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2007年5～9月在地处西辽河平原的内蒙古民族大学实验农场对1年生、2年生、3年生、4年生、6年生紫花苜蓿需磷规律及其土壤供磷能力进行了研究。结果表明,紫花苜蓿体内磷含量总体上随着生长年限的增加而降低,尤以第1茬和第4茬更为明显;2年生紫花苜蓿全年磷输出量最高,3年生紫花苜蓿根的磷积累量最高;随着生长年限的增加,紫花苜蓿地土壤速效磷含量总体上呈先降后升的变化趋势,而土壤全磷含量则与之相反。不同种植年限紫花苜蓿地在20～30cm、30～40cm土层内速效磷含量均下降明显。生产中对多年生紫花苜蓿追施磷肥以秋季第3茬刈割后或春季返青前为宜,且宜适当深施。
From May to September in 2007, the law of phosphorus demand of alfalfa and the phosphorus supply ability of alfalfa for one year, two years, three years, four years and six years were studied in experimental farm of Inner Mongolia University for Nationalities in the West Liaohe Plain. The results showed that the content of phosphorus in alfalfa decreased with the increase of growing years, especially in the first and fourth stubble. The annual phosphorus output of the two-year alfalfa was the highest, and the phosphorus content in the roots of the three-year alfalfa With the increase of growing years, the available phosphorus content in alfalfa land decreased first and then increased, while the total phosphorus content in the soil was the opposite. The available phosphorus content of alfalfa land under 20 ~ 30cm and 30 ~ 40cm soil layers decreased obviously in different planting years. Production of perennial alfalfa topdressing phosphate fertilizer in the autumn after the third cropping or spring back to green before appropriate, and should be appropriate deep facilities.