MULTIPLE YEAR-RESPONSE OF WETLAND RICE TO POTASSIUM FERTILIZER AND APPARENT POTASSIUM BALANCE IN SOIL

摘要

A field study was conducted from 1990-1994 in dry (January to June) and wet (July to November) seasons at the Bangladesh Rice Research Institute (BRRI) experimental farm, Gazipur, Bangladesh, to determine the optimum K rate and the K balance for better understanding of K management in wetland rice. Five levels of K-0, 30, 60, 90, 120 kg/ha- were tested. Rice yield increased with K fertilizer application in both the dry and wet seasons. The response of rice to applied K fertilizer could be explained by quadratic equations. The economic optimum rate of K in different years varied between 54 to 89 kg/ha for the dry season and 65 to 82 kg/ha for wet season. The variation in the economic optimum K rate was not consistent with the year. Internal K use efficiency of rice decreased as the applied K rate increased. Apparent K balance in the soil calculated from K input and K uptake data revealed a negative K balance of 379.9 kg K/ha at K-control plots. The negative K balance was observed even up to 60 kg/haof the applied K level with diminishing magnitude. At the 90 and 120 kg K/ha level, the balance was rather positive. A simple linear regression analysis between K balance and applied K was done. The regression equation suggested that an amount of about61,34 kg K/ha would be required to sustain soil native K for rice cropping.