Experiment Research Of Alfalfa Soil Compaction By Mowing Machine

As one of the highest valuable grazing, alfalfa has the longest plant history and the biggset plant area. In resent years, its production has been widely expanded. There are many kinds of machines which were used in the mowing, racking, transporting procedure. In these courses, there are all 54-72 times operation in 6 to 8 years that farm yield was compacted by mowing machine, racking and transporting vehicle. All this would cause soil compaction. Mowing machine is the most important tool in the harvest of alfalfa. It is the first-used machine. Additionly, its contact pressure is higher than other machines. There was usually several times of tires passes in the same area. Therefore, soil compaction caused by mowing machine is more obvious than others. On the account of this, HW320 Self-Propelled windrower(79KW engine power)was seclected as an typical kind of machine to carry on the soil compaction experiment. The effect of soil physical characters and the yield of alfalfa which caused by soil compaction was studied, the correlation between soil compaction and the yield of alfalfa and the relationship of soil compaction and soil stress was researched. Meanwhile, the predicable model of soil compaction which will be fit for alfalfa soil in china was obtained. The results of this research would provid reference for the reasonable movement of mechanized alfalfa harvest craft and the sustainable development of mechanized alfalfa production. .Field tests were conducted in the use of New Holland HW320 Self-Propelled windrower on alfalfa soil during alfalfa harvest period, the aim of it was to check the compacting effects and the alfalfa yield changes resulting from one to ten passes of the mowing machine in the same track. Then the changes of the soil bulk density, soil hardness under different passes and different depths were measured. In the same time, porosity, three phases of soil were also calculated. The relationship of soil compaction and alfalfa yield has been researched. The effect and the precision of Emmanuel C predicate model have been proved. In this paper, a compaction coefficient was introduced and the relationship of soil bulk density and compaction coefficient was given. Finite element method was used to study the change of agricultural soil stress which was caused by soil compaction. The results are as follows:1. New Holland HW320 Self-Propelled windrower can cause: The surface soil bulk density increased by 17.29%, soil bulk density in 30cm depth increased by 4.16%, it fundamently has no change under 30cm depth; Soil porosity decreased by 14% in surface soil and 11% in bottom soil; The effect of compaction to soil hardness in the surface 10cm depth is bigger than other depths. The hardness of surface soil was increased to 3.7 times of the original field soil. The hardness of surface soil can also approach or exceed the plough pan soil hardness which is always harder than other soil depth; The increasment of solid phase is 29% in surface soil and 0.47% in bottom soil, the decrease of gas phase was up to 55.7%, in 10~20cm depth and this trend appeared in other soil depths, the value was from17.6% to 27.7%, Soil liquid phase increased by 17.6% in 10~20cm depth and other depths have no significant change; The change of soil permeability is sensitive when soil compaction occurred, which makes soil permeability decrease rapidly.2. Soil compaction caused by mowing machine could influence the alfalfa yield. The yield increasment of alfalfa was 4464kg ha-1 annually after ten passes compared with the alfalfa yield in the original field soil. There is a relationship of negative correlation between the soil bulk density ,soil hardness and the alfalfa yield. The relationship could be described by quadratic equation.3. Emmanuel C model has a better effect to predict 0~20cm depth soil compaction in the experiment region soil (medium loam soil), in which alfalfa was planted. Compaction coefficient can make soil compaction and alfalfa yield together well. It can reflect the relationship of soil compaction and alfalfa yield.4. The change of soil stress and soil displacement is mainly caused by the first tires pass. The maximum stress occurred in 5~8cm depth under the surface soil. The change of soil stress under 30cm depth is not obvious. The soil compressed displacement in 0~30cm depth are 72.8% and 95.2% respectively after 1 pass and 7 passes compared with the compressed displacement after 10 passes. When the number of tires passes is up to 9, an soil compression invalidation was appeared; when soil was compacted, it is imbalanced in all parts of soil that is under the wheel, the stress under the middle of wheel tack is higher than the edge of wheel tack. From contact area of soil–machine to the deeper depth, the effect range of soil stress caused by compaction has extended with the increase of the number of tire passes. For a same compaction effect, the smaller contact area, the more number of tires passes,. The relationship of soil compressed displacement in 0~30cm and ground pressure can express as a parabolic curve. The soil compressed displacement in 0~30cm depth is also directly proportional to Logarithm LgN of the number of tire passes N.