10 



crops" — turnips of the natural order Cruciferce, and sugar-beet, and 

 mangel-wurzel of the order Chenopodiaceoe. The table records the 

 results for thirty-six years in succession, 1845-18S0 ; but it should be 

 stated that during three of those years barley was interposed without 

 any manure, in order, as far as possible, to equalise the condition of 

 the land before re-arranging the manurir.g; and during two other 

 years the turnips failed, and there was no crop. It should be further 

 explained that, without manure of any kind, root-crops, after a few 

 years, give scarcely any produce at all, and hence the results selected, 

 and recorded in the table, are those obtained by the use of mineral 

 manures, but without any supply of nitrogen. 



During the first eight years (four years Norfolk whites and four 

 years Swedes), the turnips gave an average of 42 pounds of nitrogen 

 per acre per annum, or very much moi'e than either of the cereal 

 crops. During the next three years barley (without manure) yielded 

 243 pounds, or even somewhat less than the yield in wheat or barley 

 with mineral manures in the earlier years of their continuous growth. 

 During the next fifteen years (thirteen with Swedish turnips and two 

 without any crop), the yield was reduced to 18*5 pounds ; during the 

 next five years, with sugar-beet, to 13"1 pounds ; and during the last 

 five years, to 1880 inclusive (with mangel-wurzel), to 15'4 pounds. 

 Lastly, over the whole thirty-six years, the average annual yield of 

 nitrogen was 25"2 pounds. 



Here, then, compared with wheat or barley, we have with the 

 root-crops, the growth of which extends much further into the 

 autumn months, a much higher annual yield of nitrogen in the earlier 

 y?ars, and with this a much more rapid rate of decline subsequently, 

 the annual yield over the last ten years being only about one-third as 

 much as over the first eight years ; whilst the yield in the later years 

 is actually less than in either wheat or barley with the same complex 

 mineral manure. Here, again, the marked decline in the yield of 

 nitrogen, with liberal mineral manuring, points to a deficiency in the 

 available supply of nitrogen itself as the cause of the deficient assimi- 

 lation of it by the crop. 



It may here be observed, that those who maintain that the atmo- 

 sphere is an important source of the nitrogen of our crops assume 

 that the root-crops, if provided with a small quantity of nitro^Tenous 

 manure to favour the early development of the plant, will obtain the 

 remainder from the atmosphere. How far this is the case may be 

 illustrated by the following results, which are the average of five 

 years' successive growth of mangel-wurzel on the same plots, and in 

 each case with the same manure year after year. 



