紫花苜蓿不同茬次及年际间生产性能的动态规律

在海河平原区，先后选取22个、14个苜蓿（Medicago Stiva）品种，雨养条件下通过7年和4年的试验结果表明：不同茬次干草产量表现为逐渐降低的趋势，每年刈割4次：第1茬 > 第2、3茬 > 第4茬；刈割5次：第1茬 > 第2茬 > 第4茬 > 第3茬 > 第5茬；前2茬苜蓿年平均干草产量均占全年总产量的52%以上，第3茬干草占全年总产量的25%以下；随茬次的增加，株高总体上表现为逐渐下降的趋势；第2茬草的叶茎比极显著高于第3、4茬（P<0.01），第4茬草的叶茎比最低；粗蛋白含量为第2、3茬>第1、4茬，并且差异极显著（P<0.01）。苜蓿在海河平原区存在明显的“夏眠”现象，造成了光、温、水资源的浪费。7年连续测定结果表明，在海河平原区紫花苜蓿适宜的利用年限为4~5年。

Dynamic Analyzing on the Production Performance of Alfalfa between Different Cutting Times and Years

In order to illustrate the dynamic change of the production performance of alfalfa between cutting times and years,two experiments for seven years (22 varieties) and four years (14 varieties) were conducted in the Hai River Plain.The results indicated that the average dry matter yields decreased with the cutting times increasing;the dynamic of dry matter yields for 4 times one year was:1st cutting ＞ 2na and 3ra cutting ＞ 4th cutting,the dynamic of dry matter yields for 5 times one year was:1st cutting ＞ 2nd cutting ＞ 4th cutting ＞ 3rd cutting ＞ 5th cutting.The average dry matter yields of the 1st and 2nd cutting accounted for over 52％ of the whole year,and the yields of 3rd cutting could only account for less than 25％.The average plant height (both 22 varieties and 14 varieties) declined with the cutting times increasing.The average Leaf-Stem ratio (both 22 and 14 varieties) of the 2nd cutting was significantly higher than the 3rd and 4th cutting (P＜0.01),the 4th cutting was the lowest.The average crude protein content (both 22 and 14 varieties) of the 2nd and 3rd cutting were higher than the 3rd and 4th cutting,and the differences were significant (P＜0.01).There were obviously "summer slump" phenomena which could cause the waste of light,temperature and water resources.The seven years continuous test showed that the yields decreased from the fifth years,therefore the suitable utilized years were 4～5 year in the Hai River Plain.