FERTILIZER EXPERIMENTS. The investigations of the agricultural chemist in studying the fer tilizer requirements of different crops, the value of different forms of plant food and their effect on the quality of the crop, and a wide iange of similar problems, are conducted either in pots or in plats in the field. The preliminary studies are often made in pots or boxes, filled with sterile sand, to which definite amount: of humus and fertilizers have been added. The conditions are under complete control, and every part of the plants can be saved for analysis. These pots are usually mounted on trucks, so that they can he plaeed under cover at night or during a rain. The plat work is especially for testing theories under field conditions, studying fertilizer requirements, the draught of different kinds of crops, the changes in humus content and fertility of the soil under various systems of treatment, and the like. The plats are most commonly about one-tenth of an neve in area, selected with much attention to uniformity of the soil, and often under-drained and provided with basins for collecting the Ira lunge water front each plat. Great care is exercised in pre paring the land, applying the fertilizers, culti vating the (Tops. and harvesting them, so as to have the treatment of all uniform except as re gards special experimental feature. For studying soils in the field. samples are taken at intervals with a tube specially made for the pur pose, xvhieli is driven into the ground to the depth required, removing a core of the soil. These sam
ples are taken to the laboratory and tested or analyzed. These studies of plant production and soil fertility have been neeompanied by a gradual refinement of methods, and a great deal of inves tigation has had purely that aim. The field covered has been very broad. and has not always heen strictly chemical. Por example, the discovery of the ability of leguminous plants (clovers, peas, and the like) to appropriate to their use the free nitrogen of the atmosphere. and thus, under cer tain conditions. to enrich the soil with nitrogen the most expensive fertilizing element) from the air, was made by a German agricultural chemist. who also demonstrated the agency of bacteria in bringing about this assimilation. See also GREEN I:\ 1ANFRING ; POTATION OF CROPS.
BIBLIOGRAPHY. Among the more important Bibliography. Among the more important treatises on agricultural chemistry, the following may he mentioned: Johnston, Lectures on the Application of Chemistry and Geology to Agri culture (New York, 1850) ; Johnson, //o• Crops Pied (New York, 19001 ; .Tohnson. flow Crops Grow (New York, 1900) ; Storer. Agriculture in Sonic of Its Relations with Chemistry (New York, 1897) ; Wiley, Principles mul Practice of Agricultural Analysis (3 vols., Easton, Pa.. 1894 :17 ) ; Dehilrain, de chintie agricole ( Pa ris, 1892 ) Sachsse. Lehrbach der Agrieulturehemic (Leipzig, 1888) ; Mayer, Lehrbuch der Agricul turchemic (Heidelberg, 1895). See Fool): and the special articles upon the principal foods.