Development of a quality certification and maturity classification method for liquid fertilizer by measuring the electrical conductivity (EC) of swine manure

The increasing need for liquid fertilizers along with the high production and treatment rate of swine manure pose a great concern in regard to the quality control and certification of fertilizers rapidly produced. In this study, 66 liquid manure samples were collected from national livestock manure co-recycling centers. These 66 samples were tested and classified into three categories based on Liquid Fertilizer Germination Index (LFGI). In addition, the physiochemical parameters of manure specimens were tested, including pH, NaCl, total sulfur (TS), total nitrogen (TN), ammonium-nitrogen (NH -N), nitrate-nitrogen (NO-N), total phosphorus (TP), potassium (K), and electrical conductivity (EC). EC had a positive correlation with TN (0.879), NH-N (0.816), K (0.693), and NaCl (0.625) with a significance of p < 0.01 but a negative correlation with LFGI (-0.719). This study demonstrated that EC could be used as an indicator in rapid testing methods for quality control to certify the maturity level of liquid manure fertilizers.