PLASTER OF PARIS. 



PLASTER OF PARIS. 



Liebig contends that the nature of gypsum 

 consists in, its giving a fixed constitution to 

 the nitrogen, or ammonia, which is brought 

 into the soil, and is indispensable for the nutri- 

 tion of plants. He says, that 100 Ibs. of gyp- 

 sum give as much ammonia as 6250 Ibs. of 

 horses' urine would yield it : 4 Ibs. of gypsum, 

 he affirms, increase the produce of the mea- 

 dow 100 Ibs. The decomposition of gypsum 

 is slow, which, he says, explains the reason 

 why the action of gypsum lasts for several 

 years. See AMMONIA. 



I have noticed, in applying gypsum to 

 grasses, that the weather, at the time of 

 spreading it, has a very material influence 

 upon the result of the experiment. Its effects 

 are never soon apparent when it is sown in 

 dry weather; but if the season is damp, so that 

 the white powdered gypsum adheres to the 

 leaves and stalks of the-young grass, the good 

 effect is then immediate. This observation 

 was made many years since by Arthur Young, 

 by Mr. Smith, and by the American farmers : 

 it is a well-known fact with the sainfoin grow- 

 ers, of the Berkshire and Hampshire chalk 

 formation ; the clover cultivators of the gravels 

 and loams of Surrey and Kent; and on the lu- 

 cern grounds of the alluvial soils of Essex and 

 Middlesex. The farmers of the United States, 

 when dressing their clover or turnips with 

 gypsum, always found it answer best when 

 spread in rainy weather. 



The result of the analysis of the clover and 

 sainfoin grasses shows that an ordinary crop 

 of these usually contains from 1 to 2 cwt. per 

 acre of sulphate of lime. Now, this is pre- 

 cisely the proportion of gypsum which the best 

 cultivators find to be attended with the maxi- 

 mum benefit; those of Kent and Hampshire 

 find it useless to apply more ; but then they 

 all agree that the annual repetition of the 

 dressing, as long as the grass is suffered to re- 

 main on the ground, is attended with renewed 

 benefit. It is here again that the experiments 

 of the chemist and the farmer mutually con- 

 firm and illustrate each other; the very quan- 

 tity of sulphate of lime which the first shows 

 to beftarried off the land in the clover, is pre- 

 cisely that which the latter returns to it in his 

 dressings with gypsum. 



One of the chief reasons why gypsum has 

 not been universally employed by all cultiva- 

 tors of the artificial grasses, arises perhaps 

 from the fact that many good soils naturally 

 contain sulphate of lime in sufficient abun- 

 dance for the service of the plant; and, in con- 

 sequence, to such lands the application of gyp- 

 sum is useless it is an attempt to supply a 

 deficiency which doe not exist. I have inva- 

 riably found in those soils to which gypsum is 

 not a manure an abundance of this salt. It is 

 not, however, necessary for the farmer to have 

 his soil analyzed to determine the probable ad- 

 vantages of applying gypsum to his clover and 

 other grasses; there are several easy observa 

 lions which will readily indicate to him the 

 nature of the case. Thus, when he finds that 

 those fields which once produced luxuriant 

 crops of red clover or sainfoin will no longer 

 yield them in abundance ; if he notices that the 

 voung plants soring up very numerously, but 

 898 



die awa, as the summer advances ; if he finds 

 that his fields will only grow clover success- 

 fully once in 8 or 12 years, and that his neigh- 

 bours tell him his land is tired of clover, or "clo- 

 ver-sick ;" if he notices that even the application 

 of farm-yard compost hardly adds to the luxu- 

 riance of his grasses ; he may then safely con- 

 clude that his crops have gradually exhausted 

 his land of sulphate of lime ; and he may, with 

 every confidence of success, apply a dressing 

 of gypsum, at the rate of 2 cwt. per acre, taking 

 care to choose a wet morning for the applica- 

 tion; and this may be done at any season of 

 the year, but it is best either in April or the 

 first days of May. These facts I can attest 

 from the results of my own observations and 

 experience. In an old grass paddock, of about 

 70 acres, in the vale of Kennett, in Berkshire, 

 the grass had for many years gradually be- 

 come less and less productive, and this in spite 

 of all kinds of applications ; the earths (such 

 as clay and chalk), farm-yard compost, &c., 

 had been liberally and repeatedly spread, with- 

 out producing any thing like a luxuriant crop: 

 but it was found at last that the peat ashes of 

 the banks of the Kennett, when spread at the 

 rate of about 40 bushels per acre, produced the 

 very best results, an excellent crop, both in 

 weight and in colour; certainly more than a 

 ton of hf y per acre beyond what the soil yield- 

 ed before. The fact was now evident that it 

 was gypsum that the soil needed; for as these 

 peat ashes contain about 12^ per cent, of sul- 

 phate of lime, more than 2 cwt. of gypsum was 

 conveyed into the land in them ; it constitutes, 

 in fact, by far the chief fertilizing ingredient 

 in these peat ashes, the remainder being about 

 40 per cent, of sand, and the rest chalk, red 

 oxide of iron, and a small quantity of common 

 salt. 



If this conclusion, therefore, was correct, as 

 to the gypsum being the only valuable portion 

 of the peat ashes, it was certain that an appli- 

 cation of 2 cwt. per acre of gypsum to the same 

 land would produce similar beneficial results; 

 and, upon a trial, it was found that benefits 

 fully equal to any yielded by the application 

 of the peat ashes resulted. 2 cwt. per acre of 

 gypsum, in fine powder, was spread on a por- 

 tion of the grass with the most excellent effect: 

 the grass not only grew with greatly increased 

 vigour, but a quantity of white clover and 

 other grasses made their appearance on the 

 portion dressed, in so marked a manner as to 

 attract the attention of the tenant to the fact. 

 The soil on which these experiments were tried 

 consists of 



Parts. 



Organic matter, chiefly vegetable - - 3*5 

 Soluble matters - - - - - 3- 



Carbonate of lime and magnesia - - 19* 



Oxide of iron- ----- 275 



Alumina ------ 8'5 



Sand and gravel ..... 62- 



98-75 



This is about 10 inches deep, and it rests on a 

 thin stratum of gravel and thin chalk. 



There is another fact which clearly sup- 

 ports these conclusions, viz., the great use of 

 common coal-ashes as a top-dressing to clover, 

 i sanfoin, and lucern ; there is no manure uni- 



