Abstract: Green manure is considered a clean source of organic fertilizer. It plays an important role in enhancing soil fertility and the substitution of chemical fertilizer. Quantifying green manure yield and nutrient concentration at the regional level can provide a theoretical basis and supporting data for green manure application and fertilizer replacement. This study, by searching the China National Knowledge Infrastructure (CNKI) database and related books, collected 3431 data, including information on 17 different common green manure crops across China. The green manure yield and nutrient concentration data from across China were systematically analyzed and compared, and the nitrogen fertilizer replacement effect was evaluated for different regions of China. It was found that the average yield of fresh green manure in China was 38.0 t·ha^-1 (moisture content was 81.0% on average), but a wide range (0.7-186.7 t·ha^-1) was noted. The average yields of ryegrass, erect milkvetch, Stylosanthes, and red clover were higher than 43 t·ha^-1, and significantly higher than other green manure species. The average nitrogen concentration of 17 kinds of common green manures was 28.0 g·kg^-1 (in the hay). The nitrogen concentration of common vetch, vetch, alfalfa, burclover, and white clover were all above 30.0 g·kg^-1, and this was significantly higher than other green manure types. The average phosphorus concentration of different common green manure crops was 7.0 g·kg^-1, and vetch and February orchid contained greater phosphorus concentration (above 8.0 g·kg^-1) than other green manures. The average potassium concentration of different common green manure crops was 25.3 g·kg^-1, and the February orchid and milk vetch were highest with a potassium concentration of more than 32.0 g·kg^-1. The average accumulation of nitrogen, phosphorus and potassium of green manure crops was 214.4 kg N·ha^-1, 48.4 kg P₂O₅·ha^-1 and 165.1 kg K₂O·ha^-1. There were significant differences in the accumulation of nitrogen, phosphorus and potassium in different common green manures, among which the accumulation of nutrients was the highest in erect milkvetch, ryegrass, red clover, alfalfa, and Stylosanthes, above 250.0 kg N·ha^-1, 50.0 kg P₂O₅·ha^-1 and 191.7 kg K₂O·ha^-1, respectively. Linking the nutrient accumulation data with regional climatic data, our further analysis found that: milk vetch is most suitable for planting in the southern hilly valley and interplanting zone; common vetch is suitable for planting in the northeast grain rotation area and the Yangtze River Basin; vetch is suitable for planting in the rice-cotton complex intercropping area of the Yangtze River Basin; alfalfa is most suitable for planting in the coastal multiple cropping area; white and red clover are most suitable for planting in the grain-grass intercropping area of the southwest mountainous hills and the northeast grain and grass rotation area; and ryegrass is most suitable for planting in rice-grass multiple cropping area. According to the nitrogen fixation potential assessment of the yield, nitrogen fixation amount and planting area of major leguminous green manure in different regions, the current planting area of green manure in China is about 4.49 million ha, equivalent to the production of 400-810 thousand tons of nitrogen fertilizer. If we estimate the potential area of green manure fertilizer in China at 46 million ha, this is equivalent to the production of 4.0-8.28 million tons of nitrogen fertilizer. Thus, leguminous green manure fertilizer has a high potential of fertilizer replacement. In formulating regional recommendations for green manure crop production, the green manure crop with strong adaptability and performance in each region should be identified and promoted.

Key words: Green manure, regional, yield, nutrient accumulation, potential for nitrogen replacement