In‐Field Spatial Variability of Corn Stalk Nitrate Test Results

Abstract

The corn (Zea mays L.) stalk nitrate test (CSNT) is a postharvest plant test that provides feedback on N supply vs. crop needs of a growing season. As such, test results can provide information on the need for adjustments in N management in future years. However, CSNT‐N can be variable within fields. The aim of this study was to (i) describe and relate within‐field CSNT‐N and corn silage yield spatial variability and (ii) to evaluate a yield‐based, targeted, CSNT sampling alternative. In 2013, five corn fields were grid sampled to determine the impact of sampling density on accuracy of CSNT‐N classification for the whole field. Close‐proximity variability (within a 3‐m row) was determined as well. In 2014, the study was expanded to include three additional fields with 2013 and 2014 yield data. Results showed similar means and standard deviation (SD) for close‐proximity sampling and whole‐field sampling. Thus, time and resources invested in CSNT sampling can be reduced with close‐proximity sampling. Current sampling guidelines (composite sample per field using a sampling intensity of 2.5 stalks ha−1) resulted in probabilities of estimating a field's mean CSNT‐N of 25, 32, and 72% for coefficients of variation (CV) of ±6.4, ±11, and ±22%, respectively. High‐yielding areas had more homogenous CSNT‐N values than low‐yielding areas. The analysis of corn stalks per yield zone resulted in reduced CSNT‐N spatial variability. Even intense sampling strategies for whole fields can result in interpretation errors while yield‐based CSNT sampling results in more meaningful information for N management.Core Ideas Corn stalk nitrate test results help corn growers fine‐tune N management. Within‐field corn stalk nitrate test‐N variability can lead to incorrect interpretations. Adoption of corn stalk nitrate test use can be enhanced with yield‐based field sampling. The ratio of yield and corn stalk nitrate test‐N may be helpful to identify areas with sufficient N.