14 
MANURING EXPERIMENTS WITH PADDY RICE (SECOND YEAR). 
sesquioxides which are known to be of inferior effect on crops ; 
and those portions which remain in a more soluble form, 
become through the same chemical process likewise less and 
less assimilable in the course of time. Compounds of the 
character of bog iron, to the formation of which our soil is 
greatly inclined, no longer yield to the plants the phosphoric 
acid deposited in them. The comparative experiments on the 
effect of various phosphates on rice to be described later on, 
will give further evidence that processes of this kind are 
actually accomplished in our soil. 
The changes of the solubility of phosphates in soils are 
dependent on two factors, the character of the phosphate applied 
and the condition of the soil. Owing to its great solubility 
in water, the sodium phosphate among the common phos¬ 
phates, certainly yields most easily its acid to the basic com¬ 
pounds of the soil, and, from this point of view, the results 
obtained with it are also valid for the phosphates of ammonium 
or potash recently manufactured in Europe for manuring pur¬ 
poses. On ferruginous soils poor in lime such phosphates will 
certainly have less effect than dicalcium phosphate, Thomas 
phosphate, etc., and may even prove to be inferior to super¬ 
phosphate. This point will be further referred to in a later 
part of this paper. 
The capacity of a soil for rendering soluble phosphates in¬ 
accessible to the roots is, of course, limited ; and if various 
quantities of such fertilizers are mixed with equal volumes of 
soil, the conversion into insoluble forms will be more complete 
with the small than with the large doses. This is clearly 
intimated in our experiments by the progressive quantities 
consumed from the residual phosphoric acid ; the larger the 
amount of the residue, the higher was its percentage exhaustion 
by the subsequent crop. We may indeed deduce from the 
figures in the above table that in all the six trials on the 
assimilability of residuary phosphoric acid, an equal proportion, 
about 5.7 grms. per plot, entirely lost the capacity of being 
consumed by the plants. If we deduct this quantity in each 
