CALCIUM SULPHATE. 155 



even on calcareous soils when the latter is deficient in sulphuric acid. 

 If we calculate the amount of sulphuric acid removed from the soil by 

 crops we get the following figures per hectare: 5'8 kilogrammes for 

 grain crops, 6-1 kilogrammes for leguminous seed crops, Id-l kilo- 

 grammes for leguminous fodder crops, 7 kilogrammes for industrial 

 plants, 43-4 kilogrammes for root plants, 12 kilogrammes for tubers. 

 These amounts of sulphuric acid must therefore be returned to the 

 soil, as well as the other elements recognized as indispensable to 

 vegetable life. The analyses of the ash show that all plants have not 

 such an affinity for salts containing sulphuric acid ; thus plaster does 

 not produce the same effect on different crops. Plastering, which is 

 excellent for leguminosse, is of less value to cruciferse, tobacco, flax, 

 hemp, millet, and only slightly improves cereal crops. On the other 

 hand, plastering is capable of quintupling the crops of leguminous 

 fodder plants, such as lucerne, sainfoin, trefoil, and tares. Plaster has 

 thus an indirect action on the composition of the soil in rendering 

 soluble and assimilable for plants the compounds in the soil which 

 contain potash. The property which sulphate of lime possesses of 

 rendering the potassic compounds diffused through certain soils soluble 

 has been recognized by Peters. Deherain has shown that when 

 plaster is added to the soil the formation of sulphate of potash is 

 induced, and it is found that trefoils manured with plaster contained 

 more potash in their ashes than the check samples. The sulphate of 

 potash forms in contact with the carbonate of lime which encloses and 

 renders the humic matter insoluble, carbonate of potash, M^hich dis- 

 solves the humus. Owing to this action plaster is especially favourable 

 on soils rich in humus. But argilo-calcareous and silico-argillaceous 

 soils, impermeable, humid, and cold vitiate this action. Plaster can 

 thus not only improve the crops which require its constituent elements, 

 lime and sulphuric acid, but likewise those which require potash or 

 humus. It acts, therefore, with advantage on soils rich in humus or 

 well-manured ground. Applied in large doses along with good manur- 

 ing plaster gives excellent effects in vine-growing. It is the chemical 

 analysis of the soil and that of the ash of plants which can alone 

 furnish information as to the necessity for plastering and on the 

 quantity to spread on the fields, for the proportions of plaster to use 

 in all soils cannot be given exactly. Muntz and Girard advise massive 

 doses at distant intervals owing to the comparative solubility of sulphate 

 of lime. On the other hand, they recommend only to make 

 plastering really useful to the growing plant at the moment of spread- 

 ing. This treatment will, therefore, be every two years for hardy 

 leguminous plants, such as lucerne ; for meadows, which form part of a 

 rotation, plastering is only done when their turn comes round. When 

 clover is grown with a grain crop it is better not to plaster the ground 

 until after the grain crop has been harvested, and not at the time of 

 sowing the seed so that the treatment may only benefit the leguminous 

 crop. As already said, it would likewise be well for the vine-grower 

 to use plaster along with abundance of manure. The average dose 

 per hectare is 400 kilogi-ammes the first year and 200-300 kilo- 

 grammes the following year. The most favourable time for plastering 



