NOX-DIFFUSION OK MTU A IKS I\ >()||. •-, 



in the sanu' way the aniomit of iiitrairs jn-.'sciit at racli .|r|,ili 

 in the subsoil water l)el()W Pints (>. 7. an<l ^, is pcrfeetlv 

 ilistinct and eliaracteristic of the mannrinu^ applied to tlir 

 ijiuface. 



Additional evidence of the laek of lateral <litfnsion of tlie 

 nitrates in the soil water is to be seen in the permanent ^M-ass 

 plots; although no path separates the plots rec(ivin<: nitrate of 

 soda from the neighbom'ing plots, the eharactei-istic ve;^'ctatioii 

 induced by the nitrate of soda manuring shows no tendenev i«» 

 stray across the division line. For example, Plot 11. rcccivin;^' 

 a complete manure containing 550 lb. per acre of nitrate of 

 soda, is innnediately contiguous to Plot 1, receiving nitrogen 

 only as ammonium-salts; the vegetation on the two plots is in 

 marked contrast, yet the dividing line is singularly sharp, and. 

 <lespite the many years Plot 14 has received this large dressing 

 of nitrate of soda, there is not the least sign of its ditiusion into 

 the subsoil below the adjoining plot. 



V. — The Nitratks in DKAfN,\(;K Watkrs. 



The processes of nitrification in soils can also be studied by 

 the examination of the drainage water beneath cultivate(l lan<l. 

 It has long l)een known that all the soluble compounds of 

 nitrogen are retained by the soil with the exception of the 

 nitrates, hence an examination of the amoimt of nitrates 

 present in the water reaching the drains will tliiow liuht on tin- 

 rate at which nitrates are produced in the soil, and on ilieir 

 ultimate fate. 



At Rothamsted the water which })ercolates thiongli tin- 

 drain-gauges is stored, and the nitrates are regularly determineil 

 in proportionate samples representing the percolation for the 

 month. These results have been combined for twenty-six years. 

 1878-1903, and the averages are set out in the accompanying 

 curves (Fig. 45), which show the rainfall, the percolation in 

 inches through '20 inches of bare soil, the c..iic.iiiiati(.n of the 

 percolating water in parts of nitric nitrogen per million, and the 

 total amount of nitric nitrogen reduced to lb. per acre. 



