This paper reviews the factors affecting trace metal behaviour in estuarine and riverine floodplain soils and sediments. Spatial occurrence of processes affecting metal mobility and availability in ...floodplains are largely determined by the topography. At the oxic–anoxic interface and in the anoxic layers of floodplain soils, especially redox-sensitive processes occur, which mainly result in the inclusion of metals in precipitates or the dissolution of metal-containing precipitates. Kinetics of these processes are of great importance for these soils as the location of the oxic–anoxic interface is subject to change due to fluctuating water table levels. Other important processes and factors affecting metal mobility in floodplain soils are adsorption/desorption processes, salinity, the presence of organic matter, sulphur and carbonates, pH and plant growth. Many authors report highly significant correlations between cation exchange capacity, clay or organic matter contents and metal contents in floodplain soils. Iron and manganese (hydr)oxides were found to be the main carriers for Cd, Zn and Ni under oxic conditions, whereas the organic fraction was most important for Cu. The mobility and availability of metals in a floodplain soil can be significantly reduced by the formation of metal sulphide precipitates under anoxic conditions. Ascending salinity in the flood water promotes metal desorption from the floodplain soil in the absence of sulphides, hence increases total metal concentrations in the water column. The net effect of the presence of organic matter can either be a decrease or an increase in metal mobility, whereas the presence of carbonates in calcareous floodplain soils or sediments constitutes an effective buffer against a pH decrease. Moreover, carbonates may also directly precipitate metals. Plants can affect the metal mobility in floodplain soils by oxidising their rhizosphere, taking up metals, excreting exudates and stimulating the activity of microbial symbionts in the rhizosphere.
Research attention is growing for biochar as amendment for anaerobic digestion (AD), as it may improve both the AD process and digestate properties. In this study, two biochars (from insect frass or ...the woody fraction of green waste, both pyrolyzed at 450 °C) were added (5 % w/w) during semi-continuous AD of organic kitchen waste and chicken manure. Biochar was mixed either during the AD process or to the digestate post-treatment. The impact of biochar addition on the AD process, NH3 and greenhouse gas emissions, as well as C and N mineralization following soil application, was examined. Biochar did not affect the biogas yield, but did lead to a reduction in NH3 levels in the biogas and NH4+-N sorption onto the biochars, reducing the risk of AD inhibition. N sorbed as NH4+-N onto the biochar was more available for mineralization than N sorbed as NH3. N sorption on biochar-amended digestates did not result in trade-offs when these digestates were applied to soil: the sorbed N was not released as NH3 or N2O after soil application and was not released as mineral N in either the short or medium term. The C-rich biochars increased the OC content of the digestate, which enhanced its value as soil improver. Additionally, mixing biochar with digestate decreased the soil CO2 emissions up to 33 % when it was added after AD; no priming effects were observed. These findings highlight the potential benefits of incorporating biochar into AD systems and the subsequent application of biochar-amended digestate in agricultural practices.
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•Biochar decreased NH3 levels in the biogas due to N sorption onto the biochars.•The sorbed N was not released after soil application of the digestates.•Mixing biochar with digestate decreased soil CO2 emissions up to 33 %.•Biochar-enriched digestate serves as a valuable soil improver and fertilizer.
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•Biochar reduces NH3 emissions during cattle slurry storage up to 20%•Biochar improves the separation efficiency and the quality of the solid fraction.•Biochar increases C, (organic) ...N and water-available P in the solid fraction.•S° is only successful for reducing NH3 emissions in combination with biochar.•Biochar results in a short term priming effect on the C mineralization of manure.
Cattle slurry storage is a major source of gaseous N emissions. The aim of this study was to evaluate the effects of biochar, clinoptilolite and elemental sulfur (S°) on (1) NH3 and greenhouse gas emissions during storage of cattle slurry and (2) after soil application of the enriched solid fractions; and (3) on the agronomic quality of the solid and liquid fractions. In the first phase, biochar was added to the slurry (10 g L-1); subsequently in the second phase, clinoptilolite (50 g L-1), S° (1 g L-1) and 40 g L-1 extra biochar were added. Gaseous emissions were monitored by a semi-continuous multi-gas analyzer and the agronomic quality of solid and liquid fractions was assessed after separation. The enriched solid fractions were applied to soil to study the effects on gaseous emissions, N and C mineralization. Amendment of biochar reduced NH3 emissions during cattle slurry storage by 12% during the first 7 days. Extra amendment of biochar, clinoptilolite and S° in combination with biochar resulted in a decrease of NH3 emissions of approximately 20%. The N sorbed from the slurry by the biochar was not released as NH3 during soil application of the solid fractions and was not released as mineral N in the short term (within 28 days). A short-term positive priming effect of biochar on the C mineralization of manure and biochar-manure mixture applied to soil was observed. The biochar-enriched solid fractions contained more C, total and organic N and water-available P with a slow release.
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•Higher P leaching from farmyard manure amended soils than from compost amended soils.•Long term amendments of farmyard manure reduced the soil P sorption.•There is a large seasonal ...trend in soil P availability.•The seasonal trend in soil P availability is independent from the fertilizer type.
This study was set up to identify the role of dairy farmyard manure and green waste or farm compost used as a source of stable organic matter on soil P availability and P leaching. We sampled two long term field trials (8 and 16 years) on silt loam soil, with continuous amendment of dairy farmyard manure (FYM) and 6 types of organic waste (VFG, BIO), municipal solid waste (MSW), sludge (GWS) or organic farm waste (CMC1, CMC2) composts. Soil P availability was measured as 0.01M CaCl2 extractable P (P-CaCl2) and hot water extractable P (HWP) and fresh subsamples were used to conduct a leaching experiment in unsaturated conditions in the laboratory. Since the P fertilization history was not equal among the treatments, P leaching concentrations (TP) were standardized with the total P content of the soil (Ptot). P-CaCl2, HWP and the P leaching experiment revealed that in long term farmyard manure amended soils, more P becomes available and is susceptible to leaching than in long term VFG, BIO, MSW, CMC1 and CMC2 compost amended soils. We observed a seasonal trend in P-CaCl2 with minimum and maximum at end of winter (February) and mid-summer (July), respectively. Although this trend was independent of the fertilizer type amended on the soil, the P-CaCl2 significantly increased for farmyard manure amended soil, compared to compost amended soil at any time during the sampling period of >1 year. A sorption experiment with radiolabelled orthophosphoric acid (33PO4) revealed that increased soil P availability and P leaching are related to a decrease in orthophosphate sorption in farmyard manure amended soils, which was not observed in compost amended soils. It is concluded that farmyard manure derived P is more available and more prone to leaching compared to compost derived P due to differences in PO4 sorption.
•Limited compost use despite farmers’ recognition of the benefits.•Mixed method approach used to reveal barriers to compost use in agriculture.•Twenty-eight barriers were revealed, analyzed and ...categorized.•The most prevalent barriers are either financial, institutional or informational.•Five recommendations to potentially alleviate some of the barriers to compost use.
Maintaining and increasing soil quality and fertility in a sustainable way is an important challenge for modern agriculture. The burgeoning bioeconomy is likely to put further pressure on soil resources unless they are managed carefully. Compost has the potential to be an effective soil improver because of its multiple beneficial effects on soil quality. Additionally, it fits within the bioeconomy vision because it can valorize biomass from prior biomass processing or valorize biomass unsuitable for other processes. However, compost is rarely used in intensive agriculture, especially in regions with high manure surpluses. The aim of this research is to identify the barriers to on-farm composting and the application of compost in agriculture, using a mixed method approach for the case of Flanders. The significance of the 28 identified barriers is analyzed and they are categorized as market and financial, policy and institutional, scientific and technological and informational and behavioral barriers. More specifically, the shortage of woody biomass, strict regulation, considerable financial and time investment, and lack of experience and knowledge are hindering on-farm composting. The complex regulation, manure surplus, variable availability and transport of compost, and variable compost quality and composition are barriers to apply compost. In conclusion, five recommendations are suggested that could alleviate certain hindering factors and thus increase attractiveness of compost use in agriculture.
•Biochars were tested both for NH4+-N and NH3 sorption.•Both tests enable to select biochars to use in processes for N mitigation.•NH4+-N sorption was higher for manure-based biochars.•NH3 sorption ...showed a positive linear relationship with NH4+-N sorption.
Biochar amendment during biomass processing can improve those processes and products, and reduce the emissions of greenhouse gases and NH3, resulting in ecologic and economic benefits. The potential positive effects of biochar are related to NH4+-N and NH3 sorption, which in turn are depending on different biochar characteristics. By knowing the relationship between biochar characteristics and NH4+-N and NH3 sorption, biochar production can be steered towards a higher N sorption or existing biochars can be selected for targeted applications for high N sorption. Therefore, this study aims to develop fast screening tests to estimate the potential for both NH4+-N and NH3 sorption of biochar, before application in biomass processing. Further, the effects of feedstock, pyrolysis temperature, biochar characteristics and biochar treatments on N sorption are studied. The results show that NH4+-N sorption varied between 0 and 1.54 mg NH4+-N/g fresh biochar and was highest for manure-based biochars with a high nutrient content and cation exchange capacity, produced at lower temperatures (300–450 °C). For some biochars, the feedstock itself had a higher NH4+-N sorption than the biochar. Grinding and washing increased the NH4+-N sorption. In addition, a general linear model was proposed to predict the NH4+-N sorption based on three chemical characteristics· NH3 sorption varied between 0 and 100 % of the negative control and showed a linear positive relationship with the NH4+-N sorption, moisture retention factor and cation exchange capacity. Pyrolysis temperature and feedstock type did not significantly affect NH3 sorption. NH4+-N and NH3 desorption varied amongst biochar type.
•We conducted a long term field trial, to compare several types of organic fertilizers.•We examined changes in P availability, soil P and C levels, crop yield and P leaching.•Compost, farmyard manure ...and cattle slurry lead to minor differences in crop yield.•Farmyard manure increased P availability and P leaching.•Application of compost increased the soil C levels without increasing P leaching risks.
The main objective of the present study was to compare fertilizer types in their ability to increase the soil organic matter content without increasing potential P leaching losses. Differences in soil organic carbon content, crop yield, P-CaCl2, P-AL, P export by the crop and P leaching from soil supplied with three compost types, cattle slurry, farmyard manure or mineral fertilizers were compared in a 8 years field experiment with arable, vegetable and fodder crops. P leaching losses were assessed separately in a soil column leaching experiment. As expected, farmyard manure and compost are the better options to increase the soil organic carbon level. Cattle slurry and mineral fertilizers tended to produce lower crop yields. P-CaCl2 was increased when farmyard manure was used as organic fertilizer, leading to an increased P leaching but not to an increased crop P export. Therefore it seems that the higher dissolved P concentrations in the soil solution for farmyard manure, measured as P-CaCl2 in the soil, are a source of potential P losses. All three compost types could gradually increase soil organic carbon levels without increasing P leaching losses.
Chitin is a valuable peat substrate amendment by increasing lettuce growth and reducing the survival of the zoonotic pathogen Salmonella enterica on lettuce leaves. The production of chitin-catabolic ...enzymes (chitinases) play a crucial role and are mediated through the microbial community. A higher abundance of plant-growth promoting microorganisms and genera involved in N and chitin metabolism are present in a chitin-enriched substrate. In this study, we hypothesize that chitin addition to peat substrate stimulates the microbial chitinase production. The degradation of chitin leads to nutrient release and the production of small chitin oligomers that are related to plant growth promotion and activation of the plant's defense response. First a shotgun metagenomics approach was used to decipher the potential rhizosphere microbial functions then the nutritional content of the peat substrate was measured. Our results show that chitin addition increases chitin-catabolic enzymes, bacterial ammonium oxidizing and siderophore genes. Lettuce growth promotion can be explained by a cascade degradation of chitin to N-acetylglucosamine and eventually ammonium. The occurrence of increased ammonium oxidizing bacteria, Nitrosospira, and amoA genes results in an elevated concentration of plant-available nitrate. In addition, the increase in chitinase and siderophore genes may have stimulated the plant's systemic resistance.
We investigated the potential of C-rich byproducts to replace wood chips as bulking agent (BA) during composting. The impact of these alternatives on the composting process and on compost stability ...and characteristics was assessed. Three BA (chopped heath biomass and spent growth media used in strawberry and tomato cultivation) were used for processing leek residues in windrow composting. All BA resulted in stable composts with an organic matter (OM) content suitable for use as soil amendment. Using chopped heath biomass led to high pile temperatures and OM degradation and a nutrient-poor compost with high C/P ratio appropriate for increasing soil organic carbon content in P-rich soils. Spent substrates can replace wood chips, however, due to their dense structure and lower biodegradation potential, adding a more coarse BA is required. Generally, the nutrient content of the composts with growth media was higher than the composts with wood chips and chopped heath biomass.
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•Chopped heath and spent growth media can be used as bulking agents.•Chopped heath compost has a high OM content and C/P ratio.•Clear differences in N immobilization between bulking agents were observed.•NIRS can monitor quickly the chemical properties and stability during composting.
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