262 SYSTEMS OF PERMANENT AGRICULTURE 



In one series of tests, crimson clover was regularly seeded in the 

 corn to be plowed under later as a green manure, and in another 

 series rye was employed in a similar manner, the third test being 

 made without special provision for organic matter. Table 42 gives 

 a summary of these investigations for all forms of phosphorus 

 that were used under the three different conditions: 



TABLE 42. MARYLAND EXPERIMENTS WITH DIFFERENT FORMS 



OF PHOSPHORUS 

 Twelve Years' Work : Yields per Acre : Average of Three Plots 



Here are represented thirty-three separate tests (three plots for 

 eleven years) for each form of phosphorus. As an average, the raw 

 rock has given nearly the same results as the bone and slag. The 

 average increase in yield is very marked with wheat, less marked 

 with hay, and practically no effect is seen with corn. The value 

 of the total increase in twelve years is about ten times the cost of 

 the raw rock phosphate, at Illinois prices, and still more at Mary- 

 land prices, for farm produce. In commenting upon his experi- 

 ments, Director Patterson says: 



"The results obtained with the insoluble phosphates has cost usually less 

 than one half as much as that with the soluble phosphates. 



"The results show decidedly that plants are able to utilize insoluble rock 

 phosphates. 



"The use of an abundance of organic matter in the soil when insoluble 

 phosphates are applied was evidently a necessity for their best effects. 



"Soluble phosphates produced the best yield of wheat. 



"Florida soft phosphate produced the best yield of corn. 



"Reverted phosphates produced the best yield of hay. 



