Yield of Nitrogen in Wheat and Barley. 



The first series of results relates to the yield of nitrogen in wheat 

 grown thirty-two years in succession on the same land without 

 manure. It is seen that, over the first eight years, the yield was 

 25*2 pounds of nitrogen per acre per annum, over the next twelve 

 years 22'6 pounds, and over the last twelve of the thirty-two years 

 only 15-9. There has thus been a considerable reduction in the 

 annual yield of nitrogen over each succeeding period; and for the 

 third period of twelve years the average is less than two-thirds as 

 much as for the first period of eigh u years. 



Excluding the first eight years of the growth of wheat, the 

 average annual yield of nitrogen over the next twenty-four years 

 was 19'3 pounds per acre per annum ; and the table shows that over 

 the same twenty-four years, barley without man ire yielded 18"3 

 pounds ; and whilst with the wheat the decline in yield was from 

 22'6 pounds over the first twelve of the twenty-four years to 15'9 

 over the second twelve, it was with the barley from 220 to 14'6 

 pounds, or almost in the same proportion 



It might be objected that here the evidence is not conclusive that 

 the falling off is due to the gradual reduction in the amount of 

 nitrogen annually available from the soil. But the results with the 

 two crops, where there is a liberal supply of mineral constituents 

 every year, exclude the supposition that the decline is due to the 

 exhaustion of mineral constituents. Thus, over the same twenty- 

 four years, with a complex mineral manure, such as is very effective 

 in conjunction vrith artificial supply of nitrogen to the soil, the yield 

 of nitrogen in the wheat falls off from 270 pounds per acre per 

 annum over the first twelve years, to 17'2 pounds over the second 

 twelve yeara ; and in the barley, over the same two periods, it declines 

 from 26"0 to 18'8 pounds. 



The similarity in the actual yield, and in the rate of decline 

 of yield, of nitrogen over the same periods in these two closely allied 

 crops, though growing in different fields, and with somewhat different 

 previous manurial history, is very striking. The slightly higher 

 yield in both cases with than without the mineral manure is doubtless 

 due to more complete utilisation of the previous accumulations 

 within the soil, and not to increased assimilation from atmospheric 

 sources. 



Yield of Nitrogen in Boot-crops. 



We now come to the yield of nitrogen by plants of other natural 

 families, and the first of such results relate to the so-called " root- 



