Alternativas de secuestro de carbono orgánico en suelos y biomasa de Galicia

Se realiza una revisión de la capacidad de secuestro de Carbono por los suelos y biomasa de Galicia discutiendo posibles alternativas y poniendo de manifiesto su importancia ambiental y económica

Carbono orgânico nos solos do norte de Espanha (Galiza, Astúrias, Cantabria e País Basco)

The soil organic carbon content was analyzed in more than 7 000 soil samples under different land uses, climates and lithologies from northern Spain (Galicia, Asturias, Cantábria y País Vasco). GIS maps (1:50 000) were made of the % SOC and SOC stocks. The % SOC varies according to land use (higher in forest and scrub soils and lower in agricultural soils) and climate, and there is a highly significant correlation between SOC content and mean annual precipitation. There are significant differences between the soils of Galicia/Western Asturias (GAw) and those of the rest of the study area (Central and Eastern Asturias, Cantabria and País Vasco) (AceCV), although these are neighbouring regions. In forest and/or scrub soils with a udic soil moisture regime, in GAw, the SOC is usually > 7% and the average stocks 260 t ha -1 (0-30 cm), and >340 t ha-1 (0-50 cm) in soils with thick organic matter rich horizons (> 40 cm); these values greatly exceed the average contents observed in forest soils from temperate zones. Under similar conditions of vegetation and climate in soils of AceCV the SOC average is 3% and the mean stocks 90-100 t ha-1 (0-30 cm). The andic character of acid forest soils in GAw and the formation of C-Al,Fe complexes are pointed out as the SOC stabilization mechanism, in contrast to the neutral and calcareous soils that predominate in AceCV, where the main species of OC are easily biodegradable.Se analiza el contenido de carbono orgánico (CO) en más de 7.000 muestras de suelos del norte de España (Galicia, Asturias, Cantábria y País Vasco) bajo diferentes tipos de ocupación, condiciones climáticas y litología, y se elaboran mapas SIG (1:50 000) del porcentaje y stock de carbono en los suelos. El porcentaje de CO varía de acuerdo al uso del suelo (mayor en suelos forestales y con matorral, y menor en suelos de cultivo) y al clima, reconociéndose una correlación altamente significativa entre el porcentaje de CO y la precipitación media anual. En cualquier caso, aún tratándose de regiones próximas, se establecen diferencias importantes entre los suelos de Galicia-oeste de Asturias (G/Ao ) y los del resto del área de estudio (Asturias central y oriental, Cantabria y País Vasco) (AceCV). En suelos forestales y/o con matorral y régimen de humedad údico, en G/Ao , el porcentaje de CO es habitualmente > 7% y el stock medio 260 tC ha-1 (0-30 cm) y puede ser > 340 tC ha-1 (0-50 cm), teniendo en cuenta la abundancia de suelos con rasgos cumúlicos y horizontes humíferos con > 40 cm de espesor; los valores obtenidos superan ampliamente los contenidos medios señalados por diferentes autores para suelos forestales de áreas templadas. En similares condiciones de vegetación y clima, el contenido medio de CO en suelos de (AceCV) es de 3% y el stock medio 90-100 tC ha-1 (0-30 cm). El carácter ándico de los suelos forestales ácidos de G/Ao, y la formación de complejos C-Al,Fe se señala como mecanismo de estabilización del CO, en contraste con los suelos neutros y calcáreos que predominan en AceCV, en los que la especie principal es el CO fácilmente biodegradable.Analisou-se o teor de carbono orgânico en mais de 7.000 amostras de solo do norte de Espanha (Galiza, Astúrias, Cantábria e País Basco), sob diferentes usos, condições climáticas e litologias, e procedeu-se ao mapeamento SIG (1:50 000) da percentagem e stock de carbono nos solos. A percentagem de CO varia de acordo com o uso do solo (maior em solos de floresta e mata e menor em solos agrícolas) e condições climáticas, observando-se uma correlação altamente significativa entre a percentagem de CO e a precipitação média anual. Em qualquer caso, mesmo para regiões vizinhas, registam-se diferenças significativas entre os solos da Galiza-oeste e das Astúrias (G/Ao) e o resto da área em estudo (Astúrias central e oriental, Cantabria e País Basco) (AceCV). Em solos de floresta e/ou de mata e regime de humidade údico, em G/Ao, a percentagem de CO é geralmente > 7% e o stock médio 260 t C ha-1(0-30 cm), e > 340 t C ha-1 (0-50 cm) em solos com espessos horizontes ricos em matéria orgânica (> 40 cm); estes valores excedem largamente os teores médios observados em solos florestais de zonas temperadas. Em condições semelhantes de vegetação e clima, em solos de AceCV, o teor médio de CO é de 3% e o stock médio de 90-100 t C ha-1 (0-30 cm). O carácter andico dos solos florestais ácidos da Galiza, e a formação do complexos C-Al,Fe são apontados como o mecanismo de estabilização do CO, em contraste com os solos neutros e calcários prevalecentes em AceCV, onde a espécie predominante é o CO facilmente biodegradável.This study was supported by the Spanish Ministry of Science and Innovation, National Plan I+D, through project CGL2009-13857S

Predicting C aromaticity of biochars based on their elemental composition

Three models were examined to predict C aromaticity (f(a)) of biochars based on either their elemental composition (C, H, N and O) or fixed C (FC) content. Values of f(a) from solid state C-13 nuclear magnetic resonance (NMR) analysis with Bloch-decay (BD) or direct polarisation (DP) techniques, concentrations of total C, H, N, and organic O, and contents of FC of 60 biochars were either compiled from the literature (dataset 1, n = 52) or generated in this study (dataset 2, n = 8). Models were first calibrated with dataset 1 and then validated with dataset 2. All models were able to fit dataset 1 when atomic H to C ratio (H/C) 1, high concentrations of carbonate or high inorganic H. These models need to be further tested with a wider range of biochars before they can be recommended for classification of biochar stability

The fate of phosphorus of ash-rich biochars in a soil-plant system

The objectives were to investigate (i) the forms and release pattern of P from an ash-rich biochar-amended sandy soil; (ii) the transformation of biochar P in a soil-plant system. Several methodologies (a bioassay test, soluble P extractions, a sequential P fractionation and successive P extractions via resin strips) were used to study the bioavailability and transformation of P in a sandy soil fertilised with either conventional P fertilisers [Ca(H2PO4)(2) (CaP) and Sechura phosphate rock (SPR)] or biochars produced from cattle manure (MAe) and alum-treated biosolids (BSe) at four temperatures (250, 350, 450, and 550 A degrees C). Biochar P mainly contributed to increase soil resin-extractable P- and inorganic NaOH-extractable P-fractions, and thus to plant available P. The decrease in P concentrations of those fractions was caused by the uptake of P by plants rather than their transformations into more stable forms. P release rates diminished following the order: CaP > MAe > BSe > SPR, which indicates a decline in P availability from these P sources. Phosphorus-rich biochar can be used as a slow-release fertiliser. It is necessary to determine available P (either soil or fertiliser tests) in biochars prior to its application to soil, so that dose, frequency and timing of application are correctly established

Investigating the Influence of Biochar Particle Size and Depth of Placement on Nitrous Oxide (N₂O) Emissions from Simulated Urine Patches

The use of biochar reduces nitrous oxide (N2O) emissions from soils under specific conditions yet the mechanisms through which interactions occur are not fully understood. The objectives of this glasshouse study were to investigate the effect of (i) biochar particle size, and (ii) the impact of soil inversion—through simulated mouldboard ploughing—on N2O emissions from soils to which cattle urine was applied. Pine biochar (550 °C) with two different particle sizes (<2 mm and >4 mm) was mixed either into the top soil layer at the original 0⁻10 cm depth in the soil column or at 10⁻20 cm depth by inverting the top soil to simulate ploughing. Nitrous oxide emissions were monitored for every two to three days, up to seven weeks during the summer trial and measurements were repeated during the autumn trial. We found that the use of large particle size biochar in the inverted soil had significant impact on increasing the cumulative N2O emissions in autumn trial, possibly through changes in the water hydraulic conductivity of the soil column and increased water retention at the boundary between soil layers. This study thus highlights the importance of the role of biochar particle size and the method of biochar placement on soil physical properties and the implications of these on N2O emissions

Alternativas de secuestro de carbono orgánico en suelos y biomasa de Galicia

Se realiza una revisión de la capacidad de secuestro de Carbono por los suelos y biomasa de Galicia discutiendo posibles alternativas y poniendo de manifiesto su importancia ambiental y económica.A review of the C sequestering capacity of soils and biomass of Galicia is presented here, together with a discussion of possible alternatives, and a description of the environmental and economical importance of this topic

Chemical and bioassay characterisation of nitrogen availability in biochar produced from dairy manure and biosolids

Biochar is charcoal made from waste biomass and intended to be added to soil to improve soil function and reduce emissions from the biomass caused by natural degradation to CO2. Nitrogen (N) forms in biochar can be complex and their lability likely to be influenced by pyrolysis temperature which, together with the nature of carbon (C), will influence N mineralisation or immobilisation. These complex relationships are poorly understood, yet impact strongly on the potential agronomic value of biochar. In this study, N in different biochar samples produced from human and animal waste streams (biosolids and cow manure; each mixed with eucalyptus wood chips in a 1:1 dry wt. ratio) at different pyrolysis conditions (highest heating temperature 250, 350, 450 and 550 °C) was extracted with 6 M HCl. The acid hydrolysable, extractable N (THN) was fractionated into ammonia N (AN), amino acid N (AAN), amino sugar N (ASN) and uncharacterisable hydrolysable N (UHN). Biochar samples were also treated with 0.167 M K2Cr2O7 acid to determine N potentially available in the long term. An incubation study of the different biochar samples mixed with acid washed sand was conducted at 32 °C for 81 days to study both C and N turnover. During incubation, the CO2 released was trapped in NaOH and quantified. Hydrolysable N decreased as pyrolysis temperature increased from 250 to 550 °C. Fractionation into AN, AAN, ASN and UHN revealed progressive structural rearrangement of N with pyrolysis temperature. Based on HCl hydrolysis and dichromate oxidation results, C and N in biochar became more stable as pyrolysis temperature increased. The ratio of volatile C to THN was a useful indicator of whether net N mineralisation or immobilisation of N in biochar occurred. THN thus seems a sound estimate of the labile N fraction in biochar in the short term; however, dichromate-oxidisable N is probably more meaningful in the long run. Further studies using different types of biochar need to be conducted under more realistic conditions to obtain more information on N availability in biochar once in soil

Predicting phosphorus bioavailability from high-ash biochars

Biochars are highly variable in nutrient composition and availability, which are determined by types of feedstock and pyrolysis conditions. The aim of this research was to (a) study the bioavailability of phosphorus (P) in biochars using different feedstocks and pyrolysis conditions; (b) develop a robust chemical method for biochar P availability measurements. In the present study, (a) chemical analysis - including total P and extractable P (2% citric acid, 2% formic acid, and neutral ammonium citrate extraction), and (b) a bioassay test using rye-grass grown in a P deficient sandy soil were used to compare the P bioavailability of different biochars. Biochars were produced from two different feedstocks (dairy manure-wood mixture, MAe; biosolid-wood mixture, BSe) at four different pyrolysis temperatures (250, 350, 450, and 550A degrees C). Results showed that P in feedstock was fully recovered in the biochars. After 6 harvests, the biochars were as effective as the P fertilizers tested [Sechura phosphate rocks (SPR) and calcium dihydrogen phosphate (CaP)] in increasing the shoot yield. However, P uptake followed the order of CaP > MAe biochars > BSe biochars > SPR, on a same TP basis. Based on the Mitscherlich equation, 2% formic acid was the most sensitive indicator of P bioavailability in biochars. The results suggest that high-ash biochars with high P concentrations are potential P sources with high-agronomic efficiency. We propose the use of 2% formic acid extraction to predict the availability of P in ash-rich biochars