Pedotransfer Functions for Estimating Soil Bulk Density Using Image Analysis of Soil Structure.

Soil bulk density is one of the most important soil properties. When bulk density cannot be measured by direct laboratory methods, prediction methods are used, e.g., pedotransfer functions (PTFs). However, existing PTFs have not yet incorporated information on soil structure although it determines soil bulk density. We aimed therefore at development of new PTFs for predicting soil bulk density using data on soil macrostructure obtained from image analysis. In the laboratory soil bulk density (BD), texture and total organic carbon were measured. On the basis of image analysis, soil macroporosity was evaluated to calculate bulk density by image analysis (BDim) and number of macropore cross-sections of diameter ≥5 mm was determined and classified (MP5). Then, we created PTFs that involve soil structure parameters, in the form BD~BDim + MP5 or BD~BDim. We also compared the proposed PTFs with selected existing ones. The proposed PTFs had mean prediction error from 0 to -0.02 Mg m-3, modelling efficiency of 0.17-0.39 and prediction coefficient of determination of 0.35-0.41. The proposed PTFs including MP5 better predicted boundary BDs, although the intermediate BD values were more scattered than for the existing PTFs. The observed relationships indicated the usefulness of image analysis data for assessing soil bulk density which enabled to develop new PTFs. The proposed models allow to obtain the bulk density when only images of the soil structure are available, without any other data.

Phytoextraction of heavy metals after application of bottom ash and municipal sewage sludge considering the risk of environmental pollution.

Waste management to reduce the loss of natural resources has become a basis of sustainable development and a circular economy. When using waste, the heavy metal (HM) concentration must be taken into account since HMs can be potentially released to the environment, posing a toxicity threat. The aim of the study was thus to estimate the availability for plants of Cr, Ni, Cu, Zn, Cd, and Pb introduced into the soil with waste. We hypothesized that the prepared waste mixtures containing coal or biomass ash and municipal sewage sludge would reduce the environmental risk compared to the studied waste used separately. The research was conducted during a 6-year field experiment with grasses and legumes. HM concentration in soil, waste, and plant biomass; tolerance index; and uptake of HMs by plants were measured. The ash-sludge mixtures had a more favourable effect on the soil in terms of pHKCl, TOC, total nitrogen, and total exchangeable bases than the waste used separately. This provided beneficial conditions for plant growth and development. Consequently, the ash-sludge mixtures increased the plant yield as compared to ash alone, while the mixture containing the biomass ash also enhanced the yield in relation to the sewage sludge. The study showed that the mixtures allowed for a reduction of environmental risk arising from the HM input with waste to the soil. It was proven that HM availability for plants could be beneficially modified by mixing waste. Combining the coal ash with the sewage sludge is particularly recommended, owing to the unfavourable properties of coal ash for plants. The application of the higher dose of the coal ash-sludge mixture showed a better effect than the lower dose, while the influence of both doses of the biomass ash-sludge mixture was similar. Under the ash-sludge treatment, plants took up more HM than under the ash used separately, and the HM concentration in the obtained biomass did not generally exceed that observed under single wastes. This should reduce the accumulation of HMs in the soil during a long-term use of the waste and facilitates the utilisation of the produced biomass.

Application of ash and municipal sewage sludge as macronutrient sources in sustainable plant biomass production.

Owing to the growing volumes of ash and sewage sludge waste, there is a requirement for theoretical and practical research into the use of these wastes as a source of nutrients. However, there are relatively few studies on the transfer of macronutrients in soil-plant systems amended with ash-sewage sludge mixtures under field conditions. The aim of the study was to determine the effect of bituminous coal ash (AC), biomass ash (AB), and municipal sewage sludge (MSS) on the quantity and quality of a grass-legume mixture. During a 6 year field experiment on a sandy loam soil treated with the wastes, applied as mixtures or separately, the plant yield; N, P, K, Na, Mg, and Ca uptake by plants; macronutrient content and ratios in the plant biomass; and the recovery rate of macronutrients by plants were evaluated. The AB-MSS treatment increased the yield in comparison to that where the wastes were applied separately. The N, P, and Ca contents in the plant biomass and N and P uptake under ash-sludge treatments were in the range observed for the ash and sewage sludge. The AB-MSS co-application resulted in the highest K uptake. The AC-MSS treatment increased K and Mg uptake in relation to AC treatment. When AC or AB was added to the MSS, the Ca uptake increased relative to the MSS treatment. The plant biomass under the AB treatment was optimal for biofuel purposes in terms of the chemical composition. The co-application of AC or AB with MSS resulted in the optimum Ca:Mg ratio for fodder purposes. The recovery rate of the macroelements decreased in the following order: K, N, P, Mg, Na, and Ca. The results support the co-application of solid wastes such as ash and municipal sewage sludge to improve productivity, support the recycling of macronutrients, improve sustainability through the reduction of ash and sewage sludge disposal, and reduce reliance on mineral fertilizer.