In only three years, from 1993 to 2012, the grain yield did not
increase significantly (P > 0.05) above the control value following
both application rates of fertilizer K (Table 3). Correspondingly, the
average grain yield increased to approximately 1.0 t ha1
with
average increases of 15.1 and 13.8% in K113 and K225 treatments,respectively, during the experimental period. Soil indigenous K
(control) maintained an average grain yield 7.0 t ha1
per year
during the two decades of the experiment.