90 Kansas Academy of Science. 



gen represents the amount needed to produce 800 bushels of 

 corn, stalks and grain, or 26% bushels per acre for thirty years, 

 assuming that everything is removed from the land and that 

 no nitrogen is lost in the drainage water. Such farming prac- 

 tice would be possible only with virgin soils well stocked with 

 nitrogen and organic matter. Crops use a certain per cent of 

 the nitrogen in the soil, and for that reason complete soil ex- 

 haustion is impossible. But soils are considered exhausted 

 when the total amount of plant food possible for the crop to 

 obtain is less than is required to produce a profitable crop. If 

 a soil has been cultivated for thirty years to corn and has pro- 

 duced an average of twenty-six bushels per acre during this 

 time, it will not be possible to produce this amount of corn in 

 the next thirty years with the same method of farming prac- 

 tice. It is a common observation of farmers that it takes more 

 work than formerly to produce crops. Cultivation is one of the 

 means of producing usable plant food. In new soils that plant 

 food which is most easily made usable is transformed first. 

 When this has been used up the first flush of abundant crop 

 production passes, and more work is required by the farmer. 



In the third and fourth columns are shown the percentage 

 losses of nitrogen and organic matter. The per cent loss of 

 nitrogen varies from 22.6 per cent in the sample from Brown 

 county to 43.5 per cent in the samples from Reno county. The 

 next greatest losses are found in the samples from Butler and 

 Greenwood counties, where according to the popular concep- 

 tion the farmers have the means of conserving soil fertility. 

 Brown county shows the smallest loss, and in this part of the 

 state proper systems of crop rotations have been used more. 

 The per cent loss of organic matter varies from 23.3 in the 

 Brown county samples to 51.3 in the Reno county samples. In 

 every case the percentage loss of organic matter is greater than 

 the percentage loss of nitrogen. These figures show that the' 

 cultivated soils of Kansas have lost on the average more than 

 one-third of their original stock of organic matter. The seri- 

 ousness of this situation can not be overemphasized. While 

 these figures show the percentage of total loss, they do not tell 

 anything about the quality of organic matter lost. This fact 

 will be discussed later. 



In the fifth column is found the per cent of nitrogen in or- 

 ganic matter. In every case the per cent of nitrogen is greater 



