Exporting large volumes of municipal sewage sludge through turfgrass sod production

Abstract

The nutrient content of sludge produced by municipal water treatment works often far exceeds the requirements of nearby crops. Transporting sludge further afield is not always economically viable. This study reports on the potential to export large volumes of anaerobically digested municipal sewage sludge through turfgrass sod production. Hypotheses examined are that sludge loading rates far above recommendations based on crop nutrient removal (i) are possible without reducing turf growth and quality, (ii) do not cause an accumulation of N and P below the active root zone, (iii) can minimize soil loss through sod harvesting, and (iv) do not cause unacceptably high nitrate and salt leaching. An 8 Mg ha−1 sludge control (the recommended limit) was compared with sludge rates of 0, 33, 67, and 100 Mg ha−1 on a loamy, kaolinitic, mesic, Typic Eutrustox soil near Johannesburg, South Africa. Sludge application rates up to 67 Mg ha−1 signifi cantly improved turfgrass establishment rate and color. The ability of sods to remain intact during handling and transport improved as the sludge application rate increased to 33 Mg ha−1 but deteriorated at higher rates. A sludge application rate of 100 Mg ha−1 was needed to eliminate soil loss, but this rate was associated with unacceptably high N leaching losses. All our hypotheses were accepted for application rates not exceeding 33 Mg ha−1 on the proviso that some soil loss was acceptable and that the leaching fraction was carefully managed during the first 2 mo after sludge application.