ABSTRACT
Rice (Oryza sativa) is the world’s most important food crop, raised on ~22% of the total grain-cultivated area and representing 28% of the total grain production. Most rice is grown in Asia, followed by Africa and the Americas (South America, Northern America, Central America and Caribbean), whereas only relatively small rice production areas are situated in Oceania and Europe (Haefele et al. 2014). To meet the demand of the rapidly increasing human population, it is expected that
the world’s annual rice production must increase from the present 520 million to at least 880 million tonnes by 2025 (Harada et al. 2005). However, with the increasing production of rice from paddy fields, some severe environmental challenges need to be addressed. It is well known that a rice paddy is an important human-made ecosystem and emission source for global greenhouse gases (GHGs), including methane (CH4) and nitrous oxide (N2O). Conventional burning and direct incorporation of rice residues into the soil have resulted in increasing soot and CH4 emissions (Gustafsson et al. 2009; Yuan et al. 2014). In addition, the overuse of conventional chemical fertilizers results in serious nutrient leaching and losses from paddy fields through ammonia volatilization, denitrification, surface runoff, and leaching (Lin et al. 2007; Tian et al. 2007; Xing et al. 2002), resulting not only in severe eutrophication in waterways and lakes of irrigated areas but also in unsafe drinking water (Conley et al. 2009). Furthermore, soil degradation resulting from very intensive crop rotation is becoming increasingly serious worldwide. One-third of the total rice in the world is grown on very poor soils, with very limited indigenous nutrient supplies, low nutrient retention capacity, and very acidic soil reaction (Haefele et al. 2014). Therefore, a main challenge for the sustainable development of modern agriculture is to increase rice productivity while maintaining paddy soil health and reducing various nonpoint pollutions from the paddy field ecosystem.
