| The degradation of paddyfield ecosystem due to unreasonable fertilization is becoming a serious problem which may impact the rural economy and sustainable agriculture. To prove up the mechanism of paddyfield ecosystem's degradation and the techniques for restoring paddyfield ecosystem degraded, a studying task was set up with three aspects: the first was the experiment that carried out under unreasonable fertilization; the second was ones for restoring paddy soils' degradation due to either deficiency of all of nitrogen, phosphorous, and potassium, or deficiency of phosphorous, or deficiency of potassium; the last was to study the regularity of paddy soil quality's change under various fertilization based on seven experimental sites in Hunan province for long time. The main results were summarized as follows.The results of long term fertilization experiment with various fertilizations are as follows. (1) The contents of total and available nitrogen, phosphorus, and potassium under CK (deficiency of fertilizer) were decreased, and that under application of chemical fertilizer and organic manure were increased. Application of organic manure could enhance the content of total and available nitrogen, phosphorous, and potassium. (2) The contents of exchangeable calcium were increased significantly under fertilization treatments, in which the order for increasing exchangeable Ca value in the same soil was: OM30> OM60> NPK> CK, in Yellow clayey earth, Alluvial sandy earth, and Reddish yellow clayey earth, in which content of calcium was less; contrarily, the contents under CK in Blue gray clayey earth, whitish clayey earth, and Purple tidal clayey earth, in which contents of calcium was more, were much higher than that under NPK, OM30, and OM60, in which the exchangeable Ca value negatively correlated to the amount of organic manure applied. The contents of exchangeable magnesium under fertilization treatments decreased in Purple tidal clayey earth, Blue gray clayey earth, Alluvial sandy earth, Yellow clayey earth, and Whitish clayey earth, but increased significantly in Reddish yellow clayey earth. The contents of available sulfur under NPK treatment were more than that under CK in Purple tidal clayey earth, Blue gray clayey earth, Yellow clayey earth, and Whitish clayey earth, which have a high sulfur concentration, and less in Alluvial sandy earth and Reddish yellow clayey earth which have a low sulfur concentration; however, the contents of available sulfur under OM30 and OM60 were increased in all the experimental soils. The contents of available silicon also rose under fertilization treatments in all experimental soils. (3) Compared with CK, the contents of available B, available Cu, and available Zn in the paddy soils under fertilization treatments are either increased through freeing the trace elements from which fixed in soil by increasing organic matter and inputting B, Cu, and Zn with long term fertilization, or decreased through the plants with larger biomass taking in more available B, Cu, and Zn under NPK treatment for long term; the contents of available Fe and Mn rise with the Eh and pH declining in paddy soils and inputting Fe and Mn for fertilizing with organic manure, decline with pH rising and organic matter's adsorption intensifying. (4) The values of CEC were enhanced in various test soil as the amount of organic manure applied increasing. (5) The contents of clay particle were increased in Reddish yellow clay earth and Blue clay earth, and decreased in the other test soils under NPK treatment. Under OM30 treatment, the contents of clay particle were decreased in Blue clay earth and Purple tidal earth, and increased in the other test soils. Under OM60 treatment, the contents of clay particle were enhanced in Yellow clay earth and Alluvial sandy earth, declined in the other test soils. The change of silt content was just reverse. (6) Under NPK treatment, the contents of fine sand were increased in Yellow clay earth, Blue clay earth, Alluvial sandy earth, and Purple tidal clay earth, and decreased in Reddish clay earth and Whitish clay earth. Under OM30 treatment, the contents of fine sand were increased in Yellow clay earth, Alluvial sand earth, Reddish yellow clay earth, and Purple tidal clay earth, decreased in rest test soils. Under OM60 treatment, the content of fine sand in Alluvial sand earth (Lingxiang site) increased, decreased in the rest test soils. The change of coarse grain content was just reverse. (7) In the soil particle which size less than 20 urn, the order of content of various clay mineral was: illite > kaolilite > 1.4nm mineral, in all of experimental soil except Alluvial sandy earth in Linxiang which order of that was: kaolilite> illite> 1.4nm mineral. The contents of illite in soils under CK treatment were higher than that under NPK and OM60 treatment except Whitish clay earth, in which the order of treatment for content of illite increasing was: OM60> NPK> CK. The content of kaolilite and 1.4nm mineral were changed in a reverse trend as illite were in various type of paddy soil.The kinetics of degradation of healthy paddyfield ecosystem due to unreasonable fertilization are as follows. (1) The rice growth was interfered and the structure of microbe population was altered through applying excessive nitrogen fertilizer, while the yield of rice was decreased later and the secretion was reduced from rice root, which induced the Eh and the quantities of Bacterium and Actinomycetes declining, and the contents of MBC, MBN, MBP low in the soil. All of that made the capacity of accommodating nutrient weak in microbe ecosystem. At the same time, the environment of paddy field was impacted severely due to leaching loss of N nutrient because of low utilization efficiency of nitrogen fertilizer. (2) Application of excessive organic manure did not interfere the rice growth and the structure of microbe population because of it's releasing N, P, and K nutrition mildly. As a result, the rice yield stabilized, and the content of organic matter, available N, P, and K increased gradually. On the other hand, the quantities of microbe and the content of MBC, MBN, and MBP rose, and the value of microbial activity were higher due to rice growing normally and inputting organic manure. However, leaching loss of macronutrient, secondary element nutrient, and micronutrient intensified due to the concentration of dissolved of all the nutrient increasing after inputting excessive organic manure. (3) Under deficiency of fertilizer, the rice grew slowly and the biomass was less than that under other treatments due to exhaustion of nutrient in soil. As a result of that, the quantities of microbe and the content of MBC, MBN, and MBP decreased in the soil. However, the leaching loss of various nutrient was lower than that under other fertilization treatments and confined in range of permission.The restoring effects of various fertilizations on the degraded paddy soils with deficiency of N, P, and K nutrients are as follows. The rice growing normally through balanced fertilization induced the rice yield increasing and forming a benign circulation among the paddy soil microbe ecosystem: the quantity of microbe, the microbial activity, and the content of MBC, MBN, and MBP increased significantly due to large amount of secretion and oxygen from rice root. So the capacity of accommodating nutrition in microbe ecosystem was strengthened, and the function of microbe ecosystem in paddy soil was enhanced. All of the restoring treatments increased the content of organic matter, available nitrogen, available phosphorous, available potassium, and the beneficial values of microbial character, especially, the ZYM had the best effects in all of treatments. Although the leaching loss of nutrient in restoring treatments were severer slightly than CK (deficiency of fertilizer) in the initial stage of rice growth, the concentration of various nutrient in leaching water was confined in safety to environment in most parts of period of rice duration, and under ZYM the value of the concentrations in leaching water was the lowest.The restoring effects of various fertilizations on the degraded paddy soils with deficiency of K fertilizer are as follows. The rice growing normally through adding potassium fertilizer and organic manure induced the rice yield increasing and forming a benign circulation among the paddy soil microbe ecosystem: the quantity of microbe, the microbial activity, and the content of MBC, MBN, and MBP increased significantly due to large amount of secretion and oxygen from rice root. So the capacity of accommodating nutrition in microbe ecosystem was strengthened, and the function of microbe ecosystem in paddy soil was enhanced. All of the restoring treatments increased the content of organic matter, available nitrogen, available phosphorous, available potassium, and the beneficial values of microbial character, especially, the NPhKM had the best effects in all treatments. Although the leaching loss of nutrient in restoring treatments were severer slightly than CK (deficiency of potassium fertilizer) in the initial stage of rice growth, the concentration of various nutrient in leaching water was confined in safety to environment in most parts of period of rice duration, and under NPKSi and NPKM the value of the concentration in leaching water was the lowest.The restoring effects of various fertilizations on the degraded paddy soils with deficiency of phosphorous fertilizer are as follows. The rice growing normally through adding phosphorous fertilizer and organic manure induced the rice yield increasing and forming a benign circulation among the paddy soil microbe ecosystem: the quantity of microbe, the microbial activity, and the content of MBC, MBN, and MBP increased significantly due to large amount of secretion and oxygen from rice root. So the capacity of accommodating nutrition in microbe ecosystem was strengthened, and the function of microbe ecosystem in paddy soil was enhanced. All of the restoring treatments increased the content of organic matter, available nitrogen, available phosphorous, available potassium, and the beneficial values of microbial character, especially, the NKhPM had the best effects in all treatments. Although the leaching loss of nutrient in restoring treatments were severer than CK (deficiency of phosphorous fertilizer) in the initial stage of rice growth, the concentration of various nutrient in leaching water was confined in safety to environment in most parts of period of rice duration, and under NKhPM the value of the concentration in leaching water was the lowest.Based on all the restoring effects, the treatment to restore paddy soil with deficiency of fertilizer should be chosen to apply rice special fertilizer and reasonable amount of organic manure, the treatment to restore paddy soil with deficiency of potassium fertilizer should be chosen to add reasonable amount of potassium fertilizer and organic manure, and the treatment to restore paddy soil with deficiency of phosphorous fertilizer should be chosen to apply more phosphorous fertilizer and reasonable amount of organic manure.
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