Other studies have highlighted the importance of balanced K application for sustainable agricultural development (Singh et al., 2002; Liu et al., 2009). In Northern Shandong Province, K balance in one wheat–maize rotation study was −163 kg ha−1 year−1 (Ju et al., 2007) and in Heilongjiang, K balance was −20.1 kg ha−1 year−1 (Zhou et al., 2000).