A CLOVEK-SICK FIELD. 159 



efit from this manuring only in the first stage of devel- 

 opement, while the condition of the lower layers re- 

 mained unaltered, just as if the field had received no 

 nutriment of any kind. 



The manures applied by Messrs. Lawes and Gilbert 

 were superphosphates of lime (300 Ibs. of bone-earth 

 and 225 Ibs. of sulphuric acid per acre) ; sulphate of 

 potash (500 Ibs.) ; sulphate of potash and superphos- 

 phate, mixed alkaline salts (500 Ibs. of sulphate of pot- 

 ash, 225 Ibs. of sulphate of soda, 100 Ibs. of sulphate of 

 magnesia) ; mixed alkalis with superphosphate ; fur- 

 ther, salts of ammonia alone, and the same salts with 

 superphosphate or mixed alkalis ; farm-yard manure 

 (15 tons), together with lime, or with lime and super- 

 phosphate, or with lime and alkalis in the most varied 

 proportions ; then soot ; soot with lime ; soot with 

 lime, alkalis, and superphosphate. None of these ma- 

 nures had the slightest effect ; the clover-sick field con- 

 tinued just as unproductive for clover as before. 



The reason why these manures were inoperative is 

 not difficult to find. Messrs. Lawes and Gilbert, in 

 their report, leave us, indeed, in the dark as to the na- 

 ture and condition of the soil upon which their experi- 

 ments were made ; but from some incidental observa- 

 tions in previous papers, we know that the fields at 

 Rothamstead consist of a rather heavy loam, very well 

 suited for cereals, and especially for barley. 



From experiments upon the absorptive power of 

 loam, we may assume, without risk of error, that one 

 cubic decimetre (=61 cubic inches of loam) will absorb 

 2000 milligrammes (=31 grains of potash), and 1000 

 milligrammes (=15*5 of phosphate of lime). 



The surface of an acre of loam (405,000 square 

 decimetres) will therefore absorb to a depth of 1 deci- 

 metre (=4: inches) 805 kilogrammes (=1,771 Ibs.) of 

 potash, and 405 kilogrammes (=891 Ibs.) of phosphate 

 of lime. 



The most copious dressing with sulphate of potash 

 which Messrs. Lawes and Gilbert gave to their field 

 amounted to 500 Ibs. ( =270 Ibs.) of potash ; the most 



