88 IMPROVEMENT OP THE SOIL 



rant. Effete lime and marl are more certain in their 

 effects, when judiciously employed. They seldom fail 

 to benefit any soil not highly charged with calcareous earth. 



In the application of all mineral manures, of concen- 

 trated animal manures, and even of yard-dung, upon which 

 fermentation has exhausted its powers, one rule applies, 

 viz., that they should be blended, as intimately as is prac- 

 ticable, with the surface of the soil, in preference to being 

 buried deep with the plough. The tendency of all of 

 them is to sink. 



Lime is not only an alterative, rendering a cohesive 

 soil more porous, and a porous soil more compact, but it 

 changes and neutralizes many matters that often abound 

 in soils, that are deleterious and hurtful to farm-crops ; — 

 as, for instance, some of the acids, and the oxydes of iron 

 and other salts. In this way it destroys sorrel, and often 

 converts a barren ferruginous soil, charged with the oxydes 

 of iron, into one of fertility. The prevailing opinion is, 

 that lime soon loses its caustic quality, however fresh 

 from the kiln, when it is either spread upon the surface 

 of a field, or buried in the soil ; and that its principal 

 benefits to agriculture result rather from its use as a car- 

 bonate, than from its caustic properties. 



Gypsum^ or plaster of Paris^ is lime combined with 

 sulphuric acid. Common limestone is called carbonate 

 of lime, from the union of carbonic acid with the base. 

 Gypsum is called sulphate of lime, from the acid which 

 it contains. This substance exists in soils, is found in 

 plants, and is consequently contained in manures ; yet it 

 is applied to certain crops, upon dry, sandy, and gravelly 

 soils, with almost certain advantage — except on the sea- 

 board — and the poorer the soil the more apparent its 

 benefit — probably because such soils contain little or no 

 gypsum, and have received little or no manure. Its 

 mode of operation is yet matter of dispute. Sir H. Davy 

 considers it a necessary element in some kinds of plants ; 

 and his opinion is strengthened by the facts, that its ap- 

 plication proves beneficial to such crops as afford it on 

 analysis, as clover, lucerne, Indian corn, and broad-leaved 

 plants generally ; that it is seldom of direct benefit to 



