Straw return increases crop grain yields and K-use efficiency under a maize-rice cropping system

Straw return is an effective way to improve crop grain yield and potassium (K) use efficiency by increasing soil K content. However, the effects of straw return on soil K supplying capacity, replacement of K fertilizer, and K-use efficiency under maize (Zea mays L.)–rice (Oryza sativa L.) cropping systems are little studied. A two-year field experiment was conducted to determine the physiological determinants of K-use efficiency under straw return with four K fertilization rates. Sr33 (straw returned plus 33% of K fertilizer applied) and Sr67 (straw returned plus 67% of K fertilizer applied) increased annual crop yields by 1.5% and 3.2% and increased agronomic K-use efficiency by respectively 2.9 and 1.3-fold on average in the two years, compared with the conventional practice S0K100 (no straw returned plus normal amounts of K fertilizer applied). The Sr33 and Sr67 treatments resulted in significantly greater equilibrium K concentration ratios (CR0K) and specifically exchangeable K (KX) values according to quantity/intensity (Q/I) relationship analyses, indicating improvement of the potential soil K supply capacity. However, the Sr67 better maintained the soil exchangeable K level and K balance. The results suggested that K released from maize and rice straw can replace about half of chemical K fertilizer, depending on the available K content in maize–rice cropping system production.