EXPERIMENTS OF THE BUREAU OF PLANT INDUSTRY. 



29 



was the same; so that at harvest time the uncultivated plats were 

 quite free from weed growth and the cultivated plats were more or 

 less weedy. An example of this is shown in figure 9, which illustrates 

 a carefully conducted experiment on a rather stiff clay soil at the 

 Arlington Experimental Farm. On the uncultivated plats of this 

 experiment the weeds started growing immediately after planting to 

 about the same extent as on the cultivated plats. But as the season 

 progressed and the weed seeds in the surface inch or two of soil germi- 

 nated and the seedlings were destroyed, the weed growth became 

 gradually less, while on the cultivated plats the weeds continued to 

 grow thriftily throughout the season. This tendency was shown in a 

 number of experiments on soils of this kind. The reason for this may 



Fig. 9.— Two plats at the Arlington Experimental Farm, the cultivated at the left and the unculti- 

 vated at the right, showing the difference in weed growth under the two methods of treatment. 



be due to the condition of the soil on the uncultivated plats discour- 

 aging germination of weed seeds beneath the surface inch or two and 

 the inability of the seedlings to push up through the hard crust, 

 whereas on the cultivated plats the friable surface soil permitted the 

 seedlings to push up from a considerable depth and the tillage imple- 

 ments were constantly bringing up weed seeds into the surface soil 

 where conditions were more conducive to germination. 



It was observed that on other soils, however, especially those of a 

 loose, deep, moist character, the weed growth on the two sets of plats 

 was about the same throughout the season. 



Whether or not it is desirable to discourage the germination of weed 

 seeds can not be stated definitely at the present time. It may be 



257 



