Towards a standardised procedure for determining the potentially mineralisable nitrogen of soil

Reliable techniques for predicting N mineralisation dynamics in soil are required for sustainable management of land resources. The concept of potentially mineralisable N (N0) and its determination procedures were re-appraised in this study. Leaching soil before incubation removed considerable amounts of soluble organic N. But the leached soils had higher rates of net N mineralisation than the unleached controls during a subsequent 2-week incubation, suggesting that using the total amount of leached- (organic + inorganic) N for calculating N0 may not be warranted. N0 and the mineralisation rate constant k estimated with the conventional model-fitting technique varied significantly with soil, incubation time, temperature and moisture, without consistent trends. To obtain an N0 value that is unequivocally indicative of soil N mineralisation capacity, the incubation should be conducted under standardised temperature (35°C) and moisture (55–65% water holding capacity or –30 to –10 kPa) conditions, and a standard mineralisation rate constant (k¯=0.054 week^–1) should be used for all soils. Assuming that N0 for a soil does not change with environmental conditions, its value was then fixed as a constant when fitting the first-order kinetic model to estimate k under non-standard conditions. This technique eliminated the confounding relationship between N0 and k, which is inherent in the conventional curve-fitting procedure, and thus basically precluded the effect of incubation time on N0 estimation. The resultant N0 represents not only the quantity, but also the quality of substrates and their interaction with the soil matrix. The k values showed close and consistent relationships with temperature and moisture.     

Nitrous oxide and methane fluxes from organic soils under agriculture

Trace gas fluxes of N₂O and CH₄ were measured weekly over 12 months on cultivated peaty soils in southern Germany using a closed chamber technique. The aim was to quantify the effects of management intensity and of soil and climatic factors on the seasonal variation and the total annual exchange rates of these gases between the soil and the atmosphere. The four experimental sites had been drained for many decades and used as meadows (fertilized and unfertilized) and arable land (fertilized and unfertilized), respectively. Total annual N₂O-N losses amounted to 4.2, 15.6, 19.8 and 56.4 kg ha^–1 year^–1 for the fertilized meadow, the fertilized field, the unfertilized meadow and the unfertilized field, respectively. Emission of N₂O occurred mainly in the winter when the groundwater level was high. At all sites maximum emission rates were induced by frost. The largest annual N₂O emission by far occurred from the unfertilized field where the soil pH was low (4.0). At this site 71% of the seasonal variation of N₂O emission rates could be explained by changes in the groundwater level and soil nitrate content. A significant relationship between N₂O emission rates and these factors was also obtained for the other sites, which had a soil pH between 5.1 and 5.8, though the relation was weak (R² = 15–27%). All sites were net sinks for atmospheric methane. Up to 78% of the seasonal variation in CH₄ flux rates could be explained by changes in the groundwater level. The total annual CH₄-C uptake was significantly affected by agricultural land use with greater CH₄ consumption occurring on the meadows (1043 and 833 g ha^–1) and less on the cultivated fields (209 and 213 g ha^–1).     

Nitrous oxide emissions from kharif and rabi legumes grown on an alluvial soil

Nitrous oxide (N₂O) emissions were monitored for a period of 60 days in a pot culture study, from two kharif (June-September) and two rabi (October-March) season legumes, which were grown on a Typic Ustochrept, alluvial sandy loam soil. Black gram (Vigna mungo L. Hepper), var. T-9, and soybean (Glycine max L. Merril), var. Punjab 1, were taken up in kharif season whereas lentil (Lens esculenta Moench), var. JLS-1, and Bengal gram (Cicer arietinum L.), var. BGD-86, were grown in rabi season. All the crops were grown with and without urea and one pot (containing soil but with no fertilizer or crop) was used as a control. Nitrous oxide emissions were significantly higher in unfertilized cropped soil than in the control, while the addition of urea to the crops further increased the emissions. Significant emissions occurred during third and seventh week after sowing for all the treatments in both kharif and rabi seasons. In kharif, soil cropped with soybean had higher total N₂O-N emission than soil sown with black gram both under fertilized and unfertilized conditions; while in rabi, lentil had a higher total N₂O-N emission than Bengal gram under both fertilized and unfertilized conditions. In kharif, total N₂O-N emissions ranged from 0.53 (control) to 3.84 kg ha^-1 (soybean+urea), while in rabi it ranged from 0.45 (control) to 3.06 kg ha^-1 (lentil+urea). Higher N₂O-N emissions in kharif than in rabi was probably due to the favorable effect of temperature on nitrification and denitrification in the former season. The results of the study indicated that legume crops may lead to an increase in N₂O formation and emission from soils, the extent of which varies from crop to crop.     

No significant difference in N2O emission,fertilizer-induced N2O emission factor and CH4 absorption between anaerobically digested cattle slurry and chemical fertilizer applied timothy (Phleum pratense L.) sward in central Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) and methane (CH₄) fluxes from a fertilized timothy (Phleum pratense L.) sward on the northern island of Japan were measured over 2?years using a randomized block design in the field. The objectives of the present study were to obtain annual N₂O and CH₄ emission rates and to elucidate the effect of the applied material (control [no nitrogen], anaerobically digested cattle slurry [ADCS] or chemical fertilizer [CF]) and the application season (autumn or spring) on the annual N₂O emission, fertilizer-induced N₂O emission factor (EF) and the annual CH₄ absorption. Ammonium sulfate was applied to the CF plots at the same application rate of NH₄-N to the ADCS plots. A three-way ANOVA was used to examine the significance of the factors (the applied material, the application season and the year). The ANOVA for the annual N₂O emission rates showed a significant effect with regard to the applied material (P?=?0.042). The annual N₂O emission rate from the control plots (0.398?kg N₂O-N ha^?1?year^?1) was significantly lower than that from the ADCS plots (0.708?kg N₂O-N ha^?1?year^?1) and the CF plots (0.636?kg N₂O-N ha^?1?year^?1). There was no significant difference in the annual N₂O emission rate between the ADCS and CF plots. The ANOVA for the EFs showed insignificance of all factors (P?>?0.05). The total mean?±?standard error of the EFs (fertilizer-induced N₂O-N emission/total applied N) was 0.0024?±?0.0007 (kg N₂O-N [kg N]^?1), which is similar to the reported EF (0.0032?±?0.0013) for well-drained uplands in Japan. The CH₄ absorption rates differed significantly between years (P?=?0.014). The CH₄ absorption rate in the first year (3.28?kg CH₄?ha^?1?year^?1) was higher than that in the second year (2.31?kg CH₄?ha^?1?year^?1), probably as a result of lower precipitation in the first year. In conclusion, under the same application rate of NH₄-N, differences in the applied materials (ADCS or CF) and the application season (autumn or spring) led to no significant differences in N₂O emission, fertilizer-induced N₂O EF and CH₄ absorption.     

The influence of nitrate and ammonium fertilization on N2O release and CH4 uptake of a well-drained topsoil demonstrated by a soil microcosm experiment

The effects of the application of KNO₃ and NH₄Cl (100 kg N ha^?1) on N₂O release and CH₄ uptake by a well-aerated topsoil (porosity: 55%, water-filled pore space: 67% of the total pore space) were studied in a laboratory incubation experiment over 50 days using a soil microcosm system with an automated registration of N₂O and CH₄ fluxes. The total N₂O-N losses over 50 days were low for all treatments and amounted to 0.9 mg m^?2 for the control, 1.2 mg m^?2 for the soil columns fertilized with KNO3, and 7.3 mg m^?2 for the soil columns fertilized with NH₄Cl. The slightly elevated N₂O release after the application Of NH₄Cl was associated with the nitrification of NH₄⁺ added. Only ?0.06% of the fertilized NH₄?N was lost as N₂O. This nitrogen fertilization reduced the CH₄ uptake of the soil columns by 43% (NH₄Cl) and 21% (KNO₃), respectively.     

Nitrous oxide and nitric oxide emissions from maize field plots as affected by N fertilizer type and application method

N₂O and NO emissions from an Andisol maize field were studied. The experimental treatments were incorporation of urea into the plough layer at 250 kg N ha^-1 by two applications (UI250), band application of urea at a depth of 8 cm at 75 kg N ha^-1 plus incorporation of urea into the plough layer at 75 kg N ha^-1 (UB150), band application of polyolefin-coated urea at a depth of 5 cm at 150 kg N ha^-1 (CB150), and a control (without N application). N₂O fluxes from UI250 and UB150 peaked following the incorporation of supplementary fertilizer, and declined to the background level after that, while the N₂O flux from CB150 was relatively low but remained at a constant level until shortly after harvest. Accordingly, the total N₂O emissions during the whole cultivation period from the three treatments were not significantly different. The fertilizer-derived N₂O-N losses from UI250, UB150 and CB150 were 0.15%, 0.27% and 0.28% of the applied N, respectively. However, it was suggested that, due to the low plant N recovery, UI250 had a significantly larger potential for indirect N₂O emission than the other treatments. On the other hand, NO emissions from UI250 and UB150 were 12 times higher than that from CB150, and the fertilizer-derived NO-N losses from the three treatments were 0.16%, 0.27% and 0.026% of the applied N, respectively. Significant NO fluxes were detected only when urea-N fertilizer was surface-applied and incorporated into plough-layer soil.     

Mitigation of N2O emission from an alluvial soil by application of karanjin

An incubation experiment was conducted to study N₂O emissions from a Typic Ustochrept, alluvial soil, fertilized with urea and urea combined with different levels of two nitrification inhibitors, viz karanjin and dicyandiamide (DCD). Karanjin [a furano-flavonoid, obtained from karanja (Pongamia glabra Vent.) seeds] and DCD were incorporated at rates of 5, 10, 15, 20 and 25% of applied urea-N (100 mg kg^-1 soil), to the soil adjusted to field capacity moisture content. The highest N₂O flux (366 µg N₂O-N kg^-1 soil day^-1) was obtained on day 1 after incubation from soil fertilized with urea without any inhibitor. The presence of the inhibitors appreciably reduced the mean N₂O flux from the urea-treated soils. The application of karanjin resulted in a higher mitigation of total N₂O-N emission (92-96%) compared to DCD (60-71%). Rates of N₂O flux ranged from 0.9 to 140 µg N₂O-N kg^-1 soil day^-1 from urea combined with different levels of the two inhibitors (coefficient of variation=24-272%). Karanjin (62-75%) was also more effective than DCD (9-42%) in inhibiting nitrification during the 30-day incubation period.     

Denitrification, N2O and CO2 fluxes in rice-wheat cropping system as affected by crop residues, fertilizer N and legume green manure

Use of renewable N and C sources such as green manure (GM) and crop residues in rice-wheat cropping systems of South Asia may lead to higher crop productivity and C sequestration. However, information on measurements of gaseous N losses (N₂O+N₂) via denitrification and environmental problems such as N₂O and CO₂ production in rice-wheat cropping systems is not available. An acetylene inhibition-intact soil core technique was employed for direct measurement of denitrification losses, N₂O and CO₂ production, in an irrigated field planted to rice (Oryza sativa L.) and wheat (Triticum aestivum L.) in an annual rotation. The soil was a coarse-textured Tolewal sandy loam soil (Typic Ustochrept) and the site a semi-arid subtropical Punjab region of India. Wheat residue (WR, C:N=94) was incorporated at 6 t ha^-1 and sesbania (Sesbania aculeata L.) was grown as GM crop for 60 days during the pre-rice fallow period. Fresh biomass of GM (C:N.=18) at 20 or 40 t ha^-1 was incorporated into the soil 2 days before transplanting rice. Results of this study reveal that (1) denitrification is a significant N loss process under wetland rice amounting to 33% of the prescribed dose of 120 kg N ha^-1 applied as fertilizer urea-N (FN); (2) integrated management of 6 t WR ha^-1 and 20 t GM ha^-1 supplying 88 kg N ha^-1 and 32 kg FN ha^-1 significantly reduced cumulative gaseous N losses to 51.6 kg N ha^-1 as compared with 58.2 kg N ha^-1 for 120 kg FN ha^-1 alone; (3) application of excessive N and C through applying 40 t GM ha^-1 (176 kg N ha^-1) resulted in the highest gaseous losses of 70 kg N ha^-1; (4) the gaseous N losses under wheat were 0.6% to 2% of the applied 120 kg FN ha^-1 and were eight- to tenfold lower (5-8 kg N ha^-1) than those preceding rice; (5) an interplay between the availability of NO₃^- and organic C largely controlled denitrification and N₂O flux during summer-grown flooded rice whereas temperature and soil aeration status were the primary regulators of the nitrification-denitrification processes and gaseous N losses during winter-grown upland wheat; (6) the irrigated rice-wheat system is a significant source of N₂O as it emits around 15 kg N₂O-N ha^-1 year^-1; (7) incorporation of WR in rice and rice residue (C:N=63) in wheat increased soil respiration, and increased CO₂ production in WR- and GM-amended soils under anaerobic wetland rice coincided with enhanced rates of denitrification; and (8) with adequate soil moisture, most of the decomposable C fraction of added residues was mineralized within one crop-growing season and application of FN and GM further accelerated this process.     

Nitrous oxide concentrations in an Andisol profile and emissions to the atmosphere as influenced by the application of nitrogen fertilizers and manure

A field experiment was conducted to determine N₂O concentrations in the soil profile and emissions as influenced by the application of N fertilizers and manure in a typical Japanese Andisol, which had been under a rotation of oat and carrot for the previous 3 years. The treatments include ammonium sulphate (AS), controlled-release fertilizer (CRF) and cattle manure (CM) in addition to a control; all the fertilizers were applied either at 150 kg N ha^-1 or 300 kg N ha^-1 at the time of sowing carrot. N₂O emissions from the soil surface were measured with closed-chamber techniques, while N₂O concentrations in the soil profile were measured using stainless steel sampling probes inserted into the soil at depths of 10, 20, 40, 60, 80 and 100 cm. Moreover, soil water potential, soil temperature and rainfall data were also recorded. The results indicated that N₂O concentrations in the soil profile were always greater than in the atmosphere, ranging from 0.36 µl N₂O-N l^-1 to 5.3 µl N₂O-N l^-1. The relatively large accumulation of N₂O in the lower profiles may be a significant source for N₂O flux. Taking the changes of soil mineral N into consideration, most emissions of N₂O were probably produced from nitrification. The accumulation of N₂O in the soil profile and emissions to the atmosphere were differently influenced by the amendments of N fertilizers and manure, being consistently higher in CRF than in CM and AS treatments at the corresponding application rates, but no significant difference existed with respect to the various N sources.     

Effect of nitrogen fertilization on methane flux in a structured clay soil cultivated with onion in Central Hokkaido,Japan

Abstract

This study was conducted to investigate the effect of N fertilization on the soil CH₄ flux during the growing season of onion in a structured clay soil with stagnant water at depths of 70–80 cm and with a peat-mixed subsoil. The following 4 treatments were analyzed over a period of two years: T1) fertilized, onion growing, T2) fertilized, bare field, T3) unfertilized, onion growing, and T4) unfertilized, bare field. In the fertilized T1 and T2 treatments, fertilizers (mixture of 3 : 1 NH₄NO₃ : (NH₄)₂SO₄) at rates of 322 kg N ha^?1 in 1999 and 242 kg N ha^?1 in 2000 were applied as basal fertilizers before onion was transplanted. CH₄ fluxes among the treatments ranged from ?0.06 to 0.12 mg CH₄-C m^?2 h^?1 in 1999, and from ?0.03 to 0.01 mg CH₄-C m^?2 h^?1 in 2000, which were high after heavy rain in summer. Cumulative CH₄ flux from May to November in the fertilized T1 and T2 treatments was 59 mg CH₄-C m^?2 for both treatments in 1999, and 3.2 and ?0.9 mg CH₄-C m^?2 in 2000, respectively. On the other hand, in the unfertilized T3 and T4 treatments, the cumulative CH₄ flux was 0.2 and ?9.2 mg CH₄-C m^?2 in 1999, and ?26 and ?20 mg CH₄-C m^?2 in 2000, respectively. Although the cumulative CH₄ flux in each treatment was higher in 1999 than in 2000, the fertilized treatments in both years showed a significantly higher cumulative CH₄ flux than the unfertilized treatments. This might be ascribed to the higher level of nitrification in the fertilized treatments, because a high nitrate concentration was observed in the fertilized treatments in the onion growing season. The results also revealed that onion growing did not exert a significant influence on the CH₄ flux. The precipitation from May to November was 642 mm in 1999 and 1,008 mm in 2000, and the CH₄ emission increased when the precipitation was low. In addition, the CH₄ concentration in the soil profile increased with the increase of the depth in summer as the soil was dry. These findings indicated that CH₄ diffusion from the soil to the atmosphere was inhibited by rainwater.     

Effects of rate and depth of fertilizer application on emission of nitrous oxide from soil fertilized with anhydrous ammonia

Summary Field studies to determine the effect of different rates of fertilization on emission of nitrous oxide (N₂O) from soil fertilized with anhydrous ammonia showed that the fertilizer-induced emission of N₂O-N in 116 days increased from 1.22 to 4.09 kg ha^–1 as the rate of anhydrous ammonia N application was increased from 75 to 450 kg ha^–1. When expressed as a percentage of the N applied, the fertilizer-induced emission of N₂O-N in 116 days decreased from 1.6% to 0.9% as the rate of fertilizer N application was increased from 75 to 450 kg N ha^–1. The data obtained showed that a 100% increase in the rate of application of anhydrous ammonia led to about a 60% increase in the fertilizer-induced emission of N₂O.Field studies to determine the effect of depth of fertilizer injection on emission of N₂O from soil fertilized with anhydrous ammonia showed that the emission of N₂O-N in 156 days induced by injection of 112 kg anhydrous ammonia N ha^–1 at a depth of 30 cm was 107% and 21 % greater than those induced by injection of the same amount of N at depths of 10 cm and 20 cm, respectively. The effect of depth of application of anhydrous ammonia on emission of N₂O was less when this fertilizer was applied at a rate of 225 kg N ha^–1.     

Soil N<Subscript>2</Subscript>O emissions and N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio as affected by different fertilization practices and soil moisture

The objective of this work was to evaluate the effect of the chemical nature and application frequency of N fertilizers at different moisture contents on soil N₂O emissions and N₂O/(N₂O+N₂) ratio. The research was based on five fertilization treatments: unfertilized control, a single application of 80 kg ha⁻¹ N-urea, five split applications of 16 kg ha⁻¹ N-urea, a single application of 80 kg ha⁻¹ N–KNO₃, five split applications of 16 kg ha⁻¹ N–KNO₃. Cumulative N₂O emissions for 22 days were unaffected by fertilization treatments at 32% water-filled pore space (WFPS). At 100% and 120% WFPS, cumulative N₂O emissions were highest from soil fertilized with KNO₃. The split application of N fertilizers decreased N₂O emissions compared to a single initial application only when KNO₃ was applied to a saturated soil, at 100% WFPS. Emissions of N₂O were very low after the application of urea, similar to those found at unfertilized soil. Average N₂O/(N₂O+N₂) ratio values were significantly affected by moisture levels (p = 0.015), being the lowest at 120% WFPS. The N₂O/(N₂O+N₂) ratio averaged 0.2 in unfertilized soil and 0.5 in fertilized soil, although these differences were not statistically significant.     

Influence of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in comparison to dicyandiamide (DCD) on nitrous oxide emissions, carbon dioxide fluxes and methane oxidation during 3 years of repeated application in field experiments

In a 3-year field experiment, the effect of the nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) on the release of N₂O, CO₂, and on CH₄ oxidation, was examined in comparison to that of dicyandiamide (DCD) on N-fertilized and unfertilized experimental sites. Soil samples were analysed simultaneously for the concentrations of N₂O retained in the soil body, NH₄⁺, NO₂^-, NO₃^-, and for the degradation kinetics of DMPP as well as DCD. DMPP decreased the release of N₂O on fertilized plots by 41% (1997), 47% (1998) and 53% (1999) (on average by 49%) while DCD reduced N₂O emissions by 30% (1997), 22% (1998) and 29% (1999) (on average by 26%). In addition, the NIs seemed to decrease the CO₂ emissions of each fertilized treatment. DCD reduced the release of CO₂ by an average of 7% for the 3 years (non-fertilized 10%), and DMPP reduced it by an average of up to 28% (non-fertilized 29%). Furthermore, both NIs failed to affect CH₄ oxidation negatively. The plots that received either DCD or DMPP even seemed to function as enhanced sinks for atmospheric CH₄. DMPP apparently stimulated CH₄ oxidation of N-fertilized plots by ca 28% in comparison to the control. In total, DCD and DMPP reduced the global warming potential of N-fertilized plots by 7% and 30%, respectively. Further, DCD and DMPP diminished the amount of N₂O retained in the soil by 52% and 61%, respectively. The concentrations of NH₄⁺ remained unaffected by both NIs, whereas the amounts of NO₂^- diminished in the plots treated with DCD by 25% and with DMPP by 20%. In both NI treatments NO₃^- concentrations in the soil were 23% lower than in the control. DMPP and DCD did not affect the yields of summer barley, maize and winter wheat significantly. DCD was mineralized more rapidly than DMPP.     

Nutrient balance in Scots pine (Plnus sylvestris L.) forest. 3. Fluxes of N2O from lysimeter as influenced by nitrogen input

Forest soils may become an increasingly important source of N₂O, due to disturbances to the forest ecosystem (e.g. fertilization to increase growth, or atmospheric deposition of air-borre nitrogen compounds such as NH₃, NO₃ and NO_x). A lysimeter experiment was used to study the effects of different amounts of N input [0 (control), 30 kg (Medium) and 90 kg (High) N ha^?1 y^?1 as NH₄NO₃] on fluxes of N₂O, measured by the close chamber method. The estimated annual N₂O flux were about 0.4 kg N₂O-N ha^?1 for control, 0.9 kg N₂O-N ha^?1 for medium N and 1.8 kg N₂O-N ha^?1 for high N treatments. The relation between the estimated annual N₂O flux and fertilizer dose showed an almost perfect proportionality between fertilizer dose and the increase in N₂O flux. This is important, since one crucial question is wether we can extrapolate results from high N-doses to situations with low amounts of N inputs prevailing in forests exposed to moderate input of N. The increase in N₂O fluxes from the control to the fertilised treatments corresponds to 1.7% of the annual N input in the medium N treatments and 1.6% of the annual input in the high N treatment.     

Nitrous oxide emissions from a rainfed-cultivated black soil in Northeast China: effect of fertilization and maize crop

Nitrous oxide emission (N₂O) from applied fertilizer across the different agricultural landscapes especially those of rainfed area is extremely variable (both spatially and temporally), thus posing the greatest challenge to researchers, modelers, and policy makers to accurately predict N₂O emissions. Nitrous oxide emissions from a rainfed, maize-planted, black soil (Udic Mollisols) were monitored in the Harbin State Key Agroecological Experimental Station (Harbin, Heilongjiang Province, China). The four treatments were: a bare soil amended with no N (C0) or with 225?kg?N ha^?1 (CN), and maize (Zea mays L.)-planted soils fertilized with no N (P0) or with 225?kg?N ha^?1 (PN). Nitrous oxide emissions significantly (P?<?0.05) increased from 141?±?5?g N₂O-N?ha^?1 (C0) to 570?±?33?g N₂O-N?ha^?1 (CN) in unplanted soil, and from 209?±?29?g N₂O-N?ha^?1 (P0) to 884?±?45?g N₂O-N?ha^?1 (PN) in planted soil. Approximately 75?% of N₂O emissions were from fertilizer N applied and the emission factor (EF) of applied fertilizer N as N₂O in unplanted and planted soils was 0.19 and 0.30?%, respectively. The presence of maize crop significantly (P?<?0.05) increased the N₂O emission by 55?% in the N-fertilized soil but not in the N-unfertilized soil. There was a significant (P?<?0.05) interaction effect of fertilization?×?maize on N₂O emissions. Nitrous oxide fluxes were significantly affected by soil moisture and soil temperature (P?<?0.05), with the temperature sensitivity of 1.73–2.24, which together explained 62–76?% of seasonal variation in N₂O fluxes. Our results demonstrated that N₂O emissions from rainfed arable black soils in Northeast China primarily depended on the application of fertilizer N; however, the EF of fertilizer N as N₂O was low, probably due to low precipitation and soil moisture.     

Variables controlling denitrification from earthworm casts and soil in permanent pastures

Summary Denitrification (using the acetylene block method) was determined in earthworm casts and soils from permanent, drained or undrained pasture plots fertilized with 0 or 200 kg N ha^-1 year^-1 as ammonium nitrate. Rates of N₂O production from soil cores were about three times higher from the fertilized than from the unfertilized plots while drainage had a relatively small effect. Denitrification rates from casts were 3–5 times higher than those from soil irrespective of the drainage treatment. Casts generally had higher NO _inf3 ^sup- , NH _inf4 ^sup+ , and moisture contents, and higher microbial respiration rates than soil. Rates of N₂O production were determined primarily by NO _inf3 ^sup- supply, secondarily by moisture; available C did not appear to limit denitrification in these pastures. Estimates of the potential contribution of casts to denitrification ranges from 10.1% of 29.3 kg ha^-1 year^-1 from the unfertilized, drained plot to 22% of 82.5 kg ha^-1 year^-1 from the fertilized undrained plot.     

Methane and nitrous oxide emissions as affected by organic–inorganic mixed fertilizer from a rice paddy in southeast China

Purpose

The effects of commercial compost fertilizer application on trace gas emissions are not well understood due to a lack of field experiments. The objective of this study was to evaluate the emissions of methane (CH₄) and nitrous oxide (N₂O) along with grain yield from a rice paddy as affected by different organic–inorganic mixed fertilizer (OIMF) treatments.

Materials and methods

A field experiment was initiated in 2006 with chemical compound fertilizer (CF) and three OIMF amendments including pig manure compost (PMC), Chinese medicine residue compost (CMC), and rapeseed cake compost (RCC), from a rice paddy in southeast China. The emissions of CH₄ and N₂O were simultaneously measured using the static opaque chamber method over the entire rice growing season in 2011. Soil biotic parameters were measured in soil collected after the rice was harvested in 2011.

Results and discussion

Relative to the control, the OIMF treatments significantly increased CH₄ emissions by 56–99 %, mainly due to exogenous organic substrate input, whereas no difference was observed in the CF treatment. The N₂O emissions were stimulated substantially by an average of 40 % due to nitrogen fertilization compared with the control. Consecutive OIMF application tended to increase the grain yield, making it marginally higher than that of the CF treatment (7 %, P?=?0.06). Compared with the control, the CF treatment slightly decreased the global warming potential and greenhouse gas (GHG) intensity, while they were remarkably increased in the OIMF treatments. Over the 5-year period of 2006–2011, the annual soil carbon sequestration rate was estimated to be 1.19 t C ha^?1 year^?1 for the control and 1.73–1.98 t C ha^?1 year^?1 for the fertilized treatments.

Conclusions

Our results suggest that despite the beneficial effects of increasing both grain yield and soil organic matter, OIMF application such as PMC, CMC, and RCC may be responsible for increased global warming due mainly to the stimulated CH₄ emissions. This effect should be thus taken into account when balancing agricultural production and GHG mitigation.     

Effects of different organic fertilizers on nitrous oxide and methane emissions from double-cropping rice fields

Rice fields are a major source of greenhouse gases,such as nitrous oxide (N₂O) and methane (CH₄).Organic fertilizers may potentially replace inorganic fertilizers to meet the nitrogen requirement for rice growth;however,the simultaneous effects of organic fertilizers on N₂O and CH₄emissions and crop yield in paddy fields remain poorly understood and quantified.In this study,experimental plots were established in conventional double-cropping paddy field...     

Nitrous oxide emissions from artificial urine patches applied to different N-fertilized swards and estimated annual N2O emissions for differently fertilized pastures in an upland location in Germany

Abstract. Artificial urine containing 20.2 g N per patch of 0.2 m² was applied in May and September to permanent grassland swards of a long‐term experiment in the western uplands of Germany (location Rengen/Eifel), which were fertilized with 0, 120, 240, 360 kg N ha^?1 yr^?1 given as calcium ammonium nitrate. The effect on N₂O fluxes measured regularly during a 357‐day period with the closed‐chamber technique were as follows. (1) N₂O emission varied widely among the fertilized control areas without urine, and when a threshold water‐filled pore space >60% was exceeded, the greater the topsoil nitrate content the greater the flux from the individual urine patches on the fertilized swards. (2) After urine application in May, 1.4–4.2% of the applied urine‐N was lost as N₂O from the fertilized swards; and after urine application in September, 0.3–0.9% of the applied urine‐N was lost. The primary influence on N₂O flux from urine patches was the date of simulated grazing, N‐fertilization rate being a secondary influence. (3) The large differences in N₂O emissions between unfertilized and fertilized swards after May‐applied urine contrasted with only small differences after urine applied in September, indicating an interaction between time of urine application and N‐fertilizer rate. (4) The estimated annual N₂O emissions were in the range 0.6–1.6 kg N₂O‐N per livestock unit, or 1.4, 3.6, 4.1 and 5.1 kg N₂O‐N ha^?1 from the 0–360 kg ha^?1 of fertilizer‐N. The study demonstrated that date of grazing and N‐fertilizer application could influence the N₂O emission from urine patches to such an extent that both factors should be considered in detailed large‐scale estimations of N₂O fluxes from grazed grassland.     

Nitrous oxide emission from different fertilizers and its mitigation by nitrification inhibitors in irrigated rice

 N₂O emissions from a transplanted irrigated rice grown on a Typic Ustochrept soil at New Delhi, India, were studied to evaluate the effect of N fertilizers, i.e. urea and (NH₄)₂SO₄, alone and in combination with the nitrification inhibitors dicyandiamide (DCD) and thiosulphate. The addition of urea and (NH₄)₂SO₄ increased N₂O emissions considerably when compared to no fertilizer N application (control). N₂O measurement in the field was done by a closed-chamber method for a period of 98 days. The application of urea with DCD and thiosulphate reduced N₂O fluxes considerably. The highest total N₂O-N emission (235 g N₂O-N ha^–1) was from the (NH₄)₂SO₄ treatment, which was significantly higher than the total N₂O-N emission from the urea treatment (160 g N₂O-N ha^–1). DCD reduced N₂O-N emissions by 11% and 26% when applied with urea and(NH₄)₂SO₄, respectively, whereas thiosulphate in combination with urea reduced N₂O-N emissions by 9%. Total N₂O-N emissions were found to range from 0.08% to 0.14% of applied N. N₂O emissions were low during submergence and increased substantially during drainage of standing water. Received: 20 October 1999