Showing papers by "Sean C. Thomas published in 2019"

Biochar Particle Size and Post-Pyrolysis Mechanical Processing Affect Soil pH, Water Retention Capacity, and Plant Performance

Abstract: It has become common practice in soil applications of biochar to use ground and/or sieved material to reduce particle size and so enhance mixing and surface contact between soils and char particles. Smaller particle sizes of biochars have been suggested to enhance liming effects and nutrient exchange, and potentially to increase water storage capacity; however, data remains scarce and effects on plant growth responses have not been examined. We manipulated biochar particle size by sieving or grinding to generate particles in two size ranges (0.06–0.5 mm and 2–4 mm), and examined effects on soil pH, soil water retention, and plant physiological and growth performance of two test species (ryegrass: Lolium multiflorum, and velvetleaf: Abutilon theophrasti) grown in a granitic sand culture. The small particle sieved biochar had the largest liming effect, increasing substrate pH values by an additional ~0.3 pH units compared to other biochars. Small particle size biochar showed enhanced water retention capacity, and sieved biochars showed 91%–258% larger water retention capacity than ground biochars of similar particle size, likely because sieved particles were more elongated than ground particles, and thus increased soil interpore volume. The two plant species tested showed distinct patterns of response to biochar treatments: ryegrass showed a better growth response to large biochar particles, while velvetleaf showed the highest response to the small, sieved biochar treatment. We show for the first time that post-processing of biochars by sieving and grinding has distinct effects on biochar chemical and physical properties, and that resulting differences in properties have large but strongly species-specific effects on plant performance in biochar-amended substrates.

Variation in Feedstock Wood Chemistry Strongly Influences Biochar Liming Potential

Abstract: Chars intended for use as soil amendment (“biochars”) vary greatly in their chemical and physical properties. In the present study, 19 Canadian temperate wood feedstocks were charred across a range of pyrolysis temperatures from 300–700 °C. The resulting 95 biochars were tested for their physio-chemical properties and liming capacity. Data indicated increasing base cation concentrations including Ca, Mg, and K (elements that characteristically form liming compounds, i.e., carbonates) as pyrolysis temperature increased. Acidic surface functional groups were analyzed with modified Boehm titration: Carboxylic and lactonic functional group concentrations decreased and phenolic group concentration increased with pyrolysis temperature. Functional group composition also varied greatly with feedstock: In particular, conifer-derived biochars produced at pyrolysis temperatures <500 °C showed much higher carboxylic and lactonic functional group concentrations than did angiosperm-derived biochars. Liming capacity was assessed using soil incubation experiments and was positively related to biochar pH. Both acidic surface functional group concentration and nutrient element concentration influenced biochar pH: we developed a non-linear functional relationship that predicts biochar pH from the ratio of carboxylic to phenolic moieties, and concentrations of Ca and K. Biochar’s liming components that are inherited from feedstock and predictably modified by pyrolysis temperature provide a basis for optimizing the production of biochar with desired pH and liming characteristics.

Patterns of nitrogen-fixing tree abundance in forests across Asia and America

Abstract: Symbiotic nitrogen (N)-fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N-fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N-fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N-fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N-fixing trees were consistently rare in the forest plots we examined. Within the tropics, N-fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N-fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N-fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N-fixing trees. By analysing a large dataset of ~4 million trees, we found that N-fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N-fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N-fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.

Biochar and high-carbon wood ash effects on soil and vegetation in a boreal clearcut

Abstract: Additions of fire residues in the form of charcoal and wood ash may better emulate natural disturbance processes in managed boreal forests. We examined the effects of a poplar (Populus) wood biocha...

Biochar enhancement of facilitation effects in agroforestry: early growth and physiological responses in a maize-leucaena model system

Abstract: Biochar, or pyrolyzed organic matter intended for use as a soil amendment, has a variety of properties of interest from the perspective of agroforestry, in particular its potential to increase soil C sequestration and enhance yields by increased retention of soil mineral nutrients. Nitrogen-fixing legumes commonly show large growth responses to biochar, and we hypothesized that combinations of legumes and non-legumes would show increased enhancement of yields in mixture due to enhanced facilitation related to increased nutrient retention. This hypothesis was tested in a glasshouse pot trial involving the leguminous tree leucaena (Leucaena leucocephala), and maize (Zea mays) grown for 120 days in mixture and monoculture in both an unamended soil and soil amended with a slow-pyrolysis coconut husk biochar at 10 t/ha. Responses were quantified in terms of biomass production and partitioning, leaf-level gas-exchange, leaf chlorophyll content, and (for leucaena) root nodule formation. Consistent with predictions, leucaena showed more pronounced growth and physiological responses to biochar than did maize. The system also showed increased total biomass yields relative to monocultures in the two-species mixtures with biochar (relative yield in mixture [RYM] = 1.69; 95% CI 1.41–1.81), but not in the control treatment (RYM = 1.25; 95% CI 0.93–1.76), and positive effects of biochar on yield were generally greater for both species when grown in mixture. Growth responses to biochar were most pronounced for stem and root biomass, and growth responses were consistent with changes in leaf-level photosynthesis and chlorophyll content. In addition, biochar had large effects on biomass partitioning, enhancing stem allocation in both species. Our results suggest that biochar additions may augment facilitative interactions in agroforestry and intercropped systems on acidic, nutrient-deficient soils by enhancing system nutrient retention.

Stand age and species composition effects on surface albedo in a mixedwood boreal forest

Abstract: . Surface albedo is one of the most important processes governing climate forcing in the boreal forest and is directly affected by management activities such as harvesting and natural disturbances such as forest fires. Empirical data on the effects of these disturbances on boreal forest albedo are sparse. We conducted ground-based measurements of surface albedo from a series of instrument towers over 4 years in a replicated chronosequence of mixedwood boreal forest sites differing in stand age (to 19 years since disturbance) in both post-harvest and post-fire stands. We investigated the effects of stand age, canopy height, tree species composition, and ground vegetation cover on surface albedo through stand development. Our results indicate that winter and spring albedo values were 63 % and 24 % higher, respectively, in post-harvest stands than in post-fire stands. Summer and fall albedo values were similar between disturbance types, with summer albedo showing a transient peak at ∼10 years stand age. The proportion of deciduous broadleaf species showed a strong positive relationship with seasonal averages of albedo in both post-harvest and post-fire stands. Given that stand composition in mixedwood boreal forests generally shows a gradual replacement of deciduous trees by conifers, our results suggest that successional changes in species composition are likely a key driver of age-related patterns in albedo. Our findings also suggest the efficacy of increasing the proportion of deciduous broadleaf species as a silvicultural option for climate-friendly management of the boreal forest.

Trees are larger on southern slopes in late-seral conifer stands in northwestern British Columbia

Abstract: Mid-latitude forests commonly show increased productivity and ultimately produce larger trees on shaded, northern aspects compared with those on sunny, southern aspects. Little research has been co...