Quantification of Amorphous Silicon by Optimizing the 1% Na2CO3 Method from Intensively Cultivated Rice and Sugarcane Soils in a Tropical Climate

The 1% Na2CO3 method used for measuring amorphous silicon (ASi) in soils was initially developed by DeMaster (1981) for measuring biogenic silica in marine sediments. Although this method is widely used for quantifying ASi content in soil, it has a few limitations which requires specific attention in case of the digestion period. In this study, we quantified the ASi content by optimizing the extraction of ASi from tropical soils collected from an intensively cultivated area with rice and sugarcane by using the 1% Na2CO3 method. The results of batch experiments suggested that a 3 to 5 hour digestion period as recommended by DeMaster (1981) is not sufficient for ASi determination in tropical soils. Hence, we recommended that the same method can be adopted for tropical soils with a modified digestion period of up to 3 to 6 hour instead of 3 to 5 hour. The results revealed that ASi content varied from 0.62 to 2.94 and 0.60 to 3.77 g kg−1 in rice and sugarcane soil, respectively. We also focused on the effect of vegetation on ASi content in the soil and observed that ASi content was higher in southern transition zone and coastal zone soils of sugarcane than rice, which indicates extent of recycling of crop residues mainly influence ASi content of soils. Our results also reflected that clay can act as a major source of ASi content in rice and sugarcane soils.