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 CO2 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 CO2 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 CO2 burst, POXC, ACE‐soil protein, and NO3‐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 NO3‐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 CO2 burst (r = 0.48) with RY. Soil health indicators (CO2 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.