Green waste biochar effects on sandy soil physicochemical properties

The organic amendment of degraded soil in South East of Tunisia was used to restore the chemical, and physical properties of soil quality investigated in this study. Biochar derived from pyrolyzed green waste at 360°C was used like organic amendment.  Nines randomized plots with one square meter of the area of each plot in three replicates have been installed in the Institute of Arid Area in Mednine South East of Tunisia, with two rates of biochar 20 and 40 t/ha were investigated: 20 tons/ha (B20) (2 kg/m²) and 40 tons/ha (B40) (4 kg/m²). The results showed that biochar had a positive effect on soil's physical and chemical properties compared to non-amended soil (Untreated soil). Biochar supply at rates of 20 and 40 tons/ha, causes a decrease in electrical conductivity to achieve 2.66 mS/cm for the B40 dose after 1 year of amendment, also a decrease in the bulk density at the surface layer (0-20 cm) has been registered, the total porosity which was decreased with depth. The hydraulic conductivity is favored by the incorporation of biochar in the soil which increases the volume of voids and tends to create preferential flow paths

Seasonal and depth variation of soil physical parameters irrigated with treated wastewater in the case of light textured soil

In places with scarce water supplies, treated wastewater (TWW) can be used for irrigation. This is the case in many places on the Mediterranean coast. In order to examine changes in soil physical proprieties irrigated with secondary-treated wastewater for >38 years, a study was conducted under real agricultural conditions and three different sampling seasons (Summer, autumn and winter). Five soil depth distribution (0-20, 20-40, 40-60, 60-80 and 80-100 cm was also investigated. The soil parameters studied were: salinity (EC), permeablity (K) and  structural stability (IS). The results demonstrate that K and IS depended significantly on the season and varied throught the soil profile. However, only the depth had an impact on the EC. The maximum EC and K were observed in summer at 0-60 and 0-20 cm, respectively. The highest IS, although, was detected during the winter at 40–60 cm depth layer. More interstingly, to take into consideration the interactions of both factors, a positive correlations were shown between K and EC, and IS (r =0.56***, r = 0.62***, respectively) and between EC and IS (r = 0.44**) in summer. In contrast, only K and EC showed a negative correlation (r = -0.35*) in the autumn, but no correlation was detected between all parameters in winter. The results indicate that treated wastewater is a suitable alternative during hot seasons, especially in sandy soils. Further research is required to investigate the effect of this wastwater on crops responses

Variation of soil properties with sampling depth in two different light-textured soils after repeated applications of urban sewage sludge

Semi-arid agricultural soils have increasingly been subjected to urban sewage sludge (USS) applications due to accelerated soil depletion and shortages in manure supply. Research studies addressing USS reuse have mostly been conducted in cropping systems and focused on changes in topsoil properties of a given texture. Therefore, sludge-soil interactions could be largely influenced by the presence of plants, soil particle composition and depth. In this field study, two agricultural soils (sandy, S and sandy loam, SL) received simultaneously four annual USS applications of 40, 80, and 120 t ha−1 year−1 in absence of vegetation. Outcomes showed the increase of carbon and macronutrients in both soils proportionally to USS dose especially in the topsoil profile (0–20 cm). Subsoil (20–40 cm) was similarly influenced by sludge rates, showing comparable variations of fertility parameters though at significant lower levels. The depth-dependent improvement of soil fertility in both layers enhanced the microbiological properties accordingly, with significant variations in soil SL characterized by a higher clay content than soil S. Besides, positive correlations between increases in sludge dose, salinity, trace metals, and enzyme activities in both soils indicate that excessive sludge doses did not cause soil degradation or biotoxic effects under the described experimental conditions. In particular and despite high geoaccumulation indices of Ni in both soils and profiles, the global concentrations of Cu, Ni, Pb, and Zn were still below threshold levels for contaminated soils. In addition, the maintenance of pH values within neutral range and the increase of organic matter content with respect to control would have further reduced metal availability in amended soils. Therefore, we could closely investigate the effects of texture and depth on the intrinsic resilience of each soil to cope with repetitive USS applications.This research study was financially supported by the Ministry of Higher Education and Scientific Research of Tunisia

Monitoring the variation of soil quality with sewage sludge application rates in absence of rhizosphere effect

Agricultural soils in semi-arid regions have frequently been degraded due to adverse climatic conditions, organic matter depletion, and poor farming practices. To enhance soil quality, this study examines the reuse of sewage sludge (SS) as an available source of organic matter in a typical Mediterranean sandy-loam soil. Accordingly, we studied the cumulative effect of two annual applications of 40, 80 and 120 tons of sludge per ha on soil quality in absence of vegetation. The dose-dependent improvement of organic matter content was the most significant event that reflected sludge application rates, and consequently influenced other soil properties. Accordingly, soil structural stability increased by 13.3%, 28.8% and 59.4% for treatments SS-40, SS-80 and SS-120 respectively as compared to unamended control. Structural stability improvement was also confirmed by the dose-dependent variation of other edaphic factors including calcium content, the microbial quotient as well as Welt and C:N ratios. These parameters are involved in cementing soil aggregates by cation bridging, the formation of microbial mucilage, and clay-humic complexes. Soil magnetic susceptibility (SMS) was measured in situ as a possible rapid tool to evaluate soil condition. SMS showed significant correlation with sludge dose and stability amelioration testifying to the aggregation role that can play Al2O3 and particularly Fe2O3 minerals added by the hematite-rich sludge. Besides, analytical results and field observations revealed no trends of soil salinization or acidification by excessive sludge amounts. By avoiding the rhizosphere effect, outcomes could reflect the resilience and intrinsic capacity of the soil to cope with excessive sludge loads.This study was financially supported by a research grant from the Tunisian Ministry of Higher Education and Scientific Research. The authors would like to thank the National Sanitation Utility (ONAS) for providing urban sewage sludge. The technical support of Rym Ghrib is hereby acknowledged

Assessment of Earthworm Viability and Soil Health after Two Years of Raw and Composted De-Inking Paper Sludge Amendment

The improvement of soil fertility properties is a priority for meeting sustainable development goals and world food security. One potential benefit of using paper sludge in agriculture is the reduction of waste and associated environmental impacts. By using paper sludge as a soil amendment, it is possible to divert away this material from landfills and instead use it to improve soil fertility and support the growth of crops. However, it is important to note that paper sludge may contain contaminants harmful to plants and soil health, of which earthworm viability serves as a key indicator. The present investigation aimed to evaluate changes in soil properties after the application of raw and composted de-inking paper sludge for two years. Accordingly, a field study was conducted in Manouba, a semi-arid region of Tunisia with a clay loam soil. The raw de-inking sludge (DS) and composted de-inking paper sludge (DSC) were applied at 30 and 60 t ha−1 and 20 and 40 t ha−1, respectively. Soil treatments were compared to unamended soils (C), to determine the optimal sludge treatment and rate for increasing the soil quality. Soil chemical (soil organic matter SOM, total carbon TC, and nitrogen TN, nutrient soil contents organic matter fractioned), physical (porosity and structural stability), and biological parameters (earthworms viability) were assessed. The results showed an increase of soil OM in the DS and DSC amended soils with the lowest rates (30 and 20 t ha−1). The humic fraction was found to be the dominant form. TC and TN were improved in the DS and DSC amended soils with the highest rates: 60 (DS2) and 40 t ha−1 (DSC2). Phosphorus and potassium were also increased in a dose-dependent manner. However, the soil porosity decreased in all treatments. The composted de-inking sludge was toxic for epigeic species, which could be explained by the use of litter while composting. Overall, the application of DS and DSC at low rates (30 and 20 t ha−1, respectively) might be a promising alternative for improving soil quality and at the same time ensuring the proper management of these wastes

Stability and maturity indexes of organic fraction compost

Composting is an environmentally friendly way to turn wastes into useful product (compost). This study aimed to monitor various chemical,physical, and biological parameters over the course of the co-composting of three organic compounds. In this context, 55 kg (55%) ofgreen waste (GW) were co-composted with 40 kg (40%) of poultry manure at 40 kg (40%) and 5 kg (5%) green waste biochar (GWB).The monitoring of this experiment continues until the final product is stable. According to several previous studies, it was generallyagreed that it was better to employ a combination of multiple tests to be sure that the compost has really reached a state of maturityand stability. During this study, a series of tests were used to determine the maturity and stability of co-composting organic wastes forsafe use. Tests used during this follow-up include the pile temperature, pile moisture, pH, total nitrogen, total carbon, C/N ratio, microbialactivity (CO2 emission), germination index, and a scanning electron microscopy. According to the results of tests carried out during thisexperiment, the compost had attained maturity on the 54th day from the beginning of the composting

Stability and maturity indexes of organic fraction compost

Composting is an environmentally friendly way to turn wastes into useful product (compost). This study aimed to monitor various chemical,physical, and biological parameters over the course of the co-composting of three organic compounds. In this context, 55 kg (55%) ofgreen waste (GW) were co-composted with 40 kg (40%) of poultry manure at 40 kg (40%) and 5 kg (5%) green waste biochar (GWB).The monitoring of this experiment continues until the final product is stable. According to several previous studies, it was generallyagreed that it was better to employ a combination of multiple tests to be sure that the compost has really reached a state of maturityand stability. During this study, a series of tests were used to determine the maturity and stability of co-composting organic wastes forsafe use. Tests used during this follow-up include the pile temperature, pile moisture, pH, total nitrogen, total carbon, C/N ratio, microbialactivity (CO2 emission), germination index, and a scanning electron microscopy. According to the results of tests carried out during thisexperiment, the compost had attained maturity on the 54th day from the beginning of the composting

Green waste biochar effects on sandy soil physicochemical properties

The organic amendment of degraded soil in South East of Tunisia was used to restore the chemical, and physical properties of soil quality investigated in this study. Biochar derived from pyrolyzed green waste at 360°C was used like organic amendment.  Nines randomized plots with one square meter of the area of each plot in three replicates have been installed in the Institute of Arid Area in Mednine South East of Tunisia, with two rates of biochar 20 and 40 t/ha were investigated: 20 tons/ha (B20) (2 kg/m²) and 40 tons/ha (B40) (4 kg/m²). The results showed that biochar had a positive effect on soil's physical and chemical properties compared to non-amended soil (Untreated soil). Biochar supply at rates of 20 and 40 tons/ha, causes a decrease in electrical conductivity to achieve 2.66 mS/cm for the B40 dose after 1 year of amendment, also a decrease in the bulk density at the surface layer (0-20 cm) has been registered, the total porosity which was decreased with depth. The hydraulic conductivity is favored by the incorporation of biochar in the soil which increases the volume of voids and tends to create preferential flow paths

Short-Term Effects of Biosolid Application on Two Mediterranean Agricultural Soils and Durum Wheat Yield

This study evaluated the effects of de-inking paper sludge (DPS) and sewage sludge (SS) application on soil properties, and durum wheat growth and yield. A pot experiment was performed on Calcaric cambisol (clCM) and Cromic Luvisol (coLV) soils. Three DPS rates (0, 30, and 60 Mg ha−1) were studied with and without nitrogen fertilizer (280 kg NH4NO3 ha−1). DPS was also mixed with SS at two rates (5 and 10 Mg ha−1) to highlight the benefits of organic nitrogen compared to mineral nitrogen. DPS improved total organic carbon and nitrogen, mineral nitrogen, and soils cation exchange capacity, the 30% rate provided the greatest improvement in both soils. DPS increased grain and root P, K, Ca, and Mg contents in both soils. It also increased wheat straw N, P, Mg, and Ca for the same soil compared to the control. Mixed DPS treatments with nitrogen fertilizer enhanced grain yield by up to 38% and increased root biomass in the studied soils. Thus, DPS is a potential source of organic matter and a liming agent for acid soils when appropriate supplemental fertilizer is provided

Carbon mineralization, biological indicators, and phytotoxicity to assess the impact of urban sewage sludge on two light-textured soils in a microcosm

The agricultural reuse of urban sewage sludge (USS) modifies soil properties depending on sludge quality, management, and pedo-environmental conditions. The aim of this microcosm study was to assess C mineralization and subsequent changes in soil properties after USS addition to two typical Mediterranean soils: sandy (Soil S) and sandy loam (Soil A) at equivalent field rates of 40 t ha−1 (USS-40) and 120 t ha−1 (USS-120). Outcomes proved the biodegradability of USS through immediate CO2 release inside incubation bottles in a dose-dependent manner. Accordingly, the highest rates of daily C emission were recorded with USS-120 (3.7 and 3.9 mg kg−1 d−1 for Soils S and A, respectively) after 84 d of incubation at 25 °C. The addition of USS also improved soil fertility by enhancing soil macronutrients, microbial proliferation, and protease activity. Protease showed significant correlation with N, total organic C, and heterotrophic bacteria, reflecting the biostimulation and bioaugmentation effects of sludge. Soil indices like C/N/P stoichiometry and metabolic quotient (qCO2) varied mostly with mineralization rates of C and P in both soils. Despite a significant increase of soil salinity and total heavy metal content (lead, nickel, zinc, and copper) with USS dose, wheat germination was not affected by these changes. Both experimental soils showed intrinsic (Soil A) and incubation-induced (Soil S) phytotoxicities that were alleviated by USS addition. This was likely due to the enhancement of biodegradation and/or retention of phytotoxicants originating from previous land uses. Urban sewage sludge amendments could have applications in soil remediation by reducing the negative effects of allelopathic and/or anthropogenic phytoinhibitors.This study was supported by a grant from the Ministry of Higher Education and Scientific Research of Tunisia. The authors thank the National Sanitation Office for providing urban sewage sludge