Grain yield and soil potassium fertility changes arising from different potassium-bearing materials in rice–wheat rotation

The uneven global distribution of potash salts makes accessing and applying adequate potassium (K) fertilizers difficult, exacerbating K deficiency worldwide. Thus, there is an urgent need to identify alternatives to potash salts and investigate their performance in agricultural production. This study investigated the feasibility of using four K-bearing materials as K fertilizers in rice–wheat rotation agriculture. Field experiments were conducted in the downstream region of the Yangtze River, China, from 2014 to 2016. Six treatments used included CK (no K applied), straw incorporation (wheat and rice straw), KCl (muriate of potash), Kr1 (K-bearing rock powder; kaliophilite, 72%; phlogopite, 25%), Kr2 (feldspar, 37%; KCl, 4%), and Kr3 (feldspar, 68%; hydromica, 32%). The results showed that straw incorporation led to higher crop yields (wheat 5.7%, rice 5.4%) in the first year but lower yields (wheat 5.7%, rice 5.4%) and soil K fertility (HNO 3 -extracted K) in the second year than KCl. No significant differences were found for wheat yield and soil K fertility among the Kr1, Kr2, and KCl treatments, but Kr1 and Kr2 treatments significantly increased rice yields (averages of 7.7% and 13%, respectively, for two separate years) compared with KCl treatment. However, Kr3 significantly decreased crop yields (2-year averages: wheat, 24%; rice, 4.6%) led to a significantly positive soil K balance (205 kg ha −1 ) compared with KCl (−41.2 kg ha −1 ), but straw incorporation caused a significantly negative soil K balance (−91.0 kg ha −1 ). In conclusion, crop straw, Kr1, and Kr2 are suitable K fertilizers, but Kr3 alone cannot be used as a K fertilizer in rice–wheat rotation in the study area. Countries with a lack of potash salts should make full use of their straw resources and promote the exploration of the use of K-bearing rocks. Graphical abstract CK means no K applied; Straw means straw incorporation; KCl refers to muriate of potash; Kr1, Kr2, and Kr3 refer to three kinds of K-bearing rock powder.