154 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



oped facilities and methods for the production of a variety of labeled com- 

 mercial phosphate fertilizers — normal phosphates, concentrated and 

 ammoniated superphosphates, and various combinations of calcium and 

 phosphates. The individual laboratory should attempt to obtain its 

 labeled fertilizers from the Department of Agriculture before making its 

 own preparations. Differential fertilizer placement machines have been 

 developed which are adeciuate for the field application of radioactive fer- 

 tilizers (47, 48). 



It will be recalled from Chap. 1 that important studies of rooting pat- 

 terns have been made possible by the delivery of radiophosphorus to 



H C) 



tC 





G 



Fig. 4-25. Schematic diagram of probe for placement of P^^ solution at specified loca- 

 tions in soil. Typical dimensions: length, 3 ft; outside diameter, % in.; head, P^ in. 

 from ports to tip. {From N. S. Halt, W. V. Chandler, C. H. M. van Bavel, P. H. Reid, 

 and J. H. Anderson, A Tracer Technique to Measure Growth and Activity of Plant Root 

 Systems, N. Carolina Agr. Expt. Sta. Tech. Bull. 101, October, 1953.) 



known locations in the soil around the plant. The technique of delivery 

 has been described by Hall et al. (49). Figure 4-25 presents a schematic 

 diagram of the probe employed. It is important that the diameter of the 

 collar C be slightly larger than that of the shaft, and that the head H and 

 the shaft be of the same diameter. The shaft should have a small diam- 

 eter but should be sufficiently rigid to withstand bending upon insertion 

 into the soil. Usually ^-s-i^^- pipe is satisfactory, but greater rigidity 

 would be desirable in heavy soils. The rubber cap G provides a seal for 

 the hypodermic needle and allows pressure to be applied to clear the 

 outlet ports P. 



The probe is usually inserted to the required depth and then pulled 

 back about 3^^ in. The solution containing the tracer is drawn into a 

 hypodermic syringe with a No. 22 needle and then injected through the 

 rubber cap G. The injection rate should be such that the liciuid pen- 

 etrates the surrounding soil and is not forced back up the channel made 

 by the probe. 



GENERAL REFERENCES 



1. Coleman, H. S., ed.: "Laboratory Design," Reinhold Pviblishing Corporation, 

 New York, 1951. 



2. Manov, George G.: Radioisotope Laboratories for Animal and Agricultural 

 Research, in "The Role of Atomic Energy in Agricultural Research," Proceedings 



