The effect of K fertilizer application on maize yield was significant
among the three regions (Table 7). In Shuangcheng, significant
maize yield response to K application was found starting in the
first year, in Gongzhuling significant yield response to K was found
starting in the third year, and in Shenyang maize yield response to K
application was unstable from 1993 to 2006. Yield effect of K application
was similar in Xinji and Luoyang, which showed significant
difference between the two fertilizer treatments in the seventh year
of the study. It appeared that maize was more sensitive to K application
than wheat, and significant yield increase occurred one year
earlier for maize than wheat. In Linfen, yield effect of K application
was not significantly different among years except 2000, 2001, and
2005. Effect of K fertilizer application on yield varied widely in the
northwest. In Yinchuan, yield effect of K fertilizer was significant in
maize starting in 2000 and in wheat starting in 2002. No significant
yield increase from K application was found in Xining. In Changji,
K fertilizer had a significant yield effect on maize starting in 1995
and had no effect on wheat during the study period.