THE COMPOSITION OF THE SOIL 



127 



was generally from cri to I atmosphere. The seasonal varia- 

 tions are shown in Fig. 16. 



These various methods naturally give different results. 

 The general conclusion, however, seems to be that the solution 

 in a normal agricultural soil contains mainly calcium nitrate 

 and bicarbonate ; with some organic matter, sodium, mag- 

 nesium, silica, chlorine, sulphuric acid, less potassium, a trace 

 of ammonia, and only little phosphate. In ordinarily moist 



24W*s 32WKS. 40WKS. 



JuUO.Jui24.Au62J. Ocr23 Dtc.18. F.I7 MAY I 



Time from planting. 



FIG. 16. Variations in concentration of soil solution with crop and season, show- 

 ing that the barley crop much lowers the concentration even after its 

 removal in August. On the vertical axis one-quarter of each freezing-point 

 depression is plotted :* an approximate estimate of the corresponding osmotic 

 pressure is obtained by multiplying the plotted value by 50 (Hoagland and 

 Sharp, 1366). 



soil it has a concentration of the order of OT to I'O per cent., 

 or some O'5 to 5 atmospheres osmotic pressure ; this varies 

 however, with the rainfall and the manuring. The propor- 

 tions of the components also varies, again changing with the 

 season and the manuring. The nitrates are perhaps the most 

 variable constituents, but the calcium and potassium also vary 

 both relatively and absolutely excepting in van Zyl's ex- 

 periments. 



The numerous analyses of land drainage water that have 



