356 Jones and Skive.—Influence of Ammonium Sulphate 
Iron supplied in small quantities, 0-83 milligram per litre, in the form ot 
ferric phosphate, does not appear to be available for the plants growing in 
the Tottingham solutions, but is sufficient to meet the requirements of the 
plants growing in the solutions containing ammonium sulphate. Ferrous 
sulphate, on the other hand, produces excellent growth in the Tottingham 
solutions, but when it is introduced into a solution containing ammonium 
sulphate it brings about a condition which is very toxic to plants. It was 
therefore necessary to work out the proper form and amounts of iron to be 
supplied to each series of cultures so that this element could not become 
a limiting factor for growth. As this was not done for each separate solution 
used, only general conclusions may be drawn. It must be emphasized that 
the results presented in this paper for soy beans may not wholly agree with 
those for wheat previously reported, since these are two very different types 
of indicator plants. 
A review of the literature shows that the substitution of ammonium 
sulphate, either partially or wholly, for nitrate nitrogen is not a new 
procedure. Thus Lehmann (27) concluded that some plants require nitrate 
nitrogen for their normal development, others require ammonium nitrogen 
during the first half of their growth period and nitrate nitrogen during the 
last half of the life cycle. 
Hutchinson and Miller (17, 18) obtained good growth with wheat and 
pea plants grown in a nutrient solution with ammonium sulphate as the 
source of nitrogen in such a way that nitrification could not occur, showing 
that the nitrogen was derived from the ammonium sulphate as ammonium 
and not as nitrate. They conclude that ‘ agricultural plants of various 
kinds can produce normal growth when supplied with nitrogen in the form 
of ammonium salts under conditions which exclude the possibility of 
nitrification ’. 
Other investigators interpret their data to the effect that the ammonium- 
ion is directly absorbed by the plant, but the possibilities of nitrification 
were not entirely removed. 
There is one crop which apparently requires the ammonium-ion, and 
this is rice. Kellner (23) found that rice in nutrient solutions did better in 
the early stages with its nitrogen supplied in the ammonium form. Later 
on nitrate is better, but it does best with a combination of the two forms of 
nitrogen. Nagaoka (29) recognized the superiority of ammonium salts over 
the nitrate forms for rice. Krauss (25, 26), Daikuhara (4), Kelley (21, 22), 
Trelease (39) with his co-workers Paulino (40) and Jurado (41) are other 
investigators who have found ammonium salts the best source of nitrogen 
for rice. 
% 
Wolkoff (43) has successfully used ammonium sulphate with nitrate 
in a four-salt solution, as have Espino ( 6 ) and Jones and Shive ( 20 ). 
The following experiments were undertaken for the purpose of studying 
