Relationship of Properties of Rice and Sugarcane Soils and Plant Available Silicon in Karnataka, South India

Understanding on the bioavailability of silicon (Si) in intensively cultivated agricultural ecosystem still remains a challenging topic which requires attention by the scientific community. Monosilicic acid (soluble Si) and polysilicic acid (insoluble Si) affect various physicochemical properties of the soil. Thus, quantification of plant available silicon (PAS) content is a crucial step in order to understand the Si-mass balance for a particular region. The main objectives of this study were to quantify the vertical distribution of the PAS content in soils of four different agro-climatic zones of Karnataka and to evaluate the relationship between the physico-chemical properties of soils and PAS content. Four agro-climatic zones of Karnataka namely southern dry zone (SDZ), southern transition zone (STZ), coastal zone (CZ) and central dry zone (CDZ) were chosen for this study. The PAS content extracted by 0.01 M CaCl2 and 0.5 M CH3COOH is referred to as dissolved silicon (DSi) and adsorbed silicon (AdSi), respectively. Irrespective of the crop, SDZ and CDZ have medium DSi content (between 20 to 40 mg kg−1) and STZ and CZ have high DSi content (more than 40 mg kg−1). Irrespective of the crop, lowest DSi and AdSi concentration was recorded in SDZ and CZ, respectively. The AdSi content was generally higher than DSi content. On an average, the AdSi content was 2.4 and 4 times higher than DSi in CDZ and SDZ soil profiles of rice, respectively. In case of soil profiles of sugarcane, 2.6 and 4 times higher AdSi content compared to DSi were noticed in CDZ and SDZ, respectively. The depth wise increase in either DSi or AdSi content can be substantiated by the pH effect. Correlation studies indicated that irrespective of the crop, with increase in pH the release of AdSi and DSi content to the solution significantly increased and decreased, respectively. This study also suggested that PAS is essentially released from the finer fractions of soils rather than coarser fractions. Irrespective of the crop, a positive correlation existed between DSi and total organic carbon (TOC) content, whereas TOC correlated negatively with AdSi content. This study suggested that TOC and inorganic carbon (IC) may act as the main and/or potential source of DSi and AdSi content in soil, respectively.