Soil aggregates and associated carbon and nitrogen storage in circular grass buffer integrated cropping systems

Purpose Grass buffer strips enhance ecosystem services of irrigated landscapes. However, their impacts on soil structure and associated soil organic carbon (SOC) and nitrogen (N) cycling have not been documented well for arid and semi-arid agroecosystems. This study aimed to evaluate the seasonal dynamics of dry soil aggregate size distribution, mean weight diameter (MWD), and aggregate-associated SOC and N under buffer strip grasses (BSG), adjacent buffer strip corn (BSC), and continuous conventional corn (CCC) fields without grass buffer in the semi-arid US Southern High Plains. Methods Five circular perennial grass strips alternating with five corn strips in a 3.88-ha quarter-circle area were established under a center pivot irrigation system in the fall of 2016. Soil samples (0-20 cm depth) were collected in the spring, summer, and fall of 2021, 5 years after the long-term grass buffer establishment. Soil aggregate properties were evaluated in grass-corn edge (GCE) and at different distances from the edges in BSC and BSG and various locations in CCC. Results The results show the responses of dry soil aggregate properties varied between treatments and samplings. Specifically, the proportion of macroaggregates (2-8 mm and 0.25-2 mm) varied among treatments in fall and microaggregates (0.053-0.25, < 0.053) in spring and fall. The BSG had 20.2% and 14.8% greater 2-8 mm aggregate size and MWD than GCE in fall. In spring, the 0.053-0.25 proportion in BSC was lower than CCC. Similarly, the BSC accumulated 7.52% greater SOC in 2-8 mm aggregates than in same-size aggregates in CCC. The BSG had 7.6-11.1% greater SOC in < 0.053 mm fraction than under corn. The edge effects of grass strips on corn were observed in macroaggregates (2-8 mm) and SOC storage in these aggregates. The wind erodible fraction (< 0.25 mm) was 4.83-30.1% less with BSC than with CCC. The CCC had 16.5-126% greater soil inorganic N than BSC, suggesting aggregate breakdown and N mineralization from SOC in these aggregates. Conclusion Grass buffer strips can enhance SOC sequestration by improving soil structure and increasing aggregate-associated SOC in semi-arid cropping systems.