Phosphorus plant-availability as influenced by silicon fertilization

To create sustainable plant cover in oil-affected areas, sufficient phosphorus (P) in plant-available form should be provided. The level of soil P assimilation by plants is very low (20-30%) because the applied P is strongly fixed by Ca, Mg, Fe and Al or leached from upper soil horizon. Silicon (Si) substances were found to significantly increase the P plant-availability; however the underlying mechanisms remain unclear. Thermodynamic calculations of the solubility of phosphates Ca(H2PO4)2 and CaHPO4 in the presence of silicic acid evidence that the soluble P concentration can increase several times as a result of a replacement reaction of phosphate-anion by silicate-anion and a competing reaction for Ca-ion. The competing reaction can occur at pH ≥ 2, while the reaction of replacement proceeds at any pH from 1 to 9. Field experiments being conducted in China and Russia showed that Si-rich substances (chemically pure SiO2 and commercial Si soil amendments and Si fertilizers) considerably increased the yields of rice (by 16-62%) and barley (by 9-20%), simultaneously increasing the contents of plant-available P in soil and total P in plant leaves. Combined application of P and Si fertilizers could be recommended for enhancing the P fertilizer use efficiency.