Effekt av biokull på jordfysiske egenskaper og klimagassutslipp

Climate change and production of adequate amounts of food to feed the growing human population are key challenges facing the modern world. These two challenges often involve a trade-off between solving the one, while exacerbating the other. Application of biochar (BC) in agriculture has been suggested to be a win-win strategy for both climate change mitigation and increased crop production. Biochar is a carbon-rich, alkaline material, produced by heating biomass in a limited oxygen environment. In soil, BC is relatively stable and therefore it has a potential to contribute to carbon sequestration. The motivation for adoption of BC technology for use in acidic, coarse-textured soils particularly in the tropics, lies mainly in the ability of BC to increase crop production at low cost, thus contributing to food security, while the benefit of climate change mitigation remains in the background.Klimaendring og produksjon av tilstrekkelige mengder med mat for en voksende befolkning er sentrale utfordringer verden står overfor. Disse utfordringer innebærer en avveining hvor en løsning for det ene kan være negativt for det andre. Bruk av biokull (BC) i landbruket har blitt nevnt til å være en win-win strategi som kombinerer klimaendringstiltak og økt matproduksjon. Biokull er et karbonrikt, alkalisk materiale, produsert ved å brenne biomasse ved begrenset oksygentilgang. I jord er BC relativt stabilt slik at det har potensial til å bidra til karbonbinding. Begrunnelsen for en vellykket bruk av BC i surt jordsmonn med grov tekstur, særlig i tropene, ligger hovedsakelig i BCs evne til å kunne øke avlinger ved lave kostnader, slik at det kan bidra til å bedre matvaresikkerhet. Bidraget til å motvirke klimaendring kommer ofte i andre rekke

The potential of biochar in improving drainage, aeration and maize yields in heavy clay soils

Heavy clay soils are globally widespread but their poor drainage and poor aeration limit their use for agriculture. This study was designed to test the effect of the amendment of biochar (BC) from woody shrubs on drainage/saturated hydraulic conductivity (Ksat), soil aeration/air capacity, available water capacity and biomass and grain yields of maize. In a field experiment, BC from Gliricidia sepium was applied in planting basins or rip lines at 2.5% and 5% w/w in addition to a control without BC. The maize biomass and grain yields were higher in BC treated plots compared to control (p0.05). In contrast, bulk density decreased linearly by 0.011±0.002 g cm-3 per percent BC added (p<0.001). Ksat and air capacity of the soil were 288 cm day-1 and 30.9%, respectively falling within the generally accepted optimal range. Both Ksat and air capacity followed a significant quadratic relation (p<0.05) upon BC addition, decreasing at low BC doses, reaching a minimum at 3–5% BC and increasing at higher doses. Results allowed a partial attribution of the yield increases to changes in soil physical properties such as changes in bulk density and not clearly to Ksat and air capacity.publishedVersio

Effect of biochar on crust formation, penetration resistance and hydraulic properties of two coarse-textured tropical soils

Biochar (BC) has been reported to improve a number of soil structural and hydraulic properties but detailed studies are scant on how BC affects crust formation, penetration resistance, water repellency and saturated hydraulic conductivity (Ksat). The objective of this study was to quantify the effect of maize cob BC of three different particle sizes on soil crusting (penetration resistance), water repellency, and Ksat of loamy fine sand and sandy loam in Zambia. The BC particle sizes were 0.05). No effect of BC on penetration resistance was found in the loamy fine sand (p > 0.05). In dry sandy loam with moisture content <1% v/v, the proportion of wettable crusted surface was significantly smaller (25%) than in moist soil (98%) with moisture content of ∼ 10% v/v. Only fine BC of <0.5 mm increased WDPT of the crusted surface of sandy loam (p < 0.05), reducing the proportion of wettable surface from 98 to 80% in moist soil and from 25 to 18% in dry soil. Coarser BCs, instead, increased the proportion of wettable crusted surface from 25% to 45% and 90% for 3% 0.5–1 mm BC and 4% 1–5 mm BC addition, respectively, in dry soil. Biochar significantly reduced Ksat (p < 0.05) in sandy loam below the crust by 0.17 ± 0.07 cm h−1 per percent BC added. However, no effect was found in loamy fine sand. Since BC amended sandy loam below the crust showed no water repellency, reduction in Ksat cannot be explained by water-repellent nature of BC. Instead, this may be due to clogging of soil pores by BC or to collapse of soil structure near water saturation.Effect of biochar on crust formation, penetration resistance and hydraulic properties of two coarse-textured tropical soilsacceptedVersio

Vertical and lateral transport of biochar in light-textured tropical soils

Field experiments were conducted in Arenosols (loamy fine sand) and Acrisols (sandy loam) in Zambia to quantify vertical and lateral transport of biochar (BC) using the BC and soil 13C isotope signatures and total organic carbon contents. There were three experimental treatments composing of no BC, ≤0.5 and 0.5–1 mm BCs each with three replicates arranged in completely randomized design. The applied BCs were made from rice husk, except 0.5–1 mm BC in sandy loam, which was from maize cob. One year after mixing BC homogeneously in the 0–5 cm surface layer, soil down to 20 cm depth was sampled. The downward migration of BC was significant down to 8 cm depth in sandy loam and down to 6 cm in loamy fine sand. Below these depths, there was no significant difference in BC amounts between the BC amended and the reference plots. There was a general tendency for greater downward migration for the ≤0.5 mm than for 0.5–1 mm BC. Total BC recovery at 0–5 cm depth in the BC-treated soils amounted to 45–66% of the total applied amount of BC. As only 10–20% was recovered in the deeper soil layers, 24–45% of the applied BC could not be accounted for in the soil profile. Although, decomposition and downward migration to below 20 cm depth may contribute to the loss of BC from the surface soil, much can be attributed to lateral transfer through erosion. This is the first study that explicitly focuses on the theme of BC dispersion and shows that in Arenosols and Acrisols of the tropics, the downward migration of BC is limited.Vertical and lateral transport of biochar in light-textured tropical soilsacceptedVersio

Significant build-up of soil organic carbon under climate-smart conservation farming in Sub-Saharan Acrisols

Conservation farming (CF) involving minimumtillage, mulching and crop rotation may offer climate change adaptation and mitigation benefits. However, reported effects of CF, as applied by smallholders, on storage of soil organic carbon (SOC) and soil fertility in Sub-Saharan Africa differ considerably between studies. This is partly due to differences in management practice, soil type and adoption level between individual farmers. Where CF involves planting basins, year-to-year changes in position of basins make SOC stock estimates more uncertain. Here we assess the difference in SOC build-up and soil quality between inside planting basins (receiving inputs of lime and fertilizer; basins opened each year) and outside planting basins (no soil disturbance or inputs other than residues) under hand-hoe tilled CF in an Acrisol at Mkushi, Zambia. Seven years of strict CF husbandry significantly improved soil quality inside planting basins as compared with outside basins. Significant effects were found for SOC concentration (0.74 ± 0.06% vs. 0.57 ± 0.08%), SOC stock (20.1 ± 2.0 vs. 16.4 ± 2.6 t ha−1, 0–20 cm), soil pH (6.3 ± 0.2 vs. 4.95± 0.4) and cation exchange capacity (3.8 ± 0.7 vs. 1.6 ± 0.4 cmolc kg−1). As planting basins only occupy 9.3% of the field, the absolute rate of increase in SOC, compared with outside basins, was 0.05 t C ha−1 yr−1 . This corresponds to an overall relative increase of 2.95‰SOC yr−1 in the upper 20 cm of the soil. Also, hot water extractable carbon (HWEC), a proxy for labile organic matter, and potential nitrification rateswere consistently greater inside than outside basins. The significant increase in quantity and quality of SOC may be due to increased inputs of roots, due to favorable conditions for plant growth through input of fertilizer and lime, along with increased rainwater infiltration in the basinsSignificant build-up of soil organic carbon under climate-smart conservation farming in Sub-Saharan AcrisolsacceptedVersio

Data from: Effect of soil pH increase by biochar on NO, N2O and N2 production during denitrification in acid soils

Biochar (BC) application to soil suppresses emission of nitrous- (N2O) and nitric oxide (NO), but the mechanisms are unclear. One of the most prominent features of BC is its alkalizing effect in soils, which may affect denitrification and its product stoichiometry directly or indirectly. We conducted laboratory experiments with anoxic slurries of acid Acrisols from Indonesia and Zambia and two contrasting BCs produced locally from rice husk and cacao shell. Dose-dependent responses of denitrification and gaseous products (NO, N2O and N2) were assessed by high-resolution gas kinetics and related to the alkalizing effect of the BCs. To delineate the pH effect from other BC effects, we removed part of the alkalinity by leaching the BCs with water and acid prior to incubation. Uncharred cacao shell and sodium hydroxide (NaOH) were also included in the study. The untreated BCs suppressed N2O and NO and increased N2 production during denitrification, irrespective of the effect on denitrification rate. The extent of N2O and NO suppression was dose-dependent and increased with the alkalizing effect of the two BC types, which was strongest for cacao shell BC. Acid leaching of BC, which decreased its alkalizing effect, reduced or eliminated the ability of BC to suppress N2O and NO net production. Just like untreated BCs, NaOH reduced net production of N2O and NO while increasing that of N2. This confirms the importance of altered soil pH for denitrification product stoichiometry. Addition of uncharred cacao shell stimulated denitrification strongly due to availability of labile carbon but only minor effects on the product stoichiometry of denitrification were found, in accordance with its modest effect on soil pH. Our study indicates that stimulation of denitrification was mainly due to increases in labile carbon whereas change in product stoichiometry was mainly due to a change in soil pH

Short-term effect of field application of biochar on cation exchange capacity, pH, and electrical conductivity of sandy and clay loam temperate soils

Biochar soil amendment is known to improve soil chemical properties. Synchronized addition of biochar and mineral fertilizer nitrogen (N) could increase agronomic benefits and remedy the adverse environmental impact of fertilizer N. The objective of this study was to compare the short-term effect of a synchronized addition of biochar and fertilizer N (NB) with sole N fertilizer (NF) on cation exchange capacity (CEC), pH, and electrical conductivity (EC). We hypothesized that mixing biochar with inorganic N would improve the CEC, pH, and EC of sandy soils. Soil samples were taken at the end of the cropping season of 2018 and 2019 from Efaw and Lake Carl Blackwell (LCB), OK, USA following maize (Zea mays L.) grain harvest. The study had ten treatments and used a randomized complete block design with three replications. Biochar and N rates were 5, 10, and 15 t·ha−1, and 50, 100, and 150 kg·N·ha−1, respectively. Overall, results indicated significant improvement in CEC and pH under NB. At Efaw, CEC and pH were greater with NB by 4%, than NF while EC was lower with NB by 5%. At LCB, CEC, pH, and EC values with NB increased by 16%, 3%, and 7%, respectively compared to NF. Averaged across experimental sites, CEC, pH, and EC increased with NB by 10%, 4%, and 1%, respectively compared to NF. Significant responses of CEC to biochar addition were observed on coarse soil texture (p < 0.05). Alongside increasing the retention of nutrient cations, the significant increase in pH (p < 0.05) suggest that synchronized application of biochar and inorganic N could alleviate soil acidity. In the future, the amount of N fertilizer used in sandy soils may reduce under biochar application

The potential of biochar in improving drainage, aeration and maize yields in heavy clay soils.

Heavy clay soils are globally widespread but their poor drainage and poor aeration limit their use for agriculture. This study was designed to test the effect of the amendment of biochar (BC) from woody shrubs on drainage/saturated hydraulic conductivity (Ksat), soil aeration/air capacity, available water capacity and biomass and grain yields of maize. In a field experiment, BC from Gliricidia sepium was applied in planting basins or rip lines at 2.5% and 5% w/w in addition to a control without BC. The maize biomass and grain yields were higher in BC treated plots compared to control (p<0.05) during the 2012 and 2013 seasons. There was no significant difference in the yields between 2.5% and 5% BC treatments (e.g. grain yield were 6.6 and 8.1 t ha-1 in 2012 and 9.3 and 10.3 t ha-1 in 2013 compared to control with 4.2 and 6.7 t ha-1 in 2012 and 2013, respectively). Soil from the same field site was also mixed with a similar woody shrub BC from Eupatorium adenophorum in the laboratory at rates of 2.5%, 5% and 10% BC w/w and a control without BC. The mixtures were then incubated and subjected to two wet-dry cycles for two weeks. Core samples were taken from the incubated soil and tested for bulk density, Ksat and pF measurements. Total porosity and moisture at field capacity and wilting point were 72.3%, 43.7% and 23.7%, respectively, and not affected by BC amendment (p>0.05). In contrast, bulk density decreased linearly by 0.011±0.002 g cm-3 per percent BC added (p<0.001). Ksat and air capacity of the soil were 288 cm day-1 and 30.9%, respectively falling within the generally accepted optimal range. Both Ksat and air capacity followed a significant quadratic relation (p<0.05) upon BC addition, decreasing at low BC doses, reaching a minimum at 3-5% BC and increasing at higher doses. Results allowed a partial attribution of the yield increases to changes in soil physical properties such as changes in bulk density and not clearly to Ksat and air capacity

Data from: The potential of biochar in improving drainage, aeration and maize yields in heavy clay soils

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