ASPECTS OF THE STUDY OF 0.01 molL~(-1) CaCl_2 AS EXTRACTING SOLUTION FOR DIFFERENT N FRACTIONS IN SOILS
Shao Xiaohou (Hohai University) Hu Aitang (Nanjing Agricultural University) V. J. G. Houba I. Novozamsky (Wageningen Agricultural University, The Netherlands)
Eight Dutch surface soils were used in this study to analyse different N fractions in 0.01 molL~(-1) CaCl_2 extracts and percolates at different temperatures.The resulcs obtained showed that:(1) The temperature of 0.01 molL~(-1) CaCl_2 extracting and percolating solution had no influence on amount of No_3~- -N,the extractability of other N fractions (NH_4~+ -N,total soluble N and reduced N),however,was evidently affected by the temperature in 0.01 molL~(-1) CaCl_2 solution.The hydrolysis of organic N was the predominant reason for this influence.(2) The release of organic soluble N obeyed the first order kinetics.A nonlinear least square method could bestfit the experimental data into the model N_t=N_0(1——e~(-kt))with Rsquared being higher than 0.99.(3) The kinetic values No were highly consistent with the soluble reduced N in extraction experiment.The 0.01 molL~(-1) CaCl_2 solution extracted and released the labile organic N fraction.The determination of soluble org anic N in 0.01 molL~(-1) CaCl_2 solution looked promising as a property for prediction of N mineralization,N fertilization and N pollution.