Objective  Decomposition and nutrient release of green manure after returning to soil in citrus field were studied.

  Method  Using nylon mesh bags to contain Dolichos lablab, Astragalus sinicus, Viciavillosa Rothvar, Medicago sativa, or Lolium multiflorum and plowed into the soil at a depth of 20 cm. Soil samples were taken on the 20^th , 40^th, 60^th, 8^0th, and 100^th day after manure turning over to determine carbon, nitrogen, phosphorus, and potassium contents. Carbon/nitrogen ratio, material degradation, and nutrient release were tabulated for analysis.

  Result  The manure decomposition and nutrient release were at a high rate in 0–20 d after the deposit but slowed down from the 20^th to the 100^th day. The rate of material decay reached 35.52%–73.96% after 20 d, and 79.13%–90.25% after 100 d. For the 5 green manures, the releases of C, N, P, and K ranged 38.10%–78.59%, 66.92%–87.63%, 28.60%–80.92%, and 80.22%–96.72%, respectively, in 20 d, and 80.90%–95.48%, 94.63%–97.64, 59.66%–96.28%, and 94.46%–99.64%, respectively, in 100 d. The cumulative nutrient release was K＞N＞C＞P, and the C/N ratio increased as the decomposition progressed.

  Conclusion  Among the 5 green manures, A. sinicus displayed the highest cumulative decay rate, D. lablab the most cumulative N and K releases, and L. multiflorum the greatest cumulative C and P releases.