| Based on the analysis of the present situation of available phosphorus in the surface soil of rice fields and dry land soils in the subtropical region,this paper focuses on the critical value of phosphorus leaching in the typical subtropical paddy field and its main influencing factors,mainly studies the available phosphorus content and phosphorus leaching in the subtropical rice fields,and comes the main conclusions as follows:1.The results of soil available phosphorus in the topsoil of subtropical arable land claimed that the relative values of available P in the surface soil of the The relative values of available P in the surface soil of the paddy field were significantly different treated rice fields were significantly different,and With the decrease of latitude of the sampling area,the available phosphorus content in the surface soil of rice field showed an increasing trend: according to the relative value of available phosphorus in soil layer of rice field,it came the order---Gaozhou City >Taishan County >Guiyang County >Yingde City > Wuming County > Xingan County > Qianjiang City>Wugang City > Xishui County >Taoyuan County;If the available phosphorus content in the surface soil of subtropical rice field is 50 mg / kg,which is the saturated soil capacity of paddy soil,the risk of phosphorus migration in paddy soil is less in Xishui,Qianjiang,Taoyuan,Wugang etc,and There is a certain risk of soil phosphorus migration in Guiyang,Xingan,Wuming etc.so as to control the application of phosphate fertilizer accordingly.Comparison with the average relative value,relative value range and the size sequence of available phosphorus in paddy soil,the average relative values of available P in the surface soils of the affected counties(cities)were significantly higher,the changes were obviously observed,and according to the relative value of available P in soil layer of dry land,it came the order---Gaozhou City >Taishan County >Wugang City >Taoyuan County >Guiyang County >Xingan County>Wuming County >Xishui County>Qianjiang City>Yingde City;Meanwhile,different from the available P in soil layer of rice field,there wasn't any zonal distribution with latitude in that of dry land;Comparison with the risk of soil phosphorus migration in rice field,there was a certain risk in the dry land of Taishan and Gaozhou,and a little risk in other 8 counties(cities);However,the effective phosphorus contents in a section of dry land in Taishan and a majority in Gaozhou were high,so as to strictly control the application of phosphate fertilizer.2.The stimulation results of soil available phosphorus leaching in the subtropical arable land claimed that the average critical values of available P in the treated subtropical rice field was 88.12mg/ kg,the change range was 56.6~122.8(mg/ kg),the average critical values of available P in the treated dry land was 82.4mg/ kg,the change range was 56.6~122.8(mg/ kg);the analysis of distribution frequency of stimulation critical values of phosphorus leaching claimed that the stimulation critical values of phosphorus leaching in the rice field was 95~105(mg/ kg),the distribution frequency was 71.4%,and the stimulation critical values of phosphorus leaching of dry land was 56~80(mg/ kg),the distribution frequency was 66.7%;In the dry land of subtropical arable land,especially the dryland formed in Quaternary red soil and red sandstone soil,the critical value of phosphorus leaching in soil is relatively higher than that in the dryland,The critical value of phosphorus leaching in paddy soil is low.In addition,CEC,exchangeable Mg and Fe2O3 had a great influence on the critical value of soil phosphorus leaching in seven chemical properties such as pH of the tested soil,clay,CEC,organic matter,exchangeable Ca,exchangeable Mg,and Fe2O3,Where CEC acted positive,and exchangeable Mg and Fe2O3 negative.3.The results of analysis of the available phosphorus content and phosphorus leaching in paddy soil of Subtropical lakes,showed that there was a significant linear correlation between the total phosphorus content and the available phosphorus content in the paddy soils while treated with different fertilization(r = 0.984).Although the application of inorganic phosphate alone could not significantly increase the total phosphorus content of the surface layer of soil,it can significantly improve the available phosphorus content;while treated with.mixed application of the inorganic and organic,both of the total phosphorus content and the available one in soil surface increased continuously with the increasing application of pig manure.When the application of pig manure reached NK6 M,and the amount of pig manure was increased continuously and treated(to NK8M),both of the total phosphorus content and the available one in soil surface showed a drop.There was no significant difference in both of the total phosphorus content and the available one in soil surface of paddy field in different water management methods.Seen from the soil profile,the available phosphorus content in the 20 cm soil layer of the paddy field was 40.75 mg / kg.That in the soil of 20 ~ 40 cm underground reached the maximum of 7.76 mg / kg.With the treatment of NK8 M,the available phosphorus content reached the maximum of 7.86 mg / kg in the soil of 40 ~ 60 cm underground,and that in the soil of 60 ~ 80 cm underground was 8.09 mg / kg.Additionally,the results of the two-stage linear fitting showed that the available phosphorus saturation capacity in the paddy field of Subtropical lakes is 39.2 mg / kg.If this criterion is used,we can conclude that there is risk of effective phosphorus leaching in such three fertilization treatments as NK4 M,NK6M and NK8 M,especially NK6 M.4.The results of analysis of the available phosphorus content and phosphorus leaching in paddy soil of Subtropical hilly area,showedthat the available phosphorus content in the surface soil of the paddy field reached the extremely significant level under different fertilization modes: there exists linear positive correlation between the available phosphorus content in the surface soil of the paddy field and the N,P and K fertilization;and more specifically,the linear correlation with K fertilization was significant,while that with N and P fertilization was extremely significant.There was a significant difference among the available phosphorus content in the treated soil of paddy with different P fertilization and there existed significant linear positive correlation between different P fertilization in different surface of paddy soil.(correlation coefficient was.976).The results of the two-stage linear fitting showed that the available phosphorus saturation capacity in the paddy soil of hilly area was 47.6 mg / kg,and if this criterion is used,we can conclude that there was a risk of available phosphorus leaching in such treatment of fertilization as 3M,2M + 2P,2M + 4P and 2M + 6P,especially 2M + 6P treatment.Moreover,it can improve,on a certain extent,the pH value of paddy field with the treatment of cow dung in the paddy field of hilly red soil.5.The results of analysis of the available phosphorus content and rice yield showed that there was a continuous increase in both theavailable phosphorus contents in the surface soil of paddy field and rice yield with the treatments of CK,NPK,1M,2M to 3M;but the growth patterns were different,the former was almost exponential growth,while the latter logical growth;In the mixed treatments of organic and inorganic fertilization,there was no synchronous change rule between the available phosphorus content and rice yield in the surface soil of paddy field.There was no significant correlation between the available phosphorus content and rice yield in different soil layers. |
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