444 INVESTIGATION BY CULTURE EXPERIMENTS 



effect of the plant food applied by comparing the yields of the 

 treated and the untreated plots, but we must not assume that all 

 systems of treatment that appear profitable from this comparison 

 will prove to be absolutely profitable in continued practice. 



The common soil at Wooster contains about 1880 pounds of 

 total nitrogen, 960 pounds of acid-soluble phosphorus (perhaps 

 uoo pounds of total), and 31,000 pounds of total potassium, in 2 

 million pounds of the surface soil. Thus it is markedly deficient 

 in both nitrogen and phosphorus, and it may also be stated that 

 this soil is distinctly acid. During the last six or eight years liberal 

 applications of lime have been made to half or all of each of the 

 five series, the unfertilized plots having been limed the same as the 

 others; and in practically all cases distinct benefit has resulted 

 for all crops, the most marked effect being upon clover, and then 

 naturally upon the crops following clover. 



Table 82 illustrates very well the fact that the farmer cannot 

 always afford to raise the largest possible crops that can be pro- 

 duced by applications of commercial plant food. The largest 

 gross return from the five acres is from the No. 12 plots ($71.54), 

 but the amount of net profit and the per cent of net profit from that 

 plot are less than from any other profitable treatment. 



It is plain that, as an average, for this rotation, phosphorus is 

 the most limiting element, but, after phosphorus, the nitrogen limit 

 is also very distinct. Thus phosphorus alone increases the returns 

 from five acres from $42.34 to $55.32, with a net profit of $10.58, 

 or 441 per cent on the money invested in the 20 pounds of the 

 phosphorus applied. The addition of $11.40 worth of nitrogen 

 (with sodium) with phosphorus produces an increase of $11.65 

 more than with phosphorus alone, thus showing a net profit for 

 nitrogen of 25 cents, or 5 cents an acre, or 2 per cent on the money 

 invested. In all other cases nitrogen, as well as potassium, has 

 been applied at a loss, and in every other case wherever the use of 

 commercial plant food has been profitable the entire profit has been 

 made by the phosphorus, and after the phosphorus had paid for 

 some net loss caused by the other elements. 



Both the invoice (soil analysis) and the crop yields agree in the 

 deficiency of nitrogen and phosphorus; but these two sources of 

 information appear to disagree as to the need of potassium. There 



