Relationship between the aboveground dry matter accumulation of alfalfa and the effective accumulated temperature in the first cutting

The results of field experiments on relationship between dry matter yield of the fouryear alfalfa in the first cutting and 5 ℃ accumulated temperature indicated that 1) The dry matter growth pattern of different parts of alfalfa varieties was same. The order of the production potential of dry matter, maximum growth rate, average growth rate were whole plant stem leaf. But the ranges of the effective accumulated temperature for the maximum growth rate and average growth rate were different. The maximum growth rates of whole plant, stem and leaf were reached while the effective accumulated temperatures were 504.72 to 609.45 ℃, 574.47 to 643.91 ℃, 444.53 to 543.25 ℃ respectively. And for the average growth rates, they were 384.61 to 716.54 ℃, 424.48 to 773.36 ℃, 320.42 to 642.48 ℃; 2) The dry matter growth of different alfalfa varieties was different. For whole plant, stem and leaf of Lobo, Amerigraze 401 and Meiguozajiao, their potential dry matter growth, maximum growth rates and average growth rates in peak of growing season were higher.