Study On Determination Methods For Available Phosphorus In Paddy Soil Of Sichuan Basin

The testing of soil nutrient is premise in soil testing and fertilizer recommendation,analyzing the content of the soil available nutrient quickly and exactly,then acting on the content of soil nutrient,and put forward the reasonable advice.Selecting the appropriate methods that use the testing of available nutrient in different soil are the most basic and important question in soil testing and fertilizer recommendation.Content of the soil available nutrient is the basis of soil nutrient supplies level and soil testing.In all necessary nutrients of crops,nitrogen,phosphorus and potassium affected the most on the growth and yield of crops;this is why they are called the three nutrient elements.In conventional measurement of soil nutrient,nitrogen,phosphorus,potassium is measured using chemical reagents in the extraction,extraction of soil P is complex.The purpose of soil testing is to design a suitable application of phosphate fertilizer.The object of this study was paddy soils in Sichuan basin.The purpose of this research was compared with the related coefficient between the content of nutrient and the reference standard that were rice yield,the relative yield of ric and increase rate of rice yield.So as to reflect the exact extent on soil nutrient availability,and select suitable methods for the regional soil available phosphorus testing,offer scientific basis for available phosphorus test in soil testing and fertilizer recommendation.The main results were as follows:1.The contents of available phosphorus in paddy soil measured by Oisen,ASI and Mehlich 3 methods were different great,the average value of three methods were l l.8mg/kg,8.63mg/kg and 18.2mg/kg,respectively and showed in the order of M3 method＞Olsen method＞ASI method. Among measurements of three methods,there was a significant or great significant interactive effects,the correlation coefficients were 0.651^**～0.911^**.The appearance at different soil pH,using different methods and different utilization of paddy soil was the same.2.Result of paddy soil available phosphorus determined by Olsen method in different temperature condition showed that temperature had an important influence on the determined value of available phosphorus.In the range of 10℃to 30℃,the available phosphorus value was increased with the increment of temperature,the difference decreases in every five Celsius degree,and the increase value was different with the changd of content of soils available phosphorus.There was significant correlation among the determined value of different temperature(r =0.992^**,0.978^**,0.992^**and 0.987^**, respectively).The result was also applicable when determined different soils of different pH.The correlation coefficients between increase rate of yield and relative yield,uptake phosphorus of rice, uptake phosphorus of straw and total uptake phosphorus were not significant.It was conclude that temperature had great influence on the determined value of available phosphorus,so it was important to control the temperature of extraction as using Olsen method..3.The result of continuous extraction of soil available phosphorus by Olsen method showed that the extraction time had great influence on the contents of soil available phosphorus.The cumulative value of different extraction time was increased with the times,the increased values were different by every extraction duo to the different content of paddy soil.There were significant correlations among the cumulative value of different extraction time(r=0.995^**,0.990^**,0.985^**. The great significant correlation existed between the content of continuous extraction available phosphorus by Olsen method and increase rate of yield and relative yield of rice(zero-phosphate),and was significant with relative yield of rice(zero-fertilizer).From the correlation analysis,the available phosphorus content of the first extraction were better correlation with every index,it was concluded that the determination value of first extraction could reflect available phosphorus requirement of crops.4.The correlation analysis among rice yield,relative yield,increase rate of yield,phosphorus uptake of grain,phosphorus uptake of stem,total phosphorus uptake by rice and soil available phosphorus value by the methods of M3,ASI and Olsen showed that:the content of soil available phosphorus determined by Oslen method had not significant correlation with all indices,the correlation was great signature between the available phosphorus by ASI method and relative yield.The correlation was significant or great significant between the available phosphorus by ASI method and increase rate of yield in the cultivated horizon soils;the correlation was significant or great significant between the content of available phosphorus by ASI method and relative yield.The correlation was not significant between content of available phosphorus by ASI method and production rate(zero-fertilizer)in substrate paddy soil.The correlation was signature between content of available phosphorus by ASI method with production rate(zero-phosphate)in substrate paddy soil.The correlation was insignature between content of available phosphorus by M3 method with relative yield,increase rate of yield in cultivated horizon soils.The value of correlation was 0.751^*,0.814^**and -0.675^*,-0.773^* between the content of available phosphorus by M3 method and relative yield and increase rate of yield in 20-40 cm paddy soil.From the analysis,it was considered the conclusion that M3 and ASI methods were suitable method to determine soil available phosphorus in paddy soil.5.The result of the correlation analysis between soil available phosphorus and relative yield showed that ASI method was more appropriate in paddy soil of Sichuan basin.Regard the yield of which did not fertilize as a standard,and the content of soil available phosphorus by ASI method was grade,when the rice yield was low 5000 kg/hm²,high,middle,low and very low levels of soil available phosphorus were above 10mg/kg,6～10 mg/kg,4～6 mg/kg and 0～4 mg/kg,respectively; while rice yield was above 5000 kg/hm²,high,middle,low and very low levels of soil available phosphorus were beyond 51 mg/kg,6～51 mg/kg,4～6 mg/kg and 0～4 mg/kg.