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Content of microbial biomass carbon was selected as indicator for identifying effects of extreme drought on agriculture soil ecosystem. Through a series of prototype observation experiments, changing tendencies of microbial biomass carbon content and the proportion of microbial biomass carbon in soil organic carbon were identified. The optimum mass water content of soil for microbial biomass carbon was 19.5% and the demarcation point of microbial biomass carbon to drought was 14.3%, which could be used to demonstrate alters and degradation of soil ecosystem as well as the irrigation requirement of crops. We evaluated sustainability of different drought soil ecosystems after experiencing rainstorm with rehabilitation. The results suggested that soil ecosystem which was interfered by moderate drought could recover and its tolerance to drought was improved, as well as its function and activity. Soil ecosystem could barely recover from severe drought and could not adapt to severe drought stress. Soil ecosystem could not restore from extreme drought within a few days, the function and structure were damaged. We came to the conclusion that mass water content of soil should kept above 10% to avoid destroying function and structure while soil ecosystem would better be watered when mass water content was lower than 14.3% in order to maintain high productivity.

Droughts often affect the soil ecosystem directly. To address this question, a series of prototype observation experiments were designed in this study. The objective of this study was to identify changing tendencies of microbial biomass carbon content and the proportion of microbial biomass carbon in soil organic carbon under different drought conditions. All the soil samples were collected from experiments fields about 10 cm far away from the rhizosphere of the maize, and the content of microbial biomass carbon was selected as indicator for identifying effects of extreme drought on agriculture soil ecosystem. The results showed that the optimum mass water content of soil for microbial biomass carbon was 19.5 % and the demarcation point of microbial biomass carbon to drought was 14.3 %, which could be used to demonstrate alters and degradation of soil ecosystem and the irrigation requirement of crops. Meanwhile, sustainability of different drought soil ecosystems was also evaluated after rainstorm with rehabilitation. The results suggested that soil ecosystem could recover after interfered by moderate drought, and its tolerance to drought, as well as its function and activity was improved. Soil system could not adapt to severe drought stress, could barely recover and restore from extreme drought within a few days, and its function and structure were also damaged. From this view, we could conclude that mass water content of soil should be kept above 10 % to avoid soil system function and structure being destroyed. Nevertheless, these findings suggested that soil ecosystem should be watered when mass water content was lower than 14.3 %, which provided reference for improving the soil to increase the grain output.

Summer maize is a major crop in the Northern Huaihe Plain, where is one of the most important grain producing areas in Anhui Province, while the maize yield has been seriously affected by drought stress for a long period of time. To maximize maize yield and improve water use efficiency, the rule of yield loss should be clarified which was caused by drought stress in the Northern Huaihe Plain. DSSAT-CERES-Maize model was used to simulate maize yield losses caused by water stress in Bengbu Station of the Northern Huaihe Plain, which was calibrated and validated with drought stress experiments conducted in 2013. Comparing the simulated yield with measured yield under different drought stresses at different growth stages, we found that simulated losses under mild drought were higher than that of measured in all growing stages, on the contrary, simulated data under moderate and severe drought were lower than measured ones in each stage. There were 8 years that loss percentage was higher than 20% from 1961 to 2015. Results implied that maize yield under rain-fed environment was higher than that of suitable water condition, which might benefit from overcompensation of rehydration after appropriate drought stress.