Department of Soil Investigation Ixxix 



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from the lower soil, or by the incorporation of lower soil into the 

 plowed part through the wearing away of the upper soil. 



Project II. Influence of the grozvth of certain crops on the forma- 

 tion and loss of nitrates in the soil. — Some of our experiments in 

 the field indicate that the growth of at least certain crops on the 

 land results in a decrease in the quantity of nitrates on the land so 

 cropped. In our field experiments we were not able to measure 

 the quantity of nitrates that disappeared in the drainage water or 

 otherwise to account for the appearance or disappearance of ni- 

 trates. In the soil tanks this can be done. 



Project 12. Rate of fixation of nitrogen in the soil as affected 

 by liming and by sod. — A record will be kept of the income and 

 outgo of nitrogen in all of the tanks, which will give an opportunity 

 to determine the amount of nitrogen fixed, and thus to ascertain 

 the influence of the soil reaction and of the efifect of sod on that 

 process. 



Project 13. Changes that occur in the composition and in certain 

 properties of a soil as it gradually deteriorates or improves. — The 

 process of improvement or deterioration in a soil is a very compli- 

 cated one, involving an enormous number of changes. As the soils 

 in the tanks will be under experimentation for a long period, many 

 of these changes will be sufficiently marked to measure by physical^ 

 chemical, and bacteriological means, which cannot be done in short 

 periods and is liable to error in field plats. 



Project 14. The effects of the continuous use of certain mineral 

 fertilizers on the physical and chemical properties of a soil and on 

 the bacterial flora and the activity of certain forms of bacteria. — - 

 It is well known that the physical properties of most soils are pro- 

 foundly affected by the continuous use of certain mineral fertilizers. 

 It is desired to ascertain whether this action is determined solely 

 by changes in the content of organic matter, or whether the fertiliz- 

 ers exert an independent action. 



While the investigations to be conducted in the soil tanks are de- 

 signed primarily with a view of studying the seven subjects last 

 mentioned, the data which it is intended to collect will contribute 

 much to the solution of other problems and will doubtless bring 

 to light phenomena calling for further investigation. The tanks 

 afford an incomparable means for studying the problem of main- 

 taining soil productiveness in a humid region where the climatic 

 conditions and the agricultural practices are of a nature to cause a 

 loss of fertility and a tendency to acidity through the leaching of 

 salts from the soil. 



