4 i2 INVESTIGATION BY CULTURE EXPERIMENTS 



phorus. The line marked " average of plots receiving " includes 

 the average of plots 7 to 14 for nitrogen, of plots 5, 7, and n to 14 

 for phosphorus, and of plots 5, 7, and 13 for potassium; while 

 in the next line are given the averages for the plots as indicated 

 (') for the respective elements. By subtraction we find the excess 

 or deficiency ( ). The difference between the sum of the ex- 

 cesses found in the three soil strata and the balance with respect 

 to applications and removal in crops gives us the apparent loss in 

 50 years of the respective elements, and indicates an annual loss 

 per acre of 55 pounds of nitrogen, 8J pounds of phosphorus, and 

 59 pounds of potassium, losses besides those which are ac- 

 counted for in the crops removed. In terms of plant food 

 applied, these losses amount to 63 per cent of the nitrogen, to 31 

 per cent of the phosphorus, and to 69 per cent of the potassium. 



There are two principal ways in which plant food may be lost 

 from the surface soil, aside from removal in crops; namely, by 

 leaching and by erosion (including erosion by wind action as well 

 as by water). In addition, some mechanical mixing of surface and 

 subsoil may occur, because of burrowing animals and insects, 

 soil cracking, etc., and losses of nitrogen by dentrification are 

 possible, though not probable to any important extent under 

 normal conditions. 



In Table 74 is recorded the average composition of waters col- 

 lected from the tile drains of Broadbalk field during the years 

 1866, 1867, 1868, and 1869. These averages represent the mean of 

 a large number of analyses made by Doctor Augustus Voelcker. 

 The results are given in Table 74 on the basis of 3 million pounds 

 of water, which corresponds to a drainage of 13^ inches per acre, 

 which is less than the average annual drainage (14.73 inches) 

 from the uncropped bare soil of the Rothamsted drain gauge (see 

 Table 65), and more than Dyer's estimate (10 inches) for the ordi- 

 nary cropped soils at Rothamsted, but probably not more than the 

 average for the cropped soils of central United States. The actual 

 amounts found in pounds per million of drainage water will be 

 secured by dividing these data, by three. 



Some apparent relationships may be noted between the appli- 

 cations and losses of certain elements, and also between certain 

 elements in the drainage water, such as calcium and sulfur, but 



