Characterization of yield and cumulative nitrous oxide emission of maize varieties in responses to different nitrogen application rates

The nitrogen use efficiency (NUE) of maize is usually below 60%. Considering future food supply and climate change, selective breeding of maize with high nitrogen (N)-efficient varieties, covering genetic diversities, is an effective strategy for identifying specific elements for controlling NUE and productivity per arable farming unit while reducing environmental damage. This study evaluated the yield and nitrous oxide (N₂O) emission of 30 maize varieties under two different N doses of 57.5 kg N ha^-1 (N1, N-sufficient) and 173 kg N ha^-1 (N3, N-high) applied in two equal splits on 2 and 4 weeks after germination (WAG). Then, the tested maize varieties were categorized into four groups based on the grain yield and cumulative N₂O, that is, efficient-efficient (EE) under both N1 and N3, high-N efficient (HNE) under N3 only, low-N efficient (LNE) under N1 only, and nonefficient-nonefficient (NN) under neither N1 nor N3. Maize yield was significantly positively correlated with shoot biomass, N-accumulation, and kernel-number under N1 and with N₂O-flux at 5 WAG, NH₄⁺, shoot biomass, and all of yield components under N3, whereas cumulative N₂O showed a significant positive correlation with NO₃^- under N3 only and with N₂O flux at 3 WAG under both N levels. The EE generally showed higher grain yield, yield components, N-accumulation, dry matter accumulation, root volume, and NH₄⁺ in soil and lower cumulative N₂O and NO₃^- in soil relative to NN maize varieties. The EE variety groups of maize can be a feasible strategy for increasing N fertilizer efficiency without reducing maize production as well as decrease the negative impact of N lost in agricultural system.

Effective nitrogen removal during different periods of a field-scale bioretention system

Bioretention systems are designed to manage stormwater, but they are always subject to substantial nitrate leaching. In previous laboratory-scale experiments, nitrate removal was enhanced using wood chips as a medium. However, the ability of field-scale systems to transform and remove nitrogen species is not well understood. Here, we report a wood-chip bioretention system that accepts the natural runoff from an elevated highway. The transformation of different nitrogen species indicates that the field-scale system with wood chips also inhibits nitrogen leaching. Nitrate removal was mainly found during the wet period, and was affected by the hydraulic loading rate of the system. Overall, this study showed that the field performance of the wood-chip bioretention system effectively removes nitrogen. In addition, the main period associated with the nitrogen removal process was identified.

The Importance of the Microbial N Cycle in Soil for Crop Plant Nutrition

Nitrogen is crucial for living cells, and prior to the introduction of mineral N fertilizer, fixation of atmospheric N2 by diverse prokaryotes was the primary source of N in all ecosystems. Microorganisms drive the N cycle starting with N2 fixation to ammonia, through nitrification in which ammonia is oxidized to nitrate and denitrification where nitrate is reduced to N2 to complete the cycle, or partially reduced to generate the greenhouse gas nitrous oxide. Traditionally, agriculture has relied on rotations that exploited N fixed by symbiotic rhizobia in leguminous plants, and recycled wastes and manures that microbial activity mineralized to release ammonia or nitrate. Mineral N fertilizer provided by the Haber-Bosch process has become essential for modern agriculture to increase crop yields and replace N removed from the system at harvest. However, with the increasing global population and problems caused by unintended N wastage and pollution, more sustainable ways of managing the N cycle in soil and utilizing biological N2 fixation have become imperative. This review describes the biological N cycle and details the steps and organisms involved. The effects of various agricultural practices that exploit fixation, retard nitrification, and reduce denitrification are presented, together with strategies that minimize inorganic fertilizer applications and curtail losses. The development and implementation of new technologies together with rediscovering traditional practices are discussed to speculate how the grand challenge of feeding the world sustainably can be met.

Data Build-up for the Construction of Korean Specific Greenhouse Gas Emission Inventory in Livestock Categories

Many studies on methane (CH₄) and nitrous oxide (N₂O) emissions from livestock industries have revealed that livestock production directly contributes to greenhouse gas (GHG) emissions through enteric fermentation and manure management, which causes negative impacts on animal environment sustainability. In the present study, three essential values for GHG emission were measured; i.e., i) maximum CH₄ producing capacity at mesophilic temperature (37°C) from anaerobically stored manure in livestock category (B_0,KM, Korean livestock manure for B₀), ii) EF_3(s) value representing an emission factor for direct N₂O emissions from manure management system S in the country, kg N₂O-N kg N⁻¹, at mesophilic (37°C) and thermophilic (55°C) temperatures, and iii) N_ex(T) emissions showing annual N excretion for livestock category T, kg N animal⁻¹ yr⁻¹, from different livestock manure. Static incubation with and without aeration was performed to obtain the N₂O and CH₄ emissions from each sample, respectively. Chemical compositions of pre- and post-incubated manure were analyzed. Contents of total solids (% TS) and volatile solid (% VS), and the ratio of carbon to nitrogen (C/N) decrease significantly in all the samples by C-containing biogas generation, whereas moisture content (%) and pH increased after incubation. A big difference of total nitrogen content was not observed in pre- and post-incubation during CH₄ and N₂O emissions. CH₄ emissions (g CH₄ kg VS⁻¹) from all the three manures (sows, layers and Korean cattle) were different and high C/N ratio resulted in high CH₄ emission. Similarly, N₂O emission was found to be affected by % VS, pH, and temperature. The B_0,KM values for sows, layers, and Korean cattle obtained at 37°C are 0.0579, 0.0006, and 0.0828 m³ CH₄ kg VS⁻¹, respectively, which are much less than the default values in IPCC guideline (GL) except the value from Korean cattle. For sows and Korean cattle, N_ex(T) values of 7.67 and 28.19 kg N yr⁻¹, respectively, are 2.5 fold less than those values in IPCC GL as well. However, N_ex(T) value of layers 0.63 kg N yr⁻¹ is very similar to the default value of 0.6 kg N yr⁻¹ in IPCC GLs for National greenhouse gas inventories for countries such as South Korea/Asia. The EF_3(s) value obtained at 37°C and 55°C were found to be far less than the default value.

Biochemical characterization of the purple form of Marinobacter hydrocarbonoclasticus nitrous oxide reductase

Nitrous oxide reductase (N(2)OR) catalyses the final step of the denitrification pathway-the reduction of nitrous oxide to nitrogen. The catalytic centre (CuZ) is a unique tetranuclear copper centre bridged by inorganic sulphur in a tetrahedron arrangement that can have different oxidation states. Previously, Marinobacter hydrocarbonoclasticus N(2)OR was isolated with the CuZ centre as CuZ*, in the [1Cu(2+) : 3Cu(+)] redox state, which is redox inert and requires prolonged incubation under reductive conditions to be activated. In this work, we report, for the first time, the isolation of N(2)OR from M. hydrocarbonoclasticus in the 'purple' form, in which the CuZ centre is in the oxidized [2Cu(2+) : 2Cu(+)] redox state and is redox active. This form of the enzyme was isolated in the presence of oxygen from a microaerobic culture in the presence of nitrate and also from a strictly anaerobic culture. The purple form of the enzyme was biochemically characterized and was shown to be a redox active species, although it is still catalytically non-competent, as its specific activity is lower than that of the activated fully reduced enzyme and comparable with that of the enzyme with the CuZ centre in either the [1Cu(2+) : 3Cu(+)] redox state or in the redox inactive CuZ* state.

The 18O signature of biogenic nitrous oxide is determined by O exchange with water

To effectively mitigate emissions of the greenhouse gas nitrous oxide (N(2)O) it is essential to understand the biochemical pathways by which it is produced. The (18)O signature of N(2)O is increasingly used to characterize these processes. However, assumptions on the origin of the O atom and resultant isotopic composition of N(2)O that are based on reaction stoichiometry may be questioned. In particular, our deficient knowledge on O exchange between H(2)O and nitrogen oxides during N(2)O production complicates the interpretation of the (18)O signature of N(2)O.Here we studied O exchange during N(2)O formation in soil, using a novel combination of (18)O and (15)N tracing. Twelve soils were studied, covering soil and land-use variability across Europe. All soils demonstrated the significant presence of O exchange, as incorporation of O from (18)O-enriched H(2)O into N(2)O exceeded their maxima achievable through reaction stoichiometry. Based on the retention of the enrichment ratio of (18)O and (15)N of NO(3)(-) into N(2)O, we quantified O exchange during denitrification. Up to 97% (median 85%) of the N(2)O-O originated from H(2)O instead of from the denitrification substrate NO(3)(-).We conclude that in soil, the main source of atmospheric N(2)O, the (18)O signature of N(2)O is mainly determined by H(2)O due to O exchange between nitrogen oxides and H(2)O. This also challenges the assumption that the O of N(2)O originates from O(2) and NO(3)(-), in ratios reflecting reaction stoichiometry.