DNDC Modeling on Soil Organic Carbon Dynamics Under Long-Term Application of Hairy Vetch Cover Crop and Subsequent Cotton Cultivation in Northwest Louisianan.

The agronomic benefits of using a winter cover crop, hairy vetch (HV) cultivation, in Northwest Louisiana has contributed to sustaining cotton production as well as improving soil quality. Soil organic carbon (SOC) dynamics in cotton fields were impacted by the long-term hairy vetch cultivations (30 years) during the winter. Four treatments: N 0 kg ha^-1 (check), N 45 kg ha^-1, N 67 kg ha^-1, and HV alone were compared. The Denitrification-Decomposition (DNDC) model was employed to evaluate SOC data from a long-term study at Louisiana State University Agricultural Center. The DNDC model also evaluated further scenarios in response to N fertilization on cotton yield with/without HV under irrigated and rain-fed conditions. The DNDC simulations projected low normalized root mean square error (NRMSE) values of 42.9 % under check, 24.4 % under HV alone, 30.0 % under N 45 kg ha^-1, and 18.1 % under N 67 kg ha^-1 on the validation of cotton yield. For estimating SOC contents during 30 years of study, HV treatment presented more than double in SOC contents, while the treatments of N 45 kg and 67 kg ha^-1 showed similar levels of SOC, which increased by 25 % compared to the check. In scenario analysis, the DNDC calculated that cotton yield under HV cultivation was equivalent to yields under N application. The model showed that no yield differences between irrigated and rain-fed condition under HV. In conclusion, the DNDC model can predict long-term cotton yield as well as SOC contents under different farming management practices.