44 ESSAYS ON WHEAT 



what thinly by means of a machine known as a manure 

 spreader. This practice has been found to increase the 

 yield of the crops on soils which have long been cultivated 

 and thus to add to the profits of farming. It is, there- 

 fore, doubtless destined to be much more generally adopted 

 in the future. 



On account of the low rain-fall, moisture limits the 

 yield of grain per acre. The bare fallow, or some modi- 

 fication of it, is therefore resorted to once in from two to 

 five years, more often in the dryer districts and less often 

 in the more humid ones. The summer fallow is the basic 

 practice of dry farming. Its purpose is to store moisture 

 in the soil by preventing its utilization by growing plants, 

 and by conserving it in the soil by means of a soil mulch 

 created by surface tillage. The surface tillage breaks the 

 capillary tubes in the soil and so lessens evaporation. 



In older districts, the summer fallow has a double func- 

 tion, for it is not only used to conserve moisture but also 

 to control weeds. Among the annual weeds which have 

 proved to be pests are Wild Oats (Ave^ia fatua) and vari- 

 ous members of the Mustard family ; and, among the per- 

 ennials. Sow Thistle (So7ichus arvensis), Canada Thistle 

 (Cnicus arvensis), and Quackgrass (Agropyron repens). 

 The very dry parts of southern Alberta and Saskatchewan 

 are troubled with the Russian Thistle (Salsola Kali). 

 Practically all of the noxious weeds of the West have been 

 introduced either directly or indirectly from Europe. 



Seed-wheat, before being sown, is usually cleaned by 

 passing it through a fanning mill which, by means of sieves 

 and screens and a blast of wind, removes the weed seeds, 

 smut-balls, and other impurities, and also small and 

 shrunken kernels of wheat. The seed wheat is then sub- 

 jected to treatment with formalin, which is a 40 per cent, 

 solution of foi-maldehyde. This is mixed with water in 



