CHAPTER XVII 



THE USE OF PHOSPHORUS IN DIFFERENT FORMS 



HAVING determined how to correct soil acidity (when necessary) 

 and how to keep the soil sweet, by means of ground limestone; 

 having determined how to maintain or increase the supply of or- 

 ganic matter and nitrogen in the soil, by means of farm manure 

 in live-stock farming, or by means of legume crops and catch crops 

 and crop residues in grain farming, or by a combination of these in 

 mixed or diversified farming, which is sometimes preferable and 

 more profitable than either alone; and having determined the 

 absolute necessity of maintaining or increasing the supply of phos- 

 phorus in the soil by direct applications exceeding the amounts 

 removed in crops harvested, the next most important question, 

 and the only remaining exceedingly important question, is, What 

 form or forms of phosphorus shall be used ? 



There are four general sources of phosphorus for use in soil 

 improvement: (i) farm manure, (2) bone meal, (3) phosphate 

 rock, and (4) basic slag phosphate. 



The first two are themselves farm products, and at the best only 

 provide that the phosphorus taken from the soil shall be returned 

 to the soil, and if there is any loss whatever, the ultimate effect, 

 applied to the state or country as a whole, must be a reduction 

 in the general average fertility of the soil. 



To supply to a 4o-acre field 1000 pounds of phosphorus (25 

 pounds per acre) in the form of manure made from purchased corn, 

 would require an investment of more than $3000 at 40 cents a 

 bushel for corn. While the purchase of grain and other food stuffs 

 provides a method by which soils can be positively enriched in 

 phosphorus, and while there is usually more or less profit from feed- 

 ing, so that the phosphorus thus obtained may really cost nothing 

 in the end, nevertheless, it is worth while to keep in mind that this 

 method requires large capital, special equipment, such as buildings, 



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