Spatial Variability in Yield and Corn Stalk Nitrate Test Results.

Nitrogen (N) is an essential macronutrient in plant growth and the primary nutrient limiting forage corn (Zea mays L.) production in New York. However, N applied in excess of plant N needs can be lost to the environment and increase crop production costs. A recent addition to New York State’s nutrient management policy allows farmers to override land-grant university recommendations in favor of an adaptive management approach that uses yield assessments and Corn Stalk Nitrate Test (CSNT) results. The CSNT is an end-of-season assessment tool that allows producers to identify sites that received more N than needed that season. Yield assessments done with yield monitors can be used to determine yield zones within a field and this information could aid in determination of CSNT sampling locations. The aim of this study was to (1) evaluate relationships between yield and CSNT levels and variability; and (2) to develop a protocol for optimal CSNT sampling taking into account within field variability. Five corn silage fields were sampled post-harvest for cornstalks using a sampling density of 11 stalks/ha. Yield was recorded by forage yield monitors and yield maps were created. Fields were separated in three yield zones (low, medium and high) and CSNT and yield variability were calculated for these zones. Spatial comparison between yield and CSNT showed a decline in both yield variability and CSNT variability with increase in average yield. These results suggest that high yielding areas within fields could require a lower CSNT sampling density, supporting the hypothesis that yield-based targeted sampling will result in both more meaningful information on N status of a crop and reduce sampling costs compared to grid sampling. Future research should include historical yield maps to investigate spatial relationship between CSNT and yield records for previous years.