Jan., 1916] Renewal of Plant Nutrients 103 



The surplus water is then drawn out of the pot by appH- 

 cation of suction (by means of an aspirator) to the tube at 

 the bottom and a thin layer of the melted wax is flowed over 

 the surface, completely covering the surface of the sand between 

 the funnel and the wall of the pot. Care should be taken not 

 to have the wax too hot otherwise the seedlings may be injured 

 at the point of contact between the wax and the plant. The 

 surface must be sealed to prevent loss of water by evaporation 

 from the surface of the sand and of course the walls of the pot 

 must be impervious to moisture in order that transpiration can 

 be measured and the concentration of the nutrient solution 

 controlled. The pot is now ready to receive the nutrient solu- 

 tion, which is added through the funnel at the top while the 

 water is being removed at the bottom by the application of 

 suction to the outlet tube. A double or triple portion of the 

 nutrient solution is passed through the sand at this first appli- 

 cation in order to flush out the distilled water. The pot is now 

 placed on the scales and the removal of solution is continued 

 until the sand has been reduced to the desired moisture content 

 which should be as near the optimum as possible. At the end of 

 each three-day period the pot is weighed and sufficient water is 

 added through the funnel to bring the system back to its 

 original weight. A fresh nutrient solution is now added in the 

 desired amount (250 cc. for pots of this size) , while an equivalent 

 amount of solution is removed at the bottom. A nutrient 

 solution of the same concentration may be used throughout the 

 entire growth period or it may be varied from time to time as 

 the plants continue to develop. 



The plants may be harvested at any time by removing the 

 wax seal and cutting off the plants level with the surface of 

 sand and, if desired, the roots may be recovered from the sand 

 by washing them out with a jet of water. The weight records 

 will give the transpiration of each culture and the harvest 

 records can be made to include the dry weights of both tops and 

 roots. This method also furnished a means by which the 

 original concentration of the solution can be compared with its 

 concentration after contact with the soil and with the plant 

 roots. The method is superior in many ways to water cultures 

 because it permits the plants to be grown under conditions that 

 approximate those found in the field, so far as the sub stratum 

 is concerned, and it seems probable that with some slight modi- 

 fications which are now in progress it will be possible to apply 

 the method to cultures grown in sandy and sandy loam soils. 



Department of Agronomy, Ohio State University. 



