REMEDIAL MEASURES 305 



" black alkali " ; the two substances interact to form sulphate 

 of soda and carbonate of lime. It takes, however, a large and 

 unprofitable amount of gypsum to effect this change, and a 

 more practical plan is always to use superphosphate as the 

 phosphatic manure on such land. The acid of the super- 

 phosphate will go to neutralise the alkaline carbonate of soda, 

 and the gypsum which is also present will aid in the desired 

 flocculation of the clay particles. Another remedial measure 

 is a liberal dressing of soot ; the particles of carbon have a 

 beneficial mechanical effect in lightening the texture of the 

 soil, and at the same time the ammonia salts that are present 

 in the soot are helpful in flocculating the clay. As a pre- 

 ventive, undoubtedly the simplest and wisest plan to follow 

 is to use on all strong soils, instead of nitrate of soda alone, 

 a mixture in equal proportions of nitrate of soda and sulphate 

 of ammonia, especially where considerable quantities of 

 concentrated /nitrogenous manure are required for market- 

 gardening purposes. Since one of these compounds tends to 

 produce an acid and the other an alkali in the soil, they 

 neutralise the effects of each other, and as far as the conditions 

 depend upon the manuring, such a mixture will not disturb 

 the reaction of the soil in one direction or the other. More- 

 over, there is a good deal to be said for the use of such a 

 mixture from the point of view of the nutrition of the plant ; 

 of course, the great value of nitrate of soda lies in its immediate 

 availability, but when too much is put on it may easily form a 

 solution that is injuriously strong in certain parts of the soil. 



Now the ammonium sulphate mixed with the nitrate of 

 soda would be to some extent temporarily withdrawn from 

 solution by the soil, so that an application of a mixture of 

 it with nitrate of soda would result in a less concentrated soil 

 solution than would be set up by an equivalent amount of 

 nitrate of soda alone. Yet the sulphate of ammonia would 

 begin to nitrify very rapidly, and would thus provide food for 

 the plant as the nitrate of soda was beginning to get exhausted. 



No inconveniences arise from making such a mixture ; it is 



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