Effect of forest thinning and wood quality on the short-term wood decomposition rate in a <Emphasis Type="Italic">Pinus tabuliformis</Emphasis> plantation

The effects of forest thinning and wood quality on wood decomposition in the mineral soil were investigated in a Chinese pine (Pinus tabuliformis Carriére) plantation in northern China by measuring mass loss and changes in wood properties (carbohydrates, lignin and nitrogen (N) concentrations) in wood stakes of two tree species—loblolly pine (Pinus taeda L.) and trembling aspen (Populus tremuloides Michx.). Stakes were inserted to a 20 cm soil depth in stands with three thinning levels (low, moderate, and heavy) and an unharvested control and removed after 1 year. There were significant differences in stake mass loss among the treatments. The species effect on the stake mass loss was marginally significant. Wood N content of both species increased during decomposition in all thinning treatments, and was only correlated with aspen mass loss. Wood properties of stakes placed in each stand before insertion (t?=?0) were similar, except for pine lignin concentration and aspen lignin: N ratio, but neither had any effect on thinning treatment results. Lignin concentration increased and carbohydrate concentration decreased in both aspen and pine wood stakes during decomposition across all thinning treatments, which suggests that brown-rot fungi are dominant wood-decomposers on our study site. We conclude that thinning has a significant influence on the wood decomposition in the mineral soil of this Chinese pine plantation.     

Poultry Manure as an Organic Fertilizer with or without Biochar Amendment: Influence on Growth and Heavy Metal Accumulation in Lettuce and Spinach and Soil Nutrients

This pot-based study investigated the influence of poultry manure and 1:1 mixture of poultry manure + biochar (produced from farmyard manure [FYM] or wood), on the biomass production and concentration of heavy metals in leaves of lettuce and spinach. The concentration of mineral nitrogen (N) and soluble inorganic phosphorus (P) of soils cultivated with these vegetables was also investigated. The application of poultry manure or FYM biochar in soil as 10% (equivalent to 60 t ha^–1 , an estimated 1726.8 kg ha^–1 N in poultry manure and 1353.9 kg ha^–1 N in FYM) and 15% amendment (equivalent to 90 t ha^–1 , an estimated 2590.2 kg ha^–1 N in poultry manure and 2030.8 kg ha^–1 N in FYM) significantly decreased biomass production of lettuce as compared to control (no fertilizer added) treatment. However, mixture of poultry manure with wood-derived biochar at both application rates (i.e., 10% and 15%) and with FYM biochar at lower application rate (i.e., 10%) caused 2–3-fold increase in aboveground plant biomass and 2–14-fold increase in root biomass (p < 0.05). Furthermore, as compared to control treatment, a significant ~2–3-fold increase in aboveground plant biomass was also observed in response to mixture of poultry manure with wood-derived and FYM derived biochars at 10% amendment rates. As compared to control treatment, concentration of mineral N and soluble inorganic P were higher in soils of all other treatments. In spinach, amendment of poultry manure or its co-amendment with biochar of FYM significantly increased aboveground plant biomass at 7% (equivalent to 42 t ha^–1 ) as compared to 3% and 5% amendment rates (equivalent to 18 and 30 t ha^–1 respectively). The concentration of soil mineral N and soil soluble mineral P was not different between treatments. In lettuce, wood-derived biochar did not reduce concentration of heavy metals (i.e., manganese (Mn), copper (Cu), iron, (Fe), cadmium (Cd), lead (Pb), nickel (Ni) and cobalt (Co) than FYM-derived biochar while in spinach, as compared to poultry manure, co-amendment of poultry manure with wood-derived biochar reduced concentration of heavy metals, indicating differential responses of crops to organic amendments.     

An appraisal of the utility of biochar in a rotation involving tobacco–rice in southern China

The employment of biochar in crop production can not only improve soil quality, but also helps the field ecosystem to fix carbon and reduce emissions. Although the benefits of their application in crop production have been more and more confirmed, it is not clear when it comes to the acidic soil of tobacco and rice rotation. A tobacco–rice rotation experiment was conducted in southern China to probe the application value of biochar under these conditions. Three biochar application rates were employed in this experiment. BC0 (without biochar), BC25 (25 t ha⁻¹), and BC50 (50 t ha⁻¹). The findings show that biochar significantly boosted soil fertility and crop yields. Meanwhile, the soil organic carbon of tobacco rice rotation field with biochar increased by 31.76%. After a whole growth period of tobacco and rice, the cumulative emission reduction of CO₂ and N₂O from the soil by biochar were 15,944 kg ha⁻¹ and 1810 g ha⁻¹, respectively. The use of biochar not only significantly improved the bacterial diversity of tobacco and rice rotation soil, but also altered the original microbial community structure. The profusion of Proteobacteria and Acidobacteria was reduced and the abundance of Actinobacteria and Bacteroidetes was enhanced in the treatments with biochar. Among them, Sphingomonadales, Planctomycotes, and Ktedonobacteria, which are beneficial to plant growth and soil health, have become key phylotypes. The carbon balance analysis data show that the net carbon sequestration of the two treatments with biochar is positive, while that of the treatment without biochar is negative. In terms of economic benefit, the application of biochar increased the average of 2.055 CNY kg⁻¹ consumed energy (CE) in the whole tobacco–rice rotation system. The ecological benefit was 0.51 kg C kg⁻¹ CE. In conclusion, biochar can be effectively used in the practice of tobacco–rice rotation and acidic soil improvement in southern China.     

Carbon of Chaillu forests based on a phytosociological analysis in Republic of Congo,more than meets the eye?

The objectives were to quantify aboveground, belowground and dead wood carbon pools near Mayoko in the Chaillu massif of Republic of Congo and explore relationships between carbon storage and plant diversity of all growth forms. A total of 190 plots (25 m by 25 m) were sampled (5072 stems, 211 species) and data analysed using recommended central-African forest allometric equations. Mean stem diameter at breast height was 33.6 cm, mean basal area 47.7 m² ha⁻¹ and mean density of individuals 407 ha⁻¹. Mean aboveground carbon (AGC) ranged from 13.93–412.66 Mg C ha⁻¹, belowground carbon from 2.86–96.97 Mg C ha⁻¹ and dead wood from 0.00–7.59 Mg C ha⁻¹. The maximum AGC value recorded in a plot was 916 Mg C ha⁻¹. The analysis performed using phytosociological association as basis rather than broad vegetation type is unique. AGC values for undisturbed terra firme forest sites featured among the highest recorded for African tropical forests. Considering only tree diversity, a weak, yet significant, relationship existed between AGC and species richness, Shannon-Wiener index of diversity and Fisher's alpha. However, if diversity of all plant growth forms is considered, no relationship between carbon and plant diversity existed.     

Biochar application as a tool to decrease soil nitrogen losses (NH3 volatilization,N2O emissions,and N leaching) from croplands: Options and mitigation strength in a global perspective

Biochar application to croplands has been proposed as a potential strategy to decrease losses of soil‐reactive nitrogen (N) to the air and water. However, the extent and spatial variability of biochar function at the global level are still unclear. Using Random Forest regression modelling of machine learning based on data compiled from the literature, we mapped the impacts of different biochar types (derived from wood, straw, or manure), and their interactions with biochar application rates, soil properties, and environmental factors, on soil N losses (NH₃ volatilization, N₂O emissions, and N leaching) and crop productivity. The results show that a suitable distribution of biochar across global croplands (i.e., one application of <40 t ha^?1 wood biochar for poorly buffered soils, such as those characterized by soil pH<5, organic carbon<1%, or clay>30%; and one application of <80 t ha^?1 wood biochar, <40 t ha^?1 straw biochar, or <10 t ha^?1 manure biochar for other soils) could achieve an increase in global crop yields by 222–766 Tg yr^?1 (4%–16% increase), a mitigation of cropland N₂O emissions by 0.19–0.88 Tg N yr^?1 (6%–30% decrease), a decline of cropland N leaching by 3.9–9.2 Tg N yr^?1 (12%–29% decrease), but also a fluctuation of cropland NH₃ volatilization by ?1.9–4.7 Tg N yr^?1 (?12%–31% change). The decreased sum of the three major reactive N losses amount to 1.7–9.4 Tg N yr^?1, which corresponds to 3%–14% of the global cropland total N loss. Biochar generally has a larger potential for decreasing soil N losses but with less benefits to crop production in temperate regions than in tropical regions.     

Biochar co-compost improves nitrogen retention and reduces carbon emissions in a winter wheat cropping system

Organic amendments, such as compost and biochar, mitigate the environmental burdens associated with wasting organic resources and close nutrient loops by capturing, transforming, and resupplying nutrients to soils. While compost or biochar application to soil can enhance an agroecosystem's capacity to store carbon and produce food, there have been few field studies investigating the agroecological impacts of amending soil with biochar co-compost, produced through the composting of nitrogen-rich organic material, such as manure, with carbon-rich biochar. Here, we examine the impact of biochar co-compost on soil properties and processes by conducting a field study in which we compare the environmental and agronomic impacts associated with the amendment of either dairy manure co-composted with biochar, dairy manure compost, or biochar to soils in a winter wheat cropping system. Organic amendments were applied at equivalent C rates (8 Mg C ha⁻¹). We found that all three treatments significantly increased soil water holding capacity and total plant biomass relative to the no-amendment control. Soils amended with biochar or biochar co-compost resulted in significantly less greenhouse gas emissions than the compost or control soils. Biochar co-compost also resulted in a significant reduction in nutrient leaching relative to the application of biochar alone or compost alone. Our results suggest that biochar co-composting could optimize organic resource recycling for climate change mitigation and agricultural productivity while minimizing nutrient losses from agroecosystems.     

Effects of wood bark ash on the growth and nutrition of a Scots pine afforestation in central Finland

Results are presented from a fertilization experiment with wood bark ash (0, 1, 2, 5, 10, 20 Mg ha^-1) applied to prevent and cure visible nutrient disorders of young Scots pine established on a peatland field. 13 years after fertilization, dieback of trees and other symptoms of nutrient disorders were substantially reduced or even eliminated, especially where higher doses had been applied. The volume of the growing stock was more than 70 m³ ha^-1 for the highest dose while control plots produced less than 15 m³ ha^-1. Vegetation characteristics changed following ash treatments with high ash doses favouring grasses and low ash doses promoting mosses. Some major changes in soil and foliar nutrient concentrations were evident due to ash fertilization. K and B, however, were clearly the most limiting nutrients that could be cycled where high doses of ash were used. This was particularly the case with a dose of 20 Mg ha^-1. Decomposition of the topsoil was at its highest on plots with ash doses of 5 and 10 Mg ha^-1 ash and at its lowest when the dose was 2 Mg ha^-1. This was partly due to differences in the C/N ratio of the soil. All decomposition parameters indicated a high degree of humification in the topsoil. High N content (of organic material), low C/N in the soil and optimum levels of foliar N concentrations suggested sufficient N mineralization for tree growth to have occurred in the soil.     

Carbon and nitrogen pools in a mangrove stand of <Emphasis Type="Italic">Kandelia obovata</Emphasis> (S., L.) Yong: vertical distribution in the soil–vegetation system

Attempts were made to quantify the carbon and nitrogen pools in a monospecific and pioneer mangrove stand of Kandelia obovata Sheue, Liu & Yong, Okinawa Island, Japan. The leaf C and N concentrations on a leaf area basis decreased with increasing PPFD (Photosysthetic Photon Flux Density). The total C and N stocks in foliage were estimated as 3.55 Mg ha^–1 and 0.105 Mg ha^–1, respectively. The bark (45.6–48.6% for C and 0.564–0.842% for N) contained significantly higher amount of C (P < 0.05) and N (P < 0.01) than wood (46.2–47.8% for C and 0.347–0.914% N). The total C stock of stem was 23.2 Mg ha^–1 in wood and 8.33 Mg ha^–1 in bark, and the total N stock was 0.222 Mg ha^–1 in wood and 0.116 Mg ha^–1 in bark. The root wood (37.1–45.0%) contained significantly higher amount of C than root bark (35.4–40.7%) (P < 0.01). The total C stock of root was 14.2 Mg ha^–1 in wood and 12.6 Mg ha^–1 in bark, and the total N stock of root was 0.157 Mg ha^–1 in wood and 0.155 Mg ha^–1 in bark. The soil organic C and total N stocks within 1 m soil depth were estimated as 57.3 Mg ha^–1 and 2.73 Mg ha^–1, respectively. The C pool in aboveground biomass (35.1 Mg ha^–1) was 1.3 times as large as that in belowground biomass (26.9 Mg ha^–1). However, the soil organic C pool (57.3 Mg ha^–1) was similar to the total C pool (62.0 Mg ha^–1) of vegetation, indicating that the mangrove stored a large part of production in the soil. About 50% of the C was in the soil. The N pool in aboveground biomass (0.442 Mg ha^–1) was 1.4 times as large as that in belowground biomass (0.312 Mg ha^–1). The soil N stock was 3.3 times as large as the biomass N stock (0.754 Mg ha^–1).     

Net changes of soil C stocks in two grassland soils 26 months after simulated pasture renovation including biochar addition

The use of deep‐rooting pasture species as a management practice can increase the allocation of plant carbon (C) below ground and enhance C storage. A 2‐year lysimeter trial was set up to compare changes in C stocks of soils under either deep‐ or shallow‐rooting pastures and investigate whether biochar addition below the top 10 cm could promote root growth at depth. For this i) soil ploughing at cultivation was simulated in a silt loam soil and in a sandy soil by inverting the 0 to 10 and 10‐ to 20‐cm‐depth soil layers, and a distinctive biochar (selected for each soil to overcome soil‐specific plant growth limitations) was mixed at 10 Mg ha^?1 in the buried layer, where appropriate and ii) three pasture types with contrasting root systems were grown. In the silt loam, soil inversion resulted in a general loss of C (2.0–8.1 Mg ha^?1), particularly in the buried horizon, under shallow‐rooting pastures only. The addition of a C‐rich biochar (equivalent to 7.6 Mg C ha^?1) to this soil resulted in a net C gain (21–40% over the non‐biochar treatment, P < 0.10) in the buried layer under all pastures; this overcame the loss of C in this horizon under shallow‐rooting pastures. In the sandy soil, all pastures were able to maintain soil C stocks at 10–20 cm depth over time, with minor gains of C (1.6–5.1 Mg ha^?1) for the profile. In this soil, the exposure of a skeletal‐ and nutrient‐depleted soil layer at the surface may have fostered root growth at depth. The addition of a nutrient‐rich biochar (equivalent to 3.6 Mg C ha^?1) to this soil had no apparent effect on C stocks. More research is needed to understand the mechanisms through which soil C stocks at depth are preserved.     

The legacy of harvest and fire on ecosystem carbon storage in a north temperate forest

Forest harvesting and wildfire were widespread in the upper Great Lakes region of North America during the early 20th century. We examined how long this legacy of disturbance constrains forest carbon (C) storage rates by quantifying C pools and fluxes after harvest and fire in a mixed deciduous forest chronosequence in northern lower Michigan, USA. Study plots ranged in age from 6 to 68 years and were created following experimental clear‐cut harvesting and fire disturbance. Annual C storage was estimated biometrically from measurements of wood, leaf, fine root, and woody debris mass, mass losses to herbivory, soil C content, and soil respiration. Maximum annual C storage in stands that were disturbed by harvest and fire twice was 26% less than a reference stand receiving the same disturbance only once. The mechanism for this reduction in annual C storage was a long‐lasting decrease in site quality that endured over the 62‐year timeframe examined. However, during regrowth the harvested and burned forest rapidly became a net C sink, storing 0.53 Mg C ha⁻¹ yr⁻¹ after 6 years. Maximum net ecosystem production (1.35 Mg C ha⁻¹ yr⁻¹) and annual C increment (0.95 Mg C ha⁻¹ yr⁻¹) were recorded in the 24‐ and 50‐year‐old stands, respectively. Net primary production averaged 5.19 Mg C ha⁻¹ yr⁻¹ in experimental stands, increasing by < 10% from 6 to 50 years. Soil heterotrophic respiration was more variable across stand ages, ranging from 3.85 Mg C ha⁻¹ yr⁻¹ in the 6‐year‐old stand to 4.56 Mg C ha⁻¹ yr⁻¹ in the 68‐year‐old stand. These results suggest that harvesting and fire disturbances broadly distributed across the region decades ago caused changes in site quality and successional status that continue to limit forest C storage rates.     

Heterotrophic Soil Respiration in Relation to Environmental Factors and Microbial Biomass in Two Wet Tropical Forests

We examined the correlation between fungal and bacterial biomass, abiotic factors such as soil moisture, carbon in the light soil fraction and soil nitrogen to a depth of 0–25 cm and heterotrophic soil respiration using a trenching technique – in a secondary forest (Myrcia splendens, Miconia prasina and Casearia arborea) and a pine (Pinus caribeae) plantation in the Luquillo Experimental Forest in Puerto Rico. Soil respiration was significantly reduced where roots were excluded for 7 years in both the secondary forest and the pine plantation. Microbial biomass was also significantly reduced in the root exclusion plots. In root exclusion treatment, total fungal biomass was on average 31 and 65% lower than the control plots in the pine plantation and the secondary forest, respectively, but the total bacterial biomass was 24 and 8.3% lower than the control plots in the pine plantation and the secondary forest, respectively. Heterotrophic soil respiration was positively correlated with fungal biomass (R²=0.63, R²=0.39), bacterial biomass (R²=0.16, R²=0.45), soil moisture (R²=0.41, R²=0.56), carbon in light fraction (R²=0.45, R²=0.39) and total nitrogen (R²=0.69, R²=0.67) in the pine plantation and the secondary forest, respectively. The regression analysis suggested that fungal biomass might have a greater influence on heterotrophic soil respiration in the pine plantation, while the bacterial biomass might have a greater influence in the secondary forest. Heterotrophic soil respiration was more sensitive to total N than to carbon in the light fraction, and soil moisture was a major factor influencing heterotrophic soil respiration in these forests where temperature is high and relatively invariable.     

Field Evaluations of Subterranean Termite Preference for Sap-Stain Inoculated Wood

Few studies have focused on interactions between subterranean termites and the ophiostomatoid fungal associates of pine bark beetles or root feeding weevils. Field stake tests were employed at four locations throughout Mississippi to determine the feeding preference of subterranean termites for blue-stained, unstained, and partially decayed southern pine sapwood stakes. This study also utilized wood decayed by Gloeophyllum trabeum, a fungus previously shown to elicit a positive subterranean termite feeding response, as a positive control. Stakes inoculated with G. trabeum received significantly more attacks than all other treatments after 16 weeks. Of the stakes attacked by subterranean termites, stakes inoculated with Ophiostoma minus were degraded faster than any other treatment. Subterranean termite preference for stakes treated with either of two Leptographium spp. and the untreated negative controls did not differ; however, each was fed upon less than all other treatments. The feeding rate on stakes inoculated with O. ips and G. trabeum being fed upon by subterranean termites was not significantly different. These results represent the first evidence of wood containing non-structurally degrading fungi (O. ips and O. minus) eliciting a feeding preference from subterranean termites greater than that of decayed wood. The implications of these results are particularly relevant to pine forest ecology, nutrient cycling, subterranean termite control, and the utilization of blue-stained southern pine building products in the southeastern U.S.     

Tree species and wood ash affect soil in Michigan’s Upper Peninsula

Tree species and wood ash application in plantations of short-rotation woody crops (SRWC) may have important effects on the soil productive capacity through their influence on soil organic matter (SOM) and exchangeable cations. An experiment was conducted to assess changes in soil C and N contents and pH within the 0–50 cm depth, and exchangeable cation (Ca²⁺, Mg²⁺, K⁺, and Na⁺) and extractable acidity concentrations within the 0–10 cm depth. The effects of different species (European larch [Larix decidua P. Mill.], aspen [Populus tremula L. × Populus tremuloides Michx.], and four poplar [Populus spp.] clones) and wood ash applications (0, 9, and 18 Mg ha⁻¹) on soil properties were evaluated, using a common garden experiment (N = 70 stands) over 7 years of management in Michigan’s Upper Peninsula. Soils were of the Onaway series (fine-loamy, mixed, active, frigid Inceptic Hapludalfs). The NM-6 poplar clone had the greatest soil C and N contents in almost all ash treatment levels. Soil C contents were 7.5, 19.4, and 10.7 Mg C ha⁻¹ greater under the NM-6 poplar than under larch in the ash-free, medium-, and high-level plots, respectively. Within the surface layer, ash application increased soil C and N contents (P < 0.05) through the addition of about 0.7 Mg C ha⁻¹ and 3 kg N ha⁻¹ with the 9 Mg ha⁻¹ ash application (twofold greater C and N amounts were added with the 18 Mg ha⁻¹ application). During a decadal time scale, tree species had no effects—except for K⁺—on the concentrations of the exchangeable cations, pH, and extractable acidity. In contrast, ash application increased soil pH and the concentration of Ca²⁺ (P < 0.05), from 5.2 ± 0.4 cmol_c kg⁻¹ (ash-free plots) to 8.6 ± 0.4 cmol_c kg⁻¹ (high-level ash plots), and tended to increase the concentration of Mg²⁺ (P < 0.1), while extractable acidity was reduced (P < 0.05) from 5.6 ± 0.2 cmol_c kg⁻¹ (ash-free plots) to 3.7 ± 0.2 cmol_c kg⁻¹ (high-level plots). Wood ash application, within certain limits, not only had a beneficial effect on soil properties important to the long-term productivity of fast-growing plantations but also enhanced long-term soil C sequestration.     

Short-term effects of thinning and liming on forest soils of pitch pine and Japanese larch plantations in central Korea

The influences of thinning (50% of standing density) and liming (Ca+Mg, 2 Mg ha⁻¹) on soil chemical properties were investigated for 2 years (2001, 2002) in 40-year-old pitch pine (Pinus rigida Mill.) and 44-year-old Japanese larch (Larix leptolepis Gord.) plantations established on similar soils. In general, soil properties varied significantly among plantations and treatments. For both plantations, thinning significantly increased soil organic C (SOC) concentrations whereas there were no significant changes in soil pH and Ca and Mg concentrations. In addition, thinning increased total soil N and Na concentrations for the pitch pine plantation and available P concentration for the Japanese larch plantation in the second year after the treatment. Liming did not affect soil chemical characteristics for the pitch pine plantation except for Na concentration. However, for the Japanese larch plantation, liming significantly increased soil pH and K, Ca and Mg concentrations and decreased SOC and total soil N concentrations. For both plantations, soil Al concentration did not change after thinning and liming and decreased exponentially with increased pH values. The increases in SOC and total soil N concentrations after thinning were possibly due to increases in decomposition of organic matter and root death. Although differences were not statistically significant, soil available P concentration tended to increase at early stages of liming for both plantations. These results suggested that thinning and liming seemed to regulate soil chemical properties for pitch pine and Japanese larch plantations established on similar soils.     

High surface area biochar negatively impacts herbicide efficacy

Background and Aims

Amendment of soil by biochar may reduce efficacy of soil-applied herbicides due to sorption.

Methods

Bioassays with Green Foxtail (Setaria viridis) tested the influence of two biochars on phytoavailability of S-metolachlor and sulfentrazone under biochar amendment of 0, 13, 26 and 52?Mg?ha^-1.

Results

Adsorption of both herbicides was an order of magnitude greater on a high specific surface area (SSA) biochar (EUC-800; SSA 242?m²?g^-1) than on a low SSA biochar (BC-1; SSA 3.6?m²?g^-1). Herbicide doses near the lowest recommended label rates controlled the weed at 13 and 26?Mg?ha^-1 of BC-1; sulfentrazone was also effective at 52?Mg BC-1?ha^-1. These same herbicide doses controlled weed germination and development only at 13?Mg?ha^-1 of EUC-800; at herbicide doses near the highest label rates, weed control was also achieved at 26?Mg EUC-800?ha^-1, but not at 52?Mg EUC-800?ha^-1.

Conclusions

Increased doses of soil-applied herbicides cannot necessarily offset decreases in herbicide phytoavailability in biochar-amended soils, particularly if the biochar has a high SSA. Considering the long half-life of biochar in soil, pest control needs will be best served by low SSA biochars.     

Wildfire effects on carbon and nitrogen in inland coniferous forests

A ponderosa pine/Douglas-fir forest (Pinus ponderosa Dougl., Pseudotsuga menziesii (Mirb.) Franco; PP/DF) and a lodgepole pine/Engelmann spruce forest (Pinus contorta Loud., Picea engelmannii Parry ex Engelm.; LP/ES) located on the eastern slopes of the Cascade Mountains in Washington state, USA, were examined following severe wildfire to compare total soil carbon and nitrogen capitals with unburned (control) forests. One year after fire, the average C content (60 cm depth) of PP/DF and LP/ES soil was 30% (25 Mg ha^-1) and 10% (7 Mg ha^-1) lower than control soil. Average N content on the burned PP/DF and LP/ES plots was 46% (3.0 Mg ha^-1) and 13% (0.4 Mg ha^-1) lower than control soil. The reduction in C and N in the PP/DF soil was largely the result of lower nutrient capitals in the burned Bw horizons (12–60 cm depth) relative to control plots. It is unlikely that the 1994 fire substantially affected nutrient capitals in the Bw horizons; however, natural variability or past fire history could be responsible for the varied nutrient capitals observed in the subsurface soils. Surface erosion (sheet plus rill) removed between 15 and 18 Mg ha^-1 of soil from the burned plots. Nutrient losses through surface erosion were 280 kg C ha^-1 and 14 kg N ha^-1 in the PP/DF, whereas LP/ES losses were 640 and 22 kg ha^-1 for C and N, respectively. In both forests, surface erosion of C and N was _∼1% to 2% of the A-horizon capital of these elements in unburned soil. A bioassay (with lettuce as an indicator plant) was used to compare soils from low-, moderate- and high-severity burn areas relative to control soil. In both forests, low-severity fire increased lettuce yield by 70–100% of controls. With more severe fire, yield decreased in the LP/ES relative to the low-intensity burn soil; however, only in the high-severity treatment was yield reduced (14%) from the control. Moderate- and high-severity burn areas in the PP/DF were fertilized with _∼56 kg ha^-1 of N four months prior to soil sampling. In these soils, yield was 70–80% greater than the control. These results suggest that short-term site productivity can be stimulated by low-severity fire, but unaffected or reduced by more severe fire in the types of forests studied. Post-fire fertilization with N could increase soil productivity where other environmental factors do not limit growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Woody biochar's greenhouse gas mitigation potential across fertilized and unfertilized agricultural soils and soil moisture regimes

Biochar has been widely researched as an important technology for climate smart agriculture, yet work is still necessary to identify the magnitude of potential greenhouse gas (GHG) mitigation and mechanisms involved. This study measured slow‐pyrolysis wood‐derived biochar's impact on GHG efflux, mineral N dynamics, and soil organic C in a series of two incubations across fertilized and unfertilized agricultural soils and soil moisture regimes. This research explored the magnitude of biochar's full GHG mitigation potential and drivers of such impacts. Results of this incubation indicate slow‐pyrolysis wood‐derived biochar has potential to provide annual emission reductions of 0.58–1.72 Mg CO₂‐eq ha^?1 at a 25 Mg ha^?1 biochar application rate. The greatest GHG mitigation potential was from C sequestration and nitrous oxide (N₂O) reduction in mineral N fertilized soils, with minimal impacts on N₂O emissions in unfertilized soils, carbon dioxide (CO₂) emissions, and methane (CH₄) uptake. Analysis of mineral N dynamics in the bulk soil and on biochar isolates indicated that neither biochar impacts on net mineralization and nitrification nor retention of ammonium () on biochar isolates could explain biochar's N₂O reduction. Instead, biochar amendments exhibited consistent N₂O emission reductions relative to the N₂O emission in the control soil regardless of soil type and fertilization. Results across a soil moisture gradient suggest that woody biochar may aerate soils shifting redox conditions and subsequent N₂O production. Understanding the magnitude of biochar's GHG reduction potential and the mechanisms driving these effects can help inform biochar modeling efforts, explain field results and identify agricultural applications that maximize biochar's full GHG mitigation potential.     

Aged biochar affects gross nitrogen mineralization and recovery: a 15N study in two contrasting soils

Biochar is a pyrolysed biomass and largely consists of pyrogenic carbon (C), which takes much longer to decompose compared to the biomass it is made from. When applied to soil, it could increase agricultural productivity through nutrient retention and changing soil properties. The biochar‐mediated nutrient retention capacity depends on the biochar properties, which change with time, and on soil properties. Here, we examined the effects of a wood biochar (20 t ha^?1), that has aged (21 months) in a grassland field, on gross nitrogen (N) mineralization (GNM) and ¹⁵N recovery using a ¹⁵N tracer. A field experiment was conducted in two soil types, that is a Tenosol and a Dermosol, and also included a phosphorus (P) addition treatment (1 kg ha^?1). Compared to the control, biochar with P addition significantly increased GNM in the Tenosol. Possibly, biochar and P addition enhanced nutrient availability in this nutrient‐limited soil, thereby stimulating microbial activity. In contrast, biochar addition reduced GNM in the Dermosol, possibly by protecting soil organic matter (SOM) from decomposition through sorption onto biochar surfaces and enhanced formation of organo‐mineral complexes in this soil that had a higher clay content (29% vs. 8% in the Tenosol). Compared to the control, biochar significantly increased total ¹⁵N recovery in the Tenosol (on average by 12%) and reduced leaching to subsurface soil layers (on average by 52%). Overall, ¹⁵N recovery was greater in the Dermosol (83%) than the Tenosol (63%), but was not affected by biochar or P. The increased N recovery with biochar addition in the sandy Tenosol may be due to retention at exchange sites on aged biochar, while such beneficial effects may not be visible in soils with higher clay content. Our results suggest that aged biochar may increase N use efficiency through reduced leaching or gaseous losses in sandy soils.     

Sedimentary Organic Carbon and Nitrogen Sequestration Across a Vertical Gradient on a Temperate Wetland Seascape Including Salt Marshes,Seagrass Meadows and Rhizophytic Macroalgae Beds

Coastal wetlands are key in regulating coastal carbon and nitrogen dynamics and contribute significantly to climate change mitigation and anthropogenic nutrient reduction. We investigated organic carbon (OC) and total nitrogen (TN) stocks and burial rates at four adjacent vegetated coastal habitats across the seascape elevation gradient of Cádiz Bay (South Spain), including one species of salt marsh, two of seagrasses, and a macroalgae. OC and TN stocks in the upper 1 m sediment layer were higher at the subtidal seagrass Cymodocea nodosa (72.3 Mg OC ha⁻¹, 8.6 Mg TN ha⁻¹) followed by the upper intertidal salt marsh Sporobolus maritimus (66.5 Mg OC ha⁻¹, 5.9 Mg TN ha⁻¹), the subtidal rhizophytic macroalgae Caulerpa prolifera (62.2 Mg OC ha⁻¹, 7.2 Mg TN ha⁻¹), and the lower intertidal seagrass Zostera noltei (52.8 Mg OC ha⁻¹, 5.2 Mg TN ha⁻¹). The sedimentation rates increased from lower to higher elevation, from the intertidal salt marsh (0.24 g cm⁻² y⁻¹) to the subtidal macroalgae (0.12 g cm⁻² y⁻¹). The organic carbon burial rate was highest at the intertidal salt marsh (91 ± 31 g OC m⁻² y⁻¹), followed by the intertidal seagrass, (44 ± 15 g OC m⁻² y⁻¹), the subtidal seagrass (39 ± 6 g OC m⁻² y⁻¹), and the subtidal macroalgae (28 ± 4 g OC m⁻² y⁻¹). Total nitrogen burial rates were similar among the three lower vegetation types, ranging from 5 ± 2 to 3 ± 1 g TN m⁻² y⁻¹, and peaked at S. maritimus salt marsh with 7 ± 1 g TN m⁻² y⁻¹. The contribution of allochthonous sources to the sedimentary organic matter decreased with elevation, from 72% in C. prolifera to 33% at S. maritimus. Our results highlight the need of using habitat-specific OC and TN stocks and burial rates to improve our ability to predict OC and TN sequestration capacity of vegetated coastal habitats at the seascape level. We also demonstrated that the stocks and burial rates in C. prolifera habitats were within the range of well-accepted blue carbon ecosystems such as seagrass meadows and salt marshes.

     

The significance of Cognettia sphagnetorum(Enchytraeidae) on nitrogen availability and plant growth in wood ash-treated humus soil

A laboratory microcosm experiment was established to study whether the role of Cognettia sphagnetorum (Enchytraeidae) in affecting Scots pine (Pinus sylvestris) seedling growth is influenced by wood ash-amendment, i.e., neutralisation of the raw humus soil. Coniferous forest soil, inoculated with soil microbes and nematodes, was either treated with wood ash or left as ash-free control. Wood ash (corresponding to an amount of 5000 kg ha^–1) was either spread on the soil surface or mixed into the soil. Enchytraeid and pine seedling biomass, abundance of nematodes, and water leachable NH₄ ⁺-N and NO₃ ^–-N were measured 26 and 51 weeks after initiation of the experiment and root length and N concentration of needles were measured 51 weeks after initiation of the experiment. Wood ash when mixed into the soil, reduced the biomass of C. sphagnetorum. Nematodes were unaffected by the treatments. In the ash-free soils C. sphagnetorum had little influence on pine growth, but it did decrease root length and root to shoot ratio. In the absence of enchytraeids wood ash decreased pine biomass production and root length. However, the presence of enchytraeids in the ash-treated soil compensated the ash-induced negative effects on the pine performance. Enchytraeids increased and wood ash decreased water leachable NH₄ ⁺-N in the presence but not in the absence of enchytraeids, while water leachable NO₃ ^–-N was not affected by the treatments. It was concluded that C. sphagnetorum can be important in ensuring nutrient cycling and plant growth in situations when an ecosystem encounters disturbances.