Sustainable intensification of China's agroecosystems by conservation agriculture

Agriculture in China started about 8000 BCE with cultivation of millet and rice. Thus, China's modern agriculture is rooted in a long evolutionary history of agricultural practices. China's population of 211 million in 1700 increased to 295 million in 1800, 400 million in 1900, 1266 million in 2000, and is 1409 million in 2017. Thus, China has to feed 18.5% of the world population on merely 7% of the world's arable land and with even scarcer water resources. Yet, between 1950 and 2017, the grain production in China increased at a faster rate than that of the population. Total grain production (million ton or Tg) was 113 in 1949, 305 in 1970, 462 in 2000, and 603 in 2015. The high agricultural productivity is attributed to high consumption of fertilizers (58.8 Tg in 2015), pesticides (1.81 Tg in 2014), and irrigation (65.7 Mha in 2014). However, the high production is also associated with the severe problems of soil degradation (erosion), water contamination and air pollution. It is estimated that ~40% of China's arable land is degraded to some degree. Thus, there is a strong need for a paradigm shift of sustaining high productivity while restoring quality of natural resources of soil, water and air. In this context, conversion to a system-based conservation agriculture (CA) may be an important strategy of sustainable intensification of agro-ecosystems for advancing and sustaining high production while restoring soil health, purifying water and air and improving the environment. The CA has been practiced in China since 1990s and was adopted on ~8.0 Mha in 2015. The available literature shows that conversion to CA increases soil organic C (SOC) concentration and stocks mostly in the surface layer while also producing an equivalent agronomic yield. Therefore, a widespread adoption of CA in China would necessitate a deeper understanding of its ecological underpinnings. To be effective, site-specific CA practices must reduce risks of soil erosion under dry land farming, achieve and sustain high productivity, reduce emissions of N2O and CH4, sequester SOC, and decrease inputs of fertilizers and pesticides. To be widely accepted, site-specific CA packages must also address the followings: availability of crop residues mulch, techniques of weed control, access to a seed drill, and availability of farm labor. Economically, CA must increase agronomic yield and the farm profit. Being a knowledge-intensive and complex system, there is a strong need to strengthen the extension services, and conduct long-term and farmer-driven research to alleviate specific constraints (e.g., drought, wind and water erosion, nutrient imbalance, weed control).