Effect of 15-Year-Long Fertilization on Potassium Quantity/Intensity Relationships in Black Soil in Northeastern China.

The effect of long-term fertilization and cropping on soil potassium (K)-supplying capacity has not been extensively studied. Five treatments [control, nitrogen (N), N-potassium (P), NPK, and NPK + manure (NPKM)] were used to evaluate the quantity and intensity relationship (Q/I) of K in black soil (Luvic Phaeozems soil) after a 15-year (1990-2005) long-term fertilization with a continuous corn cropping located in Changchun, Jilin Province, northeast China. Results showed that the long-term K fertilization of NPK or NPKM markedly increased the values of equilibrium active ratio (AR0K) and nonspecifically available K (-ΔK0) but decreased the potential buffering capacity (PBCK) value. Values of the AR0K and -ΔK0 in the NPK and NPKM treatment were about four and two times greater than those in the control, N, and NP treatments, respectively. Compared with the non-K fertilization, PBCK values were decreased by 40-49% under the K fertilization. The black soil suffered from K deficiency even with NPK fertilization as evidenced from the greater free energies of K+ exchanging for calcium (Ca2+) and magnesium (Mg2+) (-ΔG) (14.7-18.8 kJ mol-1) than the threshold value of 14.6 kJ mol-1, from the lower soil K+ saturation (1.34%-1.44%) than the critical value of 2.00%, and from the response of corn yield to K fertilization. Our results demonstrated that the increment of the current K application rate through fertilizer and/or manure is needed to improve corn yield in the long run in northeastern China. [ABSTRACT FROM AUTHOR]