In the last three weeks, some areas have gone from the verge of drought, to so much rain they are considering sidedressing more N on corn. The rain was very welcome, but some areas received too much of a good thing!
Our staff has been getting calls asking about side-dressing N on corn which received excessive rain. The simple answer is, there is no simple answer. The University of Minnesota has a worksheet that asks questions about soil texture, when and how N fertilizer was applied, crop appearance etc.to help you decide if you need to sidedress additional N. We are also getting questions about testing the amount of nitrate in the soil profile right now to help make the sidedress N decision.
The Pre-Sidedress Nitrate Test (PSNT) is a 0-12” soil sample taken when the corn is 6-12” tall. The initial research goes back to the early 1990’s at Iowa State University. The PSNT test helps determine if a corn field is likely to respond to an application of sidedressed N. The critical level for the PSNT test is about 25 ppm (100 lb/a for a 0-12” sample) based on university research. If a sample tests higher than 25 ppm (100 lb/a) there is a low chance of getting a yield response to additional sidedressed N. If the test is less than 25 ppm, a sidedressed N application can result in a yield increase.
The recommended sampling procedure is to collect 10 to 15 cores to a 12-inch depth. All soil cores should be placed into the sample bag and submitted to the lab within 24 hours or stored in a refrigerator. In most situations where the PSNT test is used, the soil cores are wet due to excessive rainfall. With wet sticky soil cores, it is best to send all of the soil cores to the laboratory be to dried and ground. The most critical part of PSNT testing is to get a representative sample to the lab where all of the cores can be dried and ground before testing. While the technology for testing these samples in the field is improving, it is impossible to blend wet sticky soil cores together and then select a small portion to test in the field. The only way to get an accurate and repeatable test result is to dry, grind and blend the whole sample before testing.
AGVISE provides you with a 24-hour turnaround on PSNT samples. PSNT samples are tested and reported the next business day after they arrive. Test results are posted on the AGVISOR program on our website for easy access. With AGVISE you not only get great service, you get the highest-quality data based on 40 years of testing experience.
Below are some links to research and publications on the PSNT test from various universities. The publications highlight the use and interpretation of the PSNT test based on university research in your area.