Farmland Soil Chemical Degradation Characteristics And Effect In Guanzhong Area

Soil is an important part of agricultural ecosystem, and it plays a very important role inmaintaining regional and global environmental quality.With economic growth and populationincreasing, and the area of farmland per capita decreasing year by year, which make the landbe high strength used to ensure a stable high grain yields.Guanzhong area has a long history of farming civilization, and it is an important majorgrain producing area of shaanxi province and even the whole country. The long-term highintensity agricultural production makes the soil quality degradate in guanzhong area,especililly soil chemical degradation is very serious. Due to change of crop planting system,cultivation, fertilization, and no longer using farmyard manure, soil “recalcification” byfertilization disappears. Rotary tillage land instead by the commune, calcium which is leachedin the deep soil, can not be recovered by surface soil tillage. Long-term using of inorganicnitrogen, phosphate and potash fertilizer in soil, ammonium nitrogen and potassium canchange with Ca2+in colloidal, and the chemical deposition of calcium by phosphorus also canpromote the colloidal calcium to be exchange, which lead to soil calcium saturation decline.The nitration of nitrogen in the soil makes soil acidification and rhizosphere soil compaction,which causes soil CO2bias voltage increasing, thereby accelerating the dissolution andleaching of CaCO3. Modern farmland management and use system are not good for thebalance of the surface Ca, calcium degradation is one of the main feature of its chemicaldegradation. Based on this objective reality, investigation of calcium degradation is veryimportant.Shaanxi Guanzhong area is chosed as this research object, under chemical fertilizer usingincreasd and soil calcium degradation year by year, to stuy some soil quality indexes, such assoil organic carbon, active organic carbon, calcium carbonate, and exchangeable calcium. Inparticularly, the relationship of soil carbon sequestration and quality evolution is going to beexplored, and on the basis of biological experiments, to investigate the evolution of soil Ca2+saturation and its harmfulness on crop growth, etc. The results showed as following:1. Soil organic carbon content showed an obvious variation characteristic of vertical andhorizontal directions in the whole soil profile (0~100cm) of the test area. Soil organic carbon content changed between7.00g·kg-1and23.39g·kg-1, and showed a heavy deficiency situationin the most test area. The organic carbon content in the0~20cm soil was relatively high, andshowed a decreasing organic carbon content with the distance from the village increased. Soilorganic carbon content was extreme deficiency in the40~100cm soil layer, and showed anunsignifcant difference.Carbon library activity increased from the upper to the lower soil layer; the horizontaldistribution of0~100cm soil organic carbon density was affected by both soil organic carboncontent and soil profile bulk density variation. The unit area of farmland soil organic carbondensity changed between1.45~0.50kg·m-2, and showed an increase first and then decreasewith the distance from the village increased. The results of soil carbon instability in this areashowed that soil carbon pool activity changed between0.18~0.59, and it increased in the30~40cm soil layer.2. Although content of study area0~40cm soil layer is still higher than the lowerembodies in the history of the effects of “compound calcium” measures, however, the calciumcarbonate content of a maximum83.45g·kg-1is not on the surface, but appeared in30~40cmsoil layer, and then to the region of the second soil census data as the background analysis ofcurrent farmland0~30cm soil layer, there is a clear downward leaching of calcium carbonatecontent is reduced, and the lower accumulation. Due to the changes of soil calcium complexmechanism,0~20cm soil layer the largest annual decline rate of calcium carbonate, reaching9.4%. Cultivated loessial soil was larger than that of0~10cm soil exchangeable calciumcontent is the highest, at30~50cm soil layer soil exchangeable calcium content increaseswith the increase of soil depth, which suggests that30~50cm soil layer exists obviousdecalcified problems。3. Research on regional soil calcium saturation changes between42.08%~77.46%,32.1%of the samples of the tested soil calcium saturation is lower than for most number ofcrop health of soil quality index of60%~70%. In calcareous soil region of rich calcium,calcium soil saturation distribution has significant differences. The farther the distance fromthe village, the problem of low calcium saturation of soil increased significantly. The closerfrom the village, the longer the history of the use of fertilizer, soil trace calcium effectsignificantly, soil calcium saturation is relatively high.4. Based on the relationship between different calcium saturation soil and crop growthstudy, different calcium saturation effects on soy, big green vegetables is more obvious.Calcium soil saturation handle crop growth for more than68.97%health, plant height of plantwith soil reduce with the decrease of the calcium saturation, calcium saturation (53.27%,45.00%) of the lowest two processing plant height is slightly higher but its weak color yellow leaf. Practice has proved that crops need dosage of calcium, can be accounted for80%of theground part of inorganic nutrients, lack of calcium fertilizer can cause low growth, yield,quality and disease resistance of heavy and not store a lot of harm. Soya bean ground partsand root fresh weight as calcium saturation in different treatment reduce present decreasingtrend, calcium saturation is68.97%of fresh weight rootshoot ratio is also slightly higher thanseveral other processing.