Soil carbon sequestration and biological health under pecan orchards of varying ages

Climate change and variability have affected crop production and soil health, specifically in arid and semiarid regions. Farmers have been planting crops with high market value and carbon (C) sequestration potential in orchards and plantations like pecan [Carya illinoinensis (Wangenh.) K. Koch] in the southwestern United States, compared to row crops, to cope with climate change. However, their soil health and profile C sequestration potential have not been evaluated yet. We quantified responses of selected soil health indicators and profile C storage in pecan orchards of different ages (20, 40, and 80 years) and a nearby cotton (Gossypium hirsutum L.) field as a control. Soil samples were collected from 0- to 90-cm depth and analyzed for potentially mineralizable carbon (PMC), soil organic carbon (SOC), total labile N (TLN), soil organic nitrogen (SON), and soil microbial community structure. Results showed that soil PMC content in 15- to 90-cm depth was 83%–103% greater in the 20-year-old pecan orchard than in the cotton field. The 20-year-old orchard had 99%–190% greater SOC than cotton fields at 15- to 90-cm depth. However, soil TLN and SON storage were significantly higher under the cotton field at 0- to 90-cm depth. At 0- to 90-cm depth, SOC stock was 83% higher in the 20-year-old orchard, with 91% more mineral-associated and 78% more particulate C than in the cotton field. Soil bacteria and fungi in 0- to 15-cm depth were enhanced by 30%–68% and 72%–102%, respectively. Pecan orchards can improve soil health and soil profile C sequestration, particularly in the first 20 years of establishment.