Effects of selenium and cobalt fertilization on nutrition levels of alfalfa hay

A field experiment was conducted to study absorption，utilization and recovery of selenium(Se) and cobalt(Co) in alfalfa (Medicago sativa L.) hay and as well as effects of Se and Co fertilization on main nutrients and contents of trace elements of alfalfa hays by basal application of Se and Co in alfalfa rangeland. The objectives of experiment were to produce fine and safe alfalfa products with more effective Se and Co by Se and Co single and mixed basal applications rationally. The results show that alfalfa has strong capacities to absorb, transfer and utilize Se and Co from soil, and single basal application Se or Co could increase the contents of Se and Co of alfalfa hays (the more Se in soil, the more Se in hays). If more Co is applied in soil，some Co might be wasted. Content of Co of the hays is increased when Co and Se are applied at the same time. Rational combined application of Se and Co could raise utilization rate of Se and the transfer ratio of Se from inorganic Se from fertilizers to organic Se of the forage, and the effectiveness and securement of Se are all enhanced obviously. In all experimental treatments, only high elenium-lower Co combined fertilization could enhance the contents of crude protein and ether extract (EE), and has less effects on stabilities of crude fiber (CF) and nitrogen-free extract (NFE). Other treatments tend to enhance the contents of CF, decrease the contents of EE, and have no significant effects on CP and NFE. Combined applications of Se and Co have better effects on the contents of trace elements of alfalfa hays, of all 6 kinds of trace elements，the contents of Mo are increased significantly (142.34%-256.45%)， next is Fe, Mn and Zn (48.16%-59.45%, 32.88%-41.66% and 37.10%-96.39% respectively)，and Cu and B are lowest (13.43%-37.33% and 14.60%-39.67% respectively).