ASSESSING METHODS OF AVAILABLE SILICON IN CALCAREOUS SOILS

Silicon (Si) fertilization can produce beneficial effect on the Siaccumulator—wheat (Triticum aestivum L.) grown on low available Si soils. For assessing Si availability in calcareous soils, four extractants were used to select a suitable method and a critical value for Si by correlating the extractable soil Si to the plant Si content and yield response to applied Si fertilizer of winter wheat grown on 17 field experiment plots. The quantities of Si extracted by the tests was, in descending order: 0.025 M citric acid >> buffering NaOAc-HOAc (pH 4) >> 0.19 M Na2CO3 0.5 M NaHCO3 (pH 8.5). Both the soil clay and CaCO3 contents significantly affected the extractable Si amount. All the extractable soil Si by any one of the four extractants was very significantly correlated with the Si contents in both the flag leaf and straw or with the total amount of Si uptake by wheat. The calibration test of relative wheat biomass yield response to Si fertilization showed that the NaOAc-HOAc extraction method was found to be the best for assessing Si availability for winter wheat in the calcareous soils. The critical value of available Si extracted by the classical method (NaOAc-HOAc) widely adopted for the acid and neutral soils was about 80 mg Si kg−1 (171 mg SiO2 kg−1) in the calcareous soil.