The Effect Of Alternative Freezing And Thawing On Soil Organic Matter And Nitrogen Potassium Nutrition Of Black Soil

The effect of alternative freezing and thawing is a non-biological effect exists in soil. It is the most common phenomenon in nature. It influences the physical, chemical and biological characteristics of soil directly.The black soil in the north-east district of our country exists in subhumid monsoonal climate in temperate zone. In order to determine the effect of alternative freezing and thawing on the physichemical and biological characteristics of black soil, we conducted the experiment both in the field and in the lab. The experiment mainly includes: the effect of alternative freezing and thawing tensity and frequency on the content of total organic matter, active organic matter, nitrate nitrogen, ammonium nitrogen, microbial biomass N, rapidly available potassium, available potassium, slowly available potassium and on the activities of some soil enzymes of black soil. We also conducted the experiment to study the effect of alternative freezing and thawing on the fixation amount and fixation rate of soil rapidly available potassium under adding of rapidly available potassium.The experiments results show that the effect of alternative freezing and thawing has a great influence on the organic matter, nitrogen nutrition, potassium nutrition and soil enzyme activities. It enhances the content of water soluble organic matter greatly. The content of water soluble organic matter demonstrates a significantly increasing tendency with the increase in freezing and thawing tensity and frequency. The effect of alternative freezing and thawing enhances the activities of microorganisms greatly. The content of microbial biomass C demonstrates a significantly decreasing tendency with the increase in freezing and thawing tensity and frequency. The effect of alternative freezing and thawing decreases the content of nitrate nitrogen greatly. The content of nitrate nitrogen demonstrates a significantly decreasing tendency with the increase in freezing and thawing tensity and frequency. The effect of alternative freezing and thawing enhances the content of ammonium nitrogen greatly. The content of ammonium nitrogen demonstrates a significantly increasing tendency with the increase in freezing and thawing tensity and frequency. The effect has no significant influence on the content of microbial biomass N. Under some potassium level,the effect of alternative freezing and thawing decreases the content of slow available potassium greatly, the content of slow available potassium demonstrates a significantly decreasing tendency with the increasein freezing and thawing tensity and frequency; The effect of alternative freezing and thawing enhances the content of rapidly available potassium ,available potassium greatly, the content of rapidly available potassium and available potassium demonstrates a significantly increasing tendency with the increase in freezing and thawing tensity and frequency.Under different adding amount of rapidly available potassium, the effect of alternative freezing and thawing can enhance the fixation of rapidly available potassium. With the increasing of adding amount, the fixation amount increases, while the fixation rate decreases. On the same adding level, the fixation amount and fixation rate show an increasing tendency with the increase in freezing and thawing tensity .The effect of alternative freezing and thawing can enhances the activities of some soil enzymes greatly,such as phosphatase, nitrate reductase and nitrite reductase. The activities of phosphatase,nitrate reductase and nitrite reductase demonstrate an increasing tendency with the increase in freezing and thawing tensity and frequency.The enhanced activities of some soil enzymes may enhance the mineralization of soil organic matter and change soil nitrogen nutrition.The above results show that ,the effect of alternative freezing and thawing has a great influence on the soil organic matter, soil nitrogen, soil potassium and some soil enzymes. The studying of these influences may helps to uncover the role of mineralization of soil ca...