Although the effects of nitrogen (N) on forage legume productivity have been well-studied, there is still some debate as to whether the supply of additional N is essential to support higher forage legume yields. Here, a meta-analysis was conducted to synthesize the effects of N fertilization on forage legume biomass across different climates, soil types and planting system. The results showed that forage legume biomass in pure stands generally increased after N addition and was positively correlated with plant accumulation of N, phosphorus and potassium. The direction and magnitude of forage legume biomass responses in pure stands were influenced by accumulated temperature during growth stage and soil characters including organic matter, pH and N availability. Soil pH was positively correlated while other factors were negatively correlated with forage legume biomass response. Increases in forage legume biomass were greater at sites where accumulated temperatures were lower than 2,000°C. N addition did not contribute to higher forage legume biomass in acidic soil and when soil N availability was high (e.g. soil total N content higher than 0.9 g/kg and N addition rate higher than 200 kg/ha). Moreover, forage legume biomass was negatively affected in mixed systems which was independent of N application rate. In conclusion, this meta-analysis highlights the importance of considering temperature, soil characters and planting system when evaluating the necessity of N application during forage legume production.

中文翻译：

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饲草豆类生物量对氮输入的响应取决于温度，土壤特性和种植系统：荟萃分析

尽管氮 (N) 对豆科牧草生产力的影响已得到充分研究，但关于额外的 N 供应是否对支持更高的豆科牧草产量至关重要，仍存在一些争论。在这里，进行了一项荟萃分析，以综合不同气候、土壤类型和种植系统下施氮对牧草豆科植物生物量的影响。结果表明，纯林中的牧草豆类生物量一般在添加氮后增加，并且与植物氮，磷和钾的积累呈正相关。纯林分牧草豆类生物量响应的方向和大小受生长阶段积温和土壤特征（包括有机质、pH 值和 N 有效性）的影响。土壤pH值与牧草豆类生物量响应呈正相关，而其他因素与豆科植物生物量响应呈负相关。在积温低于 2,000°C 的地点，牧草豆类生物量的增加更大。在酸性土壤中，当土壤氮利用率高时（例如，土壤总氮含量高于0.9 g / kg，氮添加速率高于200 kg / ha），氮的添加并不能促进牧草豆类生物量的增加。此外，在与施氮量无关的混合系统中，牧草豆类生物量受到负面影响。总之，这项荟萃分析强调了在评估豆科牧草生产过程中施氮的必要性时考虑温度、土壤特性和种植系统的重要性。在积温低于 2,000°C 的地点，牧草豆类生物量的增加更大。在酸性土壤中和当土壤氮的有效性高时（例如土壤总氮含量高于 0.9 g/kg 和氮添加率高于 200 kg/ha），氮添加不会导致更高的牧草豆类生物量。此外，在与施氮量无关的混合系统中，牧草豆类生物量受到负面影响。总之，这项荟萃分析强调了在评估豆科牧草生产过程中施氮的必要性时考虑温度、土壤特性和种植系统的重要性。在积温低于 2,000°C 的地点，牧草豆类生物量的增加更大。在酸性土壤中和当土壤氮的有效性高时（例如土壤总氮含量高于 0.9 g/kg 和氮添加率高于 200 kg/ha），氮添加不会导致更高的牧草豆类生物量。此外，混合系统中饲草豆类生物量受到不利影响，这与氮肥施用量无关。总之，这项荟萃分析强调了在评估豆科牧草生产过程中施氮的必要性时考虑温度、土壤特性和种植系统的重要性。9 g/kg 和 N 添加率高于 200 kg/ha)。此外，在与施氮量无关的混合系统中，牧草豆类生物量受到负面影响。总之，这项荟萃分析强调了在评估豆科牧草生产过程中施氮的必要性时考虑温度、土壤特性和种植系统的重要性。9 g/kg 和 N 添加率高于 200 kg/ha)。此外，在与施氮量无关的混合系统中，牧草豆类生物量受到负面影响。总之，这项荟萃分析强调了在评估豆科牧草生产过程中施氮的必要性时考虑温度、土壤特性和种植系统的重要性。