Estimating Electrical Conductivity of Compost Extracts At Different Extraction Ratios

Abstract

Electrical conductivity (EC) was measured on extracts from four different types of compost using two different dilution techniques. When EC was measured on extracts obtained using a saturated paste method, EC varied by 20-25% of the mean measurement. When EC was measured on extracts obtained using a quantitative dilution procedure over a range of dilution ratios, EC varied by less than 10% of the mean. For dilution ratios less than 8 (ml water/g dry compost), the increase in EC was less than expected, suggesting that at the lower dilution ratios salts were incompletely extracted or did not completely diffuse from the particle interior to the extractable solution. A method of comparing compost EC measurements obtained using different dilution ratios, including the saturated paste dilution, is presented. This method predicted the EC of the saturated paste extract in three of the four compost samples tested. These methods could be integrated into a computer data spreadsheet for a typical composting operation. Thus, this work has implications for better sampling techniques and simpler analyses for estimating the EC of compost samples.