THE REQUIREMENTS OF PLANTS 



35 



TABLE XII. INFLUENCE OF POTASSIUM SALTS ON THE ACTION OF NITROGENOUS MANURES. 



ROTHAMSTED. 



The effect of varying water supply is more conveniently studied 

 in pot experiments than in the field, since any comparison between 

 yields in wet and dry seasons is complicated by the great differences 

 in temperature conditions. Tucker and von Seelhorst (257) put up 

 three series of soil pots in which the water was kept at a definite 

 amount ; one was just moist, another moister, and a third still moisten 

 These were then each subdivided into three others, one receiving no 

 nitrogen compounds, another one dose, and the third two doses. Oats 

 were sown in all nine sets with results that are given in Table XIII. : 



TABLE XIII. INFLUENCE OF WATER SUPPLY ON THE EFFECTIVENESS OF MANURES. 



VON SEELHORST AND TUCKER (257). 



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 ofN as NaNO 3 per pot. 



1 From 400 Ib. ammonium salts. 



2 From 400 Ib. ammonium salts and 200 Ib. rape cake. 



3 The moist soil contained 14-35 per cent, of water (41-6 per cent, of saturation), 

 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 per cent. (637 per cent, of saturation). 



