PRACTICE XXVII ( 



3. Thoroughly mix 5 g. of CaC0 3 with 50 g. of the same soil, and 

 allow a second 50-cc. portion of the double superphosphate solution, 

 diluted to 300 cc., to percolate through the mixture. Determine the 

 phosphorus in 100-cc. portions of the percolate, as directed above, 

 using 5 cc. of the ammonium molybdate solution. 



cc. HNO 8 cc. KOH to mg. P mg. P per 6 cc. 



used dissolve of percolate 



ppt. 



Av : 



Per cent phosphorus fixed by the limed soil 



Calculate the results obtained, and with these record the results 

 obtained by three members of each group, as indicated in the table 

 on the following page. 



Give the general reaction for the fixation. Explain the effect of 

 the CaC0 3 . How was the fixation brought about in the noncalcareous 

 soils ? Do soluble phosphates applied on the surface penetrate deeply 

 into the soil ? How are phosphates removed from the soil largely ? 



60 



