Author(s): Jifu Li 1,2, Jianwei Lu 1,2,*, Xiaokun Li 1,2, Tao Ren 1,2, Rihuan Cong 1,2, Li Zhou 1,2
The current Asian population of 4.3 billion is projected to increase by nearly 0.9 billion people, reaching roughly 5.2 billion, by 2050 , which will result in significantly increased regional food demand. Of this, population, 80% will be distributed in China, India and the southeast regions of Asia, posing a challenge to the economic development and social stability of these countries . Rice-based cropping systems are the most productive agroecosystems in these areas and produce the most food for the most people . To meet the food demand of the region, intensification and diversification have been applied as the two main strategies for rice-based cropping systems. In addition to the rise of multiple cropping indexes, fertilization consumption has played a very important role in production increases . Compared with nitrogen and phosphorus fertilizer, potash fertilizer is often ignored by farmers, particularly in Asia -. Potash resources are comparatively limited , , and in recent years, the higher price of potash on the international market has reduced the demand of potassium, as farmers in the area are unwilling to put more potash into the soil . Soil K deficiency has become a major limiting factor in the modern agricultural process . Therefore, it is of great importance to increase potash supplementation in these regions. K-bearing organic resources such as compost, green manure, farmyard manure and crop straws, particularly abundant crop residues, are again receiving attention from farmers .
Annually, the world production of straw is approximately 3.8 billion tons, 74% of which are cereal straws ; for rice-based land in Asia, 80% of straw production consists of rice residues . Cereal straws usually have a higher potassium content than other straws (1.2%-1.7%). The results of Kaur and Benipal  have shown that returning straw to the field could improve soil available potassium to a significantly great extent than manure. A 30-years field trial conducted by Liao et al. indicated that straw management could increase exchangeable K by 26.4%, nonexchangeable K by 1.8% and SOC 21.0% in comparison to a CK treatment in reddish paddy soil . As straw potassium is primarily present in the form of K+ ions in the cell fluid , the release of K from stubble in field is influenced by rainfall . Duong et al.  found that the distance of potassium migration from organic fertilizer is 10 mm. Excepting the K + adsorbed or fixed by soil clay particles, 50% of K+ was retained in the soil solution . Furthermore, farmers prefer to input potash fertilizers one time before sowing. The loss of K in the soil solution from such applications was 1.1- and 14.5- fold that of N and P, respectively ; N and P losses were gradual, while leaching phenomena were observed for K . However, Kozak et al. found that crop residues could intercept a maximum of 29% of the water...