Initial PSNT results demonstrate nitrogen credit for corn
Despite challenging environmental conditions after planting that favored nitrate losses from leaching and denitrification, the PSNT detected substantial amounts of nitrate N in fields with high N mineralization potential.
Since this season was highlighted by excessive rain, flooding and widespread planting delays, few Michigan farmers were able to plant corn on time. The initial Pre-Sidedress Nitrate Soil Test (PSNT) results from three such corn fields are shown in Table 1. These fields had high nitrogen (N) mineralization potential based on their previous manure and alfalfa history. Corn was planted the first week of May and received 30 lb. N/A in a 2 x 2 application. Soil cores were taken on June 9, midway between 30-inch corn rows. Corn was 12 to 15 inches tall and looked pretty uniform in terms of plant stand, size and color (Photo 1). To increase accuracy, this test was performed only a few days before the sidedress N application.
Table 1. Nitrate N and Ammonium N on PSNT samples, 2011
|Field ID||Nitrate Nppm||Ammonium Nppm||Soil N Credit1lb/A|
1 Credit based on Maximum Return to Nitrogen (MRTN) approach
The results show that despite the environmental conditions that prevailed after planting, favoring nitrate losses from leaching and denitrification, the test still detected substantial amounts – 21, 14 and 16 ppm of nitrate N in these fields. Ammonium N concentrations were much lower than nitrate N and are not expected to make significant N contributions. Current PSNT recommendations are based only on nitrate N. According to MSU’s MRTN approach, the soil N credits assigned for the three fields are 90, 30 and 60 lbs./A, respectively. To make savings on fertilizer costs and prevent potential environmental losses, growers can subtract these amounts from the total N requirement. By sidedressing N at this stage, growers are able to improve N use efficiency because it coincides with time of maximum N uptake.
For the latest MSU corn N recommendations, read MSU’s Kurt Steinke’s article on Official MSU corn nitrogen recommendations.
The 2011 spring weather conditions have placed renewed interest in soil nitrate testing and sidedressing N on corn fields that have a high N mineralization potential. Growers who planted late and changed to shorter season hybrids should adjust their N rates to match the yield potential.
Additional PSNT data will be published soon. Reductions in nitrogen fertilizer applied to corn achieved as a direct result of PSNT will be tallied at the end of season for the I Know MI Numbers Water Quality Target Program.