AGRICULTURAL EXPERIMENT STATION. 



143 



by the plants from the crude phosphatic rock, ainoimiing in the 

 case of the Caribbean Sea ^uano to enough to produce more than 

 an average crop of grain. 



Experiments with Feldspar as a Source of Potash. 



In connection with the experiments with finely ground phos- 

 phatic rock as a source of phosphoric acid for plants, pot experi- 

 ments have been undertaken to determine to what extent plants 

 can avail themselves of the potash of potash feldspar. The pots 

 used for the experiments were like those described above and used 

 in the phosphate experiments. They were also filled in the same 

 manner, having first a layer of gravel at the bottom and above this 

 65 pounds of quartz sand, with the last 35 pounds of which were 

 mixed the experimental fertilizers. 



Three pots 1, 5 and 9 were supplied each with 10 grammes of 

 feldspar carrying 11.61 percent, of potash, 10 grammes of nitrate 

 of soda and 10 grammes of acid South Carolina rock. Three 

 other pots 13, 17 and 20 were fertilized with 20 grammes of feld- 

 spar and the same amount of nitrate of soda and acid phosphate 

 as was supplied to 1, 5 and 9. In these pots were planted oats. 

 When the oats were two or three inches high they were thinned out 

 to 18 plants per pot. The pots were watered in the same manner 

 as were those in which the experiment with phosphates were 

 conducted. 



In the tables below are shown the results of substituting 

 muriate of potash for feldspar as a source of potash. 



Kind and qnautity of fertilizers. 



10 grains feldspar. 



10 ■• nitrate of soda, 



10 '• acid S. C. rock. 



20 grains feldspar. 



10 '•• niti-ate of soda, 



10 "■ acid S. C. rock. 



3 grams muriate of potash, 

 10 '' nitrate of soda, 

 10 '' acid S. C. rock. 





a 







2h 

 o 

 6 





?<H 



18.37 



1 



5 



14.37 



9 



19.43 



13 



17.28 



17 



16.78 



21 



16.83 



16 



22.88 



20 



18.85 



24 



21.37 



"g 



.2 'oa 



47 

 43 

 47 



47 

 47 

 52 



67 



72 

 65 



3 B 



