174 THE YEAR-BOOK OF AGRICULTURE. 



somewhat dependent on the quantity applied, and must be materially influenced by the 

 weather in the second, third, and following seasons, as well as in the first. 



I have thus given a condensed statement of the results and opinions of practical men rela- 

 tive to the use of plaster. The conclusion adopted are those which are sustained by the ma- 

 jority of facts. It is apparent what uncertainty prevails 1 in our knowledge of this subject. 

 It remains, by means of new and more careful observations and by more rigid experiments, to 

 determine the actual value of these statements, and to acquire additional information. 



Hundreds of single results that have been published are of no value whatever in deducing 

 general rules, because the vagueness of many agricultural terms makes it impossible to know 

 what degree of truth a statement possesses. A soil is a very complex thing, and may include 

 many conditions which effect the action of a fertilizer ; yet in a report of a trial of plaster we 

 find nothing written of the soil except the prefix clayey, or sandy, or loamy. The important 

 characteristics upon which the whole result of the experiment hinges may never be recognised 

 nor mentioned ; and hence, while the fact is true that the crop was benefited or not, we have 

 no logical ground to assume that any of the mentioned causes or circumstances had any thing 

 to do with the effect, more than a number of other unnoticed causes which must have been 

 present and operative. 



Admitting that much remains to be learned, still it is evident that for practical purposes so 

 much may be accepted viz. : 



1. Leguminous plants are especially benefited by plaster, while 



2. All other plants of large foliage, whose agricultural value does not consist in the produc- 

 tion of seed, are usually aided by it in growth, upon 



3. Soils not already containing sulphate of lime, but 



4. In which all other parts of mineral plant-food are present in available form, and in suffi- 

 cient quantity ; which are, in practical language, well dunged, if not rich without manure ; 

 and which, further, 



5. Present no physical obstacles to vegetable growth which are dry, sufficiently porous, 

 and well tilled, when 



6. The climate and weather are favorable to vegetation, when the temperature is mild, and 

 rains are frequent but moderate. 



Does plaster exhaust the soil. This frequently-asked question is easily answered, and by 

 the word no. A soil is never exhausted by what is added to it, but always by what is re- 

 moved. But a little explanation is needed, for although plaster cannot exhaust the soil, 

 plastering is usually followed by exhaustion; and for the simple reason, that by its use 

 nothing but sulphate of lime (ammonia indirectly?) is added, while phosphoric acid, potash, 

 silica, &c. are removed. A purse soon gets empty if eagles are constantly taken out, though 

 cents be now and then put in. The crops which plaster enables the farmer to remove from 

 the soil exhausts it. Suppose that a few bushels of plaster raise the yield of clover upon a 

 field ten per cent. ; then, ten per cent, more of phosphoric acid, potash, &c. pass from the soil 

 into the crop than would have passed had no plaster been used. If plaster only be added, 

 then the field will be exhausted in one-tenth less time than if nothing at all had been applied. 

 In both cases, the total amount of vegetation produced until exhaustion supervenes will be the 

 same, and the amount of exhaustion the same. In the one instance, the final result might be 

 reached in ten years ; in the other, in nine years. The difference is merely one of time. If 

 benefit is to be derived from the use of plaster, it must be accompanied with other manure, or 

 its action, however good at first, will ultimately cease. Manuring a poor soil with nothing 

 but plaster is attempting to sustain vegetation on plaster alone ; and this, like feeding chil- 

 dren on little else than arrow-root, is a stupendous folly. It is trying to build brick houses 

 without brick. Plants cannot be made of sulphate of lime any more than men can be made 

 out of starch. "Out of nothing, nothing comes." The healthy plant is the result of the co-ope- 

 ration of many causes the coincidence of many conditions. One cause, one condition can only act 

 favorably when all the others but this are present. There is, there can be, no agricultural 

 panacea. 



