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.
