The Soils and Their Nutrients 



251 



NH4, ^g liter 

 ,0 200 400 200 400 200 400 200 400 200 400 600 800 1000 1200 



4 -t 



■i 



8 i 



E 



? 12 



16 



20 - 



"I — I — ' — I 

 18 Jul 



-I I — I I 



20 40 20 40 



- ; 



_] I 1 ' 



20 40 



20 40 



20 40 60 80 100 120 



NO3, /i.g liter' 



FIGURE 7-12. Profiles of NH\ and NOl concentrations in the soil solu- 

 tion from the moist meadow. 



ported from depths of 20 cm or more to the surface of a wet meadow soil 

 during the growing season. In 1973 detectable transport began on about 

 20 July and continued into September. During this period the maximum 

 net rate of flux from the well-decomposed organic layer into the mineral 

 layer above it was about 0.049 g m"^ day'. At this rate at least 2 g N m"^ 

 could be transferred from the subsoil to the rooting zone in a period of 

 about 60 days. The mechanism of transport has not yet been verified. 

 However, concentration profiles of exchangeable ammonium in the soil 

 through the summer period indicate that a diffusion mechanism is oper- 

 ating along the soil exchange complex. This may be the primary mechan- 

 ism of nitrogen transport, far exceeding the amounts that diffuse 

 through the soil solution. Results also indicate that the amount of nitro- 

 gen transported by diffusion is strongly affected by soil temperature, 

 thaw depth, and length of the thaw season. 



No experimental studies have been conducted on phosphate diffu- 

 sion in the soils of the coastal tundra at Barrow, but diffusion rates can 

 be assumed to be generally low (Olsen et al. 1962) and added phosphorus 

 fertilizer is strikingly immobile. Ten years after the last treatment, plots 

 fertilized with phosphorus by Schultz (1964) still showed levels of labile 

 and dissolved organic phosphorus that were 50 times as high as those of 



