Carbon sequestration: Do N inputs and elevated atmospheric CO2 alter soil solution chemistry and respiratory C losses?

Soil respiration is a large C flux which is of primary importance in determining C sequestration. Here we ask how it is altered by atmospheric CO₂ concentration and N additions. Swards of Lolium perenne L. were grown in a Eutric cambisol under controlled conditions with and without the addition of 200 kg NO^? ₃ ?N ha^?1, at either 350 ppm or 700 ppm CO₂, for 3 months. Soil respiration and net canopy photosynthesis were both increased by added N and elevated CO₂, but soil respiration increased proportionately less than fixation by photosynthesis. Thus, both elevated CO₂ and N appeared to increase potential C sequestration, although adding N at elevated CO₂ reduced the C sequestered as a proportion of that fixed relative to elevated CO₂ alone. Across all treatments below-ground respiratory C losses were predicted by root biomass, but not by soil solution C and N concentrations. Specific root-dependent respiration was increased by elevated CO₂, such that below-ground respiration per unit biomass and per unit plant N was increased.     

Correlating the spatial distribution of atmospheric ammonia with δ15n values at an ammonia release site

A field ammonia (NH₃) release experiment and open top chambers containing moorland monoliths continuously fumigated with NH₃ or sprayed with NH₄Cl were used to assess the potential for using δ¹⁵N values in determining the area of influence around a point NH₃ emission source. δ¹⁵N values are being increasingly used as environmental tracers and we tested the hypothesis that the δ¹⁵N signal from an NH₃ emission source is observable in nearby vegetation. Using modified monitoring devices, atmospheric NH₃ concentrations were found to decrease with distance from source, with δ¹⁵N values also reflecting this trend, producing a signal shift with changing concentration. Open top chamber studies of δ¹⁵N values of Calluna vulgaris (L.) Hull indicated a correlation with deposition treatments in current year shoots. Analysis of Calluna shoots from the NH₃ release showed a similar trend of δ¹⁵N enrichment. Significant linear correlations between δ¹⁵N and percent N in plant material were found, both in the controlled conditions of the open top chambers and at the NH₃ release site, illustrating the possible use of this technique in N deposition biomonitoring.     

In situ ground water denitrification in stratified, permeable soils underlying riparian wetlands

The ground water denitrification capacity of riparian zones in deep soils, where substantial ground water can flow through low-gradient stratified sediments, may affect watershed nitrogen export. We hypothesized that the vertical pattern of ground water denitrification in riparian hydric soils varies with geomorphic setting and follows expected subsurface carbon distribution (i.e., abrupt decline with depth in glacial outwash vs. negligible decline with depth in alluvium). We measured in situ ground water denitrification rates at three depths (65, 150, and 300 cm) within hydric soils at four riparian sites (two per setting) using a 15N-enriched nitrate "push-pull" method. No significant difference was found in the pattern and magnitude of denitrification when grouping sites by setting. At three sites there was no significant difference in denitrification among depths. Correlations of site characteristics with denitrification varied with depth. At 65 cm, ground water denitrification correlated with variables associated with the surface ecosystem (temperature, dissolved organic carbon). At deeper depths, rates were significantly higher closer to the stream where the subsoil often contains organically enriched deposits that indicate fluvial geomorphic processes. Mean rates ranged from 30 to 120 microg N kg(-1) d(-1) within 10 m versus <1 to 40 microg N kg(-1) d(-1) at >30 m from the stream. High denitrification rates observed in hydric soils, down to 3 m within 10 m of the stream in both alluvial and glacial outwash settings, argue for the importance of both settings in evaluating the significance of riparian wetlands in catchment-scale N dynamics.     

In situ measurements of nitrate leaching implicate poor nitrogen and irrigation management on sandy soils

Minimizing the risk of nitrate contamination along the waterways of the U.S. Great Plains is essential to continued irrigated corn production and quality water supplies. The objectives of this study were to quantify nitrate (NO(3)) leaching for irrigated sandy soils (Pratt loamy fine sand [sandy, mixed, mesic Lamellic Haplustalfs]) and to evaluate the effects of N fertilizer and irrigation management strategies on NO(3) leaching in irrigated corn. Two irrigation schedules (1.0x and 1.25x optimum) were combined with six N fertilizer treatments broadcast as NH(4)NO(3) (kg N ha(-1)): 300 and 250 applied pre-plant; 250 applied pre-plant and sidedress; 185 applied pre-plant and sidedress; 125 applied pre-plant and sidedress; and 0. Porous-cup tensiometers and solution samplers were installed in each of the four highest N treatments. Soil solution samples were collected during the 2001 and 2002 growing seasons. Maximum corn grain yield was achieved with 125 or 185 kg N ha(-1), regardless of the irrigation schedule (IS). The 1.25x IS exacerbated the amount of NO(3) leached below the 152-cm depth in the preplant N treatments, with a mean of 146 kg N ha(-1) for the 250 and 300 kg N preplant applications compared with 12 kg N ha(-1) for the same N treatments and 1.0x IS. With 185 kg N ha(-1), the 1.25x IS treatment resulted in 74 kg N ha(-1) leached compared with 10 kg N ha(-1) for the 1.0x IS. Appropriate irrigation scheduling and N fertilizer rates are essential to improving N management practices on these sandy soils.     

Increased bioavailability of metals in two contrasting agricultural soils treated with waste wood-derived biochar and ash

Recycled waste wood is being increasingly used for energy production; however, organic and metal contaminants in by-products produced from the combustion/pyrolysis residue may pose a significant environmental risk if they are disposed of to land. Here we conducted a study to evaluate if highly polluted biochar (from pyrolysis) and ash (from incineration) derived from Cu-based preservative-treated wood led to different metal (e.g., Cu, As, Ni, Cd, Pb, and Zn) bioavailability and accumulation in sunflower (Helianthus annuus L.). In a pot experiment, biochar at a common rate of 2 % w/w, corresponding to ～50 t ha^?1, and an equivalent pre-combustion dose of wood ash (0.2 % w/w) were added to a Eutric Cambisol (pH 6.02) and a Haplic Podzol (pH 4.95), respectively. Both amendments initially raised soil pH, although this effect was relatively short-term, with pH returning close to the unamended control within about 7 weeks. The addition of both amendments resulted in an exceedance of soil Cu statutory limit, together with a significant increase of Cu and plant nutrient (e.g., K) bioavailability. The metal-sorbing capacity of the biochar, and the temporary increase in soil pH caused by adding the ash and biochar were insufficient to offset the amount of free metal released into solution. Sunflower plants were negatively affected by the addition of metal-treated wood-derived biochar and led to elevated concentration of metals in plant tissue, and reduced above- and below-ground biomass, while sunflower did not grow at all in the Haplic Podzol. Biochar and ash derived from wood treated with Cu-based preservatives can lead to extremely high Cu concentrations in soil and negatively affect plant growth. Identifying sources of contaminated wood in waste stream feedstocks is crucial before large-scale application of biochar or wood ash to soil is considered.     

Effect of Si-rich substances on phosphorous adsorption by sandy soils

Environmental Science and Pollution Research - The poor adsorption capacity of sandy soils is one of the primary reasons of a high level of phosphorus (P) leaching. Silicon (Si)-rich soil...