WATER-CULTURE METHOD — HOAGLAND AND ARNON 481 



When large tanks are to be used with a porous bed, a heavy chicken- 

 wire netting (1-inch mesh), coated with asphalt paint, is fastened to 

 a frame and placed directly over the tank to provide support for the 

 porous bed. In constructing a frame, it is advisable to leave several 

 narrow sections not covered with wire netting, but with wooden covers 

 which can be conveniently removed for inspection of roots or for 

 adding water or chemicals. The wire netting should be stretched 

 immediately above the surface of the solution when the tank is full. 

 Cross supports may be placed under the netting to prevent it from 

 sagging (pi. 7). A carpenter or mechanic can design and build 

 suitable tanks and frames, which may take many forms. 



NATURE OF BED U 



When a porous bed is to be employed, a wire screen is covered by 

 a layer of the porous material 3 or 4 inches thick — thicker when 

 tubers or fleshy roots develop in the bed. Various cheap bedding 

 materials have been suggested: pine excelsior, peat moss, pine shav- 

 ings or sawdust, rice hulls, etc. Some materials are toxic to plants. 

 Kedwood should usually be avoided. One type of bed which has 

 produced no toxic effects in experiments carried on in Berkeley, with 

 tomatoes, potatoes, and certain other plants, consists of a layer of 

 pine excelsior 2 or 3 inches thick, with a superimposed layer of rice 

 hulls about 1 or 2 inches thick. For plants producing tubers of fleshy 

 roots, some finer material may possibly need to be mixed with the 

 excelsior. This is also essential when small seeds are planted in the 

 bed, to prevent the seeds from falling into the solution and to effect 

 good contact of moist material with the seed. In all cases, the bed 

 must be porous and not exclude free access of air. 



If seeds are planted in the bed, it must, of course, be moistened 

 at the start and maintained moist until roots grow into the solution 

 below. For the development of tubers, bulbs, fleshy roots, etc., 

 the bed should be maintained in a moist state, by occasional sprink- 

 ling. Great care should be observed to prevent waterlogging of the 

 bed, resulting from immersion of the lower portion of the bed in the 

 solution. This leads to exclusion of air and to undesirable bacterial 

 decompositions. 



PLANTING PROCEDURES 



Seeds may be planted in the moist bed, but often it is better to 

 set out young plants chosen for their vigor, which have been grown 

 from seeds in flats of good loam. Some seeds (for example, cereal 

 seeds) may also be conveniently germinated between layers of moist 



» The general arrangement of this type of bed was described by Gericke, W. F., and Tavernetti, J. R., 

 Heating of liquid culture media for tomato production, Agr. Eng., vol. 17, pp. 141-42, 184, 1936. 



