Study On Soil Quality Evolution Of Terrace Cropland And Its Fertilizing Effect On The Hilly Loess Plateau

To meet the requirement of soil management in terrace cropland as well as understanding soil resilience of terrace land on the hilly loess plateau, soil quality dynamics and its fertilizing effect of terrace soil in the hilly loess plateau of eastern Gansu Province and northern Shaanxi were investigated based on field soil sampling of different ages of terrace and long term experiment. Analyzed the distribution characteristics and influencing factors of hilly Loess Plateau of eastern Gansu Province, which were based on data of cultivated land quality investigation of Zhuanglang County. In order to understand soil quality evolution in terraces after changing from sloping cropland in the hilly Loess plateau of China, soil samples were taken from terraces with different utilizing years and sloping cropland in the hilly Loess Plateau of eastern Gansu Province. To evaluate the sustainability of crop rotation system under 21-year continuous chemical fertilization condition in terraces in the Loess Hilly Reagion, the sustainability index was caculated based on the method of area of triangle. To study the soil nutrient evolution rules, we analyzed monitoring-data based on a 21-year long-term located application of organic manure and fertilizers experiment. Understanding terrace soil quality evolution characters and influencing factors, soil quality dynamic characteristics under different fertilization treatments was meaningful for improving regional soil productivity, grain production and regional agriculture sustainable development. The main conclusions were as follows:1. Both macro and micro nutrients in the terrace soil were at medium level as a whole in the hilly loess plateau of eastern Gansu Province, and the spatial variance was mainly affected by soil types and altitude.Content of total P and available P, available K were at high level, content of organic matter, total N, available N available Cu, Fe and Mn were at medium level, content of available Zn and B were at medium and lower level according to the nutrient ranking criteria in the Loess Plateau region, while a large area of soil was lack of B. Spatial variability of macronutrient in the hilly Loess Plateau was mainly related to the soil types, which explained about 51.81% of total variability, while altitude explained 23.60% of the variability. The distribution proportion of micronutrient in higher level was increased with the elevation of altitude. Micronutrient variance of terrace soil was largely related to soil types, which accounted for 69.41% of the total variance. Besides, soil texture and altitude accounted for 17.65% and 11.76% of the variance.2. Soil quality increased obviously with the increase of terrace ages. Among the indicators which restored with the increasing years of the terraces, SOM and total nitrogen were the fastest ones, while soil physical and biological indicators restored slower comparatively. Spatial variability of soil quality was influenced by land use years, altitude, slope direction and application of organic manure and inorganic fertilizer.After slope cropland changed into terraces, the content of soil organic matter(SOM), total nitrogen, available nitrogen, phosphorous, urease and mean weight diameter of aggregate(MWD) decreased significantly and soil bulk density increased substantively compared with slope cropland. The soil quality increased obviously with the increase of terrace ages. Among the indicators which restored with the increasing years of the terraces, SOM and total nitrogen were the fastest ones, while soil physical and biological indicators restored slower comparatively. The correlation between SOM, total nitrogen, MWD, urease, SQI and terrace ages could be simulated with the following formula: y=axb. Spatial variance of soil quality in the terrace was largely related to land use years, which accounted for 54.55% of the variance. Besides, altitude and slope direction of the terrace accounted for 18.18% of the variance, soil fertilizer application amount accounted for 9.10% of the variance.3. The sustainability of terrace agriculture system in the hilly loess plateau of northern Shaanxi could be improved under long-term fertilization. Fertilization may improve terrace soil quality effectively. The effect of manure was better than that of chemical fertilizer. Chemical fertilizer was found unsustainable in this crop rotation system.The content and stability of soil aggregate under long-term fertilizing increased compared with the control(no fertilizer). The application of manure improved soil aggregate, chemical index and biological index obviously. However no significant improvement of those soil quality index mentioned above was found under chemical fertilizer treatments, although available P and K content was improved significantly under P and K fertilization. The contents of most indexes were the lowest under P and K treatments. The nutrient index, biological index, crop index and sustainability index were increased by 117.7%, 113.6%, 81% and 159% compared with the control. Manure and chemical fertilizer application resulted in a preferable sustainability in comparison with the control. Manure treatment resulted in a preferable sustainability, in which the sustainability index was 6%-54% more than the critical value(1.3). Whereas, the sustainability of chemical fertilizer application was lower than that of critical value(1.3), and was unsustainable in this crop rotation system. MNP was the optimum fertilizing mode in this terrace agriculture system.4. The terrace soil fertility quality on the hilly loess plateau of northern Shaanxi was improved under long-term fertilizing. Manure application had a longer lag influence on soil quality improvement compared with chemical fertilizer application.The effect of manure on the improvement of soil organic and total N content was much better than chemical fertilizer, and had a preferable sustainability. Single manure was more effective on the improvement compared with other fertilizing measurement and NK fertilizer was the worst one. The effect of manure on soil available N and available K content increased significantly.Whereas available N content decreased with long-term chemical fertilizer application. Available P content increased obviously with P fertilizer, and the increasing rate of soil available P improved by manure application. Application of K fertilizer could rapidly increase soil available K content, but the effect was not as long as manure. The effect of manure and chemical fertilizer on soil fertility quality was promoted to some extent. Manure was more effective than chemical fertilizer in improving soil quality. Single manure had a prolong effect on soil quality, whereas, NPK treatment had a lower persistence in soil quality improvement.