Effect of Long-term Differential Fertilization on Q/I Relationships of Potassium under Continuous Maize-Wheat System

摘要

The influence of continuous application of differential rates of N,P and K to a sandy loam soil (Typic Ustochrept)on the Q/I relationship of potassium was studied after 22 cycles of a long-term experiment involving maize-wheat sequence at the Punjab Agricultural University Farm,Ludhiana.The surface (0-15 cm)soil samples were collected from the treatment plots viz.N_0P_0K_0 N_(120)P_0K_0,N_(180)P_0K_0,N_(120)P_(40)K_0,N_(120)P_(80)K_0,N_(180)P_(40)K_0,N_(180)P_(80)K_(40)after 22 cycles of cropping.All the treatments exhibited nearly similar type of Q/I curves when activity ratio was plotted against the changes in exchangeable K.The parameters such as activity ratio at equilibrium (AR_e~K),labile K (K_L),potassium at specific and non-specific sites (K_x and K_0)and potential buffering capacity (PBC~K)were computed from Q/I plots of these soils.The AR_e~K and K_L values were higher in NPK treated plots than NP.The K_x values increased in N and NP treated plots as compared to control.The plots receiving continuous K supply gave lower K_x values than ones receiving NP fertilizers.The K_o values of different treatment plots exhibited similar trend in respect of K_L.The PBC~K values were higher in plots receiving N and NP fertilizer than NPK treated plots.The value of DELTA G (free energy change)increased with each increment of N and P whereas,it decreased in plots receiving K at 40 kg K_2O ha~(-1).Despite low AR_e~K,K_L and DELTA G values in control,N and NP plots,both maize and wheat in rotation did not show any deficiency symptoms thereby indicating that sufficient K is being released from non-exchangeable sources.