No. 63.] 253 



did little for the natural grasses. All these, however, are powerfully 

 affected by stable manure — by the very ammonia* which that manure 

 yields. And what do we observe? Clover of luxuriant growth, and 

 close along side of it, wheat without any indication of benefit re- 

 ceived, though both have been plastered alike. 



Again — Professor Liebig informs us that every shower of rain or 

 fall of snow, brings down ammonia to the ground where the plaster 

 ought to arrest it, and the plants that feed on it ought to be more 

 thrifty; but we have much testimony to show that on many fields no 

 trace of such improvement could be discovered. These facts may 

 not be inexplicable, but they appear to me at present, quite sufficient 

 to hang a doubt on. 



I am aware that we have statements in regard to the use of plas- 

 ter, of the most conflicting kinds, so that with some few exceptions, 

 what one denies another affirms; but would this be so if it acts sole- 

 ly in the manner described by Professor Liebig? A simple cause 

 might be expected to produce a uniform effect. For instance: Pou- 

 drette is a simple cause, and as far as I have understood, it operates 

 with uniform eflfect, whether on clover, wheat or cabbages. 



On some soils, indeed, plaster is uniformly inefficient — not the 

 trace of any effect is perceptible. This inertness has been more fre- 

 quently observed in the tertiary formation near the sea coast, and 

 therefore it was ascribed to the salt vapors. 



Plaster, however, succeeds well in many places on the coast, and 

 fails in others far beyond the sea breeze, so that the cause seems to 

 reside in the soil and not in the air. 



There are several substances that decompose plaster, besides the 

 carbonate of ammonia. Carbonates of potash and soda have the 

 same power. In the hands of the chemist, plaster and common salt 

 readily change into sulphate of soda and chloride of lime; and Judge 

 Peters said, " I ruined a bushel of plaster by a handful of salt — it was 

 unfit for either cement or manure." Some of the oxalates also effect 

 its decomposition. 



When this happens, the plaster no longer exists, and most of these 

 results are not known to be of much value as manures. Such fail- 

 ures, however, rarely occur on calcareous soils, or on such as contain 

 a due proportion of lime. There plaster generally proves beneficial; 

 and even in England it has succeeded on such lands. Many years 

 ago, in the southeastern part of Pennsylvania, some farmers thought it 

 would supersede the use of lime; but it gradually lost its effect, re- 

 gaining it, however, when the land was limed. Wherever plaster 

 proves of no use, therefore, try liming. On a small scale, it may 

 be done at a trifling expense, and may lead to the most beneficial re- 

 sults. 



And remember that plaster must be dissolved before it can do any 

 good. Sometimes there is not rain enough for this purpose in sum- 

 mer, and therefore there is always a risk to sow it late in the spring. 

 Let it be done early. 



* " Animal manure acts only by the formation of ammonia."— Liebig,X,136. 



