CHANGES IN SOIL CHEMICAL CHARACTERS AND ENZYME ACTIVITIES DURING CONTINUOUS MONOCROPPING OF CUCUMBER (CUCUMIS SATIVUS)

Soil sickness, a phenomenon of negative plant-soil feedback in continuous monocropping systems, can cause severe yield penalty in agricultural production. Changes in soil chemical and biological characters are thought to account for soil sickness. However, changes in soil properties in continuous monocropping systems and links between these changes and plant growth performance are still not clear. In this study, dynamics of soil chemical characters and enzyme activities were monitored in a continuously monocropped cucumber system, in which cucumber was successively monocropped in pots for nine croppings under greenhouse conditions from 2005 to 2009 in the experimental station of Northeast Agricultural University, Harbin, China. Cucumber showed an obvious stunted growth behavior in the seventh cropping and turned better in the ninth cropping. Soil pH decreased from the first cropping to the seventh cropping and increased in the ninth cropping. Contents of soil available nitrogen, phosphorous and potassium were the highest while activities of soil urease, neutral phosphatase and catalase were the lowest in the seventh cropping. Our results suggested that cucumber in the seventh cropping did not absorb enough soil nutrients, which may lead to the decrease in soil pH and changed soil biological properties. Changes in soil chemical and biological characters may be linked to the soil sickness of cucumber.