324 SOUTHERN FIELD CROPS 



nitrogen, phosphoric acid, and potash, naturally cost more 

 per ton than low-grade fertilizers. Yet the high-grade 

 fertilizers are usually more economical. The true test 

 in choosing between two fertilizers consists in calculating 

 which one affords a pound of nitrogen, potash, and avail- 

 able phosphoric acid at the lower price. 



The reason why a concentrated, high-grade fertilizer is usually 

 more economical than a low-grade fertilizer is made clear by com- 

 paring a 12 per cent acid phosphate with a 16 per cent phosphate. 

 To afford an equal amount of plant-food, say 960 pounds of avail- 

 able phosphoric acid, requires 4 tons of the low-grade fertilizer, 

 but only 3 tons of the high-grade fertilizer. This extra ton of 

 the low-grade article involves extra expense for freight, hauling, 

 mixing, and sacking. Hence, the manufacturer or dealer must 

 charge more for each pound of plant-food in the less concentrated 

 fertilizer. 



The advantage of using the highest grades of fertilizers increases 

 with the distance that the fertilizer must be shipped and hauled. 

 If, however, a fertilizer be ma^e too concentrated, there is greater 

 difficulty in mixing its constituents uniformly and in applying it 

 evenly, because the amount to be used on each acre is so small. 



293. Quantity per acre of fertilizer. — Experiments 

 in several states have shown that an application of 400 

 to 600 pounds to the acre of a fertilizer adapted to the soil 

 affords a larger profit to the acre than the use of smaller 

 amounts. At the Georgia Experiment Station a complete 

 fertihzer was used at the rate of 400, 800, and 1200 pounds 

 _ per acre. Each increase made a decided and profitable 

 increase in the yield. However, the smallest lot returned 

 much the highest percentage of profit on the investment ; 

 the 800 pounds paid a higher dividend than the largest 

 amount. This illustrates the usual rule, which is that 

 the percentage of profit on the investment in fertilizers 



