ing the drawbar load resulted in increased plant damage. How- 

 ever, the dift'erenee was not statistically didereiil when ex- 

 pressed in relative yield hasis. 



Discussion 



Results of this study indicate that significant damage is in- 

 flicted on young legume plants when subjected to tractor traffic. 

 The comparison of smooth tires and new tires demonstrates 

 that the greater the area of contact the more severe the dam- 

 age. This can be explained by the fact that more plants are 

 contacted bv a tire with a smooth surface. Increasing the draw- 

 bar pull results in an increase in plant damage. 



Where the weight of the tractor alone inflicts considerable 

 damage, the minimum ground pressure required to eliminate 

 damage appears to be below any practical application insofar 

 as size of tractor tire and weight of the tractor are concerned. 

 This suggests that tires with a minimum of contact area will 

 cause less damage despite the increased contact pressures. How- 

 ever, operating conditions often dictate the minimum sizerl 

 tire that can be used. 



Stem and Leaf Damage. Figure 7. shows several types of dam- 

 age inflicted on the young plants. Broken stems, crushed stems, 

 crushed leaves and parts of plants severed completely, were 

 connnon types of damage observed. These plants, although they 

 continued to grow, were severely retarded and by harvest time 

 were verv poorly developed and resulted in low yields. 



Crown Damage. Another type of damage inflicted was crown 

 damage. It was observed that most of the shoots present when 

 the treatments were imposed had been killed by the action of 

 the tractor tire. Figures 8 and 9 show examples of alfalfa and 

 red clover roots dug u}) and examined in the laboratory. Most 

 of the shoots arising from the damaged crowns at the time of 

 harvest were new. In several instances the crowns were so 

 severelv damaged that rotting of the root had developed. (Fig- 

 ure 9 ) . How long these damaged plants w ould continue to 

 grow and survive winter conditions is questionable as the root^ 

 were split and apparently more susceptible to disease. It i> 

 very possible that damage inflicted by field traffic to jilant^ 

 mav be a contributing factor to a reduction in a stand of 

 legumes. 



11 



