Effects of temperature and moisture on coliphage PRD-1 survival in soil

The goal of this study was to quantitatively assess the effects of temperature and soil moisture on the survival of coliphage PRD-1 in soil. PRD-1 was added to sandy loam soil at five different soil moisture levels. The soil seeded with PRD-1 was packed into sterile polyethylene jars and exposed to eight different temperatures in an oven. Samples were collected over 14 to 25 days depending on the temperature. The inactivation rate of PRD-1 increased linearly with increased temperature. The inactivation rate gradually decreased when the soil moisture level decreased from 20.9 to 8.9%. However, the inactivation rate increased when the soil moisture content reached 5.1%, suggesting the existence of an optimal soil moisture condition for PRD-1 survival. It is also possible that there is a threshold soil moisture level below which the inactivation of PRD-1 suddenly increases. Marked reductions in recoveries were observed as the soil moisture approached or fell below 5.0% as a result of evaporation. The increased inactivation of PRD-1 due to strong association with soil particles may have caused rapid reductions in recoveries. The evaporation process appeared to affect PRD-1 survival substantially at higher temperatures whereas little effect was observed at lower temperatures. A model developed from this study predicted PRD-1 survival in subsurface soil in field conditions with an average error of 11.0%.