THE CAUSES OF LOW YIELDS 255 



fair crop on the average may be obtained by good break- 

 ing done early enough to seed it about the last of May 

 to an early-maturing crop. In the drier parts such a 

 practice will only result in a profit about once in four 

 years, the reason of the low return being the lack of 

 moisture and available plant food in th« soil from the 

 previous year. In the more moist parts oats, barley and 

 potatoes are frequently grown on breaking done the same 

 season, but the practice even in these areas is to be en- 

 couraged only where the land can be well prepared by 

 being broken not less than four inches deep, packed and 

 disked and harrowed to form a good seed bed. 



Where the rainfall is low and the evaporation great 

 sowing a grain crop on spring breaking is not a good 

 practice. It not only is a losing proposition three times 

 out of four, but the land so used is seldom in good con- 

 dition for a subsequent crop, nor is it likely to give a 

 good yield until it is summerf alio wed. In the dry parts 

 flax is the crop generally used at present for sowing on 

 breaking. Potatoes are sometimes grown on such land 

 for home use, but such preparation is inadvisable for a 

 large acreage of this crop. Oats also are occasionally 

 grown on spring breaking for sheaf feed. Corn is seldom, 

 used on spring breaking, but unlike the other crops 

 mentioned it will do quite well and at the same time leave 

 the land in far better condition for a subsequent crop 

 than any of the others mentioned. 



205. Native Perennial Plants in Stubble Fields.— The 

 long-lived perennial plants commonly found growing in 

 prairie sod are often the chief causes of low yields in 

 stubble fields. Quack grass, sweet grass and rose bushes 

 are three widely spread members of this group. Such 

 perennials are reproduced by creeping roots as well as 



