Lecture 1 



— 11 — 



Survey 



insufficiency of supplying power for phosphate. The 

 design of the investigation has prevented thus far a 

 specific test of this point. 



During the first few years of cropping large losses 

 to the soil of total nitrogen occurred, without loss by 

 leaching. The nitrogen withdrawn by the crops could 

 not nearly account for the loss, so nitrogen must 

 have escaped in gaseous form under these conditions. 

 The nature of this nitrogen loss is still obscure. The 



120- 



O UNCROPPEO SOIL 

 • CROPPED SOIL 



8 10 12 



WEEKS 



16 



18 20 



Textfigure 2. — Effect of cropping on nitrate present in 

 soil solution at various periods of crop growth (barley- 

 crop). Soil solution nitrate concentration rises from low- 

 values in the spring or early summer, but with continued 

 cropping of soils recovery of soil may not be adequate for 

 requirements of a good crop. (From BURD, 1919). 



soils were not subjected to an anaerobic environment, 

 unless temporarily in local areas. Subsequently the 

 total nitrogen levels have remained constant so far 

 as can be determined. Whether or not a very slow 

 further decrease is taking place, it is not possible to 

 say. 



Apart from supplying nitrogen to the plants, the 

 nitrate ions formed from the reserve of organic mat- 



