Abstract: There is a practice of intensive, continuous cultivation of potato in Gansu province due to a high demand and good economic returns to growers. Under continuous cultivation, growers have experienced reduced tuber yield, reduced soil microbial community health, and an increased incidence of blight disease. To investigate ways to overcome these problems, an experiment was conducted on a potato field continuously cropped for 4 years, to assess the effect of different soil amendment measures on soil water relationships, microbial community structure and incidence of blight disease and tuber yield. The experiment was laid out in a randomized complete block design with three replicates. Five soil amendment treatments were tested: oxalazine, pentachloronitro benzene, Trichoderma harzianum, microbial soil amendment and conventional practice (control). It was found that T. harzianum and oxalazine treatments significantly increased the bacteria ratio. The oxalazine treatment had the lowest (P<0.05) incidence of early and late blight disease, and the highest water use efficiency, compared with other treatments. Economic yield of potatoes increased by 22.3% and 24.1% in T. harzianum and oxalazine treatments, respectively, when compared to the control. In summary, the use of the oxalazine and T. harzianum in a continuously cropped potato field improved soil microbial biomass, increased soil bacteria∶fungi ratio, reduced the incidence of blight, improved water use efficiency, increased soil water content, and improved the tuber yield of potatoes in dry land cultivation.

Key words: continuous cropping, disease, soil microorganism, soil water effect, dry land