202 . Physics of the Soil. 



it could not readily become available until after the roots 

 had penetrated below this level. 



Nor is this all ; any such crop would have locked up in 

 insoluble form, for the time being, a large portion of the 

 soluble plant food, and unless abundant and timely rains 

 were to follow the plowing speedily to develop a new sup- 

 ply, the next crop would suffer for lack of nitrates and 

 other plant foods. 



On soils naturally too wet and in wet seasons the dan- 

 gers referred to will of course not be so great and the 

 green manure crop might even be an advantage from the 

 soil moisture side by making the over-wet soil more open, 

 thus favoring stronger root action and more rapid nitri- 

 fication. 



237. Wind-breaks and Hedges, "In* sub-humid climates, 

 especially like those of our western prairies, where there 

 is a high mean wind velocity, and in the level districts 

 of humid climates, where the soils are light and sandy, with 

 a small water capacity, and which are lacking in adhesive 

 quality, the fields may suffer greatly at times, not only 

 from excessive loss of moisture, but the soil itself may be 

 greatly damaged by drifting caused by the winds. Under 

 such conditions, it is a matter of great importance that the 

 wind velocities close to the surface should be reduced as 

 much as possible." 



On the lighter sandy lands, wherever broad fields lie 

 unsheltered by any wind-break, strong dry winds frequent- 

 ly sweep entirely away crops of grain after they are four 

 inches high, and at the same time drift away even as much 

 as three or four inches of the surface soil, the best in the 

 field. In such cases wind-breaks and hedge-rows exert a 

 very strong protective influence and greatly lessen such dis- 

 astrous results. 



"Not only do trees along line fences and roadsides, un- 

 der these conditions, prevent such direct injuries to soil and 



Irrigation anrt Drainage, p. 168. 



