Ammonia and nitrous oxide emissions from two acidic soils of Nova Scotia fertilised with liquid hog manure mixed with or without dicyandiamide

Effects of dicyandiamide and Mg/P on the global warming potential of swine slurry and sawdust cocomposting

Composting is an emerging strategy for swine slurry treatment; nonetheless, significant greenhouse gases (GHG) emissions may occur during this process. We carried out two separate assays with increasing doses of dicyandiamide (DCD; up to 1.1% w/w) as a nitrification inhibitor and solutions of MgCl₂ and H₃PO₄ (Mg/P; up to 0.09/0.06 mol kg^-1) to promote struvite crystallization in order to assess their efficiencies as additives to decrease GHG emission during swine slurry cocomposting with sawdust (1:1v/v). We monitored the nitrous oxide (N₂O-N), methane (CH₄-C), and carbon dioxide (CO₂-C) emissions and the ammonia (NH₄⁺-N) and nitrate/nitrite (NOx-N) concentrations in compost reactors (35 L) during the first 4-5 weeks of composting. DCD had no effect on CH₄-C and CO₂-C emissions but decreased N₂O-N losses by up to 56% compared with control. However, DCD inactivation was favored by thermophilic conditions and N₂O-N emissions increased to same levels of control after 13 days. Mg/P was effective to decrease N₂O-N losses only at the highest dose, which also sustained higher [NH₄⁺-N] in the compost by the end of the assessment. Nonetheless, the use of 0.09/0.06 mol kg^-1 of Mg/P also decreased CH₄-C and CO₂-C emissions compared with lower doses of Mg/P and unamended treatments. Overall, DCD and Mg/P amendments decreased the global warming potential (GWP) of swine slurry composting by up to 46 and 28%, respectively. The Mg/P application may be also interesting to increase the compost quality by increasing its NH₄⁺-N availability. Graphical abstract.

Winter-Season Gaseous Nitrogen Emissions in Subtropical Climate: Impacts of Pig Slurry Injection and Nitrification Inhibitor

Controlling nitrogen (N) losses from pig slurry (PS) is a challenge under no-till because amendments are left on the soil surface. We investigated the potential of shallow injection of PS, with and without addition of the nitrification inhibitor dicyandiamide (DCD), to abate gaseous ammonia (NH) and nitrous oxide (NO) emissions in winter crops in subtropical soils. Injection was compared with surface broadcasting of PS, with and without DCD. The significance of winter season on annual NO emissions was assessed. Injecting PS reduced NH volatilization compared with surface application. However, this reduction was partly offset because NO emissions increased by 77% (+1.53 kg NO-N ha) when PS was injected. Adding DCD to injected PS reduced NO emission below levels of surface-broadcast PS without the inhibitor, indicating that DCD may be a management option when injecting PS. Compared with a reference urea treatment, PS without DCD increased cumulative NO emissions 5.7-fold (from 613 to 3515 g NO-N ha) when injected, and 3.2-fold (from 613 to 1980 g NO-N ha) when surface applied. Adding DCD significantly reduced emissions with injected PS, whereas reduction was not always significant with surface-applied PS. Nitrous oxide emissions during the winter cropping season contributed 30 to 44% of annual emissions, indicating that controlling gaseous N losses in that season is required to reduce the environmental footprint of the whole cropping system. Overall, combining PS injection with DCD was an efficient practice for reducing winter-season gaseous N losses from no-till soils under subtropical climate.

CO2 and N2O Emissions from Spring Maize Soil under Alternate Irrigation between Saline Water and Groundwater in Hetao Irrigation District of Inner Mongolia, China

Alternative irrigation between saline water and groundwater can alleviate shortages of available agricultural water while effectively slowing the adverse effects of saline water on the soil-crop system when compared with continuous irrigation with saline water and blending irrigation between saline water and groundwater. In 2018, we tested the effect on soil CO₂ and N₂O emissions by two types of irrigation regimes (alternating groundwater and saline water (GW-SW), and alternating groundwater, followed by two cycles of saline water (GW-SW-SW)) between groundwater and three levels of salinity of irrigation water (mineralization of 2 g/L, 3.5 g/L, and 5 g/L), analyzed the correlation between gas emissions and soil properties, calculated comprehensive global warming potential (GWP), and investigated the maize yield. The results show that, with the same alternate irrigation regime, cumulative CO₂ emissions decreased with increasing irrigation water salinity, and cumulative N₂O emissions increased. Cumulative CO₂ emissions were higher in the GW-SW regime for the same irrigation water salinity, and cumulative N₂O emissions were higher in the GW-SW-SW regime. The GW-SW-SW regime had less comprehensive GWP and maize yield as compared to the GW-SW regime. The 2 g/L salinity in both regimes showed larger comprehensive GWP and maize yield. The 3.5 g/L salinity under the GW-SW regime will be the best choice while considering that the smaller comprehensive GWP and the larger maize yield are appropriate for agricultural implication. Fertilizer type and irrigation amount can be taken into consideration in future research direction.

N2O emission characteristics and its affecting factors in rain-fed potato fields in Wuchuan County, China

Representing an important greenhouse gas, nitrous oxide (N₂O) emission from cultivated land is a hot topic in current climate change research. This study examined the influences of nitrogen fertilisation, temperature and soil moisture on the ammonia monooxygenase subunit A (amoA) gene copy numbers and N₂O emission characteristics. The experimental observation of N₂O fluxes was based on the static chamber-gas chromatographic method. The ammonia-oxidising bacteria (AOB) and ammonia-oxidising archaea (AOA) gene copy numbers in different periods were measured by real-time polymerase chain reaction (PCR). The results indicated that rain-fed potato field was a N₂O source, and the average annual N₂O emission was approximately 0.46 ± 0.06 kgN₂O-N/ha/year. N₂O emissions increased significantly with increase in fertilisation, temperatures below 19.6 °C and soil volumetric water content under 15%. Crop rotation appreciably decreases N₂O emissions by 34.4 to 52.4% compared to continuous cropping in rain-fed potato fields. The significant correlation between N₂O fluxes and AOB copy numbers implied that N₂O emissions were primarily controlled by AOB in rain-fed potato fields. The research has important theoretical and practical value for understanding N₂O emissions from rain-fed dry farmland fields.

Impact of dicyandiamide on emissions of nitrous oxide, nitric oxide and ammonia from agricultural field in the North China Plain

Nitrous oxide (N2O), nitric oxide (NO) and ammonia (NH3) emissions from an agricultural field in the North China Plain were compared for three treatments during a whole maize growing period from 26 June to 11 October, 2012. Compared with the control treatment (without fertilization, designated as CK), remarkable pulse emissions of N2O, NO and NH3 were observed from the normal fertilization treatment (designated as NP) just after fertilization, whereas only N2O and NH3 pulse emissions were evident from the nitrification inhibitor treatment (designated as ND). The reduction proportions of N2O and NO emissions from the ND treatment compared to those from the NP treatment during the whole maize growing period were 31% and 100%, respectively. A measurable increase of NH3 emission from the ND treatment was found with a cumulative NH3 emission of 3.8 ± 1.2 kg N/ha, which was 1.4 times greater than that from the NP treatment (2.7 ± 0.7 kg N/ha).

Injection of Dicyandiamide-Treated Pig Slurry Reduced Ammonia Volatilization without Enhancing Soil Nitrous Oxide Emissions from No-Till Corn in Southern Brazil

There is a lack of information on how placement in soil and nitrification inhibitors affects nitrous oxide (NO) and ammonia (NH) emissions from pig slurry (PS) applied under no-till (NT) conditions. Our objective was to determine the impact of injecting PS and treating it with the nitrification inhibitor dicyandiamide (DCD) on NH and NO emissions from soils under NT in subtropical southern Brazil. The emissions of these gases were compared for shallow (∼ 10 cm) injection and surface broadcasting of PS with and without DCD (8.1-10.0 kg ha; 6.5-8.4% of applied NH-N). Measurements were made at two sites during two summer growing seasons under NT corn crops. Injection reduced NH volatilization by 70% but increased NO emissions 2.4-fold (from 2628 to 6198 g NO N ha) compared with surface broadcast application. Adding DCD to PS inhibited nitrification and reduced NO emissions by an average of 28% (730 g NO-N ha) for surface broadcast and 66% (4105 g NO-N ha) for injection but did not increase NH volatilization. Consequently, NO emission factors were much higher for injection (3.6%) than for surface broadcast (1.3%) application and were reduced (0.9%) when DCD was added to injected PS. In conclusion, the injection of DCD-treated slurry is a recommendable practice for reducing NH and NO emissions when applying PS on NT corn in southern Brazil.

Greenhouse gas emissions from two soils receiving nitrogen fertilizer and swine manure slurry

The interactive effects of soil texture and type of N fertility (i.e., manure vs. commercial N fertilizer) on N(2)O and CH(4) emissions have not been well established. This study was conducted to assess the impact of soil type and N fertility on greenhouse gas fluxes (N(2)O, CH(4), and CO(2)) from the soil surface. The soils used were a sandy loam (789 g kg(-1) sand and 138 g kg(-1) clay) and a clay soil (216 g kg(-1) sand, and 415 g kg(-1) clay). Chamber experiments were conducted using plastic buckets as the experimental units. The treatments applied to each soil type were: (i) control (no added N), (ii) urea-ammonium nitrate (UAN), and (iii) liquid swine manure slurry. Greenhouse gas fluxes were measured over 8 weeks. Within the UAN and swine manure treatments both N(2)O and CH(4) emissions were greater in the sandy loam than in the clay soil. In the sandy loam soil N(2)O emissions were significantly different among all N treatments, but in the clay soil only the manure treatment had significantly higher N(2)O emissions. It is thought that the major differences between the two soils controlling both N(2)O and CH(4) emissions were cation exchange capacity (CEC) and percent water-filled pore space (%WFPS). We speculate that the higher CEC in the clay soil reduced N availability through increased adsorption of NH(4)(+) compared to the sandy loam soil. In addition the higher average %WFPS in the sandy loam may have favored higher denitrification and CH(4) production than in the clay soil.

Dicyandiamide application plus incorporation into soil reduces N2O and NH3 emissions from anaerobically digested cattle slurry

Livestock slurry application to land recycles nutrients for plant uptake, but resulting gaseous nitrogen (N) emissions pose a major challenge to the environment. This study was conducted to investigate environmentally friendly methods for the application of anaerobically digested cattle slurry (ADCS) to soil. Application techniques of control (C), surface application (S), incorporation into the soil (I) and soil amendments with and without a nitrification inhibitor (dicyandiamide, DCD) were compared in a small-scale laboratory experiment. Ammonia (NH3) volatilisation mainly occurred within 5 days after ADCS application. Cumulative NH3 volatilisation loss accounted for 57.0, 59.9, 0.7 and 1.4% of applied NH4+-N from surface applied ADCS without and with DCD, and from incorporated ADCS without and with DCD, respectively. Ammonia volatilisation from surface-applied ADCS was 56 times greater than from incorporated ADCS. The nitrous oxide (N2O) emission flux from soil where ADCS was surface-applied without DCD was significantly (P < 0.01) higher than that from the other treatments. The DCD supplement significantly (P < 0.05) reduced N2O flux from surface-applied and incorporated ADCS. Therefore, the cumulative N2O emission loss from the soil where ADCS was surface-applied was significantly greater than that from the incorporated slurry regardless of the DCD supplement. Total inorganic N (TIN) in the soil for all treatments remained constant, although NH4+-N contents in the soil without DCD decreased continuously and nitrate nitrogen (NO3–-N) contents increased continuously throughout trials. There were significant (P < 0.01) differences in TIN contents among application techniques. NH3 volatilisation from the surface application was a major cause of the differences. Consequently, the incorporation of ADCS with the DCD supplement could be a potential method to successfully reduce emissions of both NH3 and N2O.