172 THE YEAR-BOOK OF AGRICULTURE. 



with help of gypsum ; for, as is well known, caustic lime expels ammonia from all substances 

 that contain it. 



What crops are benefited by plaster? It were not difficult to find authentic cases of plaster 

 having proved useful on almost every field crop, and there is no lack of instances in which it 

 has failed on every one. But the loose way in which thfe statements of farmers are often 

 given to the public makes many of them of little or no value. It is a well-recognised fact 

 that circumstances alter cases ; when we know the circumstances, we can understand the 

 difference in the cases. Usually, in the records of experience and experiment which we find 

 in the papers, so few circumstances are taken into the account that we are actually no better 

 enlightened at the end of the story than before ; there is no making out the case. This is 

 especially true of the statements with regard to plaster ; and hence we find contradiction upon 

 contradiction, and contradiction contradicted. It is not that statements do not contain the 

 truth ; they may contain nothing but the truth, but they rarely include the whole truth. This 

 is not at present to be entirely helped, but there is vast room for improvement. In attempt- 

 ing, therefore, to give a summary of the results of practice in the use of gypsum, it is only 

 possible to assume as facts those statements which have been confirmed by the according 

 voices of many observers. 



It is the result of all experience that plaster is especially advantageous to the cultivated 

 leguminous plants viz. clover, lucerne, esparsette, vetches, peas, and beans. Its effects upon 

 clover in particular have been remarkable. European writers assert that to gypsum is largely 

 due the introduction of clover into agriculture, and the many improvements that have 

 followed its cultivation. On other crops it seems to be beneficial only by way of exception, 

 and yet the exceptions are numerous and often striking. After the above-specified plants, 

 tobacco, cabbage, rape, hemp, flax, and buckwheat are mentioned by Girardin as benefited 

 by plaster. All writers agree that grain crops are rarely influenced by it. In the United 

 States, gypsum has been reported useful on almost all crops. It is a favorite application to 

 meadows. Professor Norton used to mention the case of meadows near Springfield, Massa- 

 chusetts, on which the mere application of a few bushels of gypsum (two to three bushels, if I 

 remember rightly) per acre ensured a good yield of grass, where otherwise the growth was 

 very inferior. It is also very common to apply a handful of plaster to each hill of corn and 

 potatoes at the time of planting, or when the plants are some inches high ; how often profit- 

 ably, we have no means of knowing. It has indeed been found useful on wheat. 



There is obviously need of new trials on every kind of crop. W reasonably hope one day to 

 learn under what circumstances plaster can be useful, even to those crops for which it is not 

 usually recommended. Undoubtedly, those conditions which cause the occasional failure of 

 plaster to benefit the leguminous plants, are closely related to those which make it more 

 generally unreliable when applied to other crops ; and the conditions that make it generally 

 useful to the former, make it sometimes valuable for the latter. 



What part of the plant is most developed by plaster ? With regard to this question, expe- 

 rience answers that the increased development of a plant consequent on the use of gypsum is 

 disproportionately great in the stem and foliage : the production of seed is not greatly in- 

 creased. This observation stands naturally connected with the fact that plaster is most effi- 

 cacious on those plants used for fodder which yield a large mass of vegetation, and least valu- 

 able on the grains which are cultivated mostly for their seed. Tobacco and maize, which 

 have much foliage and stem, potatoes, which develope much foliage under cultivation, and 

 produce fleshy tubers and little seed, are further examples. A few experiments are on record 

 in which plaster applied to peas produced a decided increase of straw, but hardly affected the 

 amount of seed. Stockhardt, however, says that the seed-production is usually increased, 

 though not proportionately to the straw. 



The effect of gypsum on the quality of the plant. Whether crops, which have attained a larger 

 growth in consequence of the use of gypsum, contain a larger proportion of sulphuric acid 

 and lime than similar crops produced by the same without plaster, is not yet fully ascer- 

 tained, since experiments made to determine this point have not agreed in their results. New 

 investigations would easily settle this matter one very important for the theory of the action 

 of plaster. 



