The Evolvement Rule Of Soil Fertility Of Shajiang Black Soil Under Long-term Located Fertilization

The effects of long-term located fertilization on soil fertility and crop yields of Shajiang Black soil were studied in this paper on the basis of long-term located experiment.The results were as follow:1.Effects of long-term located fertilization on soil physical propertiesApplied organic manure(material) could reduce soil bulk density,increase all sorts of soil porosity and field water-holding capacity.Soil physical properties were improved obviously.2.Effects of long-term located fertilization on soil organic matter content and its oxidation stabilitySoil organic matter content of the treatment without fertilization in long time decreased. Applied organic manure could increase soil organic matter content significantly.Up to 2005,soil organic matter content increased by 10.5-23.5 g/kg,0.46-1.02 g/kg yearly compared to the treatment without fertilization;4.3-17.3g/kg,0.17-0.75g/kg yearly compared to the treatment only applying chemical fertilizer.Soil organic matter content increased along with the rate of organic manure(material).Long term applying chemical fertilizer could increase soil organic matter content as well.Under long-term organic manure used together with chemical fertilizer,readily oxidizable organic matter increased significantly.The ability of modulation and provide of soil nutrition improved.3.Effects of long-term fertilization on the combined forms of soil humusApplied organic manure(material),chemical fertilizer or the combination of them could both increase light organic carbon content and the ratio between light carbon and total carbon.Although applying chemical fertilizer singly could increase light organic carbon content,the increasing rate was much lower than applying organic manure and the increasing rate of organic carbon was mainly heavy organic carbon.Light organic carbon content of the treatment of long-term fallow was high than the treatment of long-term applying chemical fertilizer only,but the ratio between light carbon and total carbon was lower.Chemical fertilizer plus organic manure(material) could increase undisturbed complex rate,while the undisturbed complex degree reduced.It indicated that the increasing rate of organic carbon was not complex totally.Part of them was free form humic acid.The increased complex degree of Shajiang Black Soil was high,it was determined by the climate,soil physical and chemical properties. Applied different organic manure(material) could improve the contents of loosely combined humus,tightly combined humus and stably combined humus.The effect of stable manure was more effective than that of the straw.In the mean while,the ratio between loosely combined organic carbon and heavy organic carbon,the ratio between stably combined organic carbon and heavy organic carbon were ralateively stable,while tightly combined organic carbon decreased,compared to the treatments of fallow and without fertilization,applied chemical fertilizer increased the contents of loosely combined humus,tightly combined humus and stably combined humus,but the change of ralative content of them was small.Stable manure was more effective to increase the contents of loosely combined humus and stably combined humus,while chemical fertilizer mainly increased tightly combined humus.The ratio of loosely combined humus to tightly combined humus and stably combined humus to tightly combined humus could be increased under long-time fertilization.Applied organic manure(material) could increase the PQ value.The PQ values of loosely combined humus of the treatment with pig dung and stably combined humus of cow dung were the highest compared to other treatments.The PQ value of the treatment without fertilizer decreased slightly.The difference of the treatments of applied chemical fertilizer and without fertilizer was no different.4.Effects of long-term fertilization on the content and fractions of soil organic P and inorganic PThe results of long-term application of organic manure(material) experiment indicated that the inorganic phosphorus was the main phosphate in Shajiang Black Soil,it accounted for 62.88%of total phosphorus.The order of the contents in the various inorganic forms were Ca₁₀-P(51.52%)＞O-P(22.04%)＞Fe-P(12.56%)＞Al-P(8.06%)＞Ca₈-P(3.48%)＞Ca₂-P-P(2.35%).Organic phosphorus accounted for 37.12%of total phosphorus.The order of the contents in the various organic forms were moderately labile organic phosphorus(MLOP)(62.88%)＞moderately resistant organic phosphorus(MROP) (21.18%)＞highly resistant organic phosphorus(HROP)(14.42%)＞labile organic phosphorus(LOP)(4.12%).Compared to the treatments of control or fallow or single applying chemical fertilizers, the combined application of organic manure(material) and chemical fertilizers could increase the content of organic P significantly.The accumulative effects of different organic manure(material) on organic P was cow dung＞pig dung＞wheat straw. Long-term fertilization mainly increased the content of moderately labile organic P. Related analysis showed labile organic P was direct resource of available P,moderately labile P was the supplement of labile organic P,the availability of moderately stable organic P and highly stable organic P was lower.The contents of organic P,inorganic P and total P decreased under long-term no application of P fertilizer.The treatments of applying chemical P fertilizer or the combined application of organic manures with chemical fertilize could increase the contents of organic P,inorganic P and total P,the difference was significantly compared to the treatment without applying P fertilizer.Applied chemical P fertilizer or the combined application of organic manure(material) with chemical fertilize could increase the contents of different organic forms.The treatments of applying chmical fertilizer or straw mainly increased the contents of Ca₁₀-Pand O-P.Applying stable manure mainly increased the contents of Ca₂-P,Ca₈-P, Al-Pand Fe-P.The vailability of LOP and MLOP was the highest in inorganic P forms.The order of vailability of different inorganic P forms was Ca₂-P-P＞Ca₈-P＞Al-P＞Fe-P＞Ca₁₀-P＞O-P. Not considering the leaching loss and the transformation between different P forms,the decrease rates of different P forms could be looked as the contribution rates to plant under the condition of depleted.The contribution rates to plant of different P forms were MLOP＞Fe-P＞Al-P＞Ca₈-P＞Ca₁₀-P＞LOP＞Ca₂-P＞MROP＞O-P＞HROP.Although the vailability of LOP,Ca₂-P snd Ca₈-P was higher,the contribution rates to plant was not higher because of the the lower content.The results of N,P and K fertilizers long-term located experiment showed that the nutrition efficiencies of Ca₂-P-P and Ca₈-P were higher than that of Al-P and Fe-P when soil phosphorus was depleted,Ca₁₀-P and O-P also showed some availability.The contribution rates of Al-P and Fe-P were the highest,whileCa₂-P was even lower than Ca₁₀-P and O-P when soil phosphorus was extremely depleted.The accumulated phosphorus mainly transformed into the fractions of Al-P,Fe-P,O-P and Ca₁₀-P,the increases of Ca₂-P and Ca₈-P were small.The results of correlation and path analysis showed that available P significantly correlated to Ca₂-P,Ca₈-P,Fe-P,Al-P,O-P and Ca₁₀-P. The contribution of different inorganic phosphorus fractions to available phosphorus was Al-P＞Ca₈-P＞Ca₂-P＞Fe-P＞O-P＞Ca₁₀-P.5.Effects of long-term fertilization on crop yields The combined application of organic manure(material) and chemical fertilizer could increase crop yields compared to the single application of chemical fertilizer.The order of the effects of increasing yield was soybean＞maize> wheat.The yields difference between the treatments applying lower rate straw and straw was not significant.The effects of increasing yield of the treatment applying cow dung was the best,the annual yield, wheat yield,soybean yield and maize yield increased by 22.8%,15.6%,30.4%and 28.2% compared to the treatment applying chemical fertilizer,respectively.The stress resistance of the treatment with single chemical fertilizer was lower and the fluctuation range was bigger.Applying fertilizer could decrease the variation coefficient of crops and reduced the yield fluctuation caused by climate.The results of chemical fertilizer long-term located experiment showed nutrient supplying capacity of Shajiang Black soil could maintain produce 900 kg/ha soybean. Wheat yield of the treatment without fertilization fluctuated largely,the yield decreased yearly from 1995-2002 and stabilizated at 650 kg/ha till to 2003.The contribution rate of the natural productivity of Shajiang Black soil for the yields of Wheat,maize and soybean were 34.1%,65.1%and 44.8%,respectively.The contribution rate of chemical fertilizer for the yields of wheat,maize and soybean were 65.9%,34.9% and 55.2%,respectively.The contribution rate of the natural productivity of Shajiang Black Soil was autumn crop＞summer crops.The contribution rate of the natural productivity of Shajiang Black soil for the annual yield was 41.49%,fertilizer was 58.51%.The effects of increasing wheat and maize yields were N＞P＞K,P＞K＞N for soybean yield.The tendency of increasing wheat yield of N,P and K fertilizers ascended.The effects of increasing soybean yield of N fertilizer was not steady and even showed negative effects in some years,on the contrary,P and K fertilizers were steady and significant.In the term of annual yield,the effects of increasing yields of N fertilizer was high and steady,especially in 2002-2005,the tendency of increasing yield ascended obviously,the average increase rate was 107.3%,improved by 54.2%compared to 7 years before.The average increase rate of P fertilizer was 14.8%in 1995-1998,69.3%in 1999-2005,the difference was not significant.The effects of increasing of k fertilizer was ascensive,it showed significant difference at 2000,the average increase rate was 9.9%in the former 6 years,28.5%in the later 5 years.