Research methodology
A field experiment was conducted to study the effect of longterm crop rotation with green manure crops and ap
plication of organic materials on SOC. The general properties of the soil in the experimental field are shown in Table
1. The soil is a Typic Paleustults,Ultisols in the USDA Taxonomy system. The treatments of plots are described in
Table 2. Every year,corn was planted in May,the early rainfall period,and harvested in late August or early Septem鄄
ber. Mungbean (Vigna radiata) was used as the second crop after corn,and mimosa (Mimosa invisa),crotalaria
(Crotalaria juncea) and ricebean (Vigna umbellate) were intercropped with corn from 1976 to 2005. Corn stalks
were mulched between second crop planting except for Treatments 1 and 7 before 1980. After about 45 days of
growth,crotalaria was cut and spread on the soil as mulch from 1980 to 1988 The residue of mimosa,crotalaria
from1989 2005 and ricebean was incorporated into the soil the following year. Velvet bean (Mucuna pruriens),soy
bean (Glycine max) and sunflower (Helianthus annuus) were planted as the second crops after 2006