SOIL CONDITIONS AFFECTING PLANT GROWTH 



39 



make more growth, and can therefore utilise more nitrogen : 

 the added O'5 grm. now raises the crop by 10 grms. Again, 

 however, the water supply sets a limit, and the second o* 5 grm. 

 of nitrogen is without effect. When a liberal supply of water 

 is added the first O'5 grm. of nitrogen gives 20 grms. of crop, 

 double the previous increment ; but even this does not repre- 

 sent the whole possibility, for the second 0*5 grm. of nitrogen 

 gives a still further increase of 1 5 -5 grms. 



TABU VI. INFLUENCE OF WATER SUPPLY ON THE EFFECTIVENESS OF 

 MANURES. VON SEELHORST AND TUCKER (256). 



Dry Weight of Oat Crop. 



K = i gram of K 2 O as K 2 CO 3 per pot ; P = i gram of P 2 O 5 as Ca(H 2 PO 4 ) 2 

 per pot ; N = -5 gram of N as NaNO 3 per pot. 



The results of the phosphate series are somewhat different 

 in detail, but not in principle. The first dose of P 2 O 5 in the 

 dry soil gives an increased crop, and so does the second, the 

 first not having been large enough ; in the wetter soil, however, 

 the increase is much larger. There is a still further increase in 

 the wettest soil, but less than before, some other limiting 



1 The moist soil contained 14*35 per cent, of water (41 '6 per cent, of satura- 

 tion), the moister soil 15-41 per cent, at the beginning, increasing to 18-43 (51-7 

 per cent, of saturation) as the experiment proceeded, and the wettest soil, 16-44 

 per cent, at the beginning, increasing to 22-59 (63*7 per cent, of saturation). 



