Abstract:

To clarify the effect of returning manure and water from large-scale dairy farms on the growth of alfalfa and the physical and chemical properties of soil, 5 amounts of cow manure water of 0, 150, 300, 450 and 600 m³/hm² returning to the field after solid-liquid separation and fermentation were set in this experiment. By measuring the changes in alfalfa yield, quality, soil nutrient content and heavy metal content under different treatments, the results showed that returning manure to the field could significantly increase the hay yield of alfalfa. With the increasing in the amount returned to the field, the yield increased significantly, under the treatment of 600 m³/hm², the annual hay yield of alfalfa reached 19369.0 kg/hm²; the application of manure water could not reduce the crude protein and relative feeding value of alfalfa; the return of manure water to the field could significantly increase the pH and salt content of the soil, and it could increase the soil organic matter content. Under the condition of no fertilization throughout the year, the available nitrogen, available phosphorus and available potassium in the treated soil all showed a decline. Returning manure water to the field could not meet the annual growth needs of alfalfa, and it should be combined with fertilization for better results. The return of manure water to the field would increase the content of heavy metals such as copper, cadmium, arsenic, lead, and chromium in the soil, and the content of each heavy metal would increase the most at the level of 600 m³/hm². In general, the amount of cow manure water returning to the field should be controlled within the range of 300-450 m³/hm² to achieve double improvement of alfalfa yield and soil quality.

Key words: cow manure water, alfalfa, yield, quality, soil, physical and chemical properties, field application, heavy metals