Effects of application of lime nitrogen and dicyandiamide on nitrous oxide emissions from green tea fields

Abstract

The aim of this study was to assess the mitigating effects of lime nitrogen (calcium cyanamide) and dicyandiamide (DCD) application on nitrous oxide (N₂O) emissions from fields of green tea [Camellia sinensis (L.) Kuntze]. The study was conducted in experimental tea fields in which the fertilizer application rate was 544 kg nitrogen (N) ha^?1 yr^?1 for 2 years. The mean cumulative N₂O flux from the soil between the canopies of tea plants for 2 years was 7.1 ± 0.9 kg N ha^?1 yr^?1 in control plots. The cumulative N₂O flux in the plots supplemented with lime nitrogen was 3.5 ± 0.1 kgN ha^?1, approximately 51% lower than that in control plots. This reduction was due to the inhibition of nitrification by DCD, which was produced from the lime nitrogen. In addition, the increase in soil pH by lime in the lime nitrogen may also be another reason for the decreased N₂O emissions from soil in LN plots. Meanwhile, the cumulative N₂O flux in DCD plots was not significantly different from that in control plots. The seasonal variability in N₂O emissions in DCD plots differed from that in control plots and application of DCD sometimes increased N₂O emissions from tea field soil. The nitrification inhibition effect of lime nitrogen and DCD helped to delay nitrification of ammonium-nitrogen (NH₄⁺-N), leading to high NH₄⁺-N concentrations and a high ratio of NH₄⁺-N /nitrate-nitrogen (NO₃^–-N) in the soil. The inhibitors delayed the formation of NO₃^–-N in soil. N uptake by tea plants was almost the same among all three treatments.     

Nitrous oxide emissions from potato cropping under drip-fertigation in eastern Germany

In this article, a drip-fertigation system was compared to a control without irrigation concerning the amount of nitrous oxide (N₂O) emissions under the climatic conditions of north-east Germany. The investigation was carried out at a field research station in the federal state of Brandenburg. The mean N₂O emissions under drip-fertigation were significantly higher than under non-irrigation. The higher N₂O emissions under drip-fertigation can be explained by a constantly higher water-filled pore space (WFPS). These higher values in WFPS were caused by the necessary nutrient supply in combination with additional water application in periods with frequent rainfall.     

不同水稻、小麦品种对N2O排放的影响

Plant species of cropping systems may affect nitrous oxide (N2O) emissions. A field experiment was conducted to investigate dynamics of N2O emissions from rice-wheat fields from December 2006 to June 2007 and the relationship between soil and plant parameters with N2O emissions. The results indicated that N2O emissions from different wheat varieties ranged from 12 to 291 μg N2O-N m-2 h-1 and seasonal N2O emissions ranged from 312 to 385 mg N2O-N m-2. In the rice season, it was from 11 to 154 μg N2O-N m-2 h-1 with seasonal N2O emission of 190--216 mg N2O-N m-2. The seasonal integrated flux of N2O differed significantly among wheat and rice varieties. The wheat variety HUW 234 and rice variety Joymoti showed higher seasonal N2O emissions. In the wheat season, N2O emissions correlated with soil organic carbon (SOC), soil NO3--N, soil temperature, shoot dry weight, and root dry weight. Among the variables assessed, soil temperature followed by SOC and soil NO3--N were considered as the important variables influencing N2O emission. N2O emission in the rice season was significantly correlated with SOC, soil NO3--N, soil temperature, leaf area, shoot dry weight, and root dry weight. The main driving forces influencing N2O emission in the rice season were soil NO3--N, leaf area, and SOC.     

Nitrous oxide emissions and nitrogen cycling in managed grassland in Southern Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) emissions were measured and nitrogen (N) budgets were estimated for 2?years in the fertilizer, manure, control and bare plots established in a reed canary grass (Phalaris arundinacea L.) grassland in Southern Hokkaido, Japan. In the manure plot, beef cattle manure with bark was applied at a rate of 43–44?Mg fresh matter (236–310?kg?N)?ha^?1?year^?1, and a supplement of chemical fertilizer was also added to equalize the application rate of mineral N to that in the fertilizer plots (164–184?kg?N?ha^?1?year^?1). Grass was harvested twice per year. The total mineral N supply was estimated as the sum of the N deposition, chemical fertilizer application and gross mineralization of manure (GMm), soil (GMs), and root-litter (GMl). GMm, GMs and GMl were estimated by dividing the carbon dioxide production derived from the decomposition of soil organic matter, root-litter and manure by each C?:?N ratio (11.1 for soil, 15.5 for root-litter and 23.5 for manure). The N uptake in aboveground biomass for each growing season was equivalent to or greater than the external mineral N supply, which is composed of N deposition, chemical fertilizer application and GMm. However, there was a positive correlation between the N uptake in aboveground biomass and the total mineral N supply. It was assumed that 58% of the total mineral N supply was taken up by the grass. The N supply rates from soil and root-litter were estimated to be 331–384?kg?N?ha^?1?year^?1 and 94–165?kg?N?ha^?1?year^?1, respectively. These results indicated that the GMs and GMl also were significant inputs in the grassland N budget. The cumulative N₂O flux for each season showed a significant positive correlation with mineral N surplus, which was calculated as the difference between the total mineral N supply and N uptake in aboveground biomass. The emission factor of N₂O to mineral N surplus was estimated to be 1.2%. Furthermore, multiple regression analysis suggested that the N₂O emission factor increased with an increase in precipitation. Consequently, soil and root-litter as well as chemical fertilizer and manure were found to be major sources of mineral N supply in the grassland, and an optimum balance between mineral N supply and N uptake is required for reducing N₂O emission.     

Nitrous oxide emissions and dynamics of soil nitrogen under 15N‐labeled cow urine and dung patches on a sandy grassland soil

Grazing animals highly influence the nutrient cycle by a direct return of 80% of the consumed N in form of dung and urine. In the autumn‐winter period, N uptake by the sward is low and rates of seepage water in sandy soils are high, hence high mineral‐N contents in soil and in seepage water as well as large losses of N₂O are expected after cattle grazing in autumn. The objective of this study was the quanitfication of N loss deriving from urine and dung leaching and by N₂O emission. Therefore the deposition of urine and dung patches was simulated in maximum rates excreted by cows by application of ¹⁵N‐labeled cow urine and dung (equivalent to 1030 kg N ha^–1 and 1052 kg N ha^–1, respectively) on a sandy pasture soil in N Germany. Leachate was collected in weekly intervals from free‐draining lysimeters, and ¹⁵N‐NO , ¹⁵N‐NH , and ¹⁵N‐DON (dissolved organic N) were monitored over 171 d. Furthermore, the ¹⁵N‐N₂O emission rates and the dynamics of inorganic ¹⁵N in the upper soil layer were monitored in a field trial, adjacent to the lysimeters. After 10 d following the urine application, the urea was completely hydrolyzed, shown by a 100% recovery of urine‐N in the soil NH . The following decrease of ¹⁵N‐NH in the soil was higher than the increase of ¹⁵N‐NO , and some N loss was explained by leaching. Amounts of 51% and 2.5% of the applied ¹⁵N were found in leachate as inorganic N, 2.4% and 0.7% as DON derived from urine and dung, respectively. Release of N₂O from urine and dung patches applied to the pasture was low, with losses of 0.05% and 0.33% of the applied ¹⁵N, respectively. Overall loss of dung‐derived N was very low, but as the bulk dung N remained in the soil, N loss after mineralization of the dung needs to be investigated.     

Nitrous oxide emissions from boreal organic soil under different land-use

Nitrous oxide emissions were studied with a static chamber technique during 2 years from a drained organic soil in eastern Finland. After drainage, the soil was forested with birch (Betula pendula Roth) and 22 years later, part of the forest was felled and then used for cultivation of barley (Hordeum vulgare L.) and grass. The annual N₂O emissions from the cultivated soil (from 8.3 to 11.0 kg N₂O-N ha⁻¹ year⁻¹) were ca. twice the annual emission from the adjacent forest site (4.2 kg N₂O-N ha⁻¹ year⁻¹). The N₂O emissions from the soils without plants (kept bare by regular cutting or tilling) were also lower (from 6.5 to 7.1 kg N₂O-N ha⁻¹ year⁻¹) than those from the cultivated soil. There was a high seasonal variation in the fluxes with a maximum in spring and early summer. The N₂O fluxes during the winter period accounted for 15-60% of the total annual emissions. N₂O fluxes during the snow-free periods were related to the water table (WT) level, water-filled pore space, carbon mineralisation and the soil temperature. A linear regression model with CO₂ production, WT and soil temperature at the depth of 5 cm as independent variables explained 54% of the variation in the weekly mean N₂O fluxes during the snow-free periods. N₂O fluxes were associated with in situ net nitrification, which alone explained 58% of the variation in the mean N₂O fluxes during the snow-free period. The N₂O-N emissions were from 1.5 to 5% of net nitrification. The acetylene blockage technique indicated that most of the N₂O emitted in the snow-free period originated from denitrification.     

Nitrous oxide emissions after application of inorganic fertilizer and incorporation of green manure residues

Abstract. Emissions of N₂O were measured after application of NH₄NO₃ fertilizer and incorporation of winter wheat and rye green manures in two field experiments in southeast England. Incorporation of green manure alone resulted in temporary immobilization of soil N, small N₂O emissions and also low availability of N for the following crop. Emissions were increased after application of inorganic fertilizer, and were further increased from integrated management treatments whereby green manure residues were incorporated after fertilizer application. The highest emission was from the incorporated winter wheat green manure plus fertilizer treatment, with 1.5 kg N₂O-N ha⁻¹ (0.6% of N applied) being emitted over the first 55 days after incorporation. This high emission was attributed to the supply of C in the residues providing the energy for denitrification in the presence of large amounts of mineral N and the creation of anaerobic microsites during microbial respiration.     

Nitrous oxide emission as affected by changes in soil water content and nitrogen fertilization

Nitrous oxide emission was measured in laboratory incubations of an alluvial soil (58% clay, pH 7.4). The soil was amended with 40 mg N kg⁻¹ as NaNO₃ or NH₄Cl, or with NaCl as a control. Each fertilization treatment was adjusted to three different water contents: constant 60% WHC (water-holding capacity), constant 120% WHC, and water content alternating between 60 and 120% WHC. During an 8-day incubation period N₂O emission rates and inorganic nitrogen concentrations in soil (NH₄⁺, NO₂⁻, NO₃⁻) were determined at regular intervals. In the control and after nitrate application small N₂O emission rates occurred with only minor variations over time, and no differences between the water treatments. In contrast, with ammonium application N₂O emission rates were much higher during the first two days of incubation, with peaks in the constant 60% WHC and 120% WHC at day 1 and in the changing-water treatment at day 2, when the first wet period (120% WHC) was completed. This N₂O peak in the changing-water treatment was 4 to 9 times higher than with constant WHC and occurred when both, NH₄⁺ and NO₂⁻ concentrations declined sharply. Thus, this N₂O emission flush can be attributed to nitrifier denitrification. After the second rewetting of the NH₄⁺-amended soil no further N₂O emission peak was observed, being in accordance with small NH₄⁺ and NO₂⁻ concentrations in soil at that time. The unexpectedly small N₂O fluxes in the constant 120% WHC treatment after nitrate application were probably caused by the reduction of N₂O to N₂ under the prevailing conditions. It can be concluded that continuous wetting or flooding of a soil is an effective measure to reduce N₂O emissions immediately after the application of NH₄⁺ fertilizers.     

Nitrous oxide and methane emissions from grassland treated with bark- or sawdust-containing manure at different rates

On the main Japanese island of Honshu, bark or sawdust is often added to cattle excreta as part of the composting process. Dairy farmers sometimes need to dispose of manure that is excess to their requirements by spreading it on their grasslands. We assessed the effect of application of bark- or sawdust-containing manure at different rates on annual nitrous oxide (N₂O) and methane (CH₄) emissions from a grassland soil. Nitrous oxide and CH₄ fluxes from an orchardgrass (Dactylis glomerata L.) grassland that received this manure at 0, 50, 100, 200, or 300?Mg?ha^?1?yr^?1 were measured over a two-year period by using closed chambers. Two-way analysis of variance (ANOVA) was employed to examine the effect of annual manure application rates and years on annual N₂O and CH₄ emissions. Annual N₂O emissions ranged from 0.47 to 3.03?kg?N?ha^?1?yr^?1 and increased with increasing manure application rate. Nitrous oxide emissions during the 140-day period following manure application increased with increasing manure application rate, with the total nitrogen concentration in the manure, and with cumulative precipitation during the 140-day period. However, manure application rate did not affect the N₂O emission factors of the manure. The overall average N₂O emission factor was 0.068%. Annual CH₄ emissions ranged from ?1.12 to 0.01?kg?C?ha^?1?yr^?1. The annual manure application rate did not affect annual CH₄ emissions.     

Nitrous oxide emissions from grassland in an intensive dairy farm in the Basque Country of Spain

Abstract. Intensively managed grasslands are potentially a large source of N₂O in the North Coast of Spain because of the large N input, the wet soil conditions and mild temperatures. To quantify the effect of fertilizer type and management practices carried out by farmers in this area, field N₂O losses were measured over a year using the closed chamber technique. Plots received two types of fertilizer: cattle slurry (536 kg N ha^–1) and calcium ammonium nitrate (140 kg N ha^–1). N₂O losses were less in the slurry treatment than after mineral fertilizer. This was probably due to high, short‐lived peaks of N₂O encountered immediately following mineral N addition. In contrast, the seasonal distribution of N₂O losses from the slurry amended plot was more uniform over the year. The greater N₂O losses in the mineral treatment might have been enhanced by the combined effect of mineral fertilizer and past organic residues present from previous organic amendments. Weak relationships were found between N₂O emission rates and soil nitrate, soil ammonium, soil water content and temperature. Better relationships were obtained in the mineral treatment than in the slurry plots, because of the wider range in soil mineral N. Water filled pore space (WFPS) was a key factor controlling N₂O emissions. In the > 90% WFPS range no relationships were found. The best regressions were found for the mineral treatment in the 40–65% WFPS range, 49% of the variance being explained by soil nitrate and ammonium content. In the 65–90% WFPS range, 43% of the variance was explained by nitrate only, but the inclusion of soil ammonium did not improve the model as it did in the 40–65% WFPS range. This fact indicates that nitrification is likely to be an important process involved in N₂O emissions at the 40–65% WFPS.     

Nitrous oxide emissions under a four-year crop rotation system in northern Japan: impacts of reduced tillage,composted cattle manure application and increased plant residue input

In the context of their role in global warming, nitrous oxide (N₂O) emissions from agricultural soil under different management practices were studied in Hokkaido, northern Japan. To assess the impacts of reduced tillage, composted cattle manure-based fertilization and amendments with crop residues and green manure on N₂O emissions from soil, a field experiment was conducted under a four-year crop rotation on a well-drained Andisol. The crop rotation included potato (Solanum tuberosum L.) or sweet corn (Zea mays L.), winter wheat (Triticum aestivum L.), sugar beet (Beta vulgaris L. subsp. vulgaris) and soybean (Glycine max (L.) Merr.). The cumulative N₂O emissions for the four-year study period differed widely (0.33 to 4.90?kg?N?ha^?1), depending on the treatments imposed, being the greatest for a combination of conventional moldboard plow tillage, composted cattle manure-based fertilization and increased plant residue input, and the lowest for a combination of conventional tillage, chemical fertilizer-based fertilization and normal plant residue input treatments. The cumulative N₂O emissions under reduced tillage were all small, irrespective of fertilization and plant residue input treatments. Composted cattle manure-based fertilization (P?≤?0.01) and increased plant residue input (P?≤?0.01) significantly increased cumulative N₂O emissions. Tillage showed a significant interaction with fertilization and plant residue input, indicating that N₂O emissions were enhanced when composted cattle manure, crop residues and green manure were incorporated by conventional tillage. In the present study, the N₂O emission factors for chemical fertilizer, composted cattle manure and crop residues were 0.26?±?0.44, 0.11?±?0.16 and ?0.03?±?0.52%, respectively, all much lower than the country-specific emission factor for Japan's well-drained soils (0.62%) and the default emission factor used in the IPCC guideline (1%).     

日本茶树种植导致的环境问题及施用氨晴钙的控制效果

A field experiment, involving lime N （calcium cyanamide, CaCN2） fertilization as a control measure, was conducted to study environmental problems induced by long-term heavy N application in Japanese tea fields. Long-term tea cultivation caused serious soil acidification. Seventy-seven percent of the 70 tea fields investigated had soil pH values below 4.0, and 9% below 3.0, with the lowest value of 2.7. Moreover, excess N application in tea fields put a threat to plant growth, induced serious nitrate contamination to local water, and caused high nitrous oxide loss. Compared with the conventional high N application treatment （1 100 kg N ha^-1） without lime N, the low N application （400 kg N ha^-1） with calcium cyanamide effectively stopped soil acidification as well as achieved the same or slightly higher levels in tea yield and in total N and amino acid contents of tea shoots. The application of calcium cyanamide could be a suitable fertilization for the prevention of environmental problems in tea cultivation.     

Nitrous oxide emission derived from soil organic matter decomposition from tropical agricultural peat soil in central Kalimantan,Indonesia

Our previous research showed large amounts of nitrous oxide (N₂O) emission (>200?kg?N?ha^?1?year^?1) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N₂O fluxes and the source of nitrogen (N) substrate for N₂O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N₂O and carbon dioxide (CO₂) fluxes were measured in three conventionally cultivated croplands (conventional), an unplanted and unfertilized bare treatment (bare) in each cropland, and unfertilized grassland over a three-year period. Based on the difference in N₂O emission from two treatments, contribution of the N source for N₂O was calculated. Nitrous oxide concentrations at five depths (5–80?cm) were also measured for calculating net N₂O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607?kg?N?ha^?1?year^?1. There were no significant differences in between N₂O fluxes in the two treatments at each site. Annual N₂O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858?kg?N?ha^?1?year^?1, respectively. However, there was also no significant difference between annual N₂O emissions in the two treatments at each site. This suggests most of the emitted N₂O was derived from the decomposition of peat. There were significant positive correlations between N₂O and CO₂ fluxes in bare treatment in two croplands where N₂O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N₂O was mainly produced in the surface soil down to 15?cm in the soil. The logarithmic value of the ratio of N₂O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N₂O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N₂O was mainly produced by denitrification at high range of WFPS in surface soil.     

Nitrous oxide and nitric oxide fluxes from cornfield,grassland, pasture and forest in a watershed in Southern Hokkaido,Japan

Abstract

To develop an advanced method for estimating nitrous oxide (N₂O) emission from an agricultural watershed, we used a closed-chamber technique to measure seasonal N₂O and nitric oxide (NO) fluxes in cornfields, grassland, pastures and forests at the Shizunai Experimental Livestock Farm (467 ha) in southern Hokkaido, Japan. From 2000 to 2004, N₂O and NO fluxes ranged from –137 to 8,920 µg N m^?2 h^?1 and from –12.1 to 185 µg N m^?2 h^?1, respectively. Most N₂O/NO ratios calculated on the basis of these N₂O and NO fluxes ranged between 1 and 100, and the log-normal N₂O/NO ratio was positively correlated with the log-normal N₂O fluxes (r ² = 0.346, P < 0.01). These high N₂O fluxes, therefore, resulted from increased denitrification activity. Annual N₂O emission rates ranged from –1.0 to 81 kg N ha^?1 year^?1 (average = 6.6 kg N ha^?1). As these emission values varied greatly and included extremely high values, we divided them into two groups: normal values (i.e. values lower than the overall average) and high values (i.e. values higher than average). The normal data were significantly positively correlated with N input (r ² = 0.61, P < 0.01) and the “higher” data from ungrazed fields were significantly positively correlated with N surplus (r ² = 0.96, P < 0.05). The calculated probability that a high N₂O flux would occur was weakly and positively correlated with precipitation from May to August. This probability can be used to represent annual variation in N₂O emission rates and to reduce the uncertainty in N₂O estimation.     

树冠微域环境对茶树碳氮代谢的影响

【目的】树冠微域环境对植物的生长有着显著影响,改善植物树冠环境可提升收获对象的品质。因此茶树的生长特别是其碳氮代谢及茶叶品质可能会受到树冠微域环境影响,本文拟通过覆盖遮荫的方式人为改变茶树树冠微域环境,以探明树冠微域环境对茶树碳氮代谢等的影响。【方法】采用田间小区试验,通过在茶树树冠面上分别覆盖光热透过性能不同的三种遮荫材料,人为改变茶树树冠面的微域环境,以不覆盖为对照,比较不同树冠微域环境条件下树冠面空气温度、空气湿度、光照等环境因子的变化及光合速率等的差异,并通过氨基酸组分分析及高效液相色谱等方法对不同季节茶树新梢中碳氮初级代谢产物进行分析,以比较树冠微域环境变化对茶树碳氮代谢及茶鲜叶品质等的影响。【结果】茶树树冠面经三种光热透过性能不同的遮阳网在蓬面直接覆盖后,茶树新梢的生长小环境及碳氮代谢均发生了变化: 1）树冠面的光照强度、空气温度及叶片温度均得到了不同程度的降低,空气相对湿度得到了不同程度的提高。其中覆盖隔热网的降温效果最好,降温幅度最高可达3.1℃;覆盖银色网在早晚有较好的降温效果,降温幅度可达1.6℃,但在12时、14时和16时未有明显的降温效果。而覆盖黑网后早晨的树冠面空气温度与叶片温度却显著高于其他各处理,且随着外界温度的升高,黑网下的两种温度与不覆盖比表现出了波动现象。2）茶树被覆盖后,其净光合速率表现出显著的降低趋势,其中黑网覆盖处理与不覆盖处理均在中午12点左右出现一个低谷,出现了午睡现象,而银色网与隔热网覆盖处理没有表现出午睡现象;覆盖后茶树叶片胞间CO2浓度较不覆盖表现出升高趋势,其中以隔热网处理为最高。3）在高温强光季节对茶树进行适度遮荫覆盖,能在一定程度上促进茶树氮代谢,减弱茶树碳代谢,改善各季茶树新梢的品质。主要表现为茶新梢的叶绿素含量、氮磷钾等养分含量、游离氨基酸总量显著增加;氨基酸组分如茶氨酸、谷氨酸、天冬氨酸等也均表现出显著增加趋势;茶新梢中总碳含量及茶多酚等碳水化合物含量降低;总碳、C/N、茶多酚含量等显著降低,儿茶素组分降低但儿茶素品质指数增加、苦涩味指数降低;三种茶树微域环境中,隔热网覆盖的树冠环境对茶叶品质提升方面效果最明显。4）与不覆盖相比,茶树新梢产量表现出了降低的趋势。【结论】通过遮荫覆盖等方式调控茶树树冠微域环境会影响茶树碳氮代谢等生理活动、提高茶鲜叶品质,但茶鲜叶的产量表现出降低的趋势。     

Nitrous oxide emissions from arable soils in Germany — An evaluation of six long‐term field experiments

In this study emissions of N₂O from arable soils are summarized using data from long‐term N₂O monitoring experiments. The field experiments were conducted at six sites in Germany between 1992 and 1997. The annual N‐application rate ranged from 0 to 350 kg N ha^—1. Mineral and organic N‐fertilizer applications were temporarily split adapted to the growth stage of each crop. N‐fertilizer input and N‐yield by the crops were used to calculate the In/Out‐balance. The closed chamber technique was applied to monitor the N₂O fluxes from soil into the atmosphere. If possible, plants were included in the covers. Annual N₂O emission values were based on flux rate measurements of an entire year. The annual N₂O losses ranged from 0.53 to 16.78 kg N₂O‐N ha^—1 with higher N₂O emissions from organically fertilized plots as compared to minerally fertilized plots. Approximately 50% of the total annual emissions occurred during winter. No significant relationship between annual N₂O emissions and the respective N‐fertilization rate was found. This was attributed to site‐ and crop‐specific effects on N₂O emission. The calculation of the N₂O emission per unit N‐yield from winter cereal plots indicates that the site effect on N₂O emission is more important than the effect of N‐fertilization. From unfertilized soils at the sites Braunschweig and Timmerlah a N‐yield of 60.0 kg N ha^—1 a^—1 and N₂O emissions of 2 kg N ha^—1 a^—1 were measured. This high background emission was assigned to the amount and turnover of soil organic matter. For a crop rotation at the sites Braunschweig and Timmerlah the N In/Out‐balance over a period of four years was identified as a suitable predictor of N₂O emissions. This parameter characterizes the efficiency of N‐fertilization for crop production and allows for N‐mineralization from the soil.     

Influence of increasing temperature and nitrogen input on greenhouse gas emissions from a desert steppe soil in Inner Mongolia

We investigated the effect of increasing soil temperature and nitrogen on greenhouse gas (GHG) emissions [carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O)] from a desert steppe soil in Inner Mongolia, China. Two temperature levels (heating versus no heating) and two nitrogen (N) fertilizer application levels (0 and 100?kg?N?ha^?1?year^?1) were examined in a complete randomized design with six replications. The GHG surface fluxes and their concentrations in soil (0 to 50?cm) were collected bi-weekly from June 2006 to November 2007. Carbon dioxide and N₂O emissions were not affected by heating or N treatment, but compared with other seasons, CO₂ was higher in summer [average of 29.6 versus 8.6?mg carbon (C) m^?2?h^?1 over all other seasons] and N₂O was lower in winter (average of 2.6 versus 4.0?mg?N?m^?2?h^?1 over all other seasons). Desert steppe soil is a CH₄ sink with the highest rate of consumption occurring in summer. Heating decreased CH₄ consumption only in the summer. Increasing surface soil temperature by 1.3°C or applying 100?kg?ha^?1?year^?1 N fertilizer had no effect on the overall GHG emissions. Seasonal variability in GHG emission reflected changes in temperature and soil moisture content. At an average CH₄ consumption rate of 31.65?µg?C?m^?2?h^?1, the 30.73 million ha of desert steppe soil in Inner Mongolia can consume (sequestrate) about 85?×?10^6?kg CH₄-C, an offset equivalent to 711?×?10^6?kg CO₂-C emissions annually. Thus, desert steppe soil should be considered an important CH₄ sink and its potential in reducing GHG emission and mitigating climate change warrants further investigation.     

Nitrous oxide emissions in a winter wheat – summer maize double cropping system under different tillage and fertilizer management

An accurate estimation of nitrous oxide (N₂O) emission from 110 million ha of upland in China is essential for the adoption of effective mitigation strategies. In this study, the effects of different tillage practices combined with nitrogen (N) fertilizer applications on N₂O emission in soils were considered for a winter wheat (Triticum aestivum L.) – summer maize (Zea mays L.) double cropping system. Treatments included conventional tillage plus urea in split application (CTF1), conventional tillage with urea in a single application (CTF2), no‐tillage with straw retained plus reduced urea in a split application (NTSF1) and no‐tillage with manure plus reduced urea in a split application (NTMF1). The amounts of N input in each treatment were 285 and 225 kg N/ha for wheat and maize, respectively. Both NTSF1 and NTMF1 were found to reduce chemical N fertilizer rates by 33.3% (wheat) and 20% (maize), respectively, compared to CTF1 and CTF2. N₂O emissions varied between 3.2 (NTSF1) and 9.9 (CTF2) kg N₂O‐N/ha during the wheat season and between 7.6 (NTFS1) and 14.0 (NTMF1) kg N₂O‐N/ha during the maize season. The yield‐based emission factors ranged from 21.9 (NTSF1) to 60.9 (CTF2) g N₂O‐N/kg N for wheat and 92.5 (NTSF1) to 157.4 (NTMF1) g N₂O‐N/kg N for maize. No significant effect of the treatments on crop yield was found. In addition to reducing production costs involved in land preparation, NTSF1 was shown to decrease chemical fertilizer input and mitigate N₂O emissions while sustaining crop yield.