Abstract: Crop residue is an important organic resource, and its reasonable and effective use is getting more and more attention. Straw returning can not only increase crop yield, enhance soil organic carbon content, enrich soil fertility, but can also improve nutrient cycling and utilization, alleviate soil acidification, and reduce the application of chemical fertilizer. Nowadays, with better understanding of highly efficient utilization of resource, studies on the effects of straw returning on soil potassium in China and at abroad have made plentiful and substantial achievements. This review paper summarized recent researches on effects of straw returning on potassium mainly from three aspects including soil potassium, crop yield, and the equivalence between straw potassium and chemical potassium fertilizer. The findings are as follows: returning straw could increase the available potassium in soil by the release of potassium from the straw, especially at the early stage of decomposition while long-term straw returning might also promote the release of mineral potassium. Effective straw returning not only provides plenty of nitrogen, phosphorus and potassium for the soil, but also improves soil microbial conditions by supplying abundant carbon, and thus increases crop yield. The return rate of straw in China was currently less than 1/3, which was much less than that in Europe and America. There is still great potential to enhance the return rate of straw in China, which will gradually improve soil potassium and alleviate the contradiction of the lack of potassium resources in China. In order to enhance the return rate of straw residue and promote the circulation of potassium between the soil and crop, more researches should be focused on the reasonable incorporation of the straw returning with chemical potassium fertilizer, and the affecting mechanism of straw returning on soil potassium in both shortterm experiment and long-term monitoring.

Key words: Quercus variabilis, shaded/sunlit leaf, photosynthetic parameter, Robinia pseudoacacia, photosynthetic-CO₂ response