Study on root system growth characteristics of alfalfa

Based on the 2 years (2003 2004) investigation data at Tianshui Agrometeorological Experimental Station and Qingshui Weather Stations, the growth characteristics of alfalfa root system and the relationship between the growth and environment factors have been analyzed. The results showed that the meteorological resources which alfalfa required at each growth period depend on the time of planting. The sunlight and heat which one year old alfalfa required was higher than that of two years from seeding to pod setting period, after that, but the growth speed increased and the growth period shortened for one year old plant, compared to two years old plant. The results also indicated that the growth speed of root system had a close relationship with the growth of stem and leaves, the fastest growth period for root was in winter and autumn when leaves and stem stopped growing or grew slowly; and the slowest root growth period was in branching to reaping period when the stem and leaves grew luxuriantly. The accumulated biomass of root system nonlinearity correlated to ground (10 cm) temperature (0 ℃) , the accumulation speed increased obviously when the accumulated temperature was over 3 500 ℃. The water content was the highest at 1 580～1 815 ℃ and 5 344～5 941 ℃ accumulated ground (10 cm) temperature(0 ℃). Alfalfa made much more use of soil water than other crops, and its 100 cm soil water consumption was 30% higher than in the wheat field. The dry layer trace was deeper by 40 cm and lasted 120 days longer than wheat field.