Monitoring Soil Quality of Golf Course Fairways Irrigated with Secondary Treated Wastewater.

Hawaii has an island environment typical of the Pacific and Caribbean Basins with limited water resources that mandates water recycling for non-potable uses such as the irrigation of public golf courses. This use of wastewater, characteristically high in dissolved salts and microorganisms, can reduce the demand on fresh water. Secondary-treated wastewater is currently collected in ponds for sprinkler-applied irrigation on golf course fairways and greens. Application of wastewater produces salt build-up in the grass root zone, affecting grass quality. Surface soil samples were collected at the zero to five and five to ten centimeter depths and analyzed twice a year from the fairways.  A monthly sample was collected from the ponds for pH, EC, and sodium (Na) concentration. Spatial location data was also collected by DGPS on each sampling occasion, and matched with the analyzed data results. Geostatistical and GIS analysis of three years of collected data helped identify changes in the soil sodium, EC, and pH. Wastewater mineral concentration varied throughout the year while microorganism concentration remained high in the collection ponds. Analyses of soil samples collected at 0-5 cm and 5-10 cm depths indicated a build-up of sodium during the summer when irrigation demands were high, followed by a reduction during the winter when irrigation demands were low and rainfall was highest. Soil salinity was less than 3 dS/m on the average, and average pH was 7.6.  An overall three year trend showed slight declines in the average sodium concentration; however the average sodium concentration remained above 1000 mg kg^-1 in the soil, suggesting the need for sodium  reduction. Application of an irrigation leaching fraction to reduce salt and sodium from the root zone of the fairways and greens seems necessary.