280 PHOSPHORUS 



had been dosed with 10 mc or to feed on P^--labeled raisins, flowers, or 

 sugar solutions. Counting measurements were made directly on live 

 mosquitoes, and no self-absorption corrections were necessary. 



A typical fertilizer experiment, one of numerous similar studies that 

 have been undertaken all over the country, may be described as follows 

 (P-16) : A factorial design including placement and source was employed 

 with sugar beets, wheat, and barley. Placements were (a) phosphorus 

 mixed in a band 4 in. wide and -i in. deep (2 and 4 in. for wheat and barley) 

 and (6) phosphorus placed in a single band 4 in. deep and 4 or 5 in. to one 

 side of the row on beets. The materials studied were superphosphate, 

 calcium metaphosphate, dicalcium phosphate, and alpha tricalcium phos- 

 phate applied at the rate of 40 lb P2O5 per acre and with an activity at 

 planting time of about 0.1 mc/g P2O5. Each sugar beet plot was eight 

 rows wide and 64 ft long, and three rows 32 ft long were treated with 

 radioactive fertilizer. The wheat and barley plots were 41 ft long and 

 six rows wide, and one row of each crop 17 ft long was treated with radio- 

 active fertilizer. The dates of planting were Apr. 24 to May 3, and the 

 last sampling dates were Sept. 13-14. 



Much of the counting of plant material has been done by the briquet 

 method (P-17), since Httle effort is required in preparation of the sample. 

 A modification to increase the sensitivity has been suggested which 

 involves preparation of a cylindrical briquet and counting with a cylin- 

 drical thin-wall tube (P-18). A solution-counting technique for plant 

 materials has been described (P-19). Samples containing 1 to 30 mg P 

 were heated in 50-ml pyrex beakers at 500°C for 6 hr, and HNO3 was 

 added, evaporated to dryness, and heated at 400°C for 15 min to destroy 

 organic matter completely. Concentrated HCl was used to dehydrate 

 the siHca, and the residue taken up in 2 A'' HNO3 and made to volume, an 

 aliquot of which could be used for chemical determination. A convenient 

 arrangement of dipping Geiger tube and solution holder was used which 

 required 9 ml of sample. It was pointed out that the K^° contribution 

 could be neglected unless the P'*' sample count was only a few times 

 background. The K*" was easily corrected for, if necessary, by counting 

 a plant sample that had not received P^^ 



P^Mabeled phytin for use in poultry-nutrition experiments was pre- 

 pared from a crop of corn grown in gravel culture beds and nutrient solu- 

 tion (P-20). When the kernels were in early milk stage, the nutrient 

 solutions were replaced with tap water containing 166.25 mc P^' per 

 42 liters, equivalent to 38 g KH2PO4. The crop was harvested 31 days 

 after P^^ administration, and calcium phytate was isolated containing 

 about 470 counts/min/mg. 



A typical study of plant uptake from nutrient solution may be described 

 as follows (P-21) : Maize plants were grown individually in 1-gal crocks 



