Deficit irrigation is an important strategy to manage water, but its impacts on soil C sequestration and physical properties have not been well documented. We assessed changes in soil organic C (SOC) and soil inorganic C (SIC) concentrations and selected soil physical properties at two no-till experiments on Ulysses silt loam (a fine-silty, mixed, superactive, mesic Aridic Haplustoll) with <1% slope under six irrigation treatments (66, 86, 117, 152, 182, and 217 mm of water applied) at Garden City and three (127, 254, and 381 mm of water applied) at Tribune in western Kansas after 5 and 8 yr of management, respectively. For the 0- to 10-cm depth, SOC concentration and wet aggregate stability increased with an increase in irrigation amount, but bulk density, particle-size distribution, and SIC concentration were unaffected. At Garden City, the SOC pool in the 0- to 10-cm depth increased by 46% (11.2 vs. 16.4 Mg ha -1) from the lowest (66 mm) to the highest (217 mm) irrigation amount. At Tribune, the SOC concentration in the 5- to 10-cm soil depth increased by 30% when the irrigation amount increased from 127 (7.8 g kg -1) to 254 (10.2 g kg -1) mm. The amount of macroaggregates increased with an increase in the irrigation amount, particularly in the 5- to 10-cm depth. At Garden City, irrigation-induced increase in SOC concentration increased the mean weight diameter of aggregates ( r=0.66; P<0.001). Overall, deficit irrigation affected SOC concentration and soil structural development near the soil surface, but the magnitude of impacts was site specific.
