62 A YEAR IN AGRICULTURE 



organic matter. If clover or other legumes will not grow 

 well to furnish this organic matter, perhaps the soil is sour 

 and needs from two to five tons of ground limestone to the 

 acre. The next important requisite is the nitrogen content. 



.N 

 FIG. 8. POT EXPERIMENTS WITH FERTILIZERS 



This is best supplied by the clovers which also furnish the 

 organic matter. To get the addition of nitrogen the clover 

 must be plowed .under. The next requisite in most soils is 

 the maintenance of an adequate phosphorus supply. This is 

 most economically supplied by the use of from one to three 

 tons of fine-ground rock phosphate to the acre. This must 

 always be applied, however, where manure or other organic 

 matter is incorporated in the soil ; for the decaying of the or- 

 ganic matter is necessary to render the phosphorus in the 

 rock phosphate available for plant-food. This decaying 



