Recalibrating the Pennsylvania pre-sidedress soil nitrate test recommendations for modern corn production

The pre-sidedress soil nitrate test (PSNT) was developed over 30 years ago to determine sidedress nitrogen (N) fertilizer recommendations for corn (Zea mays L.). Since the original PSNT calibrations were developed, changes in production practices such as no-till and cover cropping and increases in corn yields and N use efficiency could affect the accuracy of PSNT recommendations. To update the PSNT recommendations in Pennsylvania and demonstrate the test's efficacy, we compiled a dataset of 32 calibration sites and 13 demonstration sites where the PSNT was conducted, and the economically optimum N rate (EONR) for corn was determined from an N fertilizer yield response curve. We recalibrated the PSNT recommendation algorithm and compared its accuracy to the original calibration. The new calibration resulted in a single long-term manure history factor that interacted with the PSNT result to adjust the sidedress N recommendation (-5.7 kg N ha(-1) [mg NO3-N kg(-1)](-1)). The new calibration also included a term for a mixed species cover crop, which increased the sidedress N recommendation 56.2 kg N ha(-1). Finally, the coefficient that scales the N fertilizer recommendation based on yield goal decreased by 29% from the original calibration to 12.9 kg N Mg-1 grain. The new algorithm for predicting EONR reduced the error of the sidedress N recommendation by one-half compared to the original calibration. The new PSNT calibration will allow users to accurately determine sidedress N recommendations in sites with a long-term manure history and underscores the importance of updating soil fertility recommendation algorithms with modern data.