Physical Properties of Retisol under Secondary Pulp and Paper Sludge Application

Abstract

A positive effect of pulp and paper mill sludges as a rich source of organic substrates on soil properties was previously found for some types of sludge and soil. In this study, the effect of secondary pulp and paper sludge on water characteristics and thermal properties of Retisol, as well as the growth parameters of lettuce (Lactuca sativa L.), was tested on the basis of a pot experiment when watering plants with a 20 or 40% sludge solution. The sludge application enhanced plant growth with an increase in biomass accumulation of 21 and 53%, respectively, for 20 and 40% sludge treatments. When the sludge dose was increased from 0 to 40%, the number of leaves increased by 25%, and the leaf mass per area value increased by 42%. Due to the accumulation of more biomass in the shoots than in the roots, sludge causes a change in the allocation of plant biomass. A significant effect of the sludge application on soil particle and microaggregate sized compositions, as well as on the saturated soil hydraulic conductivity, was not found in this study. However, fitted soil water retention curves showed an increased soil water content in sludge-treated soil at all water content values exceeding field capacity. Secondary sludge application led to an increase in the saturated water content from 0.50 to 0.56 cm3 cm−3. The 40% sludge solution increased soil thermal conductivity from 0.92 to 0.98 W m−1 K−1 under saturated water content and from 0.83 to 0.92 W m−1 K−1 under field capacity. The thermal conductivity was higher in the sludge-treated than untreated soil due to a more pronounced positive effect of increased saturated water content than the negative effect of the increased organic matter content on heat transfer. The positive impact of secondary sludge application on both plant growth parameters and physical properties of Retisol, such as increased soil water-holding capacity and thermal conductivity coefficient confirms the possibility of using it to improve soil characteristics and plant productivity.

Effect of Secondary Paper Sludge on Physiological Traits of Lactuca sativa L. under Heavy-Metal Stress

“…Not only the chemical but also the physical properties of soils can be transformed when introducing secondary paper sludge into soils [ 4 ]. Soil texture and structure play an important role in soil water availability for plants and nutrient uptake [ 36 ] and therefore successful plant growth and productivity.…”

“…Soil texture and structure play an important role in soil water availability for plants and nutrient uptake [ 36 ] and therefore successful plant growth and productivity. Secondary-sludge application when watering plants can lead to the formation of stable organo-mineral particles with an increase in the proportion of large drainage pores and saturated water content, providing increased water supply to plants [ 4 , 37 ]. The secondary sludge decreased the effective thermal conductivity of the soil in an air-dried state but increased the heat transfer in wet soil, which may be associated with the sludge-mediated increase in the soil water content [ 4 ].…”

“…Secondary-sludge application when watering plants can lead to the formation of stable organo-mineral particles with an increase in the proportion of large drainage pores and saturated water content, providing increased water supply to plants [ 4 , 37 ]. The secondary sludge decreased the effective thermal conductivity of the soil in an air-dried state but increased the heat transfer in wet soil, which may be associated with the sludge-mediated increase in the soil water content [ 4 ]. Improving the physical properties of the soil using secondary sludge, as well as the chemical properties, could have a positive effect on the physiological traits of lettuce plants under the study.…”

“…For different plant species, soil types and climatic zones, the positive effect of pulp and paper sludge on soil properties and crop yield has been established [ 1 , 2 ]. Recent studies have shown that pulp and paper sludges cause an increase in the soil organic matter and nutrient content, soil microbial complex and its activity, and improve soil physical properties [ 3 , 4 ]. Plant growth and productivity are largely dependent on nutrients and water ability in soils, as well as on soil aeration, so improving the soil with pulp and paper sludges can have a positive effect on plants.…”