ABSTRACT

Biochar is not a structured homogeneous material; rather it possesses a range of chemical structures and a heterogeneous elemental composition. This variability is based on the conditions of pyrolysis and the biomass parent material, with biochar spanning the range of various forms of black carbon. Thereby, this variability induces a broad spectrum in the observed rates of reactivity and, correspondingly, the overall chemical and microbial stability. From evaluating the current biochar and black carbon degradation studies, there is the suggestion of an overall relationship in biochar stability as a function of the molar ratio of oxygen to carbon (O:C) in the resulting black carbon. In general, a molar ratio of O:C lower than 0.2 appears to provide, at minimum, a 1000-year biochar half-life. The O:C ratio is a function of production temperature, but also accounts for other impacts (e.g., parent material and post-production conditioning/oxidation) that are not captured solely with production temperature. Therefore, the O:C ratio could provide a more robust indicator of biochar stability than production parameters (e.g., pyrolysis temperature and biomass type) or volatile matter determinations.

Abstract

Stability and transformation products of incomplete combustion of vegetation or fossil fuel, frequently called pyrogenic or black carbon and of biochar in soil, remains unknown mainly because of their high recalcitrance compared to other natural substances. Therefore, direct estimations of biochar decomposition and transformations are difficult because 1) changes are too small for any relevant experimental period and 2) due to methodological constraints (ambiguity of the origin of investigated compounds). We used 14C-labeled biochar to trace its decomposition to CO2 during 8.5 years and transformation of its chemical compounds: neutral lipids, glycolipids, phospholipids, polysaccharides and benzenepolycarboxylic acids (BPCA). 14C-labeled biochar was produced by charring 14C-labeled Lolium residues. We incubated the 14Clabeled biochar in a Haplic Luvisol and in loess for 8.5 years under controlled conditions. In total only about 6% of initially added biochar were mineralized to CO2 during the 8.5 years. This is probably the slowest decomposition obtained experimentally for any natural organic compound. The biochar decomposition rates estimated by 14CO2 efflux between the 5th and 8th years were of 7
104 % per day. This corresponds to less than 0.3% per year under optimal conditions and is about 2.5 times slower as reported from the previous shorter study (3.5 years). After 3.5 years of incubation, we analyzed 14C in dissolved organic matter, microbial biomass, and sequentially extracted neutral lipids, glycolipids, phospholipids, polysaccharides and BPCA. Biochar derived C (14C) in microbial biomass ranged between 0.3 and 0.95% of the 14C input. Biochar-derived C in all lipid fractions was less than 1%. Over 3.5 years, glycolipids and phospholipids were decomposed 1.6 times faster (23% of their initial content per year) compared to neutral lipids (15% year1). Polysaccharides contributed ca. 17% of the 14C activity in biochar. The highest portion of 14C in the initial biochar (87%) was in BPCA decreasing only 7% over 3.5 years. Condensed aromatic moieties were the most stable fraction compared to all other biochar compounds and the high portion of BPCA in biochar explains its very high stability and its contribution to long-term C sequestration in soil. Our new approach for analysis of biochar stability combines 14C-labeled biochar with 14C determination in chemical fractions allowed tracing of transformation products not only in released CO2 and in microbial biomass, but also evaluation of decomposition of various biochar compounds with different chemical properties.

Humic acid (HA), a fairly stable product of decomposed organic matter that consequently accumulates in ecological systems, enhances plant growth by chelating unavailable nutrients and buffering pH. We examined the effect of HA derived from lignite on growth and macronutrient uptake of wheat (Triticum aestivum L.) grown in earthen pots under greenhouse conditions. The soils used in the pot experiment were a calcareous Haplustalf and a non-calcareous Haplustalf collected from Raisalpur and Guliana, respectively, in Punjab Province, Pakistan. The experiment consisted of four treatments with HA levels of 0 (control without HA), 30, 60, and 90 mg kg^−1^ soil designated as HA0, HA1, HA2, and HA3, respectively. In the treatment without HA (HA0), nitrogen (N), phosphorus (P), and potassium (K) were applied at 200, 100, and 125 mg kg^−1^soil, respectively. Significant differences among HA levels were recorded for wheat growth (plant height and shoot weight) and N uptake. On an average of both soils, the largest increases in plant height and shoot fresh and dry weights were found with HA2 (60 mg kg^−1^ soil), being 10%, 25%, and 18%, respectively, as compared to the control without HA (HA0). Both soils responded positively towards HA application. The wheat growth and N uptake in the non-calcareous soil were higher than those of the calcareous soil. The HA application significantly improved K concentration of the non-calcareous soil and P and NO3-N of the calcareous soil. The highest rate of HA (90 mg kg^−1^ soil) had a negative effect on growth and nutrient uptake of wheat as well as nutrient accumulation in soil, whereas the medium dose of HA (60 mg kg^−1^ soil) was more efficient in promoting wheat growth.

cross-posted from: https://slrpnk.net/post/2639190

ABSTRACT

Land reclamation following surface mining in the Athabasca oils sands region will be extensive, with various challenges specific to local reclamation cover soils. The high economic costs associated with pre-disturbance soil salvage and placement in reclamation necessitates judicious management and application of salvaged cover soils. Soil microbial community activity and bioavailable nutrient supply are largely overlooked in reclamation analyses despite their potential in providing a sensitive measurement of ecosystem function. This study evaluates these parameters by comparing two continuous cover soils, a coarse-textured forest floor mineral mix (FFM) and an organic matter-rich peat soil (PM) at Syncrude Canada's Aurora Soil Capping Study. Shallow (10 cm) and Deep (20–30 cm) placement depths of FFM and PM were compared to a control receiving no cover soil and a harvested jack pine site as a reference. Soil function was assessed by measuring bioavailable nutrient supply rates, soil respiration, phospholipid fatty acid analysis (PLFA), and community level physiological profiles (CLPP). Non-metric multidimensional scaling (NMS) was used to quantify functional similarity with reference conditions. NMS revealed the greatest similarity between FFM and the reference site for bioavailable nutrient supply, PLFA, and CLPP. Deep FFM application shared greatest PLFA similarity to the reference site, while Shallow FFM was more similar in CLPP. Shallow PM was more similar to reference conditions than Deep for all parameters measured, suggesting that shallow cover soil applications might be sufficient for the reclamation target. Soil respiration rates were greatest in FFM, followed by the reference site and PM treatments, with no difference attributable to placement depth. PM had greater nitrogen and sulfur availability, but was lower in phosphorus and potassium when compared to FFM and the reference site. Ecosystem function was more similar in cover soils that mimicked the reference site conditions as much as possible, which in this case meant shallow placement and material salvaged from upland forests

Formed from shrinking and swelling clays, prismatic structure differs from columnar in that it is not induced through sodium deposition and does not have a rounded cap on the top. columnar

diagram

Re-uploaded.

ABSTRACT

Some areas with historically mesic climates are predicted to experience more climate extremes, including longer droughts combined with hotter days and more intense precipitation. Drought and rewetting are known to alter carbon (C) and nitrogen (N) cycling. However, little information is available on how the effects of drought on C and N cycling differ with temperature and land use in soils from humid regions. We evaluated several metrics of C and N cycling under drought with or without heat stress in a forest site and conventionally and organically managed arable sites. We sampled undisturbed soil cores from 0 to 10 cm and incubated them under either reference conditions (REF), drought (DRT), or drought combined with heat stress (D + H). Metrics of C and N cycling, including actual and potential mineralization, enzyme activities, microbial biomass, and dissolved organic C and N, and microbial community structure were assessed at the end of the stress period and 14 and 28 d after rewetting. We found that the effects of D + H differed in magnitude and direction from those of DRT: cumulative C and N mineralization followed the order DRT < REF ≤ D + H. Land management affected stress response: mineralization was always greater in the forest and organic sites than in the conventional site. Post-wet pulses of C and potential net N mineralization were 1.7 and 3.6 times higher, respectively, in the D + H soils than DRT soils, and were greatest at the forest site. Only the organic site was sensitive to DRT alone. Across sites, microbial biomass N was reduced more by stress than C, and only N-cycle parameters failed to reach reference levels after the recovery period. In agreement with previous studies, the N cycle was more affected than the C cycle. Our results suggest that climate change-induced heatwaves during drought have implications for ecosystem C and N balance in mesic climates.

In soils with very high 2:1 clay contents, the soils expand and contract as they are wetted and dried. This creates shear faces called slickenslides, like the one shown above. Essentially they clay expands so much it's forced to shear somehow, and this is the resulting shear plane.

Look how thick the Ae (first) horizon is!

Profile description:

Ah: 0-2 cm; 10YR 2/1; SCL; Weak Fine Granular; Friable

R 2-100 cm

Solonetzic soils are formed when sodium rich ground water causes 2:1 clays to disperse, forcing columns to form

The structure is caused by sodium in groundwater dispersing the clay in the soil. These soils are hard to manage since the structure creates a hardpan, which causes water to pool in the subsurface and drown agronomic plants

Note the layer of carbonates (white) in the lower profile

Soil testing a few km away in a slightly similar area indicates a grey chromosol. This area has some of the oldest soils in Australia, possibly 370 to 320 million years ago. 20km away is 160 million years and supports a rich rainforest.

https://www.qld.gov.au/environment/land/management/soil/soil-testing/types

This is a great and publicly available book for those that are curious about soil science

Got some mud you'd like to link on the sidebar? Chuck it in here.