SPECIAL FARM TOPICS 207 



crops in this rotation are considered exhaustive crops, as they all 

 decrease rather than increase the supply of vegetable matter in the 

 soil. 



10. The practice of sowing grass seed with the grain on corn 

 land that is disced in the spring in place of fall plowing, has re- 

 sulted in securing a grass stand in nearly every instance. It has 

 proved to be the surest method of obtaining a grass stand of any 

 tried at University Farm. (Minn. Agr. Exp. Sta. Bui. 109; Re- 

 port of 10 Years on 44 Rotation Plots.) 



The analyses of the soils of the forty-four experiment plots at 

 the beginning and the close of the ten year period showed : 



(1) The maximum amount of nitrogen was lost when the 

 soils were cropped exclusively to wheat, corn, potatoes and mangels. 

 When these crops were grown continuously there was an average 

 loss of .034 per cent of nitrogen, equivalent to 1,100 pounds per 

 acre. In the case of wheat two-thirds of this nitrogen was not 

 utilized as plant food, but was lost by the rapid decay of the humus 

 with the formation of soluble ana volatile nitrogen compounds. 

 When the crops were grown continuously the soils lost .5 of a per 

 cent of carbon, representing over one per cent of humus, or 20,000 

 pounds, equivalent to an annual loss of one ton per acre. 



(2) There was an average gain of .014 per cent of nitrogen, 

 equivalent to about 300 pounds per acre, in the case of twelve stand- 

 ard rotations, consisting of wheat one year, clover and timothy two 

 years, oats one year, and corn one year, manured with stable manure 

 at the rate of eight tons per acre. From one of the twelve plots there 

 was a small loss of nitrogen. The results, taken as a whole, show 

 the nitrogen content is maintained when clover is grown two years 

 in a five course rotation, and then the application of nitrogen contain- 

 ing fertilizers is unnecessary. In practically all the rotations where 

 clover was grown, gains of nitrogen were secured. There were no 

 great differences in gains of nitrogen that could be attributed to the 

 combination of any special crops with clover. Any substitution of 

 crops in the rotation could be made without materially affecting the 

 nitrogen content of the soil, provided clover was retained. When 

 the crops were rotated, the carbon and humus content of the soil 

 was maintained and in some cases slightly increased. The results 

 show that wheat, corn, oats, barley, flax, rape, potatoes, mangels, 

 millet, bromus and timothy can be grown with clover in three, four, 

 five or six year rotations without loss from the soil of either nitrogen 

 or humus. By rotation with clover, the nitrogen content was con- 

 served, and in some cases slightly increased. The gains and losses 

 of nitrogen are practically under the control of the cultivator. 



(3) In the rotations where timothy and non-legumes were 

 substituted for clover, a loss of nitrogen occurred, but the carbon 

 (and humus) content was maintained. The conservation of the 

 humus prevented rapid nitrification, and the loss of nitrogen from 

 the soil only slightly exceeded that removed by the crops. 



(4) The potash compounds of the soil were less soluble at 

 the close than at the beginning of the ten year experimental period. 



