646 
Rotation of Crops. 
hand, can there be any doubt that the facts relating to the 
amount, and to the sources, of the nitrogen of the different 
crops, are of still greater significance than are those in regard 
to the mineral constituents. 
But, it is not only the conditions of growth, but the uses of 
the different crops when grown, that have to be taken into 
account. Thus, the cereals, when grown in rotation, yield more 
produce for sale in the season of growth than when grown 
continuously. Again, the crops alternated with them, accumu- 
late very much more of mineral constituents and of nitrogen in 
their produce, than do the cereals themselves ; and, by far the 
greater proportion of those constituents remains in circulation 
in the manure of the farm, whilst the remainder yields highly 
valuable products for sale in the forms of meat and milk. 
Further, independently of the benefits arising from the 
difference in the requirements and results of growth of the 
different crops, of the increased amount of manure available, 
and of the increased sale of highly valuable animal products, 
there are other elements of advantage of considerable import- 
ance. For example, with a variety of crops, the mechanical 
operations of the farm, involving horse and hand labour, are 
better distributed over the year, and are therefore more 
economically pei’formed. Last, but by no means least, the 
opportunities which alternate cropping afford for the cleaning 
of the land from weeds is a prominent element of advantage. 
Thus, then, the benefits of rotation are vei'y various ; and 
the explanation of them, though largely dependent on the facts 
which have been ascertained by scientific investigation, also 
largely involves considerations connected with the general 
economy of the farm ; and since, as has been seen, so large a 
proportion of the produce grown is retained on the farm, as 
stock-food or litter, it is obvious that the benefits cannot be 
fully appreciated without arriving at some definite idea of the 
importance to the farmer of the saleable animal products, and of 
the manure obtained. It is proposed to consider this subject in 
a future paper. 
John Bennet Lawes. 
JosErn Henry Gilbert. 
Rothamsted, St. Albans. 
