INTRODUCTION
Green manure is a traditional organic manure in China and has been used since ancient times. The planting area using green manures in China is the largest in the world. Production and application of green manure have played an important role in food production and improving soil fertility. Despite the long history of green manure in
China, farmers have had little enthusiasm to improve soil fertility since the 1980s. This has been mainly due to the low economic benefit of green manure in rice production and the large labor force required for winter planting of green manure. Meanwhile, the obvious benefits of artificial fertilizers have been greatly promoted. The yield increase from incorporating green manure in the year of application is not as obvious with the same investment in artificial fertilizer. Since the mid-twentieth century, the area devoted to producing green manure has