Analyses of accumulation of silica in the growth of two tropical forages using simple equations

The present study was conducted, using simple equations, to analyze the accumulation rate of silica [ARSi], that of minerals [ARM] and silica content changes with growth of Rhodes grass [Rg] and Greenleaf desmodium [Gd]. The following two equations were suggested for analyses: ARSi = 1/W · d(Si)/dt = (1/w · dM/dt) · d(Si)/dM, (A) Changes in silica content = 1/1000 · ((Si)₂/W₂-(Si)₁/W₁) = (1 - W₁/W₂) · {1/1000 · (ARSi/RGR - (Si)₁/W₁)}, (B) where W=forage dry weight (g/m²), Si=amount of silica in the forage (mg/m²), M=amount of minerals in the forage (mg/m²), (1/W)·(d(Si)/dt)=ARSi, (1/W)·(dM/dt)=ARM, (d(Si)/dM)=accumulation of silica per unit accumulation of M[ASiAM], RGR=mean relative growth rate [RGR] of forages over the interval t₁ to t₂, ARSi=mean ARSi over the interval t₁ to t₂, (1-W₁/W₂)=forage growth index [FG index], {ARSi/RGR-(Si)₁/W₁}1000=an index for forage growth dependent silica accumulation [FGDSiA index]. Analyses using equation (A) suggested that Rg showed a higher selection of silica in the accumulation of minerals, when compared with Gd. Analyses using equation (B) suggested that Rg showed less active silica accumulation than forage growth, in contrast to more active silica accumulation than forage growth in Gd. It was suggested that the present methods accounted analytically for the accumulation characteristics of silica and its content changes with growth of forages.