Evaluation of soil factors related to available silicon in agricultural soils of Western Australia

Context Plant available silicon (Si) levels in soils are of increasing interest due to the growing evidence that Si enhances plant tolerance to a range of stresses. Aim On a diverse range of agricultural soils of Western Australia (WA), the aim was to determine the relationship between the Si concentrations in CaCl2 or acetic acid extracts and soil properties and predict the prevalence of Si deficiency. Methods To assess the Si status in soils of WA, 203 geographically-dispersed soil samples were collected from the WA wheatbelt (spanning from Geraldton to Esperance) with a range of physicochemical characteristics in 2023 and 2024. Comprehensive soil analysis (CS) including organic carbon, pHCaCl2, pHH2O, texture, electrical conductivity, extractable phosphorus and potassium, DTPA-extractable micronutrients (copper, zinc, manganese and iron), exchangeable calcium, magnesium, sodium and potassium, and effective cation exchange capacity (ECEC) plus Si extraction by CaCl2 and dilute acetic acid was completed. Key results The mean ECEC, pHCaCl2 and organic carbon were 5.85 ± 0.59 cmol kg−1, 5.65 ± 0.60 and 0.68 ± 0.48%, respectively. Based on a tentative Si critical range (20–40 mg kg−1), 74.9% of samples were under 20 mg kg−1 while 88.2% were below 40 mg kg−1 (in CaCl2). For soils with SiCaCl2 < 20 mg kg−1, statistical means for SiCaCl2, pHCaCl2 and ECEC were 8.70 ± 0.35 mg kg−1, 5.45 ± 0.06 and 4.00 ± 0.36 cmol kg−1, respectively. Conclusion Based on matching our results with the mean for pH, ECEC and exchangeable cations for WA soil types, 4.62 million hectares is predicted to be low in SiCaCl2, while another 6.3 million hectares is predicted to be marginal. Implications We recommend a priority set of experiments for assessing the impact of Si in WA wheatbelt soils on mitigation of drought and salinity.