Evaluation of paper mill sludge as a soil amendment and as a component of topsoil mixtures
To evaluate paper sludge as a soil amendment, different amounts of sludge were applied once to corn field plots. The soil was Hadley fine sandy loam (Typic Udifluvent, coarse-silty, mixed, nonacid mesic) with an average pH of 6.8. Sludge additions suppressed corn germination and early growth, but corn recovered so that final yields were not suppressed.
Sludge effects on corn growth were investigated in greenhouse experiments. Mixtures were made from different amounts of sludge and soil with or without N. Seeds were sown immediately or at 21 days after mixing. Addition of sludge increased media organic matter and P contents. At 21 days, C:N ratio, pH, and salinity of media declined relative to initial values whereas total N concentration was higher. Germination was hindered for seeds sown immediately after mixing, but delaying seeding for 21 days eliminated this problem. Biomass declined as amounts of sludge increased. More than 200 kg N/ha were needed to overcome N immobilization.
In another greenhouse experiment, soil (Hadley fine sandy loam) was collected at the University of Massachusetts Research Farm (on-site), and another soil of the same type was from a site not on the Farm (off-site). Different sludge levels were mixed with or without N in on-site soil, off-site soil, or off-site soil with P. Increasing amounts of sludge in the on-site soil hindered seedling emergence. Biomass declined as sludge increased, and the least biomass was produced in on-site soil. Sludge additions decreased the average leaf total N.
Paper sludge as a topsoil component for the production of wildflower sods on plastic was investigated. Sludge was mixed with sand, cranberry presscake, rockdust or compost. Establishment and growth of wildflowers were suppressed in mixtures of sludge and sand. The best sods with respect to stand establishment and biomass production were with mixtures of sludge, sand, and compost or with the mixture of sludge, sand, compost, and cranberry presscake. Additions of compost generally improved the capacity of media to support sod production.
Paper sludge is a suitable soil amendment, but conditions for maximizing the effective use of sludge must be met according to use and soils characteristics.