Abstract
A dozen of fused phosphate (Ca-Mg-phosphate), ground to -100 and -200 mesh, was subjected to pot culture test in the greenhouse. The properties of sample are shown in Table 1. The test crop was paddy rice plant. The vitreous fused phosphates, which had the oxygen mol ratio or (ΣO)/(P+Si+Al) greater than 3.0,appeared to be practically as effective as superphosphate, but those which had the ratio less than 3.0 were outstandingly ineffective. There was a sigmoidal curve relationship between the response to the vitreous fused phosphate and its oxygen mol ratio. Fused phosphates which partially contained apatite, were not so effective as superphosphate, though its oxygen mol ratio were larger than 3.0. (see Fg. 2 and 3) The availability of P_2O_5 in the fused phosphate fertilizers is of course estimated by its solubility in 2% citric acid, but also that in the vitreous fused phosphate is subsidiarily able to be estimated by its oxygen mol ratio, which may be thought to show the strength of its chemical durability.
