Objective  The aim was to obtain a water and fertilizer management mode that regulates potato-planting soil organic carbon storage, and reveal the influence of soil enzyme activity on soil organic carbon fraction and carbon pool management index (CPMI).

Method  Field experiment was carried out in Nanning under the rain-shelter condition with two drip irrigation levels (high irrigation amount: Soil water content was maintained at 60%–70%, 70%–80%, 75%–85% and 50%–60% of field capacity at the seedling, tuber formation, tuber expansion and starch accumulation stages, respectively; Low irrigation amount: Soil water content was maintained at 50%–60%, 60%–70%, 70%–80% and 40%–50% of field capacity at the seedling, tuber formation, tuber expansion and starch accumulation stages, respectively) and three drip fertigation ratios (NK_100-0: All N,K fertilizer were applied to soil as base fertilizer; NK_70-30: 70% N,K fertilizer were applied to soil as base fertilizer and 30% as topdressing with drip fertigation; NK_50-50: 50% N,K fertilizer were applied to soil as base fertilizer and 50% as topdressing with drip fertigation). The contents of total organic carbon (TOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and labile organic carbon (LOC) and the activities of sucrase, cellulase and catalase in the soils were measured after harvesting the potato. Then CPMI was calculated and the relationships of soil organic carbon fraction and CPMI with soil enzyme activities were analyzed.

Result  Drip irrigation amount affected organic carbon contents and components in the soils significantly. Under the same fertigation ratio, high irrigation amount had higher organic carbon contents and components, CPMI and sucrase activity in the soils than those of low irrigation amount. Under the high irrigation amount condition, NK_50-50 increased TOC content by 15.2% and 7.1% respectively compared with NK_100-0 and NK_70-30, and NK_50-50 increased LOC content by 25.0% compared with NK_100-0. Moreover, NK_50-50 of high irrigation amount treatment had significant higher contents of TOC and LOC than those of other treatments. Under the same drip irrigation amount, the effect of drip fertigation ratio on the activities of three enzymes was not significant. Among all treatments, NK_50-50 of high irrigation amount treatment had the highest sucrase activity. Compared with NK_100-0, NK_50-50 increased soil CPI and CPMI by 15.1% and 25.8% respectively under the high irrigation amount condition, and NK_50-50 increased carbon pool index (CPI) and CPMI by 12.6% and 8.4% respectively under the low irrigation amount condition. Among all treatments, NK_50-50 of high irrigation amount treatment had higher CPI and CPMI. In addition, soil TOC, DOC and MBC were extremely significantly or significantly correlated with the sucrase activity (with correlation coefficients of 0.61, 0.48 and 0.46, respectively).

Conclusion  NK_50-50 of high irrigation amount treatment increases the contents of organic carbon and its components and sucrase activity in soil, and can be used as the water and fertilizer management mode regulating potato-planting soil organic carbon storage. Soil sucrase activity affects the contents of TOC, DOC and MBC.