PRINCIPLES OF TRACER METHODOLOGY 



51 



growing plant. A simple method for the study of rooting systems and 

 habits, utilizing radiopho.sphorus, has been described by Hall (129). In 

 essence, the procedure consists in injecting radiophosphorus into the soil 

 at specific locations relative to the plant and then determining the amount 

 taken up by the plant at different times by an analysis of leaf or root tis- 

 sue. A typical injection pattern as used in the study of cotton and 



^Plant 





Pattern • repeated 



Pattern • repeated 



Pattern * repeated 



12" 



16 



Fig. 1-9. Radiophosphorus injection pattern used for study of the root development 

 of cotton and tobacco. [From N. S. Hall, The Use of Phosphorus 32 in Plant Root 

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

 Fourth Annual Oak Ridge Summer Symposium {Sponsored by the Oak Ridge National 

 Laboratory and Oak Ridge Institute of Nuclear Studies, Aug. 25-30, 1952), TID-5115, 

 pp. 435-451, January, 1953.] 



tobacco is shown in Fig. 1-9 (129). This design required 20 different 

 placements and therefore 20 different plants for one complete experiment 

 (see Chap. 5 for experimental details). 



The following kinds of information can be obtained: (a) the time of 

 arrival of the roots at a given location in the soil, which is a measure of 

 the over-all growth and rate with which the root expands through the 

 soil volume; (6) the seasonal and soil effects on the root pattern; (c) the 

 time and manner of plant competition, which may lead to spacing recom- 

 mendations; (d) the effects of depth of tillage; (e) the relative importance 

 of various root segments for nutrient uptake; and (/) the efficiency of the 

 root system of a given species in utilizing added fertilizer under given 

 conditions. 



