Biochar as Soil Amendment: Impact on Soil Properties and Sustainable Resource Management

The role of biochar in improving soil fertility is increasingly being recognized and is leading to recommendations of biochar amendment of degraded soils. In addition, biochars offer a sustainable tool for managing organic wastes and to produce added-value products. The benefits of biochar use in agriculture and forestry can span enhanced plant productivity, an increase in soil C stocks, and a reduction of nutrient losses from soil and non-CO2 greenhouse gas emissions. Nevertheless, biochar composition and properties and, therefore, its performance as a soil amendment are highly dependent on the feedstock and pyrolysis conditions. In addition, due to its characteristics, such as high porosity, water retention, and adsorption capacity, there are other applications for biochar that still need to be properly tested. Thus, the 16 original articles contained in this book, which were selected and evaluated for this Special Issue, provide a comprehensive overview of the biological, chemicophysical, biochemical, and environmental aspects of the application of biochar as soil amendment. Specifically, they address the applicability of biochar for nursery growth, its effects on the productivity of various food crops under contrasting conditions, biochar capacity for pesticide retention, assessment of greenhouse gas emissions, and soil carbon dynamics. I would like to thank the contributors, reviewers, and the support of the Agronomy editorial staff, whose professionalism and dedication have made this issue possible

4D structure of biochar and its impact on soil water characteristics

Intensification of agricultural practices is necessary to support a growing global population. Water movement and storage in soils are very crucial for successful intensification of agriculture. They are important for nutrient delivery to plant and overall crop productivity. Climate change and population growth have been predicted to limit water supply especially in arid regions. Therefore, there is an urgent need to proffer solutions that would help maintain or even increase soil moisture retention. The use of biochar for improving soil hydraulic properties is a current and growing area of research. Biochar is a stable form of charcoal gotten from heating natural organic materials in a high temperature and low oxygen process known as pyrolysis. Biochar physical and chemical properties vary due to the pyrolysis process conditions, the type of feedstock, and the ratios of lignin, cellulose, and hemicellulose in the biomass. These change the structure of the biochar and will invariably affect to what extent it can improve soil water retention. To understand how biochar affects soil water properties we must understand the specific characteristics of biochar that influence these changes. Understanding the mechanisms is important for easy prediction of when and by how much biochar will improve soil water properties. The aim of this thesis is to provide new and extensive insight into 4D structural changes of biochar produced from different feedstock and pyrolysis conditions and how these affects soil moisture characteristics of different soil textures. The first aspect of the thesis was to carry out a meta-analysis of the available literature to quantify the effect of biochar on soil hydraulic properties. To enable matching of biochar to soil constraints and application needs, a thorough understanding of the impact of biochar properties on relevant soil parameters is necessary. This meta- analysis of the available literature for the first time quantitatively assessed the effect of not just biochar application, but different biochar properties on the full sets of key soil hydraulic parameters. The review shows that the key factors influencing biochar performance were particle size, specific surface area and porosity indicating that both soil-biochar inter-particle and biochar intra-particle pores are important factors. Next, the role of biochar particle size and hydrophobicity in controlling soil water movement and retention was assessed. Softwood pellet biochar in five particle size ranges was used for the experiment. These particle sizes were tested on two soil types at four different application rates in the laboratory. The results clearly show that both biochar intraporosity (pores inside biochar particles) and interporosity (pore spaces between biochar and soil particles) are important factors affecting amended soil hydraulic properties. Biochar interpores affect mainly hydraulic conductivity; both interpores and intrapores control soil water retention properties. Our results suggest that for a more effective increase in soil water retention of coarse soils, the use of hydrophilic biochar with high intraporosity is recommended. The third aspect of the thesis was to assess the 4D structural changes and pore network model of standard biomass feedstock during pyrolysis. Biochar properties are highly variable and are dependent on the biomass feedstock and production conditions. Despite these variabilities, there has been no study that uses a single sample to study the development of microstructural properties of biomass and biochar through the full range of pyrolysis temperatures. In this study, synchrotron x-ray micro-tomography (SµCT) was used to visualize the internal structure and characterise pore structure of biochar from several feedstock during pyrolysis (50 - 800 °C). The results show a wide range of variation in the pore structural characteristics of the biochar depending on feedstock and pyrolysis temperature, with observed porosity in the range of 7.41 – 60.56 %. The results from this study are not only important for the use of biochar as soil amendments but also a range of other applications relying on biochar pore characteristics, such as biochar as habitat for microbes, water, and wastewater treatments, as an absorbent for the removal of acid gases, or an additive in construction or engineering materials. In addition, the in-depth insights into changes in biomass structure during heating are valuable for research and applications related to fire safety. Finally, the data set from the SµCT was used to produce statistical models enabling the prediction of the effect of biochar on soil water holding capacity from biochar microstructural properties. The results of this thesis, therefore, clearly establish the mechanisms with which biochar improves soil hydraulic properties. It also demonstrates that by appropriately matching microstructural properties of biochar to those of the target soil, it is possible to achieve considerable improvement in soil properties using relatively low application rates of biochar. The relationship between biochar structural properties and its effect on soil moisture characteristics of specific soil texture, is an attractive pathway towards development of precisely tailored biochars aimed to enhance water use efficiency and provide low-dose, high-efficiency benefits

Effects of biochar on soil processes, soil functions and crop growth

Biochar is the carbon-rich product obtained when organic material is pyrolyzed, during which bioenergy is produced. When applied to soil, biochar is claimed to have positive effects on soil properties and processes and carbon could be sequestered. For these reasons, biochar production and application to soil is often associated with raising agricultural productivity while mitigating climate change. Especially in (tropical) highly weathered soils, biochar has shown positive effects on soil properties and crop yields, but it is uncertain whether the same positive effects can be obtained in (temperate) more fertile soils. Therefore the overarching aim of this PhD research was to get a better understanding of biochar effects on soil chemical, physical and biological properties, plant growth, and soil greenhouse gas emissions in agricultural northwestern European soils. Lab, pot and field experiments have been conducted to gain insight into biochar effects on plant and soil. 15N tracing lab experiments suggested that in the short term, biochar addition to soil stimulated mineralization of more complex SOC, thereby increasing mineral N availability. However, in the absence of plants this available N was rapidly, biotically immobilized. Furthermore, nitrification rates were increased with biochar addition. In contrast, in the longer term, these effects faded, probably due to the transient effects of biochar labile C fraction and pH. Moreover, lab experiments have shown that biochar can reduce mineral N availability in the short term, likely due to biotic or abiotic N immobilization. It is unknown when and to which extent the immobilized N could become available again. These experiments also show that biochar can increase soil pH, through which several soil processes can be affected, e.g. NH3 volatilization, nitrification and denitrification However, bulk soil pH was not always significantly increased by biochar addition. There was a trend for a higher increase in soil pH after biochar application in low pH soils while at more neutral soil pH, this was not the case as observed in the biochar field trial. It cannot be excluded that elevated pH micro-sites close to biochar particles affect soil processes, despite biochar having no effect on bulk soil pH. In the short term, likely microbial activity and abundance should be altered through biochar, as the 15N tracing experiments showed that biochar affected soil N cycling in the short term. This effect seems to be transient, probably due to a change in biochar properties, as biochar seems to act as an inert substance regarding N cycling in the longer term as biochar seems to act as an inert substance regarding N cycling in the longer term. This was shown by a 15N tracing experiment conducted with soil sampled one year after biochar application. Furthermore, biochar addition to soil did not influence soil microbiological community structure to a large extent in six European North Sea region countries during the first year after biochar application, as only certain bacterial biomarker PLFAs were significantly affected by biochar addition. It was remarkable that fungal biomarker PLFAs were not significantly influenced by biochar addition. Biochar addition to soil reduced N2O and NO emissions compared to the control soil after urea and NO3- fertilizer application, and NO emissions after NH4+ fertilizer application. N2O emissions were more decreased at high compared to low pyrolysis temperatures. Also reduced NO3- availability after biochar addition was observed. We hypothesize that decreased N2O and NO emissions were mediated by multiple interacting phenomena: stimulated NH3 emissions, microbial N immobilization, non-electrostatic sorption of NH4+ and NO3-, and pH effects. Pot trial results showed that biochar can cause short-term reductions in biomass production due to reduced NO3- availability. This effect was biochar feedstock and pyrolysis temperature dependent. Hence biochar addition might in some cases require increased fertilizer N application to avoid crop growth retardation. In the field trial, a complex interaction between soil physical parameters, time after biochar application and time of tillage operations was observed. Effects on bulk density, porosity and soil water retention curves were non-consistent over time, possibly due to interaction with tillage operations. Biochar increased soil water content in 2012, although mostly not significantly. However, in 2013, when soil water content was overall lower compared to during 2012, it was not affected by biochar addition. Under field circumstances, biochar addition to soil did not affect spring barley grain or straw yield, nor N or P uptake during the first two years after biochar application. In the field trial, biochar was applied to soil in autumn, as it was our hypothesis that there could be a negative crop response due to reduced N availability when the biochar would be applied in spring and a crop would be immediately sown. However, biochar did not affect soil mineral N availability, neither immediately after biochar application, nor afterwards. Overall, our results indicate that biochar has mixed effects on soil quality properties in the short term, as effects can be positive, negative, and neutral. The field trial results showed that in medium term, biochar does hardly affect soil properties. Our study shows relatively short-term results, and long-term data are needed to confirm these first results

A review on biochar modulated soil condition improvements and nutrient dynamics concerning crop yields: pathways to climate change mitigation and global food security

The beneficial role of biochar on improvement of soil quality, C sequestration, and enhancing crop yield is widely reported. As such we could not find a compiled source of information linking biochar modulated soil condition improvement and soil nutrient availability on crop yields. The present review paper addresses the above issues by compilation of world literatures on biochar and a new dimension is introduced in this review by performing a meta-analysis of published data by using multivariate statistical analysis. Hence this review is a new in its kind and is useful to the broad spectrum of readers. Generally, alkalinity in biochar increases with increase in pyrolysis temperature and majority of the biochar is alkaline in nature except a few which are acidic. The N content in many biochar was reported to be more than 4% as well as less than 0.5%. Poultry litter biochar is a rich in P (3.12%) and K (7.40%), while paper mill sludge biochar is highest in Ca content (31.1%) and swine solids biochar in Zn (49810 mg kg-1), and Fe (74800 mg kg-1) contents. The effect of biochar on enhancing soil pH was highest in Alfisol, Ferrosol and Acrisol. Soil application of biochar could on an average increase (78%), decrease (16%), or show no effect on crop yields under different soil types. Biochar produced at a lower pyrolysis temperature could deliver greater soil nutrient availabilities than that prepared at higher temperature. Principal component analysis (PCA) of available data shows an inverse relationship between pyrolysis temperature and soil pH, and biochar application rate and soil cation exchange capacity.The PCA also suggests that the original soil properties and application rate strongly control crop yield stimulations via biochar amendments. Finally, biochar application shows net soil C gains while also serving for increased plant biomass production that strongly recommends biochar as a useful soil amendment. Therefore, the application of biochar to soils emerges as a ‘win-win strategy’ for sustainable waste management, climate change mitigation and food security

Biochar: pyrogenic carbon for agricultural use: a critical review.

O biocarvão (biomassa carbonizada para uso agrícola) tem sido usado como condicionador do solo em todo o mundo, e essa tecnologia é de especial interesse para o Brasil, uma vez que tanto a ?inspiração?, que veio das Terras Pretas de Índios da Amazônia, como o fato de o Brasil ser o maior produtor mundial de carvão vegetal, com a geração de importante quantidade de resíduos na forma de finos de carvão e diversas biomassas residuais, principalmente da agroindústria, como bagaço de cana, resíduos das indústrias de madeira, papel e celulose, biocombustíveis, lodo de esgoto etc. Na última década, diversos estudos com biocarvão têm sido realizados e atualmente uma vasta literatura e excelentes revisões estão disponíveis. Objetivou-se aqui não fazer uma revisão bibliográfica exaustiva, mas sim uma revisão crítica para apontar alguns destaques na pesquisa sobre biochar. Para isso, foram selecionados alguns temaschave considerados críticos e relevantes e fez-se um ?condensado? da literatura pertinente, mais para orientar as pesquisas e tendências do que um mero olhar para o passad

Soil Nitrogen Supply: Linking Plant Available N to Ecosystems Functions and Productivity

This book, a printed edition of the Special Issue Soil Nitrogen Supply: Linking Plant Available N to Ecosystem Functions and Productivity, presents thoughtful research papers that will advance our understanding of this fascinating topic. New knowledge about modeling and the impact of cover crops, crop residues, soil amendment, and other management practices is presented in the context of agricultural and urban ecosystems

Restoration of soil quality using biochar and brown coal waste: A review

Soils in intensively farmed areas of the world are prone to degradation. Amendment of such soils with organic waste materials attempts to restore soil quality. Organic amendments are heterogeneous media, which are a source of soil organic matter (SOM) and maintain or restore chemical, physical, biological and ecological functionality. More specifically, an increase in SOM can influence the soil microclimate, microbial community structure, biomass turnover and mineralisation of nutrients. The search is on-going for locally sourced alternatives as many forms may be costly or geographically limiting. The present review focuses on a heterogeneous group of amendments i.e. biochar and brown coal waste (BCW). Both biochar (made from a variety of feedstocks at various temperatures) and BCW (mined extensively) are options that have worldwide applicability. These materials have very high C contents and soil stability, therefore can be used for long-term C sequestration to abate greenhouse gas emissions and as conditioners to improve soil quality. However, biochar is costly for large-scale applications and BCW may have inherently high moisture and pollutant contents. Future studies should focus on the long-term application of these amendments and determine the physicochemical properties of the soil, bioavailability of soil contaminants, diversity of soil communities and productivity of selected crops. Furthermore, the development of in situ technologies to lower production and processing costs of biochar and BCW would improve their economic feasibility for large-scale application

A reconnaissance-scale GIS-based multicriteria decision analysis to support sustainable biochar use: Poland as a case study

Although increasing numbers of research papers regarding biochar are being published worldwide, in some countries growing interest in biochar has only recently been observed; this is true of Poland. We analysed information on biochar research in Poland alongside lessons learned elsewhere in order to identify the significant opportunities and risks associated with biochar use. This data fed into a GIS-based multicriteria analysis to identify areas where biochar application could deliver greatest benefit. We found that 21.8% of agricultural land in Poland has at least moderate indication for biochar use (soil organic matter below 2% and pH below 5.5), while 1.5% was categorized as a priority as it also exhibited contamination. Potential barriers identified included biomass availability and associated risks of indirect land-use change due to possible national and transnational biomass production displacement. Biochar use could have positive global consequences as a climate change mitigation strategy, particularly relevant in a country with limited alternatives. Scaling up a mitigation technology that is viable on account of its co-benefits might be cost-effective, which could, in turn, adjust national perspectives and stronger involvement in developing mitigation policies at the regional level. Biochar has much promise in temperate conditions and further research should therefore be assigned to explore biochar’s environmental and socio-economic impacts

The effect of biochar on soil health and greenhouse gas emissions in a conventional temperate agricultural system

Biochar has been present in tropical agriculture as a soil amendment for millennia. Its ability to alter soil physical and chemical characteristics has been utilized to improve soil health and crop productivity. The use of biochar in temperate agricultural soils is a new concept, and has been practiced for about a decade. To date, few long-term field studies have quantified the temporal effects biochar has on soil health or greenhouse gas emissions (GHGs) of temperate agricultural soil. The objectives of this study were to quantify differences in soil characteristics of biochar and non-biochar amended soil, to determine the relationship between emissions and soil characteristics, and to determine temporal variations in GHG emissions in temperate agricultural soils following biochar additions. The treatments were (1) 6 t/ha poultry manure plus 135 kg/ha of nitrogen (urea) fertilizer (MN), (2) 3 t/ha poultry manure plus 3 t/ha biochar (MB) and (3) 3 t/ha poultry manure, 3 t/ha biochar plus 135 kg/ha fertilizer (MNB). It was found that the vast majority of analyzed attributes were unchanged by biochar additions. Soil moisture, temperature, and PO43- were however significantly greater (P<0.05) in the conventional treatment, while C/N ratios and light fraction distribution within the soil were temporarily altered by additions. Though not significant, biochar soils, MB and MNB, appeared favorable for corn yield and aboveground biomass accumulation (2016). The opposite effect was found for soybean yield (2017), although this was still not significant. Soil CO2 and N2O emissions were not significantly different (P<0.05) among the conventional treated soils and biochar-amended soils in 2016 and 2017. CO2 and N2O emission rates were similar in both field seasons. Results from this study revealed that a low biochar addition rate had few, or temporary impacts on soil health and greenhouse gas emissions