Sample area should be determined based upon factors that influence mineralization rates such as drainage class, slope, cropping history, and rate of manure applications. A single sample should represent no more that 15 to 20 acres. The samples should be shipped immediately to the lab for analysis. In situations when shipping is delayed, refrigerate or freeze samples until they can be shipped or delivered to the lab. Samples should be shipped early in the week to avoid weekend delays.
We understand the importance of PSNT in your nitrogen management programs, so we provide one day turnaround time for soil nitrate samples.
Most states have developed interpretive guidelines for the PSNT. While most states have very similar interpretations, we recommend looking into other states in the region to help guide you to make the best management decision for your operation.
As mentioned previously, the PSNT is intended to measure the N from organic matter decomposition, so if a high rate of N was applied pre-planting, the interpretation of the results may not be accurate. For additional information on PSNT from A&L Great Lakes Laboratories, please see our Fact Sheet.
Indiana: Purdue Extension
Ohio: Ohio State University Extension
Michigan: Michigan State University Extension
Illinois: University of Illinois Extension
Wisconsin: University of Wisconsin Extension
A&L Great Lakes Labs Fact Sheet: In-season Soil Nitrate Testing for Corn