WATER-CULTURE METHOD — HOAGLAND AND ARNON 471 



tank-culture technique was larger than any heretofore reported as 

 obtained by this method. The yield from the soil-grown plants, 

 however, was not significantly different from that of the plants grown 

 by the tank method (pi. 3). When the greenhouse yields of tomatoes 

 from either soil or solution-grown plants were computed on an acre 

 basis and compared with average yields of field-grown tomatoes, the 

 greenhouse plants gave far greater yields. But as already suggested, 

 such comparisons have no direct practical significance because of the 

 differences of climatic factors, cultural practice, and length of season 

 in the greenhouse and in the open field. 



In one California commercial greenhouse, the yields of tomatoes 

 grown in soil were of the same magnitude as those obtained in a 

 successful commercial greenhouse employing the water-culture pro- 

 cedure, and in another greenhouse using soil the yields were larger. 



Eecently, data have become available on yield of potatoes grown 

 in a bed of peat soil in Berkeley. This yield was as large as any 

 heretofore reported as produced by the water-culture method. 



The suggestion has sometimes been advanced that plants can be 

 grown more closely spaced in nutrient solutions than in soil, but no 

 convincing evidence of this has been given. In our experiments, we 

 were able to grow tomato plants as close together in the soil as in the 

 solution (pi. 3). The density of stand giving the highest yields 

 would be determined by the adequacy of the light received by the 

 plants when growth is not limited by the supply of nutrients or water 

 derived from either soil or nutrient solution. Closeness of spacing 

 under field conditions is, of course, limited by practical considerations 

 involving cost of crop production. This consideration of economic 

 factors and of the adequacy of light for plant growth does not justify 

 the view that the water-culture medium is better adapted than soil to 

 growing several different crops simultaneously in the same bed. 



Published pictures of tomato plants grown in water culture show 

 impressive height, and this growth in length of vines is frequently the 

 subject of popular comment. As a matter of fact, the ability of 

 tomato vines to extend is characteristic of the plant and not peculiar 

 to the water-culture method. Staked plants grown for a sufficiently 

 long period in a fertile soil, under favorable light and temperature 

 conditions, can also reach a great height and bear fruit at the upper 

 levels (pi. 4). In commercial greenhouse practice, growers usually 

 "top" the vines. Fruit developed at higher levels is likely to be of 

 inferior quality, and relatively expensive to produce because of labor 

 required to attach supports to the vines, and the inconvenience of 

 harvesting. Furthermore, it may become profitable to discontinue 

 the tomato harvest when prices become low in the summer and use 

 the greenhouse space to plant another crop for the winter harvest. 



