160 BOARD OF AGRICULTURE. 



failure of the attempt to keep his laud in clover. He relates 

 that in the rotations customarily practised in his neighbor- 

 hood, a good yield of clover can be relied upon once in six or 

 eight years. 



Dr. Riggs. The land was what they call " clover-sick." 



Prof. Johnson. " Clover-sick," and finally clover-dead ! 



Mr. Lawes made another interesting trial on a piece of orig- 

 inally similar ground, which had, however, been used as a 

 kitchen-garden probably for two or three centuries. It was 

 sown to clover early in 1854, and from this one sowing the 

 plant grew well, without further manure, for six years and 

 yielded in that time fourteen cuttings, at the rate of twenty- 

 six tons of hay per acre for the six years, or four and one- 

 third tons yearly. 



In discussing the causes of clover sickness, Mr. Lawes 

 suggested that the assumption that clover requires a portion 

 of food to be supplied by the soil in the form of certain or- 

 ganic compounds — vegetable matters or humus, such as are 

 contained in garden earth and come from the yard manure, 

 would perhaps explain why the crop failed on ordinary soil, 

 but should succeed in a garden which had been heavily ma- 

 nured perhaps for centuries. Mr. Lawes did not assert that 

 this was the reason, only that it might be. 



But I think we have facts enough to justify us in conclud- 

 ing that that is not the reason. When a student in Germany, 

 I saw an experiment by Dr. Wolff of tlie Academy at Ho- 

 henheim, which he was in the habit of making for the benefit 

 of his classes. He took a quantity of rather poor soil, and 

 calcined it in a clay muffle — a kind of oven which is heated 

 by fire burning all around it, so that its sides are brought to 

 a bright redness. This operation completely burned out all 

 the organic matter of whatever kind that was originally in the 

 soil. To that soil he added the various components of the 

 ashes of plants which are given in the table page 78, viz. : 

 lime, magnesia, potash, soda, phosphoric acid, etc., in proper 

 proportions, together with a certain quantity of saltpetre — 

 nitrate of potash — and in that soil he raised the most beauti- 

 ful clover. You can grow anything to perfection in that 



