the past several years many individuals DURING have done experimental work in the growing of plants without soil. Water culture, hydroponics, soilless growth, gravel culture, nutrient solution culture are some of the names that have been applied to this type of growing. Among these experimenters have been several companies with the idea that these methods might be of commercial importance. This paper deals with the present developments that are being carried on a t J. W. Davis and Company in Terre Haute, Indiana. Their greenhouses cover about 35 acres where only tomatoes and cucumbers are grown. The author is a high-school chemistry teacher who accepted the job as chemist for these experiments as a part-time job, when their regular chemist went to the Navy. The original investigations a t this plant were carried on by Kendrick Blodgett, who now is doing hydroponic work for the Army in the Ascension Islands. This work was continued by Keith Owen, Jr., who now is in the South Pacific. The previous work done has more or less standardized the procedures we use in the growing of our specialties.
But there are numerous factors that make this field an interesting and challenging one. Let us first consider the mechanical problems involved in this type of plant growing. There are two methods in common use. One is the supporting of the plants in gravel, and irrigation of these plants by flooding with the nutrient solution. The other method is the supporting of the plants over a constantly moving nutrient solution, on wire netting, and letting the roots drop into the solution. The netting must he covered with straw or some material to keep out the light and prevent the formation of algae. I t is important to have the tanks so constructed that there will he good drainage toward one end, so that the solutions may be used again. Also, these tanks must be made or lined with some inert material, as should all the equipment that comes into contact with the nutrient solution, unless it is cast iron. We use asphalt very satisfactorily for this purpose. Each of these methods has some advantages and disadvantages in operation and cost, and some types of plants seem to do better with one method than the other. For example,
it is apparent to us that tomatoes do better in the gravel culture than in the water culture. It is impossible to give the details of our equipment, but we have several hundred cucumber plants and several hundred tomato plants growing in each type of culture. Let us consider next the elements that are necessary for plant growth. All investigators are of one accord on having available the major elements, nitrogen, phosphorus, and potassium, but they are not agreed as to optimum amounts. As for minor elements essential for plant growth, there is great variance in opinion as to kinds as well as amounts that should be used. The formulas that we are satisfactorily using follow those suggested by R. B. Withrow and T. M. Eastwood in a pamphlet "Nutrient Solution Culture of Greenhouse Crops" from the Agricultural Experiment Station, Purdue University, Lafayette, Indiana. These formulas call attention to the necessity of having magnesium, calcium, manganese, and iron available for the plants. Of course, the presence of other elements may be advantageous but only experimental work can reveal whether some particular element will help or hinder the growth of a plant. We have almost concluded that in the case of tomatoes our water supply furnishes a sufficiency of all minor elements except iron and mafiganese. As already suggested, the workers in this field are not in agreement as to the best concentrations of nutrient elements for plant growth. It is apparent that there are desirable variances in concentration as the plant matures. There are probably countless other helps which someone will find some day. Oxygen concentration should be on the order of from four to eight parts per million, as determined by
the Winkler method. But if there is reasonable agitation this will prove no problem. The chief job that the author has is maintaining the correct concentration of salts in the nutrient. Analysis of the solutions and determination of amounts of salts present is done by standard colorimetric reactions and comparison with known standards. Space does not permit the inclusion of these tests but they are available.' Numerous experiments on the behavior of a variety of chemical agents on the growing plant have been carried out. For example, we are using indole butyric acid emulsions on the bloom to set the fruit, as well as to induce parthenocarpy. This operation works well for the tomato and can be used successfully on a large scale, although it requires a considerable number of hand operations. In conclusion, the work that the author has been doing in this field is extremely interesting. It has opened an entirely new field of thought for him, and has given him much experience which will be valuable in future teaching. This field seems to have definite commercial possibilities. It is not an easy, infallible method of satisfactorily growing any plant, for it requires much investigation to succeed. However, in some fields it has now very definite advantages over the traditional methods of growing, and as investigators continue their work it may rival growth in soil for many plants. 'THORNTON, S. E., S. D. CONNER, AND R. B. ERASER, "The Use of Rapid Chemical Tests on Soils and Plants as Aids in Determining Fertilizer Needs," Circular 204 from the Agricultural Experiment Station. Purdue University, Lafayette. Indiana.
GRAVEL C U L T ~AND E WATERC U L T ~ E .CUCUMBERS AT J. W. DAVISAND COMPANY, TERRE HAUTE, INDIANA
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