WHEAT 111 



crops; enough nitrogen for 1,000 crops and enough 

 potassium for 10,000 crops. It is true also that 

 many subsoils to the depth of several feet at 

 least, are often as rich in the mineral plant foods 

 as the surface soil. We know that in practice 

 however, a very fertile soil will not continue 

 productive by continuous cropping without fer- 

 tilization for even 100 years. After thirty or forty 

 years of continuous wheat cropping, the fertile 

 Red River Valley lands are showing decreasing 

 yields. In fact a considerable area of this splendid 

 land is now being abandoned for wheat culture 

 because it will not produce yields large enough 

 to pay for the farming. 



One reason for this condition is the waste of 

 soluable plant food by oxidation and drainage, 

 especially the nitrogen and the lime. It was 

 found at the Minnesota experiment station that 

 in growing eight crops of wheat continuously, 

 enough nitrogen disappeared from the soil to 

 produce nineteen other crops of wheat thirty 

 bushels per acre. Again the mineral plant foods 

 are locked up and become unavailable in soils 

 which reach an unfavorable physical condition, 

 due to continuous cropping and loss of organic 

 matter. 



WHEN DOCTORS DISAGREE 



It is evident therefore that theory and practice 

 do not agree. Land cannot be cropped for a 

 long time without fertilization and remain pro- 

 ductive. It is also evident that nitrogen, lime 

 and phosphorus are the limiting elements in soil 

 productivity. 



