The Effects of Long Term Wastewater Irrigation On Soil Physical Properites.

Opportunities for Pennsylvania municipalities to reuse wastewater for agriculture has been demonstrated at Penn State University’s Living Filter, which irrigates up to 250 cm of secondary treated effluent per year over crop and forest land, for over 40 years.  The removal of nutrients by crops has been demonstrated but the impact on soil physical properties and indicators of soil quality have become a concern.

In recent years, land managers believed that runoff has increased.  In 2008 and 2009, infiltration rates of the Ap and Bt horizons of irrigated and non-irrigated areas within the site were analyzed with a tension infiltrometer at 4 tensions to determine hydraulic conductivity.  Ap horizon depth, clay content, and bulk density measurements were taken along 8 transects radiating from sprinkler heads as well.  Soil profile cores were also sampled for organic matter content, SAR, EC and pH.  Prior to measurement of infiltration and soil sample collection, irrigation application ceased for at least 3 weeks to allow water contents in the irrigated and non-irrigated areas to reflect recent weather patterns.

Results show that Ap horizon infiltration rates and saturated hydraulic conductivity did not differ between the irrigated and non-irrigated areas, except that the infiltration rate at the 4 cm tension was greater in the irrigated area.  The mean saturated hydraulic conductivity was relatively high in both areas at approximately 21 cm/hr.  Bulk densities were approximately 1.4 g/cm³ in the irrigated area, compared to 1.5 g/cm³ in the non-irrigated area.  Ap horizon clay content in the irrigated area ranged from 14-16% and 17-21% in the non-irrigated area, suggesting possible translocation of clays due to excessive application rates.  Ap horizon depth decreased with distance from the sprinkler head, ranging from 30 to 25 cm in the irrigated areas, but remained constant at approximately 22 cm in the non-irrigated area.