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Four testing methods using canon exchange membrane (CEM), ammonium acetate, ASI (0.25 mol L-1 NaHCO3+0.01 mol L-1 EDTA +0.01 mol L-1 NH4P) and 1.0 mol L-1 boiling nitric acid, respectively, were used to evaluate soil available K. The soil K tested by CEM was significantly correlated with that by the other (conventional) methods (r2=0.43**~0.95***). The soil K tested by CEM saturated with NH4HCO3 (15 min extraction) was most closely correlated with that by the other methods (2 =0. 60***~0.95***). Potassium availability, as predicted by soil test, was comparable to actual K uptake by canola and wheat grown on the soils in growth chamber. Regression analyses showed that plant K uptake was more closely correlated with K extracted by CEM (r2=0.56***~0.81***) than that by the conventional methods (r2=0.46***~;0.81***), most closely correlsted with that by NH4HCO3-saturated CEM for 15 min (r2=0.81***), and worst correlated with that by HNO3 (r2=0.45**~0.72***).
Four testing methods using canon exchange membrane (CEM), ammonium acetate, ASI (0.25 mol L-1 NaHCO3 + 0.01 mol L-1 EDTA +0.01 mol L-1 NH4P) The soil K tested by CEM was significantly correlated with that by the other (conventional) methods (r2 = 0.43 ** ~ 0.95 ***). The soil K was tested with CEM saturated with NH4HCO3 (15 min was most closely correlated with that by the other methods (2 = 0. 60 *** ~ 0.95 ***). Potassium availability, as predicted by soil test, was comparable to actual K uptake by canola and wheat grown on the soils in growth chamber. Regression analyzes showed that plant K uptake was more closely correlated with K extracted by CEM (r2 = 0.56 *** ~ 0.81 ***) than that by the conventional methods (r2 = 0.46 *** ~; 0.81 ***), most closely correlsted with that by NH4HCO3-saturated CEM for 15 min (r2 = 0.81 ***), and the worst correlated with that by HNO3 (r2 = 0.45 ** ~ 0.72 ***).