Quirine Ketterings1, Karl Czymmek1,2, Sanjay Gami1, and Mike Reuter3

Cornell University Nutrient Management Spear Program1, PRODAIRY2, and DairyOne3

Since the introduction of the corn stalk nitrate test (CSNT) as an end-of-season evaluation tool for nitrogen (N) management in 2nd or higher year corn fields, the number of fields that have been tested for CSNT has been on the increase. The greatest benefit of this test is that it allows evaluation and fine-tuning of N management for each specific field. It does, however, require multiple years of testing to gain experience with on-farm interpretation. Corn stalk nitrate test results >2000 ppm indicate there was significantly more N available during the growing season than the crop needed.

The summary of CSNT results for the past eight years is shown in Table 1. In the 2013 and 2014 growing season, the CSNT testing results from the Nutrient Management Spear Program and DairyOne were summarized to obtain a distribution of CSNT categories in New York State. Quality control samples shared between the two laboratories in both years showed excellent consistency in reported data between the two laboratories. Data prior to 2013 reflect submissions to Cornell University only. For 2014, this summary shows that about 36% of all tested fields were over the 2000 ppm range, while 27% were over 3000 ppm and 14% exceeded 5000 ppm. In contrast, 29% of the 2014 samples tested low in CSNT. For 2nd or higher year corn fields, low test results (less than 250 ppm) are likely to reflect a true N deficiency. Weed pressure, disease pressure, lack of moisture and other stress factors can impact the N status of the crop, so in some circumstances, additional N might not have been able to overcome the real reason for the low CSNTs (e.g. no amount of N fertilizer can make up for a drought).

As mentioned, the CSNT is most effective when used for multiple years on the same fields to determine how each responds to the way N is being managed. Crop history, manure history, other N inputs, soil type, and growing conditions all impact CSNT results, and crop management records that include these pieces of information can be used to evaluate CSNT results and determine where changes can be made.

Table 1. Distribution of corn stalk nitrate test values for New York State corn fields sampled in 2007-2014.

Corn stalk nitrate test category20072008200920102011201220132014
Low (<250 ppm)1219302421203529
Marginal (250-750 ppm)1312141719171616
Optimal (>750-2000 ppm)2622211924222019
Excess (>2000 ppm)4948354036412936
Excess (>3000 ppm)3436222824292027
Excess (>5000 ppm)212011141214914
Total number10525236750976592314731175
Maximum value (ppm)1493313069117231396616687156711314714659