The Bulletin 81 



(practically two-thirds as large as nitrogen, phosphoric acid, and potash 

 combined) ; 



IvTitrogen combined with phosphoric acid added but slightly to the 

 inci'cased yields; 



Potash added to phosphoric acid gave profitable returns ; 



Nitrogen added to phosphoric acid and potash gave a small profit, and 

 the yields from lime added to nitrogen, phosphoric acid, and potash were 

 smaller than for the three fertilizer constituents combined. 



The main increased yields and profits, therefore, came from phos- 

 phoric acid; the next most profitable constituent was potash, nitrogen 

 being of no value except where used in combination with phosphoric 

 acid and potash, and the profit from its use then was not large. It 

 will be well to bear these facts in mind for comparison with the results 

 presented in the tables to follow. 



Effect of Varying Quantities of Nitrogefi.— These tests were planned 

 to detenrime the effect on the yield of cotton of varying quantities of 

 nitrogen, leaving the phosphoric acid and potash constant. On one 

 plat the nitrogen was reduced to one-half of the normal quantity, mak- 

 ing the application 5 pounds of nitrogen per acre or practically 1.9 

 per cent in the fertilizer mLxture. On two of the plats it was increased 

 by 2 and 3 times the normal quantity (10 pounds per acre), making the 

 application 20 and 30 pounds per acre respectively, or on the basis of 

 the fertilizer mixture 5.3 and 6.6 per cent. The average results for 

 four years on the plats in Field A show the largest yield and profit from 

 the fertilizer application containing one-half the normal or the smallest 

 quantity of nitrogen in the several mixtures. In two years' and one 

 year's tests respectively, on Fields B and C, the largest profits were ob- 

 tained from the plats receiving fertilizer application containing twice 

 the normal quantity of nitrogen in the mixture, or 20 pounds of nitro- 

 gen per acre. 



Taking the seven years' experiments together, the average results 

 show an average increased yield over the unfertilized plats of 737 

 pounds of seed cotton, worth $30.11 above the cost of fertilizer, the 

 /A?iV^'i^^°-^^ containing one-half the normal quantity of nitrogen 

 {N/2F K), (this equals 5 pounds itrogen per acre), and 777.5 pounds, 

 worth $28.47 for the fertilizer application containing twice the 

 normal quantity of nitrogen. (Ng P K.) (This equals 20 pounds of 

 nitrogen per acre.) 



These results indicate that nitrogen is not the most important or 

 controlling constituent for the production of cotton on this soil. 



Eifed of Varying Qimntities of Phosphoric Acid.—This part of the 

 experiments was planned to show the effect on the yields of seed cotton 

 ot varying quantities of phosphoric acid, the nitrogen and potash re- 

 maining the same. On one plat one-half the normal quantity of phos- 

 phoric acid was applied, or an amount represented by 87.5 pounds of 

 16 per cent acid phosphate and equivalent to 61/0 per cent phosphoric 

 acid m the fertilizer mixture. On two plats were applied two and 

 three times the normal quantities of phosphoric acid, represented by 350 

 pounds and 525 pounds of 16 per cent acid phosphate respectively or 

 06 and 84 pounds of phosphoric acid per acre. The yields show good 

 profits for all of the fertilizer mixtures, in which phosphoric acid was 



