DCD Treatment Research Articles

Active microbial taxa preferentially assimilate inorganic nitrogen in acidic upland soils using a 15N-DNA-SIP approach

Soil endogenous nitrogen is an essential source of crop nitrogen supply. Nitrogen assimilation is a vital transformation process that maintains nitrogen availability and promotes the mineralization of endogenous organic nitrogen in acidic soils. However, the dominant microbial populations that assimilate NH4+ and NO3− in acidic upland soils were unknown, and their response to long-term fertilization remained unclear. In this study, 15N-labeled NH4+ and NO3− were added to acidic upland soils characterized by long-term (32 years) differentiation in organic matter inputs. Glucose was added to facilitate nitrogen assimilation, and a nitrification inhibitor (dicyandiamide, DCD) was added to distinguish the contribution of NH4+ and NO3− assimilation. Results showed that soil inorganic N assimilation mainly occurred in the first week after inorganic N addition. Soil net inorganic N assimilation rates were 0.006–0.42 mg N kg−1 d−1 in the NH4+, NO3− and NH4++DCD treatments. The analysis of 15N-DNA-based stable isotope probing (SIP) found that the majority of inorganic N assimilation in our soils was conducted by a limited number of active microbial taxa, which accounted for 1.4%–2.0% of the entire bacterial community and 15.7%–28.8% of the fungal community. The dominant bacteria governing inorganic N assimilation in acidic upland soils included Bacillus, Burkholderia–Caballeronia–Paraburkholderia and Micrococcaceae. The primary fungi included Penicillium, Chaetomium, Aspergillus, and Fusarium. No obvious bias was detected in nitrogen assimilation rates and the dominant microbial taxa for NH4+-N and NO3−-N. Compared with unfertilized soil, long-term organic matter input decreased the dominating N assimilating microbial taxa. These findings demonstrate the feasibility of 15N-DNA-SIP technology in soil nitrogen cycling research and suggest the importance of active microbial taxa in acidic agricultural soil nitrogen retention and loss.

Cultivation and Nitrogen Management Practices Effect on Soil Carbon Fractions, Greenhouse Gas Emissions, and Maize Production under Dry-Land Farming System

Effective nitrogen management practices by using two cultivation techniques can improve corn productivity and soil carbon components such as soil carbon storage, microbial biomass carbon (MBC), carbon management index (CMI), and water-soluble carbon (WSC). It is essential to ensure the long-term protection of dry-land agricultural systems. However, excessive application of nitrogen fertilizer reduces the efficiency of nitrogen use and also leads to increased greenhouse gas emissions from farming soil and several other ecological problems. Therefore, we conducted field trials under two planting methods during 2019–2020: P: plastic mulching ridges; F: traditional flat planting with nitrogen management practices, i.e., 0: no nitrogen fertilizer; FN: a common nitrogen fertilizer rate for farmers of 290 kg ha−1; ON: optimal nitrogen application rate of 230 kg ha−1; ON75%+DCD: 25% reduction in optimal nitrogen fertilizer rate + dicyandiamide; ON75%+NC: 25% reduction in optimal nitrogen rate + nano-carbon. The results showed that compared to other treatments, the PON75%+DCD treatment significantly increased soil water storage, water use efficiency (WUE), and nitrogen use efficiency (NUE) because total evapotranspiration (ET) and GHG were reduced. Under the PON75%+DCD or PON75%+NC, the soil carbon storage significantly (50% or 47%) increased. The PON75%+DCD treatment is more effective in improving MBC, CMI, and WSC, although it increases gaseous carbon emissions more than all other treatments. Compared with FFN, under the PON75%+DCD treatment, the overall CH4, N2O, and CO2 emissions are all reduced. Under the PON75%+DCD treatment, the area scale GWP (52.7%), yield scale GWP (90.3%), biomass yield (22.7%), WUE (42.6%), NUE (80.0%), and grain yield (32.1%) significantly increased compared with FFN, which might offset the negative ecological impacts connected with climate change. The PON75%+DCD treatment can have obvious benefits in terms of increasing yield and reducing emissions. It can be recommended to ensure future food security and optimal planting and nitrogen management practices in response to climate change.

Comparative Study between Urea and Biogas Digestate Application towards Enhancing Sustainable Fertilization Management in Olive (Olea europaea L., cv. ‘Koroneiki’) Plants

Organic fertilization is a promising strategy to decrease N mineralization rates and high N losses via leaching and denitrification, thus synchronizing N application with N uptake for crops. A 230-day experiment with olive plants was realized under greenhouse conditions to compare urea and biogas digestate (BD) application on the growth, nutrient uptake, and physiological performance of Olea europaea L. plants. The following treatments were applied: (i) UREA, (ii) UREA + DCD (nitrification inhibitor), (iii) BD, (iv) BD + DCD, (v) acidified BD, (vi) acidified BD + DCD, (vii) CONTROL (typical native Marl soil type, without fertilizer application). Under BD application, significantly higher levels of organic matter, Olsen P, and exchangeable K compared to UREA were found. Significantly lower main shoot length and total plant biomass were recorded in the CONTROL soil compared to BD. Foliar N was lower in the ACID.BD and ACID.BD + DCD treatments, while leaf P was lower in UREA. The highest PSII activity was recorded in UREA + DCD, while the highest photosynthetic rate and intercellular CO2 concentration were determined in UREA. It is expected that these data will constitute a first comparative approach between urea and BD application in olive plants, which should be carefully considered, towards boosting sustainable fertilization in the frame of circular economy strategy.

Evaluation of N2O emission from rainfed wheat field in northwest agricultural land in China.

The net greenhouse gas (NGHG) emissions and net greenhouse gas intensity (NGHGI) were investigated via the determination of nitrous oxide (N2O) emission in loess soil under rainfed winter wheat monocropping system during 3years of field study in Northwest China. Five treatments were carried out: control (N0), conventional nitrogen (N) application (NCon), optimized N application with straw (SNOpt), optimized N application with straw and 5% of dicyanodiamide (SNOpt + DCD), and optimized N rate of slow release fertilizer with straw (SSRFOpt). Over a 3-year period, the NGHG emissions were achieved 953, 1322, 564, and 1162kg CO2-eq ha-1, simultaneously, and the NGHGI arrived 158, 223, 86, and 191kg CO2-eq t-1 grain in NCon, SNOpt, SNOpt + DCD, and SSROpt grain, respectively. Contrasted with conventional farming system, optimized farming methods reduced 32% of N fertilizer use without significant decrease in grain yield, but brought about 38% increase in N2O emissions, up to 28% gained in soil CH4 uptake. Thus, it was observed that the straw incorporation performs noticeable increased in N2O emissions in the winter wheat cropping season. Among the optimized N fertilizer rates compared with the SNOpt treatment, the SNOpt +DCD and SSROpt treatments decreased in N2O emissions by approximately 55% and 13%, respectively. Additionally, the N2O emission factor across over a 3-year period was 0.41 ± 0.08% derived from N fertilizer, and it was half of IPCC default values for upland corps. It is expected possibly due to low precipitation and soil moisture with the monocropping system. The 25% higher in the amount of rainfall (almost 300mm in 2013-2014) during a cropping season underwent into 1-2-fold increase in N2O emissions from N-fertilized plots. As the statistical differences among annual cumulative emissions coincided with that during winter wheat growing season, it can be concluded that crop growing season is a vital important period for the determination of N2O emissions from under rainfed monocropping system.

Relative contributions of implant hydrophilicity and nanotopography to implant anchorage in bone at Early Time Points

To compare the contributions of implant hydrophilicity and nanotopography on anchorage in bone. The effect of elevated calcium surface chemistry on bone anchorage was also investigated. A full factorial study design was implemented to evaluate the effects of ultraviolet (UV) light and/or sodium lactate (SL) and discrete crystalline deposition of nanocrystals (DCD) treatments on the osseointegration of dual acid-etched (AE) titanium alloy (Ti6Al4V) and grit blasted and AE (BAE) commercially pure titanium (CpTi) implants. Sodium hydroxide (NaOH)-treated CpTi implants were immersed in simulated body fluid (SBF) to increase calcium surface chemistry. Implants were placed in the femora of Wistar rats and tested using pull-out testing (BAE implants: 5, 9, 14days) or tensile testing (AE implants: 9days, NaOH implants: 28days). Ti6Al4V-AE implants with DCD- and UV-treated surfaces significantly increased bone anchorage compared with untreated Ti6Al4V-AE alloy implants. Pull-out testing of BAE-CpTi implants with the DCD treatment showed increased disruption force values compared with surfaces without the DCD treatment at 5, 9 and 14days by 4.1N, 13.9N and 15.5N, respectively, and UV-treated implants showed an increase at 14days by 8.4N. No difference was found between NaOH+SBF and NaOH+H2 O groups. Bone anchorage of implants was found to be improved by UV-treating implants or nanotopographically complex surfaces. However, implant nanotopography was found to have a greater contribution to the overall bone anchorage and is more consistent compared with the time-dependent nature of the UV treatment.

Effects of nitrogen fertilizer application on carbon dioxide emissions from soils with different inorganic carbon contents.

The application of nitrogen (N) fertilizer results in decreases of soil pH, but its effects on CO2 emission from soils with different inorganic carbon contents remain unclear. An closed-jar incubation experiment was conducted to examine the effects of N fertilizer and nitrification inhibitor (DCD) on soil pH and CO2 emissions from three soil types with different contents of soil inorganic carbon (SIC), including paddy soil (PS), lime concretion black soil (CS), and eum-orthic anthrosols (AS). There were three treatments for each soil type, including control (N0), 0.2 g·kg-1 N fertilizer (N0.2), and its combination with DCD (N0.2+DCD). Soil pH, contents of mineral N (NH4+, NO3-), and CO2 emissions were measured. The results showed that N fertilizer addition significantly reduced soil pH and increased soil CO2 cumulative emissions in each type of soil. Compared to control, the CO2 cumulative emissions after 49 days incubation from the three soil types were enhanced by 39.4%, 23.4%, and 71.8% for PS, CS, AS soils, respectively. The soil pH of N0.2+DCD for three soil types were significantly higher than N0.2 after 49 days incubation, indicating that DCD application inhibited soil nitrification process. There were no significant differences in the mean CO2 cumulative emissions of PS and CS soils between N0.2 and N0.2+DCD treatments; however, N0.2+DCD treatment significantly reduced cumulative CO2 emissions from AS soil by 12.5%. Soil inorganic carbon can effectively buffer soil acidification caused by N fertilizer addition. The CO2 emission in calcareous soil following N addition is not only derived from the mineralization of soil organic carbon, but also from the dissolution of inorganic carbon. Given the large differences in soil inorganic carbon content in different regions of China, the problem of soil acidification and soil inorganic carbon pool consumption caused by long-term large amount of N fertilizer inputs deserve more attention.

Variable effects of biochar application to soils on nitrification-mediated N2O emissions

Although a meta-analysis on biochar's effects on N2O emission reported an overall reduction in N2O emission by adding biochar to the soils, there are still variations in the changes in N2O emission, especially from field results. The objectives of this study are 1) to compare the effects of biochar addition on N2O emission between three agricultural upland field experiments, where soil water status was dry favoring nitrification and 2) to identify main factors explaining biochar's variable effects on N2O emission. Three field experiments were conducted: Exp A in the cultivated grassland treated with rice husk biochar at 2 ton ha−1 + urea (CHAR) and with urea only (CON); Exp B in the cabbage field with CHAR and CON treatments; and Exp C in the pepper field with CHAR, CON, and CHAR + DCD (dicyandiamide, nitrification inhibitor) treatments. In Exp A and C, cumulative N2O emissions significantly increased by 82.5% and 55.8% in the CHAR than CON treatments, respectively, while in Exp B, there was no difference in cumulative N2O emission between the CHAR and CON. Based on results from using nitrification inhibitor and soil % water filled pore space (WFPS), we assumed that the main N2O production mechanism was nitrification. Our results suggest that soil water status right after urea application is the primary determinant of different effects of biochar on N2O emission in addition to soil C status and biochar's adsorption. Principal component analysis using the 25 compiled data also supported our results. This study identified the specific field conditions under which biochar could have stimulating effects on N2O emission. Mitigation potential of biochar application should be reconsidered if biochar and urea were amended to dry soils with low C contents.

Effect of Dicyandiamide on N2O Emission in Fallow Paddy Field and Rape Cropping

The emissions of greenhouse gas in winter are often neglected, and the latest research results showed that N2O emissions in fallow paddy field and winter oilseed rape are still large, research on mitigating the N2O flux and the mechanism behind them is of significance for mitigating N2O emissions from agricultural soil. By using static chamber techniques and molecular biology techniques, the N2O emission as well as the community composition and abundance of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) from fallow paddy field, rape cropping with and without DCD treatment in Taoyuan agricultural ecological experiment station of the Chinese Academy of sciences were measured. The results showed that the addition of DCD significantly inhibited N2O emissions in fallow paddy field and rape cropping by 36.7% and 23.6%, respectively. The application of DCD in fallow paddy field inhibited the abundance of AOA and AOB by 59.3% and 73.7%, respectively, but only changed the community structure of AOA. The addition of DCD in rape cropping only changed the community structure and inhibited the abundance of AOB. This research showed that DCD application could effectively mitigate the N2O emissions in fallow paddy field and winter rape cropping under different mitigation mechanisms.

N2O emissions from banana plantations in tropical China as affected by the application rates of urea and a urease/nitrification inhibitor

In this study, we quantified N2O fluxes from banana plantations in China using a field experiment as well as static chamber and gas chromatography techniques. We utilized five levels of urea treatments, including CK (no urea addition); urea addition at a rate of 312 (U1), 415 (U2), 519 (U3), and 623 kg N ha−1 (U4); and a combination of urea (U3) and urease (NBPT) and nitrification (DCD) inhibitor (U3 + I) treatments. Soil temperature, moisture, and the concentrations of NH4 + and NO3 − have been monitored throughout the study. Compared to CK (11.8 μg m−2 h−1 and 14.2 t ha−1, respectively), urea addition significantly increased N2O emission fluxes and banana yields (88.2–177 μg m−2 h−1 and 19.4–25.0 t ha−1, respectively). The stimulation effect of urea on N2O emissions was significantly higher than its effect on banana yield. N2O emission occurred in pulses during banana cultivation due to repeated topdressing. The cumulative N2O emissions and N2O emission factor of urea applied in banana plantations were estimated to be 6.39–12.8 kg N ha−1 and 1.46–2.31 %, respectively. Notably, N2O emissions were significantly positively correlated with urea application rate, temperature, and NH4 + levels, suggesting that temperature and NH4 + availability are the most important factors controlling N2O emissions in tropical banana plantations. Combined NBPT and DCD treatment greatly reduced N2O emissions (by 65.4 %) and increased banana yields (by 4.5 %).

Phytoextraction of Cadmium and Zinc By Sedum plumbizincicola Using Different Nitrogen Fertilizers, a Nitrification Inhibitor and a Urease Inhibitor

Cadmium (Cd) and zinc (Zn) phytoavailability and their phytoextraction by Sedum plumbizincicola using different nitrogen fertilizers, nitrification inhibitor (dicyandiamide, DCD) and urease inhibitor (N-(n-Butyl) thiophosphoric triamide, NBPT) were investigated in pot experiments where the soil was contaminated with 0.99 mg kg−1 of Cd and 241 mg kg−1 Zn. The soil solution pH varied between 7.30 and 8.25 during plant growth which was little affected by the type of N fertilizer. The (NH4)2SO4+DCD treatment produced higher NH4+−N concentrations in soil solution than the (NH4)2SO4 and NaNO3 treatment which indicated that DCD addition inhibited the nitrification process. Shoot Cd and Zn concentrations across all treatments showed ranges of 52.9–88.3 and 2691–4276 mg kg−1, respectively. The (NH4)2SO4+DCD treatment produced slightly higher but not significant Cd and Zn concentrations in the xylem sap than the NaNO3 treatment. Plant shoots grown with NaNO3 had higher Cd concentrations than (NH4)2SO4+DCD treatment at 24.0 and 15.4 mg kg−1, respectively. N fertilizer application had no significant effect on shoot dry biomass. Total Cd uptake in the urea+DCD treatment was higher than in the control, urea+NBPT, urea+NBPT+DCD, or urea treatments, by about 17.5, 23.3, 10.7, and 25.1%, respectively.

Effects of Coated Urea Amended with Biological Inhibitors on Physiological Characteristics, Yield, and Quality of Peanut

Four kinds of new developed urea, some of which were amended with biological inhibitors and coated and some of which were only coated with inorganic materials, were prepared by coating conventional granular urea (nitrogen 46.0%). Using a coated urea [resin-coated urea, 90 day, (RCU)] made in China and a conventional granular urea as check, their effects on physiological characteristics, yield, and quality of peanut were examined in a field experiment. The results indicated that four kinds of urea kept greater ammonium nitrogen (NH4 + -N) and nitrate nitrogen (NO3−N) contents at flowering stage (FS) and podding stage (PS) compared to conventional urea, and coated urea + dicyandiamide + hydroquinone treatment (CU + DCD + HQ) had the greatest contents, being similar to RCU treatment. At FS and PS, the chlorophyll content, photosynthetic rate, transpiration rate, and chlorophyll fluorescence parameters were significantly increased upon CU + DCD, CU + HQ, and CU + HQ + DCD treatments. In addition, CU + HQ + DCD treatment produced 27.3% more pod yield, 6.7% more total yield, and 9.17% more protein content and decreased NO3−-N content by 46.56% as compared to conventional urea treatment. This product has excellent slow-release capacity, is inexpensive and environmentally friendly, and could be especially useful in agricultural application.

硝化抑制剂对蔬菜土硝化和反硝化细菌的影响

Nitrogen(N) loss via nitrate(NO-3) leaching from soil is one of the major contributors to environmental degradation.Vegetable soil is characterized by intensive fertilization with low nitrogen usage efficiency as a result of NO-3 leaching.Nitrification and de-nitrification are the most important processes in NO-3 formation and transformation,and are driven by functional microorganism in soil.The use of nitrification inhibitors,such as DCD,may play a key role in mitigating N loss. Investigations were conducted on the inhibitory effect of DCD to the functional microorganisms among the processes of nitrification and de-nitrification,and the relationship between DCD and nitrogen transformation.In this research,two kinds of vegetable soils were selected from Huangxing country,Changsha,reflecting long-term(about 20 years) and short-term vegetable cropping(1 year).Each sample was a mixture of 5 cores(0—20cm top soil) randomly taken in the same field.Two treatments for each soil sample were conducted: CK treatment(urea at 0.2g N/kg),and DCD treatment(urea at 0.2g N/kg with DCD 0.02g/g),each treatment with 3 replicates.The pots were incubated for 64 days at 25℃,and systematically measured NH+4 and NO-3 concentrations.According to the dynamics of NH+4 transformation,three soil samples were taken at the 3rd,7th and 64th days,which represented the increasing,peak and decreasing status of NH+4 concentration.The abundances of nitrifying gene amoA and denitrifying gene nirK were analyzed by Real-time PCR,. Results indicated that NH+4 concentrations of DCD treatments increased 248% and 225% compared to the CK treatment in the long-term and short term vegetable soils,respectively.NO-3 concentrations of DCD treatments decreased 31% and 20% compared to the CK treatment in the long-term and short-term vegetable soils separately.Furthermore,NH+4 concentration of DCD treated short term soil decreased slightly while long term soil remained the same level,suggesting that DCD had a better effect on long-term vegetable soil.The abundances of 16S rRNA gene and nirK gene had no significant difference between two treatments.However,the amoA gene abundance of DCD treatment for the long-term vegetable soil and the short-term vegetable soil had significantly decreased compared to the CK treatment,61% and 48% respectively on the 3rd day,71% and 54% respectively on the 7th day,but no differences were observed between two treatments after 64 days incubation.There was extremely significant correlation between NO-3 concentration and the amoA gene abundance. The results showed that the process of nitrification could be inhibited by DCD through restraining the growth of nitrifying bacteria.In addition,intensive application of inorganic fertilizer accelerated N element cycle in soil through the shift of composition and abundance of nitrogen-transformation functional microorganism.Thus,it might be better to use DCD together with suitable amount of fertilizer to improve nitrogen fertilizer usage efficiency and reduce nitrate loss.

Effect of nitrogen form on the rhizosphere dynamics and uptake of cadmium and zinc by the hyperaccumulator Thlaspi caerulescens

The effect of N form (NO3− versus NH4+) on growth and uptake of Cd and Zn by the hyperaccumulator Thlaspi caerulescens (Ganges ecotype) was investigated in hydroponic and rhizobox experiments. In the hydroponic experiments, NO3− or NH4+ was supplied to plants with the pH of the nutrient solution being unbuffered or buffered at around 6.0. A moderately contaminated soil was used in the rhizobox experiment with or without additions of NO3−, NH4+ or NH4+ + DCD (dicyanodiamide, a nitrification inhibitor). A higher biomass was obtained when N was supplied as NO3− in both experiments, indicating that T. caerulescens prefers NO3− over NH4+. In the hydroponic experiments, supplying NO3− resulted in a doubling of Cd concentration in the shoots compared with the NH4+ treatment, regardless whether solution pH was buffered or not. The form of N also had a noticeable effect on root Zn concentrations. In the rhizosphere box experiment, rhizosphere pH was markedly influenced by the N treatment. The acidification in the NH4+ and NH4+ + DCD treatments increased the concentrations of extractable Cd and Zn, both of which showed a considerable depletion in the rhizosphere. However, total uptake of Cd and Zn were highest in the NO3− treatment, despite the fact that concentrations of extractable Cd and Zn in the rhizosphere were the lowest in this treatment. The results showed that supplying N as NO3− promoted growth and phytoextraction of Cd and Zn by T. caerulescens compared with NH4+.

Mitigation of N2O and CH4 Emission from Rice and Wheat Cropping Systems Using Dicyandiamide and Hydroquinone

Agriculture contributes considerably to the emission of greenhouse gases, such as N2O and CH4. Here we summarize results from previous pot experiments assessing the effectiveness of urease and nitrification inhibitors reducing both N2O and CH4 emissions from wheat and rice cropping systems fertilized with urea (U). For the wheat cropping system, using a cambisol, we observed that the application of U with hydroquinone (HQ, a urease inhibitor), U with dicyandiamide (DCD, a nitrification inhibitor) and U with HQ plus DCD decreased the N2O emissions by 11.4, 22.3 and 25.1%, respectively. For the rice copping system, using a luvisol, we found that the application of U with HQ, U with DCD and U with HQ plus DCD decreased N2O emissions by 10.6, 47.0 and 62.3%, respectively, and CH4 emissions by 30.1, 53.1 and 58.3%, respectively. In terms of total global warming potential (GWP) a reduction of 61.2% could be realized via the combined addition of HQ and DCD. The addition of wheat straw reduced the activity of HQ and DCD in the rice cropping experiments. In terms of total GWP only a reduction of 30.7% could be achieved. In general, both in upland and flooded conditions, the application of HQ and DCD alone was less effective than HQ in combination with DCD, but not significantly for U plus DCD treatment. Our observations may be further constrained, however, by practical, economic or social problems and should therefore be tested at the scale of a region (e.g. a watershed) and related to an integrated abatement of agricultural N losses.

Wastewater C:N ratio effects on soil hydraulic conductivity and potential mechanisms for recovery

To sustain the performance of a land treatment system, soil hydraulic conductivity must be maintained. Biological clogging of soil pores tends to decrease hydraulic conductivity. The changes in soil biological properties and hydraulic conductivity were examined in repacked soil cores receiving weekly additions of wastewater with three C:N ratios for 28 weeks. We tested whether addition of a nitrification inhibitor (dicyandiamide, DCD) and polysaccharidase enzyme preparation (PEP) with wastewater would maintain hydraulic conductivity. Increases in wastewater C:N ratio increased soil microbial biomass, carbohydrate, and nematode population and decreased nitrate leaching and hydraulic conductivity, by up to 80%. While neither DCD nor PEP treatments lowered soil carbohydrate, both had increased hydraulic conductivity (in the range of 280–290%) in cores irrigated with high C:N wastewater, relative to `nil' treatment wastewater.

Mitigation Alternatives to Decrease Nitrous Oxides Emissions and Urea‐Nitrogen Loss and Their Effect on Methane Flux

AbstractNitrous oxide (N2O) and methane (CH4) are greenhouse gases that are contributing to global warming potential. Nitrogen (N) fertilizer is one of the most important sources of anthropogenic N2O emissions. A field study was conducted to compare N‐use efficiency and effect on N2O and CH4 flux, of urea, urea plus the nitrification inhibitor dicyandiamide (U + DCD), and a control release fertilizer, polyolefin coated urea (POCU) in irrigated spring barley (Hordeum vulgare L.) in northeastern Colorado. Each treatment received 90 kg urea‐N ha−1 and microplots labeled with 15N‐fertilizer were established. Average N2O emissions were 4.5, 5.2, 6.9, and 8.2 g N ha−1 d−1 for control, U + DCD, POCU, and urea, respectively. During the initial 21 d after fertilization, N2O emissions were reduced by 82 and 71% in the U + DCD and POCU treatments, respectively, but continued release of N fertilizer from POCU maintained higher N2O emissions through the remainder of the growing season. No treatment effect on CH4 oxidation in soils was observed. Fertilizer 15N found 50 to 110 cm below the soil surface was lower in the POCU and U + DCD treatments. At harvest, recovery of 15N‐fertilizer in the plant‐soil system was 98, 90, and 85% from POCU, urea, and U + DCD, respectively. Grain yield was 2.2, 2.5, and 2.7 Mg ha−1 for POCU, urea, and U + DCD, respectively. Dicyandiamide and POCU showed the potential to be used as mitigation alternatives to decrease N2O emissions from N fertilizer and movement of N out of the root zone, but N release from POCU does need to be formulated to better match crop growth demands.

Interaction of salinity and enhanced ammonium and potassium nutrition in wheat

Wheat (Triticum aestivum L.) was grown to maturity in a pot experiment in a calcareous silty sand soil. N was applied at two levels as granulated N-P fertilizers, amended or not with nitrification inhibitors (1% and 5% DCD, 1% N-serve). Potassium as KCl was given at three levels of application. P was applied at a uniform rate. Two levels of salinity were obtained by using the soil as such (EC= 0.3 mmho/cm) and by adding NaCl to the same soil (EC=2.4 mmho/cm). 1% DCD and 1% N-serve treatments gave significantly higher wheat grain yields and N-uptake than the other ones. Nitrate content of leachates indicated a prevalent nitrate nutrition in the treatment without nitrification inhibitors. The 5% DCD treatment showed a yield depression. In the lower N level treatments, a significant yield increase, generated by 1% DCD and N-serve was found in the salinized soil as compared to the non-saline soil. Soil salinity reduced N-uptake when nitrification inhibitors were not present. In treatments having the inhibitors, N-uptake was equal or greater in the salinized than in the non saline soil. An enhanced ammonium nutrition increased the P uptake.

Inhibition of nitrification by gamma irradiation in soil under plastic-house conditions

Abstract An incubation experiment was conducted on sandy clay loam soil treated with ammonium sulfate to study the effect of gamma irradiation (100, 200, and 300 krad) and dicyandiamide (DCD, 5 and 10 ppm) as nitrification inhibitors during 12 weeks of incubation under plastic-house conditions. The nitrification process decreased by either gamma irradiation or DCD treatment of soil. In the soil treated with DCD, there were no significant differences between a concentration of 5 and 10 ppm during the period of incubation. In the soil irradiates with 300 krad, the nitrification rate was significantly lower compared with that in the DCD treatment at concentration of 5 and 10 ppm. Nitrification inhibition was low when the soil was subjected to gamma irradiation and DCD treatment during a period of 4 weeks but the inhibition increased after 6 weeks of incubation.