June 26, 1916 



Mineral Phosphates and Plant Nutrition 



505 



Series 8 shows that dextrose in conjunction with calcium carbonate 

 did not give as good results as raw rock phosphate alone, and that 

 10 gm. of calcium carbonate was not sufficient to nullify the harmful 

 influence of the dextrose. 



Series 9 (Table XIV), wnich follows, is just the same as series 8 

 except that cowpeas are substituted for rye, the object being to deter- 

 mine the relative response of rye and cowpeas to the different treatments. 



Table XIV. — Dry matter produced in cowpeas by Tennessee brown rock phosphate with 

 the addition of dextrose and calcium carbonate — series Q 



a See note to Table XIII. 



Series 9 shows that brown rock phosphate, dextrose, and a limited 

 supply of calcium carbonate failed to give as good results with cowpeas 

 as raw phosphate alone. For further comparison see Plate LXXVIII. 



Thus far it has not seemed necessary to use calcium carbonate alone, 

 because it was thought that the plants would get enough calcium, for 

 full growth from the phosphate, however, in order to avoid criticism at 

 this point calcium carbonate was added to certain pots in the following 

 series. The quantity of this compound was increased to 48 gm. per pot, 

 which is almost five times as much as the application in the preceding 

 series. 



By making a comparison of the pots which received raw rock phos- 

 phate alone and those which received raw rock and calcium carbonate 

 very little difference in the yield is observed, only 0.6 gm. more in favor 

 of the addition of the lime compound. There is no strong evidence in 

 Table XV to show that the omission of calcium was a mistake. Where 

 lime was applied with rock phosphate and dextrose, the injury by dex- 

 trose reported earlier was nullified by the application of lime (PI. 

 LXXIX and LXXX). 



Attention is called to the percentage of phosphorus in the cowpea hay 

 grown in the pots which received soluble phosphorus. 



