Impact of long-term supplemental irrigation on soil organic carbon and nitrogen in sandy soils under conservation tillage in the southeastern United States

Abstract

Management practices that increase soil organic carbon (SOC) and nitrogen (N) stocks improve soil health, crop productivity, and agricultural sustainability. Irrigation is crucial in mitigating the effect of sporadic droughts on agricultural productivity in the southeastern Coastal Plains of the United States and is well-recognized for improving SOC and N accrual under semiarid conditions. However, our understanding of its impact on SOC and N storage in sandy soils under humid climates is limited. Our objective was to quantify the differences in SOC and N storage between irrigated and rainfed management in a humid agroecosystem. We sampled four typical southeastern Coastal Plains soils in the United States: Bonneau (BnA), Dunbar (Dn), Norfolk (NkA), and Noboco (NcA), all of which are loamy sand, both in irrigated and rainfed areas of the same experimental field. We found no significant difference in soil respiration (as 3day-CO₂-C), microbial biomass carbon (MBC), hot water-extractable carbon (HWEC), inorganic N, and labile organic nitrogen (LON) between irrigated and rainfed conditions. In addition, we found no difference in SOC and N stocks under the irrigated versus rainfed scenario. Our results indicated that 29 years of supplemental irrigation had no significant impact on soil C and N fractions or SOC and N storage compared to rainfed conditions under continuous long-term conservation tillage.