Lysimeter Experiments 



41 



RELATION OF DIFFERENT CROPS TO FORMATION OF NITRATES 



The total nitrogen removal appears to vary with different crops, and 

 it is possible that the growth of some crops would result in a larger removal 

 of nitrogen than does the maintaining of a bare soil surface. It is obvious 

 that the maintenance of clean cultivation, as is often practiced in orchards, 

 is likely to lead to excessive loss of nitrogen, while the growth of a cover 

 crop returns most of the nitrogen to the soil when the crop is plowed under. 



A study of the nitrates in the drainage water and their relation to the 

 crops produced shows the characteristic relationships that have pre- 

 viously been discussed by the writers (Lyon and Bizzell, 1913). This 

 may be seen by reference to table 20, in which -are stated the average 

 quantity of nitrogen contained in each kind of crop raised — the actual 

 quantities found being given for the tops, or aboveground parts of the 

 plants, and an estimate of one-third that amount being assumed for the 

 quantity contained in the roots — and also the quantity of nitrogen 

 contained in the drainage water flowing from the tanks during the year 

 in which the crop grew. As the nitrogen for the cropped and the un- 

 cropped soil represents the flow of drainage water for the same year, 

 the experiment is not open to the same objection as when the flow of 

 two or more different years is compared. While, therefore, the com- 

 parison instituted in table 20 is open to some objections — one of which 

 is the moisture content, which is always less during the growing season 



TABLE 20. Available Nitrogen in Soil Producing Different Crops, as Measured 

 BY THE Nitrogen of the Crop and of the Drainage Water 



(In pounds per acre) 



Crops 



Maize 



Oats 



Mixed grasses 



Timothy 



Timothy and clover 



Nitrogen in planted tanks 



In drain- 

 age 

 water 



12 

 9 

 1 

 3 

 2 



In 

 tops 



144 

 73 

 46 

 49 

 73 



In' 

 roots* 



48 

 24 

 15 

 16 

 24 



Total 



204 



106 



62 



68 



99 



Nitrogen in 

 drainage 



water 

 in corre- 

 sponding 



bare tanks 



119 

 92 

 85 

 92 

 76 



Excess 



( + ) or 



deficiency 



(— )in 



planted 



tanks 



+ 85 

 + 14 



— 23 



— 24 

 + 23 



♦Estimated at one-third the quantity in tops. 



41 



