Nitrogen Loading in Soils Irrigated with Tertiary Treated Municipal Wastewater

Excessive hydraulic and nitrogen loading due to land application of municipal wastewater can result in leaching of contaminants to the groundwater and increased salinity levels in the root zone. Municipal wastewater treatment facilities continue to research suitable scavenging forage crops for disposal of their effluents. Previous studies have shown that Elephant grass (Pennisetum sp.) can be an effective scavenging crop for agricultural fields irrigated with nitrogen rich effluent waters. Therefore the objective of our study was to test the effectiveness of two forage grasses (Elephant and Sudan) in uptaking soil nutrients, and mitigating the build up of soil salinity. Suction lysimeters were installed along transects, at 60 cm and 120 cm depths, in fields planted with Sudan grass (SG) and Elephant grass (EG). Following irrigation events, soil solution samples were analyzed for nitrate (NO3-N), total nitrogen (TN), electrical conductivity (EC) and pH. Soil salinity maps were generated from electromagnetic induction surveys conducted at the beginning and end of the cropping season. Analysis of soil solution samples collected to date indicates that there is a high degree of spatial and temporal variability in the amount of NO3-N, TN and EC for both grasses. Nutrient analysis of the harvested forages along with the salinity maps reveal that the EG had a better capability for removing nutrients throughout the profile depth; this is partly explained by the relatively deeper rooting system of the grass. Sudan grass was more effective in reducing salt levels in the top 30 cm. Spatial correlation of the various constituents measured in the lysimeter samples from both fields are being examined to determine any relationship between these water constituents with soil properties and hydraulic and nitrogen loading.