AGRICULTURAL CHEMISTRY

That branch of the science which concerns itself with the composition of the soil, fertilizers and manures, the nutrition of plants and animals, the composition of agricultural products and their value as food. One of the earliest investigators into the relation of the composition of soil to plant growth was Sir Humphrey Davy, who published the result of his researches in 1814. He attached great importance to the presence in the soil of ‘humus,’ or partially decomposed organic matter, and formed the theory that plants derived the carbon of their structure from it. Liebig, however, showed in 1840 that plants derive their carbon from carbonic acid in the air. Neverthele , the presence of humus is still held to be of great value in enabling the soil to retain moisture, in improving its physical condition, and in promoting the growth of certain bacteria which are of value in producing substances on which the plant feeds. From the soil the plant derives its nitrogen and its mineral constituents, which include lime, magnesia, potash, soda, iron, silica, chlorides,*.carbonates, sulphates and phosphates. The most important constituents of a fertilizer are nitrogen, potash and phosphates. The first promotes the growth of leaves and stems, the second of roots, the third of flowers and fruits. The analysis of a fertilizer concerns itself chiefly, therefore, with these three constituents. The analysis of foods concerns itself with the percentage of nitrogenous matter, or proteid, of fat, of carbohydrates (starch and sugar) and of fibre. One of the most important branches of agricultural chemistry is the investigation of the effect of certain feeding stuffs upon the health and growth of an animal, or in the case of cows or hens, of their output in mill - or eggs.