Are soil-water functions affected by biochar application?

Ojeda G., Mattana S., Avila A., Alcaniz J.M., Volkmann M., Bachmann J. (2015) Are soil-water functions affected by biochar application?. Geoderma. 249-250: 1-11.
Link
Doi: 10.1016/j.geoderma.2015.02.014

Abstract:

Today biochar is considered a stable-carbon source that is able to improve soil quality. However, although biochar effects on some soil properties are already becoming well known, its impact on complex soil hydrological functions has yet to be better assessed. The main objectives are: (a) to determine the impact of different biochar amendments on important physical and chemical soil properties and (b) to determine whether the origin (biomass or sewage sludge) and pyrolysis technique can change biochar properties and regulate biochar influence on important soil functions, i.e. nutrient release, water sorption, and carbon storage. Six types of biochar produced from different biomass sources (pine, poplar or sludge) and pyrolysis processes (slow, fast or gasification) were applied to a sandy-loam, low-organic-matter, calcareous soil (mean dose: 18. g/kg) and incubated in a greenhouse without seeding. Two sampling campaigns, one month and one year after biochar amendments, were performed. The overall impact of biochar, analysed by principal response curves (PRCs), indicated that it could improve or deteriorate soil hydrological properties at different intensities. Soil wettability was modified due to sludge biochar addition to soil by increased water penetration dynamics during the capillary rise process of about 18%. In contrast, water storage as a soil function during soil drying was not affected. Because no differences on aggregate stability were observed between treatments, increments on soil organic carbon could not be related to biochar physical protection caused by aggregate formation or by enhanced aggregate stability. As a result, carbon storage, considered as a soil function provided by biochar, was mainly related to its chemical stability. On the other hand, nutrient flux during soil slaking was improved, increasing nutrient release from soil to water. In terms of biochar properties, an increment of surface wettability of biochar during water drop penetration was observed after one year of its addition to soil, where the mean values of contact angle (CA) decreased 69.5%. This important result suggest that initial biochar hydrophobicity (CA. >. 90°) disappeared after 1. year. It was observed that PRC analysis was able to identify important key soil properties that should be monitored when biochar is used as soil amendment. We conclude that the impact of biochar on soil functions depends mainly on biochar feedstock rather than on the pyrolysis technique used during its production. In general, the performance of biochar obtained from sludge and vegetal biomass was markedly different. © 2015 Elsevier B.V.

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Carbon sequestration in a limestone quarry mine soil amended with sewage sludge

Ojeda G., Ortiz O., Medina C.R., Perera I., Alcaniz J.M. (2015) Carbon sequestration in a limestone quarry mine soil amended with sewage sludge. Soil Use and Management. : 0-0.
Link
Doi: 10.1111/sum.12179

Abstract:

To reclaim a limestone quarry, 200 and 400 Mg/ha of municipal sewage sludge were mixed with an infertile calcareous substrate and spread as mine soil in 1992. Soil samples were taken 1 week later and again after 17 yr of mine soil rehabilitation so as to assess changes in the amount and persistence of soil organic carbon (SOC). Sludge application increased SOC as a function of the sludge rate at both sampling times. Seventeen years after the sludge amendments, the nonhydrolysable carbon was increased in the 400 Mg/ha of sludge treatment. The recalcitrance of SOC was less in sludge-amended soils than in the control treatment at the initial sampling, but 17 yr later this trend had reversed, showing qualitative changes in soil organic carbon. The CO2-C production had not differed between treatments, yet the percentage of mineralized SOC was less in the high sludge dose. When the size of active (Cactive) and slow (Cslow) potentially mineralizable C pools was calculated by curve fitting of a double-exponential equation, the proportion of Cactive was observed to be smaller in the 400 Mg/ha sludge treatment. Soil aggregate stability, represented by the mean weight diameter of water-stable soil aggregates, was significantly greater in mine soil treated with the high dose of sludge (18.5%) and SOC tended to be concentrated in macro-aggregates (5-2 mm). Results suggest that SOC content in sludge-amended plots was preserved due by (i) replacement of the labile organic carbon of sludge by more stable compounds and (ii) protection of SOC in aggregates. © 2015 British Society of Soil Science.

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