Biochar impacts on soil properties - A review focusing on Nordic research

Biochar application as a soil amendment has improved crop productivity, soil properties, and long-term carbon (C) storage in soils. In order to ascertain these positive effects of biochar, a six-year study was conducted on deep black soil in a typical semi-arid setup of Karnataka. Biochar (prepared from Prosopis juliflora¬) was applied and mixed at rates ranging from 2.5 to 20 t ha-1 to rabi sorghum under rainfed conditions before the start of the study. The six treatment combinations were evaluated through their effects on run-off, soil loss, sorghum yields, soil properties, and increase in soil organic carbon (SOC) stock at the end of the study period. Sorghum yield increased with the levels of biochar application, with yields under 10 and 20 t ha-1 levels of addition being statistically at par. Soil loss was not significantly affected by biochar application, and so were most of the soil properties. However, there was an increase in SOC stock to the tune of 0.28 and 0.43 t ha-1y-1 through biochar application @ 10 and 20 t ha-1, respectively, pointing at the C sequestration potential of biochar. Increased crop yields by applying biochar can be attributed to enhanced soil aggregation and water holding capacity and increased nutrient cycling and uptake by plant roots.

Biochar is recommended as a soil amendment for its positive influence on soil hydrological properties, which results in improved soil fertility and crop yield. Much research in the last decade has been conducted in field and laboratory conditions on the effect of biochar on the hydraulic properties of soil. However, reported results in the literature are substantially inconsistent. Here we performed a meta‐analysis to capture the variations in change in hydraulic properties of arable soils after application of different rates of biochar. The meta‐analysis revealed that high biochar rates (>50 t ha −1 ) compared to low rates (<20 t ha −1 ) significantly improved dry bulk density in sandy and clay soils, in field and laboratory experiments. However, field capacity only improved in laboratory experiments on sandy soils. The plant available water, permanent wilting point and saturated hydraulic conductivity did not significantly increase at high rates of biochar application compared to the low rates when applied to different types of soils in both field and laboratory experiments. We discuss possible reasons for this, including hydrophobicity of the biochar with future research directions. We concluded that the current evidence does not support the notion that the application of biochar improves soils' available water capacity. Highlights Meta‐analysis clarifies the influence of biochar on soil hydraulic properties. Biochar addition at higher rates only improves the water holding capacity of sandy soils. Biochar types and pyrolysis temperatures do not influence soil hydraulic properties. The efficiency of biochar may depend on its pore size distribution and hydrophobicity.

Influence of biochar as a soil amendment have been widely reported to improve soil qualities, water retention and crop productivity. But the holistic investigation of the interactions between the soil properties, leaf area index (an important plant physiological parament) and maize productivity in biochar amended soil have not been well investigated. Also, comprehensive mechanism by which biochar addition improved crop yield, due to individual and co-application of the soil amendments has not been fully understood. Thus, utilizing a factorial design, a three-year field experiment was conducted during the dry seasons of 2016, 2017, and 2018. The treatments with maize planted were treated to deficit irrigation at 60, 80, and 100% of full irrigation requirements. Two levels of fertilizer (0 and 300 kg/ha) and five rates of biochar application (0, 3, 6, 10, and 20 t/ha) were used. Weekly measurements were made of the following maize growth parameters: plant height, number of leaves, leaf area, and leave area index (LAI). At harvest, the grain yield in each treatment's replicate was measured. At harvest, soil samples were taken from the top soil and their physico-chemical characteristics were examined. The relationship between maize yield, soil properties and LAI were determined using Pearson correlation. Soil and yield data for years 2016 and 2017 were used for the model calibration, while the year 2018 data was used for the model validation. Results of the analysis showed that soil organic matter strongly and positively correlate well with the soil nutrients and hydro-physical properties. The strongest correlation of the organic matter with the soil properties was obtained with the soil moisture content, with r = 0.93 and 0.87 under individual biochar application and co-application with inorganic fertilizer. Among the soil properties, moisture content, hydraulic conductivity and pH were the soil factors affecting the maize yield, with P-value < 0.01 under the individual application of biochar. The significant (P < 0.1) and moderate interrelationship (correlation, 0.42 > r < 0.52) between the soil nutrient, moisture content, unsaturated hydraulic conductivity and maize yield observed under co-application of the amendments showed that nutrient retention and movement are the dominant factors responsible for the improved yield. The prediction of maize yield using the soil properties improved with the inclusion of the plant physiological factor (LAI). The coefficient of determination which was used to assess the predictions showed that the inclusion of LAI increased the r2 from 6.7 to 60% during validation. Considering the magnitude of deficit irrigation applied in thisstudy to simulate climate change scenario and the different soil management practiced, the inclusion leaf area index improved the prediction of maize yield. Therefore, in order to capture the variability in maize yield due to changing climate and soil properties dynamics, it is necessary to include LAI in the prediction of crop yield with the use simple multiple linear regression.

Does biochar application improve soil aggregation? A meta-analysis

Effects of soil amendments on soil acidity and crop yields in acidic soils: A world-wide meta-analysis

The crucial factors of soil fertility and rapeseed yield - A five year field trial with biochar addition in upland red soil, China

Structural and microbial evidence for different soil carbon sequestration after four-year successive biochar application in two different paddy soils

Effects of fresh and aged biochar on soil N2O emission from a poplar plantation

Impact of soybean stover- and pine needle-derived biochars on Pb and As mobility, microbial community, and carbon stability in a contaminated agricultural soil

Soil salinity may damage crop production. Besides proper management of irrigation water, salinity reduction can be achieved through soil amendment. The objectives of this study were to evaluate the effects of rice husk biochar and compost amendments on alleviation of salinity and rice growth. Field experiments were conducted at two salt-affected paddy rice fields located in distinct sites for five continuous crops. Treatments, with four replicates, consisted of continuous three rice crops per year (RRR), two rice crops rotated with fallow in spring–summer crop (FRR), FRR plus compost at 3 Mg ha−1 crop−1 (FRR + Comp), and biochar at 10 Mg ha−1 crop−1 (FRR + BC). Salt contents and hydraulic properties of soils, plant biomass, and plant uptake of cations were investigated. Soil bulk density (BD), exchangeable sodium (Na+), and exchangeable sodium percentage (ESP) were reduced remarkably by biochar application. Biochar application significantly increased other soil properties including total porosity, saturated hydraulic conductivity (Ksat), soluble and exchangeable potassium (K+), K+/Na+ ratio, available P, and total C. Compost application also improved BD, total porosity, and available P, but not exchangeable Na+ and ESP. Total aboveground biomass of rice showed a trend of FRR + BC > FRR + Comp > FRR > RRR. Relatively higher K+ uptake and lower Na+ uptake in rice straw in FRR + BC resulted in a significant two times higher K+/Na+ ratio over other treatments. Our results highlight that biochar amendment is a beneficial option for reducing ESP and providing available K+ and P under salinity-affected P-deficient conditions, hence improving straw biomass.

Effect of Application of Surfactants on Hydraulic Properties of Soils

PurposeIran is located on the desertification strip where it has faced water shortage and poor quality soils. So it is necessary to improve the soil structure and increase irrigation efficiency. In this context, the use of industrial wastes can increase soil’s organic matter and improve its structure, also amend environmental problems related to disposal of industrial wastes. The objective of this study was to survey the effect of crumb rubber (CR) application as soil amendment on soil water retention curve indices, soil aggregate stability and soil micronutrients.MethodsIn this study, different amounts of CR (0, 0.12, 0.24, 0.36 and 0.48 g) were added to every kg of the two different soil textures (loamy sand and silty clay). Pots were kept at FC moisture conditions for 6 months. At the end of incubation time, the different soil micronutrient availability, soil structural stability and soil hydraulic properties were measured.ResultsThe results showed that application of CR as soil amendment had significant effects (p < 0.001) on increasing soil organic matter content and soil micronutrient availability including Zn and Fe. Adding CR particles by reducing the aggregate fractal dimension, soil penetration resistance and bulk density, improves soil structure in both types of soil. The results also demonstrated that the use of CR particles can improve water holding capacity in sandy soil and increased plant available water content and air capacity in clay soil (p < 0.001).ConclusionsAccording to our results adding CR particles can be considered as a low-cost solution in order to improve the hydro-physical and chemical properties of soils in these areas.

Vegetation restoration plays a crucial role in conserving soil and water, as well as rehabilitating ecosystems, by enhancing soil properties and vegetation attributes. The evaluation of the ecological consequences among different vegetation restoration types can be achieved by clarifying the impacts on carbon, water and nutrient storages. In this study, we selected four typical vegetation restoration types (Pinus tabuliformis forest (PTF), Platycladus orientalis forest (POF) and Robinia pseudoacacia forest (RPF) as typical planted forests, and the natural secondary forest (NSF) as the control treatment) in the eastern Loess Plateau of China. The soil properties (at 0–200 cm depth) and vegetation attributes (including arborous, shrubs and herbaceous plants) were measured, as well as calculated soil carbon, water and nutrient storages, with a total of 1600 soil samples and 180 vegetation survey plots. The partial redundancy analysis (pRDA) and correlation analysis were also used to analyze the contributions and relationships among environmental factors, soil eco-hydrology and nutrient supplement services in different forestry ecosystems. The results indicate the following: (1) NSF has the lowest soil bulk density (1.21 ± 0.184 g·cm−3). Soil properties varied significantly at vertical scales, and had obvious surface accumulation. (2) Soil moisture storages were better in natural forests than those in planted forests, with more drastic changes in soil moisture dynamics. (3) The soil carbon, nitrogen, and phosphorus storages significantly differed among four vegetation types, with the highest carbon storages in PTF (207.75 ± 0.674 t·ha−1), the highest nitrogen storages in POF (5.54 t·ha−1), and the highest phosphorus storages in RPF (4.33 t·ha−1), respectively. (4) Soil carbon storages depend primarily on the coupling effect of soil properties and precipitation, while nutrient storage is mainly influenced by soil properties. The results quantify the significant differences in soil water, carbon, and nutrient storage across various vegetation restoration types, and reveal the individual and combined contributions of environmental factors, providing new insights into the mechanisms driving these differences. These findings offer practical guidance for the sustainable management of forest ecosystems and the optimization of ecological restoration strategies on the Loess Plateau.

Interactions between aged biochar, fresh low molecular weight carbon and soil organic carbon after 3.5 years soil-biochar incubations

Rice is a staple food for 3 billion people in the world. In Brazil, rice is a traditional staple food mostly cultivated by smallholder farmers. Rice is better adapted to soil types and climate conditions of the Brazilian tropical Savannah than crops like corn and soybean. However, environmental and socio-economic constraints such as the variable rainfall and the limited access to mineral fertilization is a challenge for sustainable aerobic rice production in Brazil. Yields can vary from 1 to 5 Mg ha-1. In this context, the use of agronomic techniques able to improve soil properties seems a good option to increase quantity and stability of rice production. The use of biochar as a soil amendment represents one such option. Biochar is carbonized biomass, generally a by-product of bioenergy production from biomass. Its use in agricultural soils is inspired by the very fertile Terra Preta soils, which are a result of pre-Columbian human activity in the Amazon region. A key component of the fertility of Terra Preta soils is the high content of C, mostly present in form of pyrogenic C, result of carbonization of organic material. Pyrogenic C is also an important fraction of the soil organic matter present in the weathered soils of the Brazilian Savannah. These soils are mostly acidic, with low soil organic matter content, requiring liming and mineral fertilization if used for agriculture. The biochar tested in the current research is a by-product of charcoal production from eucalyptus wood via slow pyrolysis at 400-500 ‚Äöv=v£C. It is a porous material with a high C content and K, Ca and Mg availability, which make it a potentially suitable soil amendment for the low fertile soils of the Brazilian Savannah. We applied biochar in a sandy and a clay soil type of the Brazilian Central West region, where over 40% of the Brazilian total crop production is located. We investigated whether biochar amendment improves soil chemical and physical properties and how this in turn affects aerobic rice yields along four cropping seasons after a single biochar application. In both soil types, biochar decreased soil acidity up to 3.5 years after its application. On the clay soil, biochar application decreased the soil water retention capacity but increased the soil organic matter content. The effect of biochar on rice yields on the clay soil were either absent, negative or dependent on the amount of mineral N applied, as well as biochar-induced changes in soil properties, particularly soil water retention and soil organic matter. Most promising results were observed on the sandy soil, where biochar application increased the soil water retention capacity. On the sandy soil, first two seasons were drier than latter two seasons. Accordingly, effects of biochar on rice yields were divergent: the positive effects observed in the first two seasons were absent in subsequent seasons. During this study, weather conditions and rice blast infestations were factors that influenced the observed effects of biochar on rice yields. Further, biochar did not enhance N2O emissions on the clay soil. Based on these results wood biochar could be considered for use in farming systems of the Brazilian Savannah, particularly on sandy soils.