Reduced Nitrogen Input Research Articles

Source identification of nitrate contamination in the urban aquifer of Mashhad, Iran

Study regionUrban aquifer of Mashhad city, northeastern Iran. Study focusMeasuring the ratios of the stable nitrate isotopes and hydrogeochemistry of major components in order to specify the origin of nitrate contamination and potential transformation processes in the aquifer. New hydrological insights for the regionThis study represents the first isotopic characterization of groundwater nitrate to identify the sources of excessive nitrate in the urban aquifer and provides a reference for the potential implementation of executive programs on groundwater quality and protection. Nitrate concentration exceeded the limits for nitrate in drinking water in most of the wells (110 out of 261). Isotopic composition of the oxygen and nitrogen of NO3− in groundwater indicated sewage as the primary source of nitrate contamination. Denitrification was identified as a non-significant process in the aquifer. Concentrations of anions (Cl−, SO42− and PO43−) and NO3− showed strong correlations confirming potential wastewater influence. Most of the groundwater was weakly acidic, and the chemistry of the groundwater was rather affected by urbanization and land-use than by aquifer rock interactions. The absence of a reliable sewer collecting system, particularly in the central and southern parts of the study area, directly resulted in the poor water quality. Considering the lack of natural attenuation processes in the groundwater, management options need to be considered for reducing nitrogen input into groundwater.

A Roadmap for Lowering Crop Nitrogen Requirement.

Increasing nitrogen fertilizer applications have sustained a growing world population in the 20th century. However, to avoid any further associated environmental damage, new sustainable agronomic practices together with new cultivars must be developed. To date the concept of nitrogen use efficiency (NUE) has been useful in quantifying the processes of nitrogen uptake and utilization, but we propose a shift in focus to consider nitrogen responsiveness as a more appropriate trait to select varieties with lower nitrogen requirements. We provide a roadmap to integrate the regulation of nitrogen uptake and assimilation into varietal selection and crop breeding programs. The overall goal is to reduce nitrogen inputs by farmers growing crops in contrasting cropping systems around the world, while sustaining yields and reducing greenhouse gas (GHG) emissions.

Large scale prediction of groundwater nitrate concentrations from spatial data using machine learning

Reducing nitrogen inputs, in particular nitrate, to groundwater is becoming increasingly important to fulfil requirements of the European Water Framework Directive. When developing management plans for mitigation measures at larger scales, complex hydro-biogeochemical models reach their limits due to data availability and spatial discretization. To circumvent this problem, the spatial distribution of nitrate concentration in groundwater is estimated using a parsimonious GIS-based statistical approach. Point nitrate concentrations and spatial environmental data as predictors are used to train statistical models. In order to compile the spatial predictors with the respective monitoring sites, different designs of contributing areas (buffer zones) and their effects on the performance of different statistical models are investigated. Multiple Linear Regression (MLR), Classification and Regression Trees (CART), Random Forest (RF) and Boosted Regression Trees (BRT) are compared in terms of the predictive performance of each model according to various objective functions. We determine the most influential spatial predictors used in the respective models. After training the models with a subset of the data, we then predict the spatial nitrate distribution in groundwater for the entire federal state of Hesse, Germany on a 1 × 1 km grid by only the spatial environmental data. The Random Forest model outperforms the other models (R2 = 0.54), relying on hydrogeological units, the percentage of arable land and the nitrogen balance as the three most influencing predictors based on a 1000 m circular contributing area. The use of exclusively spatial available predictors is a big step forward in the prediction of nitrate in groundwater on regional scale.

Assessing non-intended effects of farming practices on field margin vegetation with a functional approach

To assess the unwanted side effects of farming practices on non-target plants, we used a nationwide survey of the vegetation of arable field margin strips. The vegetation was surveyed during two years (2013, 2014) in 430 field margins distributed over all agricultural regions of France. We used two complementary multivariate, trait-based approaches to examine how ten plant traits were related to ten environmental variables describing abiotic conditions, landscape factors, field margin management and in-field practices. Generalized additive mixed models were also developed to assess how the same environmental variables correlated with species richness, functional diversity and relative richness of agrotolerant versus hemerophobic species. Traits responded primarily to an environmental gradient of landscape diversity and field margin management. For instance, narrow field margin strips, frequent management and presence of a ditch favoured annual plants, small size at maturity and perennial plants, respectively. The second environmental gradient affecting plant traits was related to field size and intensity of in-field farming practices. On this gradient, fertilizer drift appeared to have a much stronger effect on plant trait composition of field margin strips than herbicide drift. The relationship between species richness, or functional diversity, and environment was consistent with the trait-based approach: the two former variables were negatively correlated with agriculture intensification (e.g. field size). However, this analysis also highlighted new covariates, such as a negative relationship between frequency of herbicide use and species richness. Some of the observed patterns seemed to be driven by differential responses of agrotolerant versus hemerophobic species, with the latter being more species-rich under organic than under conventional farming. Despite efforts to reduce nitrogen inputs since the 2000s, our results shows that N-fertilization still has significant non-intended effects on field margin vegetation. More generally, increasing the width of field margin strips, keeping or restoring semi-natural elements (ditches, hedges) in the field boundary, and lowering the number of management events may promote grassland plant species more typical of semi-natural habitats.

Nutrient- and Climate-Induced Shifts in the Phenology of Linked Biogeochemical Cycles in a Temperate Estuary

The response of estuarine ecosystems to long-term changes in external forcing is strongly mediated by interactions between the biogeochemical cycling of carbon, oxygen, and inorganic nutrients. Although long-term changes in estuaries are often assessed at the annual scale, phytoplankton biomass, dissolved oxygen concentrations, and biogeochemical rate processes have strong seasonal cycles at temperate latitudes. Thus, changes in the seasonal timing, or phenology, of these key processes can reveal important features of long-term change and help clarify the nature of coupling between carbon, oxygen, and nutrient cycles. Changes in the phenology of estuarine processes may be difficult to assess, however, because many organisms are mobile and migratory, key primary and secondary producers have relatively rapid physiological turnover rates, sampling in time and space is often limited, and physical processes may dominate variability. To overcome these challenges, we have analyzed a 32-year record (1985-2016) of relatively frequent and consistent measurements of chlorophyll-a, dissolved oxygen, nitrogen, and physical drivers to understand long-term change in Chesapeake Bay. Using a suite of metrics that directly test for altered phenology, we quantified changes in the seasonal timing of key biogeochemical events, which allowed us to illustrate spatially- and seasonally-dependent shifts in the magnitude of linked biogeochemical parameters. Specifically, we found that a modest reduction in nitrate input was linked to a suppression of spring phytoplankton biomass in seaward Bay regions. This was, in turn, associated with an earlier breakup in hypoxia and decline in late-summer NH4+ accumulation in seaward waters. In contrast, we observed an increase in winter phytoplankton biomass in landward regions, which was associated with elevated early summer hypoxic volumes and NH4+ accumulation. Seasonal shifts in oxygen depletion and NH4+ accumulation are consistent with reduced nitrogen inputs, spatial patterns of chlorophyll-a, and increases in temperature. In addition, these increases have likely elevated rates of organic matter degradation, thus “speeding-up” the typical seasonal cycle. The causes for the recent landward shift in phytoplankton biomass and NH4+ accumulation are less clear; however, these altered patterns are analyzed here and discussed in terms of numerous physical, climatic, and biological changes in the estuary.

Drought‐adapted plants dramatically downregulate dinitrogen fixation: Evidences from Mediterranean legume shrubs

Abstract The importance of symbiotic dinitrogen (N2) fixation in shaping the coupled nitrogen–carbon cycle is now known for most humid terrestrial ecosystems. However, whether N2 fixation can play a key role in the nitrogen and carbon budget of water‐limited and seasonally dry ecosystems remains a mystery. The maintenance of metabolically and physiologically costly symbiotic fixation in water‐limited environments is highly complex. These costs are particularly high during the first developmental season, when allocation to deep rooting and drought resistance mechanisms is essential for seedling survival of prolonged seasonal drought. We, therefore, evaluated how drought‐adapted legume species change their allocation to symbiotic nitrogen fixation as a function of soil nitrogen availability. We tested this on seedlings of a suite of four common Mediterranean legume shrubs with a strong seasonal behaviour, which we grew under controlled nitrogen and phosphorus availabilities. We asked: (1) Do species differ in their investment and regulation of nitrogen fixation? (2) Is fixation regulated via plant allocation to nodules, fixation rate or both? and (3) Does phosphorus availability limit symbiotic nitrogen fixation? All Mediterranean perennial legumes in the experiment established and grew, nodulated, and fixed nitrogen, even under severe nitrogen limitation. The four species reacted similarly to nitrogen supply, by strongly downregulating fixation through both decreased nodulation and lower rate of fixation. However, we found a significant interspecific difference in fixation (both nodulation and rate), biomass production and growth rate. Our experimental species presented a range of fixation investment strategies corresponding to life‐history and resource partitioning patterns. Phosphorus limitation had a minor influence on both fixation and plant growth. Synthesis. The high physiological cost of symbiotic fixation imposes the need to tightly regulate fixation in perennial legumes coping with severe water stress. Control of fixation allows legume species to colonize recently disturbed nitrogen‐deficient habitats, cope with grazing, survive long seasonal droughts and recover nitrogen fixation later in the wet season, and survive over time by reducing nitrogen inputs to the ecosystem.

Stability of a winter wheat population with high yield and high resource use efficiency

Using the winter wheat cultivar Tainong 18 as the experimental material, we analyzed yield stability from 2012 to 2016 under three different treatments: T1(following typical local field management practices), T2(high-yield: high nitrogen and water were supplied to foster high grain yield), and T3(high-yield, high-efficiency: optimized field management including increasing plant density, reducing nitrogen input and delaying of the sowing date). Yield related phenotypic traits, including the number of ears on the main stem and tillers, leaf area index (LAI), photosynthetically active radiation (PAR) interception, dry matter accumulation and distribution, as well as grain yield, were analyzed over four seasons to determine their relationships with annual radiation, accumulated temperature and precipitation. We then determined grain yield stability for each of the three treatments. The amount and distribution of radiation, accumulated temperature, and precipitation varied greatly within each season. The ears on the main stem represented 38.9%, 58.7%, and 66.9% of the total ears, respectively, for wheat grown in the T1, T2 and T3 treatments, indicating that T1 ears originated mainly from the tillers, T2 ears from both the main stem and the tillers, and T3 ears from the main stem. The T2 and T1 treatments produced the highest and lowest amount of dry matter and grain yield, respectively. Although having relatively lower dry matter accumulation at maturity compared with T2, T3 led to higher grain yield due to high LAI, high PAR interception and utilization, high net canopy photosynthetic rate from booting (especially from 14 days after anthesis) to maturity and a higher harvest index. Among the three treatments, T3 resulted in the lowest annual range, standard deviation, and coefficient of variation for LAI, PAR interception, and dry matter accumulation. Thus, grain yield was most stable in wheat grown in the T3 treatment mainly due to stability in biological production during all four seasons.

Source and sink mechanisms of nitrogen transport and use

Contents Summary 35 I. Introduction 35 II. Nitrogen acquisition and assimilation 36 III. Root-to-shoot transport of nitrogen 38 IV. Nitrogen storage pools in vegetative tissues 39 V. Nitrogen transport from source leaf to sink 40 VI. Nitrogen import into sinks 42 VII. Relationship between source and sink nitrogen transport processes and metabolism 43 VIII. Regulation of nitrogen transport 43 IX. Strategies for crop improvement 44 X. Conclusions 46 Acknowledgements 47 References 47 SUMMARY: Nitrogen is an essential nutrient for plant growth. World-wide, large quantities of nitrogenous fertilizer are applied to ensure maximum crop productivity. However, nitrogen fertilizer application is expensive and negatively affects the environment, and subsequently human health. A strategy to address this problem is the development of crops that are efficient in acquiring and using nitrogen and that can achieve high seed yields with reduced nitrogen input. This review integrates the current knowledge regarding inorganic and organic nitrogen management at the whole-plant level, spanning from nitrogen uptake to remobilization and utilization in source and sink organs. Plant partitioning and transient storage of inorganic and organic nitrogen forms are evaluated, as is how they affect nitrogen availability, metabolism and mobilization. Essential functions of nitrogen transporters in source and sink organs and their importance in regulating nitrogen movement in support of metabolism, and vegetative and reproductive growth are assessed. Finally, we discuss recent advances in plant engineering, demonstrating that nitrogen transporters are effective targets to improve crop productivity and nitrogen use efficiency. While inorganic and organic nitrogen transporters were examined separately in these studies, they provide valuable clues about how to successfully combine approaches for future crop engineering.

Effects of reduced nitrogen inputs on crop yield and nitrogen use efficiency in a long-term maize-soybean relay strip intercropping system.

The blind pursuit of high yields via increased fertilizer inputs increases the environmental costs. Relay intercropping has advantages for yield, but a strategy for N management is urgently required to decrease N inputs without yield loss in maize-soybean relay intercropping systems (IMS). Experiments were conducted with three levels of N and three planting patterns, and dry matter accumulation, nitrogen uptake, nitrogen use efficiency (NUE), competition ratio (CR), system productivity index (SPI), land equivalent ratio (LER), and crop root distribution were investigated. Our results showed that the CR of soybean was greater than 1, and that the change in root distribution in space and time resulted in an interspecific facilitation in IMS. The maximum yield of maize under monoculture maize (MM) occurred with conventional nitrogen (CN), whereas under IMS, the maximum yield occurred with reduced nitrogen (RN). The yield of monoculture soybean (MS) and of soybean in IMS both reached a maximum under RN. The LER of IMS varied from 1.85 to 2.36, and the SPI peaked under RN. Additionally, the NUE of IMS increased by 103.7% under RN compared with that under CN. In conclusion, the separation of the root ecological niche contributed to a positive interspecific facilitation, which increased the land productivity. Thus, maize-soybean relay intercropping with reduced N input provides a very useful approach to increase land productivity and avert environmental pollution.

A fungal endophyte consortium counterbalances the negative effects of reduced nitrogen input on the yield of field-grown spring barley

SUMMARYThe use of chemicals to fertilize crops incurs economic and environmental costs and it is widely recognized that the current level of chemical fertilizer use is unsustainable in many intensive farming systems. Any methods that can reduce fertilizer input and still maintain acceptable yields would be of great benefit to both the farmer and the environment. The use of beneficial endophytes as crop inoculants may go some way towards improving crop yields beyond that achievable using fertilizer increases alone. Field trials were conducted over two seasons on three contrasting field sites to test the effects of fungal endophytes from a wild barley relative on three barley cultivars (Mickle, Planet and Propino). Seeds were either untreated or dressed with a consortium of four endophyte strains, and three levels of nitrogen (N) were applied to both treatments: full N, 50% N and 0 N. On the field site with the lowest overall N input, the endophyte treatment with 50% N restored yield for ‘Planet’ to that associated with untreated plants receiving the full N input. On the same site and with the same cultivar, endophyte treatment increased yield by 15% under full N, and by a mean 12% for all three cultivars with 50% N input. Over both seasons and all three sites, the endophyte treatment increased yield for the cultivar Planet by a mean of 9%. For the endophyte-associated increase in the variety Planet grain yield over the untreated trials strong correlations were found between increased yield and each of low rainfall, greater evaporation and greater number of degree days above the base. Furthermore, the efficacy of the endophytes was not removed by regular foliar fungicidal treatment. These results suggest that fungal endophytes can contribute to improving barley yield grown in low rainfall areas and under a range of fertilizer input regimes, provided that endophyte treatments are applied to compatible crop cultivars and sites.

Increased root growth and nitrogen accumulation in common wheat following PGPR inoculation: Assessment of plant-microbe interactions by ESEM

Abstract The use of plant growth-promoting rhizobacteria (PGPR) meets the current need to reduce nitrogen input in order to attain greater sustainability in the production of crops, particularly cereals. This study investigated whether a commercial bio-fertiliser containing a consortium of PGPR and N-fixing bacteria (Azospirillum spp., Azoarcus spp. and Azorhizobium spp.) affects shoot and root growth, N accumulation and grain yield in common wheat (Triticum aestivum L.). Trials were conducted in a fertile, silty loam soil, firstly in rhizoboxes, by applying bacteria either as a seed-coating inoculum or by foliar + soil spraying, and then in the field by spraying the canopy at the tillering stage with decreasing levels of N fertilisation (160, 120 and 80 kg ha−1) in two consecutive years. Culm height, leaf chlorophyll content, nitrogen accumulation and yield were recorded above ground, while below ground Root Length Density (RLD) patterns were investigated by soil coring and image analysis at the flowering stage. Environmental Scanning Electron Microscope (ESEM) imaging revealed an excellent ability of bacteria to adhere to the surface of intact leaves and roots, and to colonise both leaf mesophyll and root vascular tissues in aseptic conditions. Bacteria increased the number of root tips and ramifications (+65% vs. non-inoculated controls) in sterilised rhizobox soil, regardless of the method of application, and the volumetric root length density in the open field with medium (+29%) and high (+11%) N supply, resulting in greater N accumulation (about +25 kg ha−1). Although the N dose had clear positive effects, no significant variations in grain yield (only + 1–3% vs. non-inoculated controls) or other agronomic parameters could be ascribed to bacteria inoculation. The conclusion drawn is that the use of a combination of PGPR and N-fixing bacteria offers an opportunity to improve root growth in wheat and increase plant resilience to environmental stresses, and helps to reduce N losses from agricultural ecosystems thereby offering partial fertiliser savings within crop rotations.

Increased hill density can compensate for yield loss from reduced nitrogen input in machine-transplanted double-cropped rice

Reducing external inputs, including labor and N fertilizer, is critical to sustainable double-cropped rice production in China. Dense planting is a recommended strategy to reduce N rate in rice production, and this strategy may be more practical for machine-transplanted rice as machine transplanting can achieve high hill density with less labor. However, little work has been done to demonstrate the feasibility of such a strategy in machine-transplanted double-cropped rice. This study was conducted to determine the effects of reduced N rate and increased hill density on yield attributes and grain yield in machine-transplanted double-cropped rice. Field experiments were done in two years with three treatments: (1) high N rate with low hill density (HNLD), (2) low N rate with low hill density (LNLD), and (3) low N rate with high hill density (LNHD).Results showed that LNLD had 19% and 16% less panicle number per unit land area, 27% and 26% smaller leaf area index, 18% and 14% lower biomass production, and consequently 13% and 11% lower grain yield than did HNLD in early and late season, respectively. In contrast, these yield attributes and grain yield were generally equal or higher under LNHD than under HNLD. Our study indicates that the potential negative effects of reduced N rate on yield attributes and grain yield can be compensated for by increased hill density, and suggests that dense planting is a feasible strategy to reduce N input in machine-transplanted double-cropped rice.

Trends in nitrogen isotope ratios of juvenile winter flounder reflect changing nitrogen inputs to Rhode Island, USA estuarine systems

Nitrogen isotope ratios (δ15N) in juvenile winter flounder, Pseudopleuronectes americanus, were used to examine changes in nitrogen inputs to several Rhode Island, USA estuarine systems. Fish were collected over two three-year periods with a ten-year interval between sampling periods (2002–2004 and 2012–2014). During that interval numerous changes to nutrient management practices were initiated in the watersheds of these estuarine systems including the upgrade of several major wastewater treatment facilities that discharge to Narragansett Bay, which significantly reduced nitrogen inputs. Following these reductions, the δ15N values of flounder in several of the systems decreased as expected; however, isotope ratios in fish from upper Narragansett Bay significantly increased. We believe that low δ15N values measured in 2002–2004 were related to concentration-dependent fractionation at this location. Increased δ15N values measured between 2012 and 2014 may indicate reduced fractionation or that changes in wastewater treatment processes altered the nitrogen isotopic ratios of the effluents.

Effects of reduced nitrogen input on productivity and N 2 O emissions in a sugarcane/soybean intercropping system

A seven-year (2009–2015) continuous field experiment was established at the South China Agricultural University in order to identify the effects of sugarcane/soybean intercropping and reduced N rate on ecosystem productivity, yield stability, soil fertility, and N2O emissions. The randomized block experiment was designed with four cropping patterns (sugarcane monocropping (MS), soybean monocropping (MB), sugarcane/soybean (1:1) intercropping (SB1), and sugarcane/soybean (1:2) intercropping (SB2)) and two rates of N fertilization (300 kg hm−2 (N1, reduced rate) and 525 kg hm−2 (N2, conventional rate)). The results showed that the land equivalent ratio (LER) of all intercropping systems was greater than 1 (between 1.10 and 1.84), and the SB2-N1 optimally improved the land utilization rate among all treatments. The cropping patterns and N applied rates had no significant effect on sugarcane yield. The soybean yield was influenced by different cropping patterns because of different planting densities (4, 8 and 16 rows of soybean were plant under SB1, SB2, and MB, respectively) and was adopted in this experiment. In addition, under the SB2 cropping pattern, the soybean yield at the reduced N application rate was higher than that at the conventional N application rate. Wricke’s ecovalence (Wi2), the sustainable yield index (SYI) and the coefficient of variation (CV) were used to evaluate yield stability. Different treatments had no significant effects on sugarcane yield stability, as demonstrated by three indicators (Wi2, SYI and CV), which indicated that intercropping with soybean and reduced N rate had no effect on sugarcane yield. For soybeans, the value of Wi2 demonstrated that the stability of the intercropping system was higher than its counterpart monocropping system, as SYI and CV values indicated that SB2 had higher stability than SB1. During seven years of experiments, there was no significant difference in the soil fertility between MS and SB patterns. The soybean monocropping had a higher available K, pH and lower available P content than sugarcane inter- and mono-cropping. Different cropping patterns had a slight impact on N2O emissions and the greenhouse gas intensity (GHGI) value. Higher N input promoted N2O emissions and increased GHGI values. In conclusion, the present study observed that a 40% reduced nitrogen input combined with intercropping soybeans could maintain sugarcane yield and soil sustainable utilization, and that higher N fertilizer additions induced negative impacts on greenhouse gases emissions. Sugarcane intercropping with soybeans can reduce chemical fertilizer input and simultaneously maintain crop productivity; thus, it can be considered to be a reasonable practice for field management.

Nitrous oxide fluxes and dissolved N gases (N2 and N2O) within riparian zones along the agriculturally impacted San Joaquin River

Riparian buffer zones play an important role in reducing nitrogen inputs to surface waters, but may contribute to the greenhouse effect by emitting N2O. This study investigated N2O fluxes within three abundantly vegetated riparian zones within the agriculturally impacted San Joaquin River, California. Fluxes were measured in the dry season of 2010 and 2011 at four positions perpendicular to the river: outside riparian zone, inside riparian zone, river bank and benthic sediments. Subsurface dissolved N2/Ar and N2O concentrations were measured from groundwater wells in the riparian zone simultaneously with N2O fluxes. Mean N2O fluxes from the outside riparian zone (6.5 mg ± 2.3 N2O m−2 d−1), were higher than the inside riparian zone (2.7 ± 0.7 mg N2O m−2 d−1) and four times higher than bank sediments (1.6 ± 0.2 mg N2O m−2 d−1). Fluxes from benthic sediments were similar to the outside riparian zone averaging 4.4 ± 1.0 mg N2O m−2 d−1. Dissolved excess N2 (relative to Ar) and N2O concentrations in groundwater ranged from 1.53 to 10.2 mg L−1 and 0.0–6.0 µg L−1, respectively. A spatial trend was evident along the river flowpath with higher N2O concentrations at upstream sites. The mean N2O–N/NO3−–N ratio was 0.024 with a peak of 0.34. Variations in riparian soils were complex and N2O fluxes were primarily controlled by soil pH, %WFPS, NH4+ and NO3−, while benthic N2O fluxes were regulated by variations in dissolved oxygen and river flow. Higher fluxes in the riparian soils in 2011 were attributed to several months of flooding that significantly impacted groundwater tables and nutrient availability. Dissolved N2O from groundwater within the riparian zones was not found to be a significant factor contributing to atmospheric fluxes. These results suggest that riparian zones within the agriculturally impacted San Joaquin River were a significant source of N2O when elevated NO3− was present. Different controlling factors for fluxes within benthic sediments suggested that riparian vegetation did not play a role in NO3− concentrations or fluxes within the surface water.

Characteristics of annual nitrous and nitric oxide emissions from major cereal crops in the North China Plain under alternative fertilizer management

Although nitrogen fertilizer is crucially important for China’s crop production, the overuses in the intensive cereal cropping systems of the North China Plain has caused extensive concern for its environmental consequences on nitrous oxide (N2O) and nitric oxide (NO) fluxes. To characterize the integration of environmental and agronomic aspects of fertilizer management, we conducted two annual winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) rotation cycles under five fertilization treatments, including the farmers’ conventional practice (CP) amended with synthetic nitrogen, three alternative managements of reduced nitrogen inputs with synthetic fertilizers alone (UA), synthetic fertilizers combined with poultry manure (UA+PM) or controlled-release urea combined with poultry manure (CU+PM), and the control without nitrogen fertilization (CK). The N2O and NO fluxes and direct emission factors varied seasonally and annually. These variations could be interpreted mechanically by a revised “hole-in-the-pipe” model and dual Michaelis–Menten and Arrhenius kinetics. The CK, CP, UA, UA+PM, and CU+PM treatments released N2O at 0.65, 4.64, 3.66, 2.88, and 2.40kgNha−1yr−1, respectively, and NO at least 0.42, 2.35, 2.24, 1.30, and 1.18kgNha−1yr−1, respectively. The annual direct emission factors of N2O and NO were 0.41–0.67% and 0.18–0.32%, respectively. The three alternative managements decreased both N2O and NO emissions, expressed either on an area basis or relative to grain yield, without sacrificing crop yields compared to CP. However, their mitigation effects on each gas emission were different. The UA treatment reduced only N2O emission, while UA+PM and CU+PM showed significant mitigation effects on both gases as compared to CP or UA. Overall, our results provide insight into environmental aspect of fertilizer management in major cereal crops and suggest that reducing nitrogen input coupled with organic manure incorporation could be beneficial for simultaneously mitigating nitrogen-containing trace gas fluxes and sustaining cereal grain yields.

Spatial modeling of robust crop production portfolios to assess agricultural vulnerability and adaptation to climate change

Agricultural vulnerability to climate change is likely to vary considerably between agro-environmental regions. Exemplified on Austrian cropland, we aim at (i) quantifying climate change impacts on agricultural vulnerability which is approximated by the indicators crop yields and gross margins, (ii) developing robust crop production portfolios for adaptation, and (iii) analyzing the effect of agricultural policies and risk aversion on the choice of crop production portfolios. We have employed a spatially explicit, integrated framework to assess agricultural vulnerability and adaptation. It combines a statistical climate change model for Austria and the period 2010–2040, a crop rotation model, the bio-physical process model EPIC (Environmental Policy Integrated Climate), and a portfolio optimization model. We find that under climate change, crop production portfolios include higher shares of intensive crop management practices, increasing average crop yields by 2–15% and expected gross margins by 3–18%, respectively. The results depend on the choice of adaptation measures and on the level of risk aversion and vary by region. In the semi-arid eastern parts of Austria, average dry matter crop yields are lower but gross margins are higher than in western Austria due to bio-physical and agronomic heterogeneities. An abolishment of decoupled farm payments and a threefold increase in agri-environmental premiums would reduce nitrogen inputs by 23–33%, but also crop yields and gross margins by 18–37%, on average. From a policy perspective, a twofold increase in agri-environmental premiums could effectively reduce the trade-offs between crop production and environmental impacts.

Age-related changes in nitrogen resorption and use efficiency in the perennial new crop Physaria mendocina (Brassicaceae)

Domestication of desert-adapted species and their development into perennial crops has been proposed as an alternative to increase cropping intensity in arid lands, while reducing nitrogen inputs and losses. Among traits involved in nitrogen conservation much attention has been drawn to resorption patterns. However, understanding of intra-population variability in resorption and nitrogen use efficiency is required prior to the development of new crops. Here we evaluate age-related changes in resorption patterns and nitrogen use efficiency (NUE) within a wild population of Physaria mendocina (Brassicaceae). We generated a relative age index, based on morphological traits, and we use it as an independent variable to regress nitrogen concentrations in roots and leaves (green and senesced), nitrogen resorption efficiency and use efficiency. Nitrogen in green and senesced leaves decrease with age, resorption efficiency did not change, and nitrogen use efficiency increased. The lower nitrogen concentration in green leaves and higher proficiency (lower nitrogen concentrations in senesced leaves) of older plants might be due to a decrease in acquisition capacity. Constant efficiency is explained by the lack of differences in concentration in green and senesced leaves slopes. Higher proficiency in older plants resulted in higher NUE; this relationship would be modulated by nitrogen concentration in green leaves, which, in turn, is controlled by nitrogen availability and acquisition. These findings have implications in the domestication process, since in perennial species biomass production and internal plant nitrogen turnover over multiple seasons, are central key to physiological functions such as plant re-growth and winter survival. We identified a few questions as directions for future research.

한국잔디 재배에 규산질 비료 시비가 생육과 질소이용효율에 미치는 영향

본 연구는 규산질 비료와 질소 비료 혼용이 한국잔디의 생육과 질소비료 효율에 미치는 영향을 알아보기 위해 수행하였다. 한국잔디의 초장, 지상부, 포복경과 지하부의 생체중과 건물중, 지상부 개체수, 포복경 길이는 규산질 비료 400 kg/10a와 질소비료 24 kg/10a을 혼합시비 하였을 때 질소비료의 24 kg/10a 단용처리구보다 증가하였고, 규산질 비료와 질소비료 18 kg/10a은 질소비료의 24 kg/10a 단용 처리구와 유의성이 없었다. 규산질 비료와 질소비료를 혼합하여 시비했을 경우 질소비료 약 25-30% 절감효과가 있는 것으로 판단되었으며, 토양 내 유효 규산과 유기물의 함량은 규산질 비료 시비를 하지 않은 것보다 시비를 하였을 때 더 높게 나타나 규산질 비료가 한국잔디의 생장과 밀도를 높였으며 토양의 화학적 특성에 중요한 요소로 작용하였다. This study was conducted to investigate the effect of silicate mixed with nitrogen fertilizer on improving the growth and reducing nitrogen input of zoysiagrass. Plant height, fresh and dry weight of shoots, roots, and stolons, the number of shoots and total of stolons length were increased with highest in silicate mixed with nitrogen 24 kg/10a than nitrogen 24 kg/10a, and it showed no significance in silicate mixed with nitrogen 18 kg/10a. Nitrogen use efficiency in mixed silicate fertilizer was increased by 25-30% than single nitrogen fertilization. Moreover, the contents of available <TEX>$SiO_2$</TEX>, and organic matters of silicate fertilization on soil was higher than not silicate fertilization on soil. The silicate enhanced the growth and density of zoysiagrass, while it was a crucial factor to affect the chemical property of the soil.

Methane and nitrous oxide emissions from a subtropical estuary (the Brisbane River estuary, Australia)

Methane (CH4) and nitrous oxide (N2O) are two key greenhouse gases. Their global atmospheric budgeting is, however, flout with challenges partly due to lack of adequate field studies determining the source strengths. Knowledge and data limitations exist for subtropical and tropical regions especially in the southern latitudes. Surface water methane and nitrous oxide concentrations were measured in a subtropical estuarine system in the southern latitudes in an extensive field study from 2010 to 2012 and water–air fluxes estimated using models considering the effects of both wind and flow induced turbulence. The estuary was found to be a strong net source of both CH4 and N2O all-year-round. Dissolved N2O concentrations ranged between 9.1±0.4 to 45.3±1.3nM or 135 to 435% of atmospheric saturation level, while CH4 concentrations varied between 31.1±3.7 to 578.4±58.8nM or 1210 to 26,430% of atmospheric saturation level. These results compare well with measurements from tropical estuarine systems. There was strong spatial variability with both CH4 and N2O concentrations increasing upstream the estuary. Strong temporal variability was also observed but there were no clear seasonal patterns. The degree of N2O saturation significantly increased with NOx concentrations (r2=0.55). The estimated water–air fluxes varied between 0.1 and 3.4mgN2Om−2d−1 and 0.3 to 27.9mgCH4m−2d−1. Total emissions (CO2-e) were N2O (64%) dominated, highlighting the need for reduced nitrogen inputs into the estuary. Choice of the model(s) for estimation of the gas transfer velocity had a big bearing on the estimated total emissions.