Nitrous oxide production in aerobic soils under varying pH,temperature and water content

Laboratory studies were conducted to evaluate the effect of soil pH, temperature and water content on the rate of nitrification and on the amount of N₂O evolved from samples of Plano silt loam soil. The rate of nitrification of added NH₄⁺-N increased with increasing soil pH (4.7, 5.1 and 6.7), temperature (10, 20 and 30°C) and water content (0.1, 0.2 and 0.3 m³ m^?3). At soil water contents of 0.1 and 0.2 m³ m^?3, corresponding to 18 and 36% water-filled pore space, respectively, N₂O evolution was proportional to NO₃^? production. Approximately 0.1–0.2% of the nitrified N was evolved as N₂O-N. At 0.3 m³ m^?3 water content (54% water-filled pore space) and 20 and 30°C, the ratio of N₂O-N evolved to N nitrified was significantly higher (range of 0.3–1.1%).An additional experiment was conducted using diurnally fluctuating temperatures (10–30°C). The pattern of N₂O evolution was markedly different when the system was sampled at 10 and 30°C than at 20°C. The apparent N₂O emission rates were approximately equal for 12-h periods during which the temperature increased from 10 to 30°C or decreased from 30 to 10°C. In contrast, the apparent N₂O emission rates were significantly lower for the 12-h period when the incubation flasks were sampled at 20°C following the daily minimum temperature compared to the 12-h period when the samplings were at 20°C following the daily maximum temperature. This provides additional evidence that temperature fluctuation in the surface soil is a factor in-observed diurnal variations in N₂O emissions under field conditions.Our findings indicate that an interaction of three factors (soil pH, temperature and water content) affects the amount of N₂O evolved during nitrification in soils. In relatively dry soils, estimated N₂O production of ca. 0.1–0.3% of the N nitrified may be sufficiently accurate. Much higher N₂O output can be expected following rainfall or irrigation. Diurnal variability in N₂O fluxes from soils due to fluctuating temperature is an additional uncertainty in quantifying N₂O production in field soils.     

Methanotrophic communities in a landfill cover soil as revealed by [13C] PLFAs and respiratory quinones: Impact of high methane addition and landfill leachate irrigation

The soil microbial communities of a landfill cover substrate, which was treated with landfill gas (100 l CH₄ m^?2 d^?1) and landfill leachate for 1.5 years, were investigated by phospholipid fatty acid (PLFA), ergosterol and respiratory quinone analyses. The natural ¹³C depletion of methane was used to assess the activity of methanotrophs and carbon turnover in the soil system. Under methane addition, the soil microbial community was dominated by PLFAs (14:0 and 16:1 isomers) and quinones (ubiquinone-8 and 18-methylene-ubiquinone-8) related to type I methanotrophs, and 18:1 PLFAs contained in type II methanotrophs. While type I methanotrophic PLFAs were ¹³C depleted, i.e. type I methanotrophs were actively oxidising and assimilating methane, ¹³C depletion of 18:1 PLFAs was low and inconsistent with their abundance. This, possibly reflects isotopic discrimination, assimilation of carbon derived from type I methanotrophs and a high contribution of non-methanotrophic bacteria to the 18:1 isomers. Landfill leachate irrigation caused the methanotrophic community to shift closer to the soil surface. It also decreased 18:1 PLFAs, while type I methanotrophs were probably stimulated. Gram positive bacteria, but not fungi, were also ¹³C depleted and consequently involved in the secondary turnover of carbon originating from methanotrophic bacteria. Cy17:0 PLFA was ¹³C depleted in deep soil layers, indicating anaerobic methane oxidation.     

Carbon assimilation and microbial activity in soil

In order to characterise the term microbial ?activity”? three different microbial populations belonging to a luvisol (I), a phaeozem (II) and a rendzina (III) were used for studying kinetic parameters such as substrate affinity, growth rate, yield and turnover time and the metabolic quotient of basal respiration. Glucose was used as a carbon source. Specific growth rate values (μ) varied between 0.0037 and 0.015 h^?1 depending on soil type and glucose concentration and were far below the potential μ_max. The calculated turnover time was 3–11 days, respectively. The yield coefficient was in the range between 0.37 and 0.53. The maximal uptake rate of glucose–C of soil population (II) was 0.041 g C g^?1 biomass-C h^?1. The determined affinity constant (K_m) was 57 μg C g^?1 soil. The affinity to glucose was higher for the glucose-mediated CO₂ evolution with K_m values of 15.2 and 17.5 than for the glucose uptake system itself. The observed qCO₂ values of the basal respiration at temperature increments from 0 to 45° C were almost identical for the soils (I) and (II). The calulated Q₁₀ lay in the range between 1.4 and 2.0.     

Anaerobic ammonium oxidation and denitrification in a paddy soil as affected by temperature,pH, organic carbon,and substrates

Anaerobic ammonium oxidation (anammox process) widely occurs in paddy soil and may substantially contribute to permanent N removal; however, little is known about the factors controlling this process. Here, effects of temperature, pH, organic C, and substrates on potential rate of anammox and the relative contribution of anammox to total N₂ production in a paddy soil were investigated via slurry incubation combined with ¹⁵N tracer technique. Anammox occurred over a temperature range from 5 to 35 °C with an optimum rate at 25 °C (1.7 nmol N g^?1 h^?1) and a pH range from 4.8 to 10.1 with an optimum rate at pH 7.3 (1.7 nmol N g^?1 h^?1). The presence of glucose and acetate (5–100 mg C L^?1) significantly inhibited anammox activities and the ratio of anammox to total N₂ production. The response of potential rates of anammox to ammonium concentrations fitted well with Michaelis-Menten relationship showing a maximum rate (V_max) of 4.4 nmol N g^?1 h^?1 and an affinity constant (K_m) of 6.3 mg NH₄⁺-N L^?1. Whereas, nitrate addition (5–15 mg ¹⁵NO₃^?-N L^?1) significantly inhibited anammox activities and the ratio of anammox to total N₂ production. Our results provide useful information on factors controlling anammox process and its contribution to N loss in the paddy soil.     

Microbial assimilation of atmospheric CO2 into soil organic matter revealed by the incubation of paddy soils under 14C-CO2 atmosphere

Similar to higher plants, microbial autotrophs possess photosynthetic systems that enable them to fix CO₂. To measure the activity of microbial autotrophs in assimilating atmospheric CO₂, five paddy soils were incubated with ¹⁴C-labeled CO₂ for 45 days to determine the amount of ¹⁴C-labeled organic C being synthesized. The results showed that a significant amount of ¹⁴C-labeled CO₂ incorporated into microbial biomass was soil specific, accounting for 0.37%–1.18% of soil organic carbon (¹⁴C-labeled organic C range: 81.6–156.9 mg C kg^?1 of the soil after 45 days). Consequently, high amounts of C-labeled organic C were synthesized (the synthesis rates ranged from 86 to 166 mg C m^?2 d^?1). The amount of atmospheric ¹⁴CO₂ incorporated into microbial biomass (¹⁴C-labeled microbial biomass) was significantly correlated with organic C components (¹⁴C-labeled organic C) in the soil (r = 0.80, p < 0.0001). Our results indicate that the microbial assimilation of atmospheric CO₂ is an important process for the sequestration and cycling of terrestrial C. Our results showed that microbial assimilation of atmospheric CO₂ has been underestimated by researchers globally, and that it should be accounted for in global terrestrial carbon cycle models.     

Nitrification Inhibition in Iowa Soils Treated with Stay‐N 2000 as Affected by Temperature and Matric Potential

The effects of temperature and water potential on nitrification were investigated in two Iowa soils treated with Stay‐N 2000. The soils were incubated at 10, 20, and 30 °C after soil water potentials of ?1, ?10, or ?60 kPa were applied to each soil. A first‐order equation was used to calculate the maximum nitrification rate (K _max), duration of lag period (t′), period of maximum nitrification (Δt), and termination period of nitrification (t _s). The highest K _max were 18 and 24 mg kg^?1 d^?1 nitrate (NO₃ ^?)–nitrogen (N), respectively, at 30 °C and ?10 kPa in both the Nicollet (fine‐loamy, mixed, superactive, mesic Aquic Hapludoll) and Canisteo (fine‐loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) soils and reduced to 4 and 16 mg kg^?1 d^?1 NO₃ ^?‐N when Stay‐N 2000 was added. The extension of t′ due to the addition of Stay‐N 2000 was as high as 7 d in the Nicollet soil at 10 °C and ?1 kPa and as little as 2 d in the Canisteo soil at 20 °C and ?10 kPa.     

Effects of temperature,glucose and inorganic nitrogen inputs on carbon mineralization in a Tibetan alpine meadow soil

High levels of available nitrogen (N) and carbon (C) have the potential to increase soil N and C mineralization. We hypothesized that with an external labile C or N supply alpine meadow soil will have a significantly higher C mineralization potential, and that temperature sensitivity of C mineralization will increase. To test the hypotheses an incubation experiment was conducted with two doses of N or C supply at temperature of 5, 15 and 25 °C. Results showed external N supply had no significant effect on CO₂ emission. However, external C supply increased CO₂ emission. Temperature coefficient (Q₁₀) ranged from 1.13 to 1.29. Significantly higher values were measured with C than with N addition and control treatment. Temperature dependence of C mineralization was well-represented by exponential functions. Under the control, CO₂ efflux rate was 425 g CO₂–C m^?2 year^?1, comparable to the in situ measurement of 422 g CO₂–C m^?2 year^?1. We demonstrated if N is disregarded, microbial decomposition is primarily limited by lack of labile C. It is predicted that labile C supply would further increase CO₂ efflux from the alpine meadow soil.     

Relevance of soil physical properties for the microbial oxidation of methane in landfill covers

The microbial oxidation of methane in landfill cover soils offers great potential to reduce methane emissions from landfills. High methane degradation rates can only be accomplished if the supply of atmospheric oxygen to the methanotrophic community is adequate. Thus, if environmental variables such as pH or nutrient status are not limiting, system performance is suggested to be governed by the share of pores available for gas transport. Diffusion tests as well as column studies were conducted to investigate the effect of air-filled porosity and degree of compaction on diffusivity and methane oxidation efficiency. Results show that the effective diffusion coefficient governing oxygen migration through soil is exponentially related to air-filled porosity space and can be significantly decreased by compaction. Discontinuity and tortuosity of the pore system strongly impeded diffusive migration at air-filled porosities below 10%. In the column study, soil gas composition and methane oxidation rates correlated with both the degree of compaction and the magnitude of advective bottom flux. Low aeration and hence low methane oxidation rates prevailed at high compaction rates and/or high bottom fluxes whereas high rates could be maintained at lower fluxes and/or low compaction rates. At a low degree of compaction (75% of the Proctor density), fluxes of 3.5 g CH₄ m⁻² h⁻¹ could be fully oxidized at all times by a sandy loam, the capacity limit of which was not reached during the experiment. Our studies suggest that soils intended for use as methane-oxidizing biocovers are to maintain an air-filled porosity of at least 14 vol.%. At low and medium degree of compaction, this is provided by sands, loamy sands, sandy loams and some of the coarsely textured loams.     

Changes in the soil C and N contents,C decomposition and N mineralization potentials in a rice paddy after long-term application of inorganic fertilizers and organic matter

A long-term experiment on combined inorganic fertilizers and organic matter in paddy rice (Oryza sativa L.) cultivation began in May 1982 in Yamagata, northeastern Japan. In 2012, after the 31^st harvest, soil samples were collected from five fertilizer treatments [(1) PK, (2) NPK, (3) NPK + 6 Mg ha^?1 rice straw (RS), (4) NPK + 10 Mg ha^?1 rice straw compost (CM1), and (5) NPK + 30 Mg ha^?1 rice straw compost (CM3)], at five soil depths (0–5, 5–10, 10–15, 15–20 and 20–25 cm), to assess the changes in soil organic carbon (SOC) content and carbon (C) decomposition potential, total nitrogen (TN) content and nitrogen (N) mineralization potential resulting from long-term organic matter addition. The C decomposition potential was assessed based on the methane (CH₄) and carbon dioxide (CO₂) produced, while the N mineralization potential was determined from the potassium chloride (KCl)-extractable ammonium-nitrogen (NH₄⁺-N), after 2, 4, 6 and 8 weeks of anaerobic incubation at 30°C in the laboratory. Compared to NPK treatment, SOC in the total 0–25 cm layer increased by 67.3, 21.0 and10.8%, and TN increased by 64.2, 19.7 and 10.6%, in CM3, RS and CM1, respectively, and SOC and TN showed a slight reduction in the PK treatment by 5.2 and 5.7%, respectively. Applying rice straw compost (10 Mg ha^?1) instead of rice straw (6 Mg ha^?1) to rice paddies reduced methane production by about 19% after the soils were measured under 8 weeks of anaerobic incubation at 30°C. Soil carbon decomposition potential (Co) and nitrogen mineralization potential (No) were highly correlated with the SOC and TN contents. The mean ratio of Co/No was 4.49, lower than the mean ratio of SOC/TN (13.49) for all treatments, which indicated that the easily decomposed organic matter was from soil microbial biomass and soil proteins.     

Atmung eines Bodens im Gemüsebau zu Beginn der Vegetationsperiode

Respiration of a soil used for vegetable crops at the beginning of the vegetation period Soil respiration was measured with a new portable soil respiration system (PP Systems, Hitchin, England) in vegetable plots in the greenhouse and field near Bonn from January to May 1996 with the following results:

• 1 The equipment proved suitable for the purpose over a wide range of temperatures.
• 2 Soil respiration ranged from less than 26 mg CO₂ in winter, 30–180 mg CO₂ in spring to 700 mg CO₂ m^?2 h^?1 in summer with large variations.
• 3 The largest soil respiration was recorded from peat-based commercial potting compost with small variations between measurements.
• 4 The Q₁₀ was 2,5 (±0,6) in the field for temperatures between 5–25°C.
• 5 The rate of soil respiration was affected by soil cultivation with the effect declining with temperature: Ploughing, which unveiled cold and produced a coarse soil surface, reduced soil respiration, whereas soil respiration was increased by fine soil cultivation.
• 6 In vegetable plots, soil respired 6–12 kg in cold (4°C), 40–50 kg CO₂ in cool (14°C) conditions in April and 170–210 kg CO₂/ha and 24 hours in warm (27°C) weather.

     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.     

Microbiological transformation of carbon and nitrogen compounds in forest soils of Central Evenkia

It has been found that the total productivity of bacteria and micromycetes in the 0- to 50-cm layer of homogeneous cryozems (Cryosols) on slopes of northern and southern exposures varies from 1.2 to 1.4 t/ha, respectively, and the calculated content of microbial carbon varies in the range 0.7–0.9 t/ha. The respiratory activity of the upper soil layer is 2.5–2.6 μg C–CO₂/(g h); the potential methane formation capacity reaches 0.13 nmol CH₄/(m² day) for soils on slopes of northern exposure and 0.16 nmol CH₄/(m² day) for slopes of southern exposure. Accumulation of sorbed ammonium is recorded in the range 15–17 mg NH₄/100 g soil in summer. The increase of temperature in the upper horizons of soils on slopes of southern exposure by 5°C compared to the northern slopes results in only an insignificant increase in the emission of CO₂ and CH₄. The accumulation of sorbed ammonium and nitrate nitrogen in homogeneous cryozems during the vegetation period is comparable to that in gray forest soils of the southern taiga subzone of the Middle Siberia.     

Methane dynamics of landfill cover soils and aspects of their classification

The methane dynamics of soils covering a landfill in Oldenburg, Lower Saxony, was investigated in 1996. The methane concentration was often < 20 nmol (dry g)^?1 within the cover layer and up to 9950 nmol (dry g)^?1 within the refuse body. The methane production rates correlated positively with the methane concentrations and were mostly < 10 nmol (dry g)^?1 d^?1 within the cover layer and up to 1090 nmol (dry g)^_1 d^_1 within the refuse body. The methane oxidation rates varied between 38.0–2310 nmol (dry g)^?1 d^?1. The methane emission rates showed values of up to 574 mol m^?2 h^?1, but in two cases no emission of methane was found. The data indicate that the methano-genesis of the deep refuse layers did not substantially affect the methane behaviour of the upper soil sections. It is likely that the emission of methane from landfills can be reduced by thick well aerated cover layers. The term “Reduktosol” for landfill soils is critically discussed.     

Impact of organic inputs on wettability characteristics and structural stability in silty vineyard topsoil

Organic inputs were used for 10 years on a French vineyard topsoil to improve structural stability and thus to protect against erosion. The three types of organic inputs (mulches) included: conifer compost, CC (100 m³ ha^?1 every 3 years); conifer bark, CB (300 m³ ha^?1 every 5 years); and cereal straw, S (10 t ha^?1 every 2 years). The other two types of organic inputs were cover crops of clover (C) and fescue (F). The impacts of these organic inputs on soil organic carbon (SOC) content, wettability (capillary rise and X‐ray photoelectron spectroscopy (XPS)) and structural stability were studied. The SOC content was twice as large in the CC, C and F topsoils (SOC content of 2.56–3.24%) as in the reference (R) topsoil (SOC content of 1.39%). Both apparent contact angle (θ) and surface OH:C mass ratio indicated that the R and S topsoils were hydrophilic (θ of 27.4–33.4°, surface OH:C ratio of 3.20–4.41), whereas the CB, C and F topsoils were partially hydrophobic (θ of 69.1–79.8°, surface OH:C ratio of 1.36–2.86), and the CC topsoil had intermediate values (θ of 46.9°, surface OH:C ratio of 2.43–2.81). Moreover, the greater the θ value, the smaller the water sorptivity value and the greater the proportion of water‐stable aggregates, Ag_w. The increase in SOC content had beneficial effects on Ag_w, particularly for the partially hydrophobic C and F topsoils (Ag_w of 22.3–44.5%) against the hydrophilic R and S topsoils (Ag_w of 8.2–12.7%). Development of hydrophobicity, correlated with the decrease in the surface OH:C ratio and the increase in the C–O, C–N proportion on surface C, should be attributed to humified organic matter or/and to plant and microbial polysaccharides. As the XPS and aggregate stability data describe soil physical processes at small scales (nm to mm), we suggest an experimental and modelling framework for upscaling these results for practical improvement and management of vineyard soils.     

Driving factors of temporal variation in agricultural soil respiration

Investigations of diurnal and seasonal variations in soil respiration support modeling of regional CO₂ budgets and therefore in estimating their potential contribution to greenhouse gases. This study quantifies temporal changes in soil respiration and their driving factors in grassland and arable soils located in Northern Germany. Field measurements at an arable site showed diurnal mean soil respiration rates between 67 and 99 mg CO₂ m^–2 h^–1 with a hysteresis effect following changes in mean soil temperatures. Field soil respiration peaked in April at 5767 mg CO₂ m^–2 day^–1, while values below 300 mg CO₂ m^–2 day^–1 were measured in wintertime. Laboratory incubations were carried out in dark open flow chambers at temperatures from 5°C to 40°C, with 5°C intervals, and soil moisture was controlled at 30%, 50%, and 70% of full water holding capacity. Respiration rates were higher in grassland soils than in arable soils when the incubating temperature exceeded 15°C. The respiration rate difference between them rose with increasing temperature. Monthly median values of incubated soil respiration rates ranged from 0 to 26.12 and 0 to 7.84 µg CO₂ g^–1 dry weight h^–1, respectively, in grassland and arable land. A shortage of available substrate leads to a temporal decline in soil respiration rates, as indicated by a decrease in dissolved organic carbon. Temporal Q₁₀ values decreased from about 4.0 to below 1.5 as temperatures increased in the field. Moreover, the results of our laboratory experiments confirmed that soil temperature is the main controlling factor for the Q₁₀ values. Within the temperature interval between 20°C and 30°C, Q₁₀ values were around 2 while the Q₁₀ values of arable soils were slightly lower compared to that of grassland soils. Thus, laboratory studies may underestimate temperature sensitivity of soil respiration, awareness for transforming laboratory data to field conditions must therefore be taken into account.     

Effect of nitrogen fertilization on methane and carbon dioxide production potential in relation to labile carbon pools in tropical flooded rice soils in eastern India

In an incubation experiment with flooded rice soil fertilized with different N amounts and sampled at different rice stages, the methane (CH₄) and carbon dioxide (CO₂) production in relation to soil labile carbon (C) pools under two temperature (35°C and 45°C) and moisture (aerobic and submerged) regimes were investigated. The field treatments imposed in the wet season included unfertilized control and 40, 80 and 120 kg ha^?1 N fertilization. The production of CH₄ was significantly higher (27%) under submerged compared to aerobic conditions, whereas CO₂ production was significantly increased under aerobic by 21% compared to submerged conditions. The average labile C pools were significantly increased by 21% at the highest dose of N (120 kg ha^?1) compared to control and was found highest at rice panicle initiation stage. But the grain yield had significantly responded only up to 80 kg ha^?1 N, although soil labile C as well as gaseous C emission was noticed to be highest at 120 kg ha^?1 N. Hence, 80 kg N ha^?1 is a better option in the wet season at low land tropical flooded rice in eastern India for sustaining grain yield and minimizing potential emission of CO₂ and CH₄.     

Experimental drought alters rates of soil respiration and methanogenesis but not carbon exchange in soil of a temperate fen

The impact of intensified drought and rewetting on C cycling in peatlands is debated. We conducted drying/rewetting (DW) experiments with intact monoliths of a temperate fen over a period of 10 months. One treatment with original vegetation (DW-V) and one defoliated treatment (DW-D) were rewetted after an experimental drought of 50 days; another treatment was kept permanently wet (W-V). Soil water content was determined by the TDR technique, C fluxes from chamber measurements and gas profiles in the soils, and respiration from mass balancing CO₂ and CH₄ fluxes in the peat using hourly to weekly data. Zones of high root associated respiration were determined from a ¹³C labeling experiment. Autotrophic respiration contributed from 55 to 65% to an average ecosystem respiration (ER) of 92 (DW-D), 211 (DW-V), and 267 mmol m^?2 d^?1 (W-V). Photosynthesis ranged from 0 (DW-D) to 450 mmol m^?2 d^?1 (W-V), and strongly declined for about 30 days after rewetting (DW-V), while ER remained constant during the drying and rewetting event. Drying raised air-filled porosity in the soil to 2–13%, temporarily increased respiration to estimated anaerobic and aerobic rates of up to 550 and 1000 nmol cm^?3 d^?1, and delayed methane production and emission by weeks to months. Root associated respiration was concentrated in the uppermost peat layer. In spite of clear relative changes in respiration during and after drought, the impact on carbon exchange with the atmosphere was small. We attribute this finding to the importance of respiration in the uppermost and soil layer, which remained moist and aerated, and the insensitivity of autotrophic respiration to drought. We expect a similar dynamics to occur in other temperate wetland soils in which soil respiration is concentrated near the peatland surface, such as rich minerotrophic fens.     

Einfluß von Bodeneigenschaften,Bodennutzung und Bodentemperatur auf die N-Mobilisierung von Kulturböden

Influence of soil characteristics, agricultural use and soil temperature on the N-mobilization of cultivated soils A new N-mobilization model, which considers also the short term and seasonal N-supplying capacity of soil is presented. At a fixed time the potential mobilizable N (N-MOB) is a sum of difficultly mobilizable N (N-MOB_s) originating from the pool of difficultly mobilizable N (N_s) and the easily mobilizable N (N-MOB₁) originating from the pool of easily mobilizable N (N₁). It is possible to characterize soil according to their M₁, N-MOB_s and v (N-MOB_s per day) values. Usefulness of these parameters in N-nutrition and ground water burden from N has been discussed. Basic parameters of this model have been experimentally determined independently with the help of two different experiments i. e. laboratory incubation and column lysimeter using surface soil samples. The easily mobilizable N pool (N₁) values were found in the range of 142 to 814 kg N ha^?1 which corresponded to 1.2 to 7.4 % of organic N content of these soils. The difficultly mobilizable N per day (i. e. v = N-MOB_s per day) in an incubation experiment (35°C) were found in the range of 1.5 to 24kg N ha^?1. However, in the column lysimeter experiment, in contrast, these values at 10°C ranged between 0.05 to 0.9 kg N ha^?1. These values correspond to N-MOB_s values in the range of 11–182 kg N·ha^?1 for a period of 200 days which approximate to a vegetation period. For practical purposes, the N₁ and v values could be calculated by just measuring 3–4 points after 14 days of incubation at 35°C. The results show that N-MOB_s values strongly correlated compared to N₁ values to total N, organic carbon and clay content and non significantly to pH and silt content. The results of an laboratory incubation experiment carried out to assess the effect of temperature on N-mobilization show that even at 0°C there was N-mobilization. The results revealed that in the temperature range of 0–8°C (a range of soil temp. usually observed in winter months) and in the range of 25–40°C (range of summer months temp. for surface arable soil), a small change in the soil temperature would result in enormous increase in the quantity of mobilized N. The highest mobilized N quantity was found above 60°C.     

Mulching Affects Soil Properties and Greenhouse Gas Emissions Under Long‐Term No‐Till and Plough‐Till Systems in Alfisol of Central Ohio

Agricultural activities emit greenhouse gases (GHGs) and contribute to global warming. Intensive plough tillage (PT), use of agricultural chemicals and the burning of crop residues are major farm activities emitting GHGs. Intensive PT also degrades soil properties by reducing soil organic carbon (SOC) pool. In this scenario, adoption of no‐till (NT) systems offers a pragmatic option to improve soil properties and reduce GHG emission. We evaluated the impacts of tillage systems (NT and PT) and wheat residue mulch on soil properties and GHG emission. This experiment was started in 1989 on a Crosby silt loam soil at Waterman Farm, The Ohio State University, Columbus, Ohio, USA. Mulching reduced soil bulk density and improved total soil porosity. More total carbon (16.16 g kg⁻¹), SOC (8.36 mg L⁻¹) and soil microbial biomass carbon (152 µg g⁻¹) were recorded in soil under NT than PT. Mulch application also decreased soil temperature (0–5 cm) and penetration resistance (0–60 cm). Adoption of long‐term NT reduced the GHG emission. Average fluxes of GHGs under NT were 1.84 g CO₂‐C m⁻² day⁻¹ for carbon dioxide, 0.07 mg CH₄‐C m⁻² day⁻¹ for methane and 0.73 mg N₂O‐N m⁻² day⁻¹ for nitrous oxide compared with 2.05 g CO₂‐C m⁻² day⁻¹, 0.74 mg CH₄‐C m⁻² day⁻¹ and 1.41 mg N₂O‐N m⁻² day⁻¹, respectively, for PT. Emission of nitrous oxide was substantially increased by mulch application. In conclusion, long‐term NT reduced the GHG emission by improving the soil properties. Copyright © 2016 John Wiley & Sons, Ltd.     

中国亚热带中部三峡库区不同土地利用方式下甲烷氧化潜力研究

To compare the CH4 oxidation potential among diferent land uses and seasons,and to observe its response to monsoon precipitation pattern and carbon and nitrogen parameters,a one-year study was conducted for diferent land uses (vegetable field,tilled and non-tilled orchard,upland crops and pine forest) in central subtropical China.Results showed significant diferences in CH4 oxidation potential among diferent land uses(ranging from 3.08 to 0.36 kg CH4 ha-1 year-1).Upland with corn-peanut-sweet potato rotation showed the highest CH4 emission,while pine forest showed the highest CH4 oxidation potential among all land uses.Non-tilled citrus orchard (0.72±0.08 kg CH4 ha-1 year-1)absorbed two times more CH4 than tilled citrus orchard(0.38±0.06kg CH4 ha-1 year-1).Irrespective of diferent vegetation,inorganic N fertilizer application significantly influenced CH4 fluxes across the sites (R2=0.86,P=0.002).Water-filled pore space,soil microbial biomass carbon,and dissolved nitrogen showed significant efects across diferent land uses (31% to 38% of variability)in one linear regression model.However,their cumulative interaction was significant for pine forest only,which might be attributed to undisturbed microbial communities legitimately responding to other variables,leading to net CH4 oxidation in the soil.These results suggested that i)natural soil condition tended to create win-win situation for CH4 oxidation,and agricultural activities could disrupt the oxidation potentials of the soils;and ii)specific management practices including but not limiting to efficient fertilizer application and utilization,water use efciency,and less soil disruption might be required to increase the CH4 uptake from the soil.