采用盈亏平衡分析方法，对黄土高原南部3个村农果复合型生态农业的营养物质平衡进行了研究.结果表明,施肥是农果复合生态系统营养物质的主要输入途径.输入的营养物质中，化石能所占比重较大，而有机肥投入相对不足.农果复合生态系统内用于循环的N、P、K仍远低于营养物质N、P、K的输出量.3村营养物质的产投比虽有差异，但总体水平仍很低.
The analysis on the balance of nutrient’s profit and loss in crop-fruit ecosystems of three villges in middle-south Loess Plateau showed that fertilization was the main input of nutrients,of which,chemical fertilizer occupied a larger proportion,while organic manure was relatively insufficient.The quantity of N,P and K spent in interior circulation was far less than that exported from the ecosystem.The ratio of nutrient’s output and input in three test villages was differed,but all at a low level.
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