25 



all of us, that no such value can be attached to the ordinary 

 use of superphosphate. Where a neglected soil is being 

 brought into good condition, the effect of superphosphate 

 and of its residue in the soil may be very great; but super- 

 phosphate and other sulphates are so largely used in ordinary 

 agriculture, and the soil is generally so well supplied with 

 their residues, that the application or omission of a dressing 

 in the last rotation of an outgoing tenant can make scarcely 

 any difference to his successor. 



We will now inquire what the rotation experiments have to 

 teach us as to the effect which carting off the swedes has upon 

 the subsequent crop of the rotation. Omitting the first rota- 

 tion, which served to equalise the land, and three other 

 rotations in which the turnip crop failed, or was very 

 small, there remain eight rotations suitable for our present 

 inquiry. 



Where the swedes had received the ample nitrogenous 

 manuring, the average produce in these eight rotations was 

 19 tons 6 cwts. of roots on the two plots from which the 

 roots were carted. The removal of these roots with their 

 leaves caused the succeeding crop of barley to be on an average 

 9j bushels less than on the corresponding two plots on which 

 the swedes were fed, or cut up and ploughed into the soil. In 

 round numbers we may say that on this highly manured land 

 the removal of 10 tons of swedes with their leaves diminished 

 the following crop of barley by 5 bushels. 



Where the rotation has received no nitrogenous manure 

 for fifty years, the swedes being grown with superphosphate, 

 and latterly with superphosphate and potash salts, the average 

 crop of roots carted in the eight rotations has been 9 tons 

 8J cwts. The carting of these roots, with their leaves, has on 

 an average diminished the succeeding crop of barley by 

 8| bushels ; or, in round numbers, the removal of 10 tons of 

 roots has occasioned a loss of 9 bushels of barley. 



It is obvious that the barley crop has been much more 

 affected by the removal of the roots on the poorer than on 

 the richer land. The average loss of barley on the highly 

 manured plots is, however, possibly too low, as in two years 

 (1858 and 1889) out of the eight the removal of the roots did 



