“…The K budget at field scale (Benbi & Biswas, 1999; Yadvinder‐Singh et al., 2004; Yang, Sun, & Zhang, 2014) and soil K test (Mallarino, Barbagelata, & Wittry, 2004; Yang et al., 2014) or estimated exchangeable K are often used to manage K over large agricultural areas (Bailey, 1983; Tan, Jin, Jiang, Huang, & Liu, 2012). While soil test critical K levels depend on clay mineralogy (Breker et al., 2019), the contribution of non‐exchangeable K (Hinsinger, 2002; Lal, Swarup, & Singh, 2007; Rupa, Srivastava, Swarup, & Singh, 2001) or interlayer K (Hinsinger & Jaillard, 1993; Øgaard & Krogstad, 2005) to plant K uptake may be substantial.…”