60 



SOIL PHYSICS AND MANAGEMENT 



the soil. The particular advantage of this is that it resecds itself 

 and follows ry.e and wheat with a good growth of renovating mate- 

 rial. Bunch grass grows very well upon the blowouts and fre- 



Fid. 58. The trailing wild bean (Strophoslylcs he'.vola. Britton) makes a large 

 growth that not only protects the sand against blowing but adds organic matter and nitro- 

 gen to the soil. Illinois. 



Fio. 59. Pines growing on sand dunes in England at Burry Port. (Carmarthen.) 



quently is the means of stopping the movement. The use of pines 

 for this purpose is shown in figure 59. 



2. Loess. Sand dunes are limited to regions where sand is 

 abundant and where vegetation does not prevent its being moved. 



