Mineralization of Nitrogen in Soils Amended with Dairy Manure as Affected by Wetting/Drying Cycles

Abstract

Interest in manure management and its effects on nitrogen (N) mineralization has increased in recent years. The focus of this research was to investigate the N‐mineralization rates of different soil types in Coastal Plain soils and compare them to a soil from Illinois. Soils with and without dairy composted manure addition were subjected to different wetting/drying cycles [constant moisture at 60% water‐filled pore space (WFPS) and cycling moisture from 60 to 30% WFPS] under laboratory conditions at three different temperatures (11°C, 18°C, and 25°C). Samples were collected from three different soil types: Catlin (Mollisols), Bama (Ultisols), and Goldsboro (Utilsols). Soil chemical and physical properties were determined to help assess variations in N-mineralization rates. Addition of composted manure greatly impacted the amount of N mineralized. The amount of manure‐derived organic N mineralized to inorganic forms was mainly attributed to the soil series, with the Catlin (silt loam) producing the most inorganic N followed by the Goldsboro (loam) and then Bama (sandy loam). This was probably due to soil texture and the native climatic conditions of the soil. No significant differences were observed between the constant and cycling moisture regimens, suggesting that the imposed drying cycle may not have been sufficient to desiccate microbial cells and cause a flush in N mineralization upon rewetting. Nitrogen mineralization responded greatly to the influence of temperature, with the greatest N mineralization occurring at 25°C. The information acquired from this study may aid in predicting the impact of manure application to help increase N‐use efficiency when applied under different conditions (e.g., climate season) and soil types.     

Microbial response of an acid forest soil to experimental soil warming

 Effects of increased soil temperature on soil microbial biomass and dehydrogenase activity were examined on organic (O) horizon material in a low-elevation spruce-fir ecosystem. Soil temperature was maintained at 5  °C above ambient during the growing season in the experimental plots, and soil temperature, moisture, microbial biomass, and dehydrogenase activity were measured during the experiment. An incubation study was also conducted under three temperature regimes, 5, 15, and 25  °C, and under four moisture regimes of 20, 120, 220, and 320% to further evaluate these environmental factors on dehydrogenase activity and microbial biomass. Soil moisture content and microbial biomass controls were significantly lower (30% and 2 μg g^–1 soil, respectively) in the heated plots during the treatment period, suggesting that moisture content was important in controlling microbial biomass. In the incubation study, temperature appeared more important than moisture in controlling microbial biomass and dehydrogenase activity. Increasing temperature between 5  °C and 25  °C resulted in significant decreases in microbial biomass and dehydrogenase activity. Received: 7 August 1998     

Isoproturon mineralization in an agricultural soil

The impact of soil moisture content and temperature on isoproturon (3-(4-isopropylphenyl)-1,1-dimethyl-urea [IPU]) mineralization activity was assessed on an agricultural soil regularly exposed to this herbicide. Mineralization of ¹⁴C-IPU was monitored on soil microcosms incubated at different temperatures (10°C, 20°C, 28°C) and soil moisture contents (9%, 12%, 15, 18%, 21%, 24%). An increase in temperature and/or soil moisture significantly enhanced the maximum rate and percentage of IPU mineralization while it decreased the lag time before mineralization. The maximum rate and percentage of IPU mineralization respectively ranged from 0.18% day⁻¹ and 9% for the lowest temperature and soil moisture content pair (10°C–9%) to 1.51% day⁻¹ and 27.1% for the highest pair (28°C–24%). Statistics revealed a cross interaction of temperature and soil moisture content on the maximum rate of IPU mineralization. The optimum conditions for IPU mineralization, estimated from the double Gaussian model, were 25.8°C and 24% soil moisture content. The influence of fluctuations in soil moisture content on IPU-mineralization was investigated by subjecting the soil microcosms to drought stress. When IPU was added at the end of the drought stress, it had no statistical effect on IPU mineralization. However, when it was added before the drought stress, two mineralization phases were observed: (1) one corresponding to the drought stress for which mineralization was low and (2) another one observed after restoration of soil moisture content characterized by higher mineralization rate. It can be concluded that climatic fluctuations affect the activity of IPU mineralizing microbial community, and may lead to an increase in IPU persistence.     

Die N-Mineralisierung von Böden im Laborbrutversuch

N mineralization in soils under laboratory incubation conditions The potential rate of release of nitrogen by the organic matter in agriculturally used soils was determined under laboratory conditions by means of incubation. Mineralization of the more resistant soil organic matter proceeded linearly with time during an incubation period of 2–3 weeks, when field-moist and air-dried samples were used and at the beginning of the incubation experiment sufficient water was added to bring them to saturation. Mineralization was taking an exponential course in soils with additions of easily decomposable organic matter or in soils with a higher proportion of organic residues from crops. For the 14 investigated arable and grassland soils great variations in the average daily rate of mineralization were found ranging from 5–60 μg N_min/10 g DM. The data correlated very well with the biomass (r = 0.96) and the cell-free protease activity (r = 0.98) of the soils. Different measures of soil management (preceding crops, application of sewage sludge, addition of heavy metals) had a more or less pronounced influence on the rate of mineralization. The optimum temperature was 50°C for N mineralization and 26°C for nitrification. Contrary to nitrification, the soil reaction had only little influence on mineralization and proved also independent of the N_min content of soils. The results indicate that ammonification of organic N compounds may largely proceed via the microbial biomass.     

Some factors affecting survival of sclerotia of Macrophomina phaseolina in soil

At least 75% of the sclerotia of Macrophomina phaseolina survived for 1 yr in most natural soils kept at 26°C and at 50–55% of the soil moisture holding capacity (m.h.c.). Although survivability was reduced in a very acid soil (pH 4.5) collected under a pine stand, 33% of the sclerotia survived for 1 yr. Soil pH had very little or no effect on sclerotial survivability. Of three organic amendments tested (alfalfa hay, chitin, pine needles) only ground alfalfa hay at 0.8% (w/w) reduced survivability of sclerotia in soil by about 75% in a year. Alfalfa hay at 0.4% reduced survivability by 36%. Various N sources added at 200 μg Ng^?1 soil had no effect on survival. Of 13 fungicides tested, only benomyl and captan at 20 μg a.i. g^?1 soil appreciably reduced populations of sclerotia in soil.Soil temperature and moisture content were the two most important factors affecting survivability of sclerotia. At ?5 or 5°C the biggest drop in sclerotial survivability occurred when the soil was incubated moist (at 50% m.h.c. or more). At 26°C the biggest drop occurred in air-dried soil (2–3% m.h.c.) and survivability was decreased to some extent at 15 and 30% m.h.c. Survivability also dropped rapidly in moist soil (50–55% m.h.c.) exposed to four cycles each having 3-week freezing (?5°C) and 1 week thawing (26°C). Sclerotia in air-dried soil (2–3% m.h.c.) continuously kept at ?5°C maintained nearly complete survivability after 16 weeks. Sclerotia survived almost 80–90% in moist soil (50–55% m.h.c.) kept for 16 weeks at 26°C or in moist soil exposed to four cycles each having 3-week thawing (26°C) and 1-week freezing (?5°C).     

Climatic conditions and crop‐residue quality differentially affect N,P, and S mineralization in soils with contrasting P status

The substitution of the widely practiced crop‐residue burning by residue incorporation in the subtropical zone requires a better understanding of factors determining nutrient mineralization. We examined the effect of three temperature (15°C, 30°C, and 45°C) and two moisture regimes (60% and 90% water‐filled pore space (WFPS)) on the mineralization‐immobilization of N, P, and S from groundnut (Arachis hypogae) and rapeseed (Brassica napus) residues (4 t ha^–1) in two soils with contrasting P fertility. Crop‐residue mineralization was differentially affected by incubation temperature, soil aeration status, and residue quality. Only the application of groundnut residues (low C : nutrient ratios) resulted in a positive net N and P mineralization within 30 days of incubation, while net N and P immobilization was observed with rapeseed residues. Highest N and P mineralization and lowest N and P immobilization occurred at 45°C under nearly saturated soil conditions. Especially net P mineralization was significantly higher in nearly saturated than in aerobic soils. In contrast, S mineralization was more from rapeseed than from groundnut residues and higher in aerobic than in nearly saturated soil. The initial soil P content influenced the mineralization of N and P, which was significantly higher in the soil with a high initial P fertility (18 mg P (kg soil)^–1) than in the soil with low P status (8 mg P (kg soil)^–1). Residue‐S mineralization was not affected by soil P fertility. The findings suggest that climatic conditions (temperature and rainfall‐induced changes in soil aeration status) and residue quality determine N‐ and S‐mineralization rates, while the initial soil P content affects the mineralization of added residue N and P. While the application of high‐quality groundnut residues is likely to improve the N supply to a subsequent summer crop (high temperature) under aerobic and the P supply under anaerobic soil condition, low‐quality residues (rapeseed) may show short‐term benefits only for the S nutrition of a following crop grown in aerobic soil.     

Effects of Temperature,Moisture, and Chemical Composition of Organic Substrates on C Mineralization in Soils

Laboratory experiments were conducted to (i) study the influence of chemical composition of organic substrates (green manure, rice straw, wheat straw, and farmyard manure) and temperature on carbon (C) mineralization under flooded and nonflooded moisture conditions, (ii) study the relationship between C mineralization and chemical composition of organic materials, and (iii) model C mineralization kinetics under different temperature and moisture conditions. The proportion of added C mineralized under nonflooded conditions ranged between 45 and 66% at 35 °C compared to 18 to 42% at 15 °C. Flooding the soil reduced the proportion of added C mineralized, which ranged between 25 to 47% at 35 °C and 6 to 20% at 15 °C. Water-soluble components, cellulose, lignin, and nitrogen content of the organic source significantly influenced C mineralization. Temperature sensitivity of decomposition depended on the quality of the organic substrate with relatively less decomposable farmyard manure (FYM) being more sensitive (Q₁₀ ?3.0) than the easily decomposable green manure (Q₁₀ ?2.5). A first-order monocomponent model that is based on relative rate of mineralization and includes a parameter for speed of aging best described C mineralization under both the temperature and moisture conditions. It was concluded that FYM with preponderance of recalcitrant components and low decomposability provides greater C sequestration potential than green manure and crop residues.     

Ethion degradation and its correlation with microbial and biochemical parameters of tea soils

Ethion, a highly persistent insecticide in soil, is extensively used in tea cultivation in the tropics. The studies on the environmental impact of ethion in tea soil ecosystems are scanty. Silty loam and sandy loam soils from tea fields of Dooars (Typic Uderthents) and Hill (Typic Dystrudepts), respectively, were investigated for the degradation and effect of ethion application on soil microbial and biochemical variables under controlled laboratory conditions. Ethion degraded faster in the Hill soil than in the Dooars soil. Higher temperature (30°C) aided in faster degradation due to the increased microbial activity in the soils. Ethion application at field rate (FR) had lower half-lives (70 days at 20°C and 42.3 days at 30°C for Dooars soil; 65.4 days at 20°C and 39 days at 30°C for Hill soil) than at ten times FR (10FR; 75.2 days at 20°C and 44.2 days at 30°C for Dooars soil; 70 days at 20°C and 41.8 days at 30°C for Hill soil). Soil microbial biomass carbon, ergosterol content, fluorescein diacetate hydrolyzing and β-glucosidase activities declined in all the treatment combinations up to day 60 for both FR and 10FR doses at 20°C, irrespective of the soil types. At 30°C, the decreasing trend was observed up to day 30 for both the soils. The toxicological effect of ethion on microbiological and biochemical parameters persisted till their corresponding half-lives. The microbial metabolic quotient and microbial respiration quotient were altered, but was short-lived, indicating ethion induced disturbances. The recovery of the depressive action at 10FR ethion spiking on the studied variables was of slightly longer duration than noticed at FR application, although the depressive effect was overcoming after the respective half-lives of ethion. The microbial and biochemical soil parameters were negatively correlated with application of ethion up to day 60 of incubation.     

Temperature responses of nitrogen processes cannot be inferred from carbon turnover in a boreal Norway spruce forest

Cold season processes contribute substantially to annual carbon (C) and nitrogen (N) budgets in boreal forest ecosystems, but little is known about how decomposition processes are affected at temperatures prevalent during wintertime. The aim of this study was to evaluate temperature responses of soil C and N processes and to test the hypothesis that there is a switch towards decomposing N‐rich material when soil temperatures drop to near 0°C. In the laboratory, soils from a boreal forest long‐term nutrient fertilization experiment were exposed to different temperatures varying from +2 to +15°C, and C mineralization, gross as well as net N mineralization/immobilization were estimated. Carbon mineralization declined exponentially as temperature decreased, whereas the response of N processes to temperature varied, with some indication that soil C and N processes are decoupled at low temperatures. We could only partially confirm that the decoupling between C and N processes at low temperature was due to a switch to N‐rich material, i.e., a change in the material undergoing decomposition. Overall, our results clearly showed that temperature responses of N processes cannot be inferred from C processes in boreal forest ecosystems, and that there is a need to improve our understanding of the relationship between the two across the range of temperatures experienced throughout the year. In particular, further research is required to establish and evaluate appropriate proxies for modelling the relationship of C and N processes at temperatures close to the freezing point.     

Regulation of microbial carbon,nitrogen, and phosphorus transformations by temperature and moisture during decomposition of <Emphasis Type="Italic">Calluna vulgaris</Emphasis> litter

To evaluate the effect of climate change on ecosystem functioning, the temperature and moisture response of microbial C, N, and P transformations during decomposition of Calluna vulgaris (L.) Hull. litter was studied in a laboratory incubation experiment. The litter originated from a dry heathland in the Netherlands where P limited vegetation growth. Fresh litter was incubated at 5, 10, 15, or 20°C and at a moisture content of 50, 100, or 200% in a full factorial design. Microbial nutrient transformations and activity were evaluated during two successive periods: an initial period of 48 days characterized by microbial growth and a second period from 48 to 206 days in which microbial growth declined significantly. Temperature and moisture response of respiration rate, the metabolic quotient (qCO₂), C, N, and P immobilization, net N and P mineralization and nitrification rates were evaluated by performing linear regressions. Microbial nutrient transformations and microbial activity depended both on temperature and moisture. In the first period, the respiration rate, qCO₂, microbial C and N immobilization, net P mineralization, net N mineralization and net nitrification rates were more strongly affected by temperature, while the microbial P immobilization rate was more strongly affected by moisture. The respiration rate, qCO₂, P immobilization rate, net P and N mineralization rate, and nitrification rate increased with temperature and moisture, while the C and N immobilization rate decreased with increasing temperature and increased with moisture. In the second period, C, N, and P immobilization and net N and P mineralization rates were significantly lower. The respiration rate and qCO₂ continued to increase with temperature and moisture, but C and N immobilization rates increased with temperature and declined with increasing moisture. Net P mineralization rate decreased at higher temperature and moisture, and nitrification rate declined with increasing temperature and increased with moisture. It was concluded that plant growth in these P-limited systems is very sensitive to climate change as it strongly relies on the competition for P with microbes, and temperature and moisture have a large effect on the immobilization rate of available P.     

Dissolved organic matter and inorganic N jointly regulate greenhouse gases fluxes from forest soils with different moistures during a freeze-thaw period

ABSTRACT

Antecedent soil moisture before freezing can affect greenhouse gases (GHG) fluxes from soils during thaw, but their critical threshold values for GHG fluxes and the underlying mechanisms are still not clear. By using packed soil-core incubation experiments, we have studied nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) fluxes from a mature broadleaf and Korean pine-mixed forest soil and an adjacent white birch forest soil with nine levels of soil moisture ranging from 10 to 90% water-filled pore space (WFPS) during a 2-month freezing at ?8°C and the following 10-day thaw at 10°C. The threshold values of soil moisture ranged from 50 to 70% WFPS for CH₄ uptake and from 70 to 90% WFPS for N₂O and CO₂ emissions from the two soils during the freeze-thaw period. Under the optimum soil moisture condition, fulvic-like compounds with high bioavailability contributed more than 60% of dissolved organic matter (DOM) in the soil. Cumulative N₂O emissions from forest soils during the freeze-thaw period were greatest when the concentration ratio of nitrate-N to dissolved organic carbon (DOC) was 0.04 g N g^?1 C. Cumulative soil CO₂ emissions and CH₄ uptake during the freeze-thaw period were both regulated by the interaction between soil DOC and net N mineralization. The activities of β-1,4-glucosidase and β-1,4-N-acetyl-glucosaminidase, microbial biomass C and N, and the microbial biomass C-to-N ratios, were all significantly correlated to the soil N₂O, CO₂, and CH₄ fluxes. Overall, upon a freeze-thaw period with different soil moistures, GHG fluxes from forest soils were jointly regulated by inorganic N and DOC concentrations, and related to the labile components of DOM released into the soil, which could be strictly controlled by the related microbial properties.     

Repeated freeze–thaw cycles changed organic matter quality in a temperate forest soil

Under temperate climate, the frequency of extreme weather events such as intensive freezing or frequent thawing periods during winter might increase in the future. It was shown that frost and subsequent thawing may affect the fluxes of C and N in soils. In a laboratory study, we investigated the effect of frost intensity and repeated freeze–thaw cycles on the quality and quantity of soil organic matter (SOM) in a Haplic Podzol from a Norway spruce forest. Undisturbed soil columns comprising O layer and top mineral soil were treated as followed: control (+5°C), frost at –3°C, –8°C, and –13°C. After a 2‐week freezing period, frozen soils were thawed at +5°C and irrigated with 80 mm water at a rate of 4 mm d^–1. Lignin contents were not significantly affected by repeated freeze–thaw cycles. Phospholipid fatty acid (PLFA) contents decreased in the mineral soil, and PLFA patterns indicate that fungi are more susceptible to soil frost than bacteria. Amounts of both plant and microbial sugars generally decreased with increasing frost intensity. These changes cannot be explained by increased mineralization of sugars or by leaching with DOM nor by a decreased microbial activity and, thus, sugar production with increasing frost intensity. Also physical stabilization of sugars due to frost‐induced changes in soil structure can be ruled out as sugar extraction was carried out on ground bulk soil. Therefore, the only possible explanation for the disappearance of plant and microbial sugars upon soil freezing are chemical alterations of sugar molecules leading to SOM stabilization.     

Extrusion of Cross‐Linked Hydroxypropylated Corn Starches II. Morphological and Molecular Characterization

A series of cross‐linked hydroxypropylated corn starches were extruded with a Leistritz micro‐18 co‐rotating extruder. Extrusion process variables including moisture (30, 35, and 40%), barrel temperature (60, 80, and 100°C), and screw design (low, medium, and high shear) were investigated. Scanning electron microscopy (SEM) of extruded starches showed a gel phase with distorted granules and granule fragments after extrusion at 60°C. After extrusion at 100°C only a gel phase was observed with no granular structures remaining. High performance size exclusion chromatography (HPSEC) equipped with multiangle laser light‐scattering (MALLS) and refractive index (RI) detectors showed extruded starches degraded to different extents, depending on extrusion conditions. The average molecular weight of the amylopectin of unextruded native corn starch was 7.7 × 10⁸. Extrusion at 30% moisture, 100°C, and high shear reduced the molecular weight of amylopectin to 1.0 × 10⁸. Hydroxypropylated normal corn starch extruded at identical conditions showed greater decreases in amylopectin molecular weight. With the addition of cross‐linking, the amylopectin fractions of the extruded starches were less degraded than those of their native and hydroxypropylated corn starch counterparts. Similarly, increasing moisture content during extrusion lowered amylopectin degradation in the extruded starches. Increasing temperature during extrusion of cross‐linked hydroxypropylated starches at high moisture content (e.g., 40%) lowered amylopectin molecular weights of the extruded starches, whereas increasing extrusion temperature at low moisture content (30%) resulted in less degraded molecules. This difference was attributed to the higher glass transition temperatures of the cross‐linked starches.     

Soil Biology Changes as a Consequence of Organic Amendments Subjected to a Severe Drought

Effect of severe drought events in combination with organic amendments (municipal solid waste, MSW, sheep manure, SM, and cow manure, CM) on soil dehydrogenase, urease, β‐glucosidase and phosphatase activities and microbial community by analyzing phospholipid fatty acids was studied under controlled laboratory conditions for one year. Two levels of irrigation were used: (1) watered soils, where the soils were maintained at 60% of their water holding capacity through the experiment, and (2) non‐watered soils, without irrigation through the experiment. The severe drought conditions negatively affected the soil enzymatic activities and total bacterial and fungal PLFA concentrations. The application of organic amendments to the soil subjected to severe drought increased soil water retention and encouraged the growth and activity of soil microbial populations. However, the chemical composition of the organic matter applied to the soil also strongly influenced soil moisture. In non‐watered soils and compared with the unamended soil, the dehydrogenase activity was 71 · 3%, 60 · 9% and 38 · 6% higher in the soil with SM, CM and MSW, respectively. Urease activity was 60 · 6%, 51 · 5% and 37% higher in the soil with SM, CM and MSW, respectively. β‐glucosidase and phosphatase activities had a similar trend. Water retention was higher when the organic wastes applied to the soils had a higher content of humic acids than fulvic acid contents. Copyright © 2016 John Wiley & Sons, Ltd.     

Soil Enzyme Activities in Waste Biochar Amended Multi-Metal Contaminated Soil; Effect of Different Pyrolysis Temperatures and Application Rates

Woody biochars derived by pyrolyzing Gliricidia sepium at 300°C and 500°C and a waste byproduct of same biomass from a bioenergy industry (BC700) were tested for their effect on soil enzymes activities and available form of heavy metals in multi-metals contaminated soil. Pot experiments were conducted during 6 weeks with tomato (Lycopersicon esculentum L.) at biochar application rates, 1, 2.5, and 5% (w/w). A reduction in polyphenol oxidase with biochars produced at increasing pyrolysis temperature compared to the control whereas the maximum activity of dehydrogenase and catalase was observed in 1% BC500 and 2.5% BC300, respectively. Soil available form of Ni, Mn, and Cr were reduced by 55, 70% and 80% in 5% BC700 amended soil, respectively. The highest geometric mean of enzyme activities was observed in 2.5% BC300 treatment. Overall the application of high dosages of high temperature derived biochar masks/deteriorates soil enzyme activities but immobilizes bioavailable heavy metals and reduces toxicity.     

Modeling aerobic decomposition of rice straw during the off-rice season in an Andisol paddy soil in a cold temperate region of Japan: Effects of soil temperature and moisture

Submerged rice paddies are a major source of methane (CH₄) which is the second most important greenhouse gas after carbon dioxide (CO₂). Accelerating rice straw decomposition during the off-rice season could help to reduce CH₄ emission from rice paddies during the single rice-growth season in cold temperate regions. For understanding how both temperature and moisture can affect the rate of rice straw decomposition during the off-rice season in the cold temperate region of Tohoku district, Japan, a modeling incubation experiment was carried out in the laboratory. Bulk soil and soil mixed with 2% of δ¹³C-labeled rice straw with a full factorial combination of four temperature levels (?5 to 5, 5, 15, 25°C) and two moisture levels (60% and 100% WFPS) were incubated for 24 weeks. The daily change from ?5 to 5°C was used to model the freezing–thawing cycles occurring during the winter season. The rates of rice straw decomposition were calculated by (i) CO₂ production; (ii) change in the soil organic carbon (SOC) content; and (iii) change in the δ¹³C value of SOC. The results indicated that both temperature and moisture affected the rate of rice straw decomposition during the 24-week aerobic incubation period. Rates of rice straw decomposition increased not only with high temperature, but also with high moisture conditions. The rates of rice straw decomposition were more accurately calculated by CO₂ production compared to those calculated by the change in the SOC content, or in its δ¹³C value. Under high moisture at 100% WFPS condition, the rates of rice straw decomposition were 14.0, 22.2, 33.5 and 46.2% at ?5 to 5, 5, 15 and 25°C temperature treatments, respectively. While under low moisture at 60% WFPS condition, these rates were 12.7, 18.3, 31.2 and 38.4%, respectively. The Q₁₀ of rice straw decomposition was higher between ?5 to 5 and 5°C than that between 5 and 15°C and that between 15 and 25°C. Daily freezing–thawing cycles (from ?5 to 5°C) did not stimulate rice straw decomposition compared with low temperature at 5°C. This study implies that to reduce CH₄ emission from rice paddies during the single rice-growth season in the cold temperate regions, enhancing rice straw decomposition during the high temperature period is very important.     

The effect of temperature and moisture on the source of N<Subscript>2</Subscript>O and contributions from ammonia oxidizers in an agricultural soil

In recent years, identification of the microbial sources responsible for soil N₂O production has substantially advanced with the development of isotope enrichment techniques, selective inhibitors, mathematical models and the discoveries of specific N-cycling functional genes. However, little information is available to effectively quantify the N₂O produced from different microbial pathways (e.g. nitrification and denitrification). Here, a ¹⁵N-tracing incubation experiment was conducted under controlled laboratory conditions (50, 70 and 85% water-filled pore space (WFPS) at 25 and 35 °C). Nitrification was the main contributor to N₂O production. At 50, 70 and 85% WFPS, nitrification contributed 87, 80 and 53% of total N₂O production, respectively, at 25 °C, and 86, 74 and 33% at 35 °C. The proportion of nitrified N as N₂O (P _N2O) increased with temperature and moisture, except for 85% WFPS, when P _N2O was lower at 35 °C than at 25 °C. Ammonia-oxidizing archaea (AOA) were the dominant ammonia oxidizers, but both AOA and ammonia-oxidizing bacteria (AOB) were related to N₂O emitted from nitrification. AOA and AOB abundance was significantly influenced by soil moisture, more so than temperature, and decreased with increasing moisture content. These findings can be used to develop better models for simulating N₂O from nitrification to inform soil management practises for improving N use efficiency.     

Estimation of sulfur mineralization and relationships with nitrogen and carbon in soils

A 25-week laboratory study was carried out to determine sulfur, carbon, and nitrogen mineralization rates in soil samples obtained from representative soils in France. Their relationship with some of the soil properties was investigated to find a predictor of mineralized S in soils. At 20°C and 80% water-holding capacity, the S mineralization rate ranged from 0.02 to 0.16 mg kg⁻¹ day⁻¹. It was significantly positively related to soil organic C and N and to C and N mineralization rates. It was weakly related to total soil S. The results suggest that the S mineralization is predominantly driven by heterotrophic microbial activity. A predictive equation for S mineralization based on soil C content, soil pH, and clay content is proposed.     

Umsetzung von Cyanamid,Harnstoff und Ammonsulfat in Abhängigkeit von Temperatur und Bodenfeuchtigkeit

Transformation of cyanamide, urea and ammonium sulfate as influenced by temperature and moisture of soil The conversion of cyanamide, urea and ammonium sulfate solutions to nitrate was investigated in a sandy silt loam (pH 6.2) in relation to temperature and soil moisture conditions. 1. Cyanamide was transformed to urea within 1–5 days. Increasing temperature (2°–100°C) accelerated the breakdown, whereas high moisture conditions (120 % of total water capacity) decreased transformation. 2. The hydrolysis of urea to ammonia took place within 5–10 days even at 2°C regardless of whether cyanamide or urea was added. Low soil moisture (40 % of total water capacity) and high temperature (up to 50°) accelerated the breakdown. 3. Following urea application (20 mg N) there was a transient formation of up to five times more nitrite (0.5 mg NO₂-N) as compared with cyanamide or ammonium sulfate treatments. 4. Clear differences were observed in the rates of nitrification. The rate was greater for urea than for cyanamide and ammonium sulfate. The formation of nitrate began at 2°C, with an optimum between 20° and 30°C. Under flooded conditions (120 % of total water capacity) and low temperature the rate of nitrification was slow. At higher temperatures rapid denitrification took place.