Dynamics of Physical Organic Matter Fractions During De‐inking Sludge Decomposition

Abstract

Replenishment of soil C and N is essential for sustainable revegetation of minesoils. Our study investigated paper de‐inking sludge as the organic amendment for revegetating an abandoned sandpit in Québec, Canada. Sludge was incorporated at 0 (check) and 105 Mg dry matter ha−1 before seeding tall wheatgrass (Agropyron elongatum (Host) Beauv.). Nitrogen (at 315, 630 and 945 kg N ha−1) and P (at 52.5 and 105 kg P ha−1) were also applied to all plots. Distribution of C and N was determined periodically in two sizes (<53 μm and >53 μm) and two densities (<1.8 g cm−3 and >1.8 g cm−3) of soil fractions during 823 d. After 823 d, C concentrations were 43 and 69% of those of Day 5, for the low and high N rates, respectively. With time, the proportion of C in the heavy (>1.8 g cm−3) fraction increased from 20 to 55%, but remained near 20% in the fine (<53 μm) fraction. Increasing N rates increased C conservation mainly in the coarse (>53 μm) fraction. The amount of N recovered in all fractions decreased after Day 86, in accordance with a previous litter bag study. Although inorganic N was positively correlated with total N in all fractions, the fine fraction was the best indicator of the size of the mineral N pool. Addition of sludge to the sandpit favored the restoration of C and N pools, and high levels of mineral N increased this effect. Residues became denser but remained relatively coarse during their decomposition.

Decomposition of paper de-inking sludge in a sandpit minesoil during its revegetation

“…In fact, only a trend (not shown) was noticed as slightly more material (~ 6% of initial amount) remained with the highest N application rate. However, measurements of whole soil and particulate C confirmed the positive effect of N on C conservation in the same study (Fierro et al, 1999c) Nitrogen immobilization was expected to be substantial in the early stages of decomposition, because of the high initial C/N ratio of sludge. Supplemental N was forethought to compensate for immobilization while allowing vegetation establishment.…”

“…However, Fierro et al (1999c) have confirmed the slow decomposition of this material based on whole-soil C and physical fraction measurements.…”

Combined primary/secondary papermill sludge as a nitrogen source in a cabbage-sweet corn cropping sequence

“…Chantigny et al (1999) reported that 60% of the total C from a primary de-inking sludge was oxidised in 2 yr. This decomposition rate from primary de-inking sludge also varies with N supply (Fierro et al 1999). Heavy metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) were present in low concentrations (Table 3) except for Mn and respected the "A" criteria for PS application to edible crops (Ministère de l'Environnement et de la Faune du Québec 1997).…”

“…This suggests that a large part of the organic N was in very labile forms or that the sludge helped to conserve soil N. It was reported that primary deinking sludge additions to soil helps to conserve N (Fierro et al 1999), which can in part be re-mineralised the following year (Simard et al 1998a).…”

Decomposition of paper de-inking sludge during revegetation of a sandpit minesoil: a reply to the comments of Beyer and Mueller

“…We discussed this point in our paper and referred to Fierro et al (1999c) in which physical fractionation was used to characterise the remaining material. Chantigny et al (2000) used wet chemistry (carbohydrate analysis) to study DPS decomposition in an arable soil.…”