d 



le 



11 



Table II. 

 Averacje produce oj Mangel-wurzel Jive years, 1876 — 1880. 



1. Superphosphate of lime, and sulphate potassium . 



2. As 1, and 36^ lbs. ammonium salts (= 7"8 lbs. N) 



3. As 1, and 400 lbs. ammonium salts (=86 lbs. N) 



Leaves. 



Tons. Cwt. 



1 



1 6 



2 16 



Thus, the annual application of about 7" 8 pounds of nitrogen, as 

 ammonium salts, has increased the crop of roots by only 30 cwts. per 

 acre per annum ; and the increased yield of nitrogen in the crop was 

 even somewhat less than the amount supplied in the manure. An 

 application of 86 pounds of nitrogen has, however, increased the crop by 

 160 cwts. more. It is obvious from these facts, that the small application 

 of nitrogen did not enable the plant to take up any from atmospheric 

 sources, and that it required further direct supply of nitrogen to 

 obtain further increase of crop. These results obviously aiford con- 

 firmation of the view that it was a reduction of the available supply 

 of nitrogen within the soil that was the cause of the decline in the 

 annual yield of the crop, and of the amount of nitrogen contained 

 in it. 



JiJ 



^ 



Yield of Nitrogen in Leguminous Crops. 



We next come to the consideration of the yield of nitrogen in 

 crops of the leguminous family, when these are grown separately, 

 year after year, on the same land. Plants of this family are said to 

 rely almost exclusively on atmospheric sources for their nitrogen. 



Table I shews that, without manure, beans gave over the first 

 twelve years an annual yield of 48-1 pounds of nitrogen, but over the 

 second twelve only 14-6 pounds. Over the first period, therefore, the 

 yield was about twice as much as in either wheat or barley, and more 

 even than with the roots. But with this greater yield in the earlier 

 years, the reduction is proportionally much greater over the second 

 period ; the yield then coming down to less than one-third, and to 

 much the same as in the later periods with the other crops. Over 

 the whole period of twenty-four years, however, there was an annual 

 yield of 31-8 pounds of nitrogen, or more than one and a half time as 

 much as in either wheat or barley, and more than in the roots. 



It was seen that in the case of the cereal crops the mixed mineral 



I 



