Abstract
Changes of silicon concentration in flooded water were investigated in detail in an enlarged paddy field where rice plants (Oryza saliva L., cv. Hitomebore) were cultivated. The experiment was conducted on Alluvial soil at Furukawa Agricultural Experimental Station located in Miyagi Prefecture during the growing seasons of 2001 and 2002. In 2002 changes of calcium, magnesium, potassium and phosphate concentrations were also investigated. The results obtained are as follows. 1) Silicon concentrations in flooded water at the water inlet ranged from 11.8 to 13.0 mg L^<-1> in 2002.However, they decreased gradually with the distance from the water inlet, and at the water outlet were between 0.20 and 5.0mgL^<-1>. A similar tendency was also observed in 2001. The silicon concentrations in flooded water near the water outlet decreased remarkably from the beginning to the end of June. However, the extent of the decrease was fairly recovered in July. 2) On the other hand, both calcium and magnesium concentrations in flooded water increased with the distance from the water inlet. The calcium concentrations ranged from 6.0 to 6.5 mg L^<-1> at the water inlet, and varied from 10.3 to 17.7 mg L^<-1> at a distance of more than 80 m from the water inlet. As for the magnesium concentrations, they ranged from 1.8 to 2.1 mg L^<-1> at the water inlet, and from 3.0 to 5.7 mg L^<-1> at a distance of more than 80 m from the water inlet. 3) Both potassium and phosphate concentrations varied from time to time and showed no obvioustendency. 4) Significant negative correlations were obtained between silicon concentrations in flooded water and calcium and magnesium concentrations (Si-Ca: γ^2=0.923^<***>, Si-Mg: γ^2=0.907^<***>, n=20).
