178 SOILS AND FERTILIZERS 



Basic Slag 



This form of phosphoric acid appears as a dry, dark gray powder 

 with a slight odor. If differs from cyanamid in that it does not 

 stain the fingers upon handling. It is alkaline to litmus paper. 



Test for phosphates as under phosphate rock. 



Acid Phosphate 



This fertilizer is a slightly deliquescent salt, brownish gray in 

 color, and finely ground. Its odor is characteristic and serves to 

 distinguish it from ground rock. Unlike floats it is partially soluble 

 in water. 



Dissolve a small amount in water. Filter and test the filtrate for 

 phosphoric acid as described above. 



Exercise III. — Comparison of fertilizer effects on plant 

 growth. 



Materials. — Fertilizers, flower pots, poor sandy soil, oat seed. 



Procedure. — The comparison of the various phosphorus fer- 

 tilizers upon crop growth, especially acid phosphate and raw rock, is 

 a valuable experiment. Fill the required number of flower pots 

 with the same amount of a poor sandy loam after thoroughly 

 mixing the fertilizer with the soil. Apply the phosphorus ferti- 

 lizers at the rate of 250 pounds per acre (1 of fertilizer to 10,000 

 of soil). Also add at the same time sodium nitrate and muriate 

 of potash at the rate of 1 of fertilizer to 5000 of soil respectively. 

 Apply one gram of lime per pot. Leave one pot untreated with the 

 phosphorus fertilizers as a check. 



Now plant the oat seed and raise the soil to optimum moisture. 

 When seedlings are a week old, thin to required number. Keep 

 pots under suitable conditions and observe relative development of 

 the various treatments. 



