SOIL CONDITIONS AFFECTING PLANT GEO WTH 39 



make more growth, and can therefore utiHse more nitrogen : 

 the added 0*5 grm. now raises the crop by 10 grms. Again, 

 however, the water supply sets a limit, and the second 0*5 grm. 

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

 is added the first 0*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 15 '5 grms. 



Table VI. — Influence of Water Supply on the Effectiveness of 

 Manures. Von Seelhorst and Tucker (256). 



Dry Weight of Oat Crop. 



K = I gram of KgO as KjCO, per pot ; P = i gram of PgOj as Ca(H2P04)2 

 per pot ; N = '5 gram of N as NaNOj per pot. 



The results of the phosphate series are somewhat different 

 in detail, but not in principle. The first dose of F2O5 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 tha,n before, 'some other limiting 



^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 (^3 '7 P^^ cent, of saturation). 



