Soil health indicators for predicting corn nitrogen requirement in long‐term cover cropping

Abstract Efforts to address economic and environmental concerns surrounding nitrogen (N) have motivated attempts to improve estimates of plant‐available N in soil. Several soil health indicators, including CO 2 burst, permanganate oxidizable carbon (C) (POXC), and autoclaved‐citrate extractable (ACE) soil protein, assess labile C and N, and therefore may help to estimate soil N mineralization in long‐term cover cropping systems (>3 years). This study evaluated the relationship of CO 2 burst, POXC, ACE‐soil protein, and pre‐sidedress nitrate test (PSNT) with agronomic optimum N rate (AONR) in corn ( Zea mays L.). The study also looked at relationship between other soil test and corn yield parameters, relative yield (RY) and yield without N sidedress at 25 long‐term cover crop sites across Virginia. Results showed relatively weak correlations between AONR and CO 2 burst, POXC, ACE‐soil protein, and NO 3 ‐N ( r = 0.00 to −0.48), which indicates that these soil health tests may not reliably predict soil N availability and corn yield. Corn yield with zero‐sidedress N rate had a negative relationship with cover crop C:N ratio ( r = −0.66) and a positive relationship with cover crop N content ( r = 0.59), and NO 3 ‐N at pre‐planting ( r = 0.54) and sidedress (PSNT) ( r = 0.63). The PSNT showed a better relationship ( r = 0.65) compared to 72‐h CO 2 burst ( r = 0.48) with RY. Soil health indicators (CO 2 burst, POXC and ACE‐soil protein) resulted in a poor or no relationship with AONR. Our results indicate that the PSNT was a more reliable indicator of the sidedress N rate in corn.