THE CHOICE OF PHOSPHATES 



201 



than the " total" amount contained in soils. Some soils may con- 

 tain a very good supply but still respond to phosphate fertilization. 

 Other soils containing lower amounts may give no indication of 

 phosphorus deficiencies. When a silt loam, for example, has had 

 its original phosphorus supply reduced one- third to one-half, and 

 is in need of phosphates, it is not necessary to add an amount of 

 fertilizer to raise the phosphorus content to the original amount, 

 but to fertilize sufficiently to enable the soil to furnish the phos- 

 phorus demanded by profitable crops. 



FIG. 133. What happened when the fertilizer missed. This particular peat soil responds 

 best to a mixture (1 to 1) of muriate of potash and acid phosphate. 



The Choice of Phosphates. When immediate results are 

 desired and when top-dressings are to be made, a soluble fertilizer 

 should be used. Acid phosphates, or superphosphates, are, there- 

 fore, especially adapted to all cases where spring top-dressing is 

 practiced; as, for example, on grass land, for clover, alfalfa, and 

 winter grains. 



Bone meal gives excellent results on soils that are open and 

 inclined to be sandy or gravelly. 



Rock phosphate has given good results on peat and muck soils 

 and on upland soils exceptionally rich in decomposable organic 

 matter. Compare Figures 132 and 133. 



