POROUS CLAY CONES FOR THE AUTO-IRRIGATION OF 



POTTED PLANTS 



BURTON E. LIVINGSTON 



The Johns Hopkins University, Baltimore, Maryland 



The auto-irrigator^ has been very extensively used in experi- 

 mental work with plant cultures where the soil moisture content 

 was to be maintained practically constant for long periods of 

 time, or where the tendency of the root system to remove water 

 from the soil was under investigation. As originally described, 

 this instrument consists essentially of oUe or more cylindrical 

 porous porcelain cups buried in the soil of the culture pot, the cup 

 being filled with water and connected (by rubber stopper and 

 tube) to a reservoir of water situated at a lower level. As water 

 is removed from the soil by the plant roots, or through direct 

 evaporation, the capillary equilibrium between the soil water and 

 the water imbibed in the porous porcelain of the cup is disturbed, 

 and water moves from the cup wall into the soil, the porcelain 

 being continually replenished from the cup cavity and eventually 

 from the reservoir. The soil moisture content when cup and soil 

 are in moisture equilibrium may have almost any value, accord- 

 ing to. the kind of soil employed and the height of the water 

 column connecting the cup with the reservoir.. When it is in- 

 convenient to give this column the actual height required, a U- 

 tube is inserted in the supply tube and sufficient mercury is placed 

 therein to give the desired pressure equivalent. Then all the 

 water absorbed by the soil is drawn from the reservoir against 

 a pressure equivalent to that of the water column plus that of the 



1 Livingston, B. E., A method for controlling plant moisture. Plant World 11: 

 39-40. 1908. Hawkins, Lon A., The porous clay cup for the automatic watering 

 of plants. Plant World 13:220-227. 1910. Livingston, B. E., and Lon, A. 

 Hawkins, The water relation between plant and soil. Carnegie Inst. Wash. Pub. 

 204: 1-48. 1915. Holmes, F. S., Moisture equilibrium in pots of soil equipped 

 with auto-irrigators. Johns Hopkins Univ. Circular, March, 1917, p. 208-210. 



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