Effect of continuous potato monoculture on soil chemical and biological prop-erties in Yellow River Irrigation Area in central Gansu Province

The irrigation area along the Yellow River in central Gansu Province is an important growing region of processing potato and seed potato in China. Continuous potato monoculture (CPM) stemming from intensive cultivation has severely affected the healthy development of local potato industry. It is necessary to increase our understanding about the barrier associated with CPM. To that, a long-term field experiment was conducted, which contained 5 potato cropping treatments corresponding to continuous potato cropping for 1-5 years, with maize-potato rotation cropping as the control. In the study, we focused on how the soil chemical and biological properties changed in CPM system, and which soil variables contributed principally to the barriers of CPM. The study showed that contrary to alkaline hydrolyzable nitrogen, NH₄OAc extractable potassium and electrical conductivity, soil organic carbon content gradually decreased with increasing years of CPM. Also compared with the control, CPM significantly increased soil NaHCO₃ extractable phosphorus content. However, there were no significant changes in total nitrogen, C/N ratio and pH. Compared with the control, long-term CPM (over 3-5 years) decreased mean soil enzyme activity by 33.07%-61.78%. The activities of urease, sucrose and dehydrogenase decreased with increasing years of CPM. Long-term CPM decreased the content of soil microbial biomass carbon, while both soil basal respiration and FDA hydrolysis activity exhibited highly significant linear negative correlation with the number of year of CPM. Results of Biolog ECO assessment indicated that long-term CPM significantly decreased total activity and function diversity of soil microbes, where Shannon diversity index for long-term CPM decreased by 11.75%-13.65% compared with the control. Principal component analysis of carbon utilization profile of soil microbes showed that long-term CPM clearly changed the structure of soil microbial community compared with the control. Among the 6 groups of carbon source substrates, carbohydrates type was most sensitive to the changes in soil microbial communities in CPM system. Long-term CPM significantly decreased the relative utilization ratio of selected carbon source substrates for soil microbes, including carbohydrates, amino acids, carboxylic acids and amines. For 31 sole-carbon source substrates, the utilization pattern of soil microbes under long-term CPM was more centralized than under the control or short-term CPM. Linear models of stepwise regression analysis and path analysis confirmed that a total of 4 soil variables (soil microbial community structure, soil microbial biomass carbon, total nitrogen and dehydrogenase) significantly affected tuber yield under CPM system, and that soil microbial community structure contributed most, followed by soil microbial biomass carbon. The results of the study suggested that soil microbial variables were the main causes of the barriers of CPM system in the Yellow River Irrigation Area in central Gansu Province.