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