Study on the growth and productivity of alfalfa with different growth years under irrigation condition

The study on the productivity of five different growth years of Medicago sativa was carried on the experimental farm of the Inner Mongolia University for Nationalities in Xiliaohe Plain from April to October in 2007. The results showed that the net photosynthetic rate of twoyear old alfalfa was higher but lower for sixyear old alfalfa in generally, and varied among cutting times. With the increase of the growing year, the content of chlorophyll a and chlorophyll b decreased in first cutting, but the content of threeyear old and fouryear old alfalfa were higher in the second, third and fourth cuttings, and the twoyear old and sixyear old alfalfa were lower. The content of Carotinoid decreased in the first cutting with the increase of the growing year, but there was no obvious correlation between the content of Carotinoid and growing years in the other cuttings. The whole year alfalfa yield ranked as: twoyearthreeyearfouryearsixyearoneyear. With the increase of growing year, the plant density of alfalfa with different growth years decreased, but the rate of rotted roots, the root crown diameter and the tiller number of root crown increased. The dry weight of major root and the number of lateral root of threeyear old alfalfa were the highest, and the dry weight of lateral root of fouryear old alfalfa was the highest in 0-50 cm soil layer.