Screening Of Extracted Methods For Soil Available Potassium And Potassium Abundant&Deficiency Indices On Rice And Oilseed Rape

Chemical extraction is the most common method for the evaluation of soil potassium (K) supplying capacity. Different extractants would result in various measured values and thus impact the accuracy of soil K evaluation. There are many factors that influence content of soil available K, so thus the value of the chemical can not entirely reflect the capacity of soil to supply K. The current determination method of soil K still is inadequate. Looking for the better method which can evaluation the biological availability of soil potassium and establishing the corresponding indices of the abundant and deficiency is very important for modern applying K fertilizer. In this study, six functional equations were selected to find a best response equation which can fit with soil K and crop yield and K uptake. Five different extractants were selected to extract soil K. The aims were:1) to compare and analyze the biological effectiveness of soil K extracted by different extractants;2) to determine a better extraction method of soil available potassium;3) to establish the corresponding indices of the abundant and deficiency and to provide a scientific basis for the further soil testing and K fertilizer recommendations. All study was based on existing K fertilizer field experiments of rice and oilseed rape. The main results are summarized below.1. In this research the soil K content in Hubei rice growing area and Yangtze River Basin (YRB) winter oilseed growing area were extracted by five different extractants (i.e., deionized water,1mol/L neutral NH4OAc,1mol/L cold HNO3,0.2mol/L NaBPh4,1mol/L boiling HNO3). Analyse the relationship between the measured values of different methods. The results showed that soil K content extracted by five different extractants displayed an order of boiling HNO3-K (B-HNO3-K)> NaBPh4-K> cold HNO3-K (C-HNO3-K)> NH4OAc-K> water solution K (WS-K). The correlation between C-HNO3-K and NH4OAc-K is best, followed by C-HNO3-K and NaBPh4-K in the relationship between soil K extracted by different extractants.2. The average yield increment with K fertilizer on rice was610kg/hm2and the average increase rate was10.1%. The average yield increment with K fertilizer on oilseed rape was304kg/hm2and the average increase rate was17.5%. Soil K extracted by cold HNO3method, NaBPh4method, NH4OAc method not only can accurately indicate the effect of K fertilizer on yield increase, but also point soil K supplying capacity. Correlation coefficients were higher, so three methods were better to evaluate the effectiveness of soil K. The best method for rice and oilseed rape was cold HNO3method and NaBPh4method, respectively.3. Six functional equations were selected to fit with soil K content and crop yield and K uptake. It was found that logarithmic, linear and power equation could comprehensive response the relationship between them and the degree of fitting are higher. Fitting the best equation was logarithmic equation. Quadratic, exponential and linear-plateau equation can comprehensive response the relationship between soil K content and four reference standards because of the failed fitting with several soil K and four reference standard. So in this article we chose the logarithmic equation to represent the relationship between soil K content and crop relative yield and then establish indices of the abundant and deficiency.4. The abundance and deficiency indices for NH4OAc method, cold HNO3method and NaBPh4method were established based on the relationship between crop relative yield and corresponding soil K content. The relative yield of85%,90%and95%were selected to establish the abundance and deficiency indices for rice. The soil K could be divided into four level (low, medium, high and pretty high). The four indices for soil available K extracted by NH4OAc method in Hubei rice-growing were<30mg/kg、30～70mg/kg、70～160mg/kg and>160mg/kg. The low, medium, high and pretty high indices for soil available K extracted by cold HNO3method were<50mg/kg,50～100mg/kg,100～195mg/kg,>195mg/kg. The low, medium, high and pretty high indices for soil available K extracted by NaBPh4method were<60mg/kg,60～140mg/kg,140～310mg/kg,>310mg/kg. The relative yield of75%,90%and95%were selected to establish the abundance and deficiency indices for oilseed rape. The soil K could be divided into four level (low, medium, high and pretty high). The low, medium, high and pretty high indices for soil available K extracted by NH4OAc method in YRB winter oilseed rape-growing were<30mg/kg,30～110mg/kg,110～170mg/kg and>170mg/kg. The four indices for soil available K based on cold HNO3method were<55mg/kg,55～170mg/kg,170～245mg/kg,>245mg/kg. The four indices for soil available K based on NaBPh4method were<65mg/kg,65～370mg/kg,370～650mg/kg and>650mg/kg.