Long-term Differences in K Balance Under Rice–wheat Cultivation Alter Potassium Supplying Ability of Soils

The aims of the present study were to provide scientific bases for rational use of crop straw to substitute chemical potassium (K) input and to protect the ecological environment. The effects of potassium fertilization and straw incorporation on soil K balance and K supplying in a long-term (14 years) field experiment. Five treatments were examined: no fertilization and straw (CK); fertilization with no straw return (NPK); only straw return at 6000 kg hm-2 per season (RS); fertilization with straw return at 3000 kg hm-2 per season (NPKS); and fertilization with straw return at 6000 kg hm-2 per season (NPK2S). K composition, K balance and quantity-intensity (Q/I) relationship were studied. Under no fertilization or low straw returned conditions, soil K was unbalance and deficiency seriously. Straw return at 6000 kg hm-2 per season with fertilization improved the soil potassium supply and K balance. Long-term K surplus (4 or 5 years), Compared with NPK, the NPK2S significantly increased non-special adsorption K (Knsa) and non-exchangeable K (Kne) by 5.7 to 11.2 mg kg-1 and 65.7 to 128.1 mg kg-1, respectively. Q/I relationship showed cropping without straw K or without fertilizer K resulted in lower quantity (nonspecifically and specifically held K i.e. –∆K0 and Kx) and intensity (equilibrium activity ratio i.e. CR0K) of K in tested soils. K-fertilization with straw maintain higher exchangeable K (EK0) and a higher difference between EK0 and minimum exchangeable K(EKmin), and would help to prevent depletion in non-exchangeable pool of soil K under intensive cropping. Additionally, The straw return mainly decreased potential buffering capacity for exchangeable pool (PBCKn), 43.92% to 48.22% of added K in soil might be converted to exchangeable pool while it was 25.67% to 29.19% be converted to non-exchangeable pool. The contribution of exchangeable K towards plant K uptake would be higher in the soil with straw than the soil without straw and the non-exchangeable K would be the long-term fixed K as a supplement to the potassium pool. K fertilizer with 6000 kg hm-2 straw return in each crop season increased soil available K and slowly available K. The contribution of exchangeable K towards plant K uptake was higher in the soil with straw than without straw and the non-exchangeable K would be the long-term fixed K as a supplement to the potassium pool. The findings underlined important of the straw return and contribution for sustain K supplying ability of soils.