Soil Quality Dynamics And Comprehensive Assessment Of Ningxia Pumping Irrigation Area

For the continued using of soil resources in Ningxia pumping irrigation area during the modern oasis process in the desert steppe, farmland soil maturation-degradation interactive pattern as entry point, by spatio-temporal mutual generation of method, we carried out such studies, soil maturation as soil fertility quality dynamic changes at different time scales, and soil degradation process as distribution characteristics and corresponding relation between soil particle composition and salt-alkali ion composition, and integrated evaluation of soil quality early changes, and so on. The whole law and mechanism of evolution of soil quality in the pumping irrigation area were then analysised, to provide a theoretical basis to maintain soil health and food security. The main results obtained are as follows:(1) Soil maturation—dynamics of soil fertility quality at different time scalesWe researched dynamics at two time scales of soil organic carbon content, components and chemical stability in middle Ningxia Yellow River irrigation area over past 40 years. The results showed that soil organic carbon in this area showed a progressive evolution with the increasing years of development at the ten-years scale (15-35a,10a as a unit), marked by a significant change of the distribution of soil labile organic carbon at 0-40 cm (15a), soil labile organic carbon content at 10-20 cm (25a), and soil organic carbon content at 10-40 cm (35a). During this process, surface soil organic carbon content and composition at 0-10 cm, chemical stability of soil organic carbon at 0-40 cm remains unchanged. At the year scale (0-12a,3 a as a unit), total organic carbon and soil labile organic carbon content of the plow layer (0-40 cm) increased firstly and then decreased. While the chemical stability of organic carbon kept stable in addition to the first three years of sharp decline. For the changes at the multi-scale of soil organic carbon in middle Ningxia Yellow River irrigation area, the quick and unstable changes occurred at the smaller time scale. But at the bigger time scales, the contents of total soil organic carbon and labile soil organic carbon kept gentle and gradual change, and increased significantly at last until 35a. while organic carbon stability exhibited the global stability across the scales. At quarter scale, there were more complex of spatio-temporal distribution relationship among available nitrogen and effective p, drived by such factors as crop absorption, water movement and field management. The dynamics of ammonium nitrogen and crop growth period was more consistent, rather than Nitrate nitrogen. The relative insufficient of P may be the main limit factors of soil quality in the crop growing period.(2) soil degradation—distribution characteristics and corresponding relation between soil particle composition and salt-alkali ion compositionSoil texture in the study area is sandy loam, including fine sand, silt, and clay particles as the main. Reclamation have significantly changed vertical distribution patterns of soil texture, as the effect by cultivation methods and cropping duration. There is a risk of desertification for corn lands under transitional utilization. Overall, Sandy corn salt ions content, unused salt ions content, medlar was significantly higher than that of corn. Unused land of the accumulation of salt ions are most prominent, effect of the lycium barbarum water desalination is more obvious. With the increase of planting age, contents of alkali ions showed a downward trend, and mobility the ability of chloride, sodium and sulfate ions. With varying degrees of salinization of soil environmental quality and characteristics of alkalization is not obvious. Based on soil particle composition and RAD analysis of saline-alkali Ionic composition,0～10 cm, and 20～40 cm soil, affecting soil salinity changes of ion concentration and particle size of 6 parameters,0～0.002 mm and 0.002～0.02 mm size sand content of soil salinity ions respond significantly to explain (P=0.002), they explain all the soil grain size parameters are interpreted respectively as 63.64%,33.77% and 69.12%,27.94%.60～80cm soil,0.02～0.05 mm grain diameter sand content on soil saline ion response has significantly sex explained (P=0.004), its explained volume accounted for all soil grain diameter parameter explained volume of 81.08%, but this a soil of total explained volume only for 37%, this may is because this a soil of soil saline ion content and changes by other ecological factor of effects more strongly, needs more near a step of research.(3) Assessment and analysis of early dynamic changes of cropland soil quality in Ningxia pumping irrigation areaHongsipu Yellow River irrigation oasis farmland early dynamic changes of soil quality were comprehensively assessed and analyzed with soil quality index method and soil quality evaluation index system of 12 direct variables and three indirect variable. Our researth was shown that in 0-9 years, the trends of different soil variables are different, in which soil organic carbon, active organic carbon, cation exchange capacity, calcium and phosphorus ratio, silt and clay content increased visibly, while total soluble salt, sand decline sharply, and the other variables was relatively stable or fluctuated.12 variables were grouped into soil fertility and soil ion environment two main ingredients with Principal component analysis, in the base of which soil quality index changes showed a typical S-shaped growth curve pattern in 0-9 years, in which the dynamics of phosphorus ratio, CEC, total organic carbon and the changes of soil quality indexes were most similar.