No. 6. 



DEPARTMENT OF AGRICULTURE. 



357 



of the roots, than the amount of total nitrogen to a depth of 72 inches 

 would indicate. 



In column III the effect of 85 years' continuous culture of wheat 

 on the same land is shown; the result is a soil richer in available 

 nitrogen than might be expected. 



The comparative effect of 17 j-ears in clover, as shown in the last 

 column, is a marked increase of available nitrogen, and shoW'S the 

 good effect of such crops in increasing the store of this important 

 element of plant food. 



The effect of permanent grass in increasing the store of nitrogen 

 in the soil is marked, and is well brought out in the following table 

 bv Sir. J. B. Lawes:" 



Table XI. 



Nitrogen in Surface Soil (dry), First 9 Inches, and Gains in Pounds 

 Per Acre in Land in Permanent Grass. 



Dates. 



o 



(U 



;» 



I.. 



<u 



3 



1856. 

 1866, 

 1879, 



1888, 



Total. 



10 

 13 

 10 



33 



It should be understood that the above field has been mowed for 

 hay every year for 33 years, with average yield of 1.7 tons per acre 

 per annum, and yet, notwithstanding this annual drain, there was an 

 increase of nitrogen in the soil of 50 pounds per acre per annum. 



Thus the state of knowledge is sufficient to indicate that all soils 

 can be kept sufficiently rich in available nitrogen by the judicious 

 use of leguminous crops in a proper system of rotation, or by the 

 use of grass and clover as a part of the same system, and this with 

 out the necessity of purchasing a single pound of nitrogen in a fer- 

 tilizer. 



