Reactive Nitrogen Losses Research Articles

Advantages of an Orychophragmus violaceus-maize rotation in reducing greenhouse gas emissions and reactive nitrogen losses and increasing net ecosystem economic benefits on the North China Plain

Introducing cover crops into crop rotation systems is widely practiced to enhance the sustainability of agricultural production, but comprehensive evaluations of farmlands in cover crop-maize rotations on the North China Plain (NCP) from environmental, economic and net ecosystem economic benefits (NEEB) perspectives have rarely been performed. Therefore, a field experiment was conducted to compare economic benefits (EB), greenhouse gas (GHG) emissions, reactive nitrogen (Nr) losses, soil nutrient cycling values (SNV) and NEEB in three farming systems. The farming systems included a conventional wheat-maize (WM) rotation system, a government-promoted monoculture maize (MM) system and an innovative Orychophragmus violaceus (O. violaceus)-maize (OvM) rotation system. The OvM rotation system achieved more EBs from the maize season but lower annual profits than the WM system, with 68.29% lower GHG emissions and 39.33% lower Nr losses. In addition, the highest SNV was achieved in the OvM rotation system, which was 700.18% and 116.97% higher than those in the WM and MM systems, respectively. Furthermore, the NEEB of the OvM rotation system was 61.92% and 29.31% higher than those of the WM and MM systems, respectively. In conclusion, the OvM rotation is recommended as a sustainable and cleaner maize production farming system for the NCP and other regions with similar ecological conditions because it led to lower annual GHG emissions and Nr losses, as well as higher SNV and NEEB than the other farming systems.

Environmental assessment of United States dairy farms

Dairy farms in the United States are diverse and although regional dairy production and farm strategy has been evaluated for environmental impact, a comprehensive national assessment is important to define national priorities for sustainable intensification. We estimated important environmental footprints of dairy production using process-level simulation and cradle-to-farm gate life cycle assessment. Dairy farms representing the sizes and management practices found in six regions were simulated with the Integrated Farm System Model (IFSM). Regional and national environmental footprints were determined as an average of all simulated farms weighted by the portion of milk contributed by each to the total. Nationally, dairy farms were found to emit 99,000 ± 8480 Gg CO2e of greenhouse gas (GHG), equivalent to 1.5% of the estimated U.S. total GHG emission, with a commodity-based intensity of 1.01 ± 0.09 kg CO2e/kg of fat and protein corrected milk (FPCM) produced. Fossil energy use was 242,700 ± 38,400 TJ, 0.3% of the U.S. total, or 2.48 ± 0.39 MJ/kg FPCM. Blue (non-precipitation) water use was 11,600 ± 2480 Tg, roughly 3.0% of the estimated U.S. total freshwater withdraw, with an intensity of 119 ± 25 kg/kg FPCM. While these environmental footprints represent a small portion of the respective national inventories, the dairy industry's contribution to reactive nitrogen (N) losses appears to be considerably greater. Losses of reactive N were estimated at 970 ± 133 Gg, with an intensity of 9.92 ± 1.36 g/kg FPCM where 66% of the total was in the form of ammonia (NH3). Although there are no national estimates of total reactive N loss, dairy farms were found to contribute 19–24% of national inventories of NH3 emissions. While strategies are available to reduce NH3 emissions, finding economical and sustainable solutions that do not result in pollution swapping remains a challenge for the dairy industry.

Nitrogen budgets of contrasting crop-livestock systems in China

The crop-livestock system is responsible for a large proportion of global reactive nitrogen (Nr) losses, especially from China. There are diverse livestock systems with contrasting differences in feed, livestock and manure management. However, it is not yet well understood which factors greatly impact on the nitrogen (N) budgets and losses of each system. In this study, we systematically evaluated the N budgets of the crop-livestock production system from 1980 to 2050 in China by identifying the differences of 20 distinct livestock systems. During 1980 to 2010, the total N flow through the crop-livestock system increased from 21.4 to 49.7 Tg, with large variations in different input/output pathways, due to the strong livestock transitions of production towards to a monogastric and landless industrial system. Different systems contributed differently to the total N budgets in 2010. For example, the landless industrial system contributed 67% of livestock product N output, but accounted for 80% of total mineral N fertilizer use and feed N imports by the whole crop-livestock system. The mixed system had the highest rate of N use efficiency at system level due to high dependence on recycled N. N losses were diversely distributed by different systems, with the mixed ruminant system responsible for the majority of NH3–N emission in livestock production, and the grazing ruminant system dominant in NO3–N losses in feed production. The total N entering the crop-livestock system is estimated to be 53.9 Tg with total N losses of 41.3 Tg in 2050 under a business-as-usual scenario. However, this amount could be significantly decreased through combined measures that indicate a considerable potential for future improvements. Overall, our results provide new insights into N use and the management of livestock production.

Temperature alters dicyandiamide (DCD) efficacy for multiple reactive nitrogen species in urea-amended soils: Experiments and modeling

Dicyandiamide (DCD) is a nitrification inhibitor (NI) used to reduce reactive nitrogen (N) losses from soils. While commonly used, its effectiveness varies widely. Few studies have measured DCD and temperature effects on a complete set of soil N variables, including nitrite (NO2−) measured separately from nitrate (NO3−). Here the DCD reduction efficiencies (RE) for nine N availability metrics were quantified in two soils (a loam and silt loam) using aerobic laboratory microcosms at 5–30 °C. Both regression analysis and process modeling were used to characterize the responses. Four metrics accounted for NO3− production and included total mobilized N, net nitrification, maximum nitrification rate, and cumulative NO3− (cNO3-). The REs for these NO3−-associated production variables decreased linearly with temperature, and in all cases were below 60% at temperatures ≥22 °C, except for cNO3- in one soil. In contrast, REs for NO2− and nitric oxide (NO) gas production were less sensitive to temperature, ranging from 80 to 99% at 22 °C and 50–95% at 30 °C. Addition of DCD suppressed nitrous oxide (N2O) production in both soils by 20–80%, but increased ammonia volatilization by 36–210%. The time at which the maximum reduction efficiency occurred decreased exponentially with increasing temperature for most variables. The two-step nitrification process model (2SN) was modified to include competitive inhibition coupled to first-order DCD decomposition. Model versus data comparisons suggested that DCD had indirect effects on NO2− kinetics that contributed to the greater suppression of NO2− and NO relative to NO3−. This study also points to the need for NIs that are more stable under increased temperature. The methods used here could help to assess the efficacy and temperature sensitivity of other NIs as well as new microbial inhibitors that may be developed.

Optimization of China's maize and soy production can ensure feed sufficiency at lower nitrogen and carbon footprints.

China purchases around 66% of the soy that is traded internationally. This strains the global food supply and contributes to greenhouse gas emissions. Here we show that optimizing the maize and soy production of China can improve its self-sufficiency and also alleviate adverse environmental effects. Using data from more than 1,800 counties in China, we estimate the area-weighted yield potential (Ypot) and yield gaps, setting the attainable yield (Yatt) as the yield achieved by the top 10% of producers per county. We also map out county-by-county acreage allocation and calculate the attainable production capacity according to a set of sustainability criteria. Under optimized conditions, China would be able to produce all the maize and 45% of the soy needed by 2035-while reducing nitrogen fertilizer use by 26%, reactive nitrogen loss by 28% and greenhouse gas emissions by 19%-with the same acreage as 2017, our reference year.

Quantifying the frequency and volume of urine deposition by grazing sheep using tri-axial accelerometers

Urine patches deposited in pasture by grazing animals are sites of reactive nitrogen (N) loss to the environment due to high concentrations of N exceeding pasture uptake requirements. In order to upscale N losses from the urine patch, several urination parameters are required, including where, when and how often urination events occur as well as the volume and chemical composition. There are limited data available in this respect, especially for sheep. Here, we seek to address this knowledge gap by using non-invasive sensor-based technology (accelerometers) on ewes grazing in situ, using a Boolean algorithm to detect urination events in the accelerometer signal. We conducted an initial study with penned Welsh Mountain ewes (n = 5), with accelerometers attached to the hind, to derive urine flow rate and to determine whether urine volume could be estimated from ewe squat time. Then accelerometers attached to the hind of Welsh Mountain ewes (n = 30 at each site) were used to investigate the frequency of sheep urination events (n = 35 946) whilst grazing two extensively managed upland pastures (semi-improved and unimproved) across two seasons (spring and autumn) at each site (35–40 days each). Sheep urinated at a frequency of 10.2 ± 0.2 and 8.1 ± 0.3 times per day in the spring and autumn, respectively, while grazing the semi-improved pasture. Urination frequency was greater (19.0 ± 0.4 and 15.3 ± 0.3 times per day in the spring and autumn, respectively) in the unimproved pasture. Ewe squat duration could be reliably used to predict the volume of urine deposited per event and was thus used to estimate mean daily urine production volumes. Sheep urinated at a rate of 16.6 mL/s and, across the entire dataset, sheep squatted for an average of 9.62 ± 0.03 s per squatting event, producing an estimated average individual urine event volume of 159 ± 1 mL (n = 35 946 events), ranging between 17 and 745 mL (for squat durations of 1 to 45 s). The estimated mean daily urine volume was 2.15 ± 0.04 L (n = 2 669 days) across the entire dataset. The data will be useful for modelling studies estimating N losses (e.g. ammonia (NH3) volatilisation, nitrous oxide (N2O) emission via nitrification and denitrification and nitrate (NO3−) leaching) from urine patches.

Agronomic, environmental, and ecosystem economic benefits of controlled-release nitrogen fertilizers for maize production in Southwest China

Effective fertilizer nitrogen (N) management plays an important role in reducing the environmental problems caused by its overuse in maize production systems. The use of enhanced-efficiency N fertilizers is an effective approach to increase crop productivity and N use efficiency. However, to the best of our knowledge, there have been no associated comprehensive evaluations of the environmental impacts using a life cycle assessment (LCA) and ecosystem economic benefits (EEB). In this study, a consecutive 2-yr plot-based field experiment was conducted in Southwest China with two N fertilizer sources, blended urea (BU) containing controlled-release urea and conventional urea (CU) at a 1:1 ratio and CU only at five N rates (0, 90, 180, 270, and 360 kg N ha−1) to determine the agronomic and environmental benefits as well as the EEB of BU in maize production. The results showed that among the five N rates tested, the N180 treatment (180 kg N ha−1) showed greater potential for maintaining a high yield (8.8 Mg ha−1) and reducing environmental impacts. The use of BU resulted in higher grain yield and agronomic efficiency compared to those with CU at 180 kg N ha−1 in 2018 but not in the following year. In addition, BU significantly reduced reactive nitrogen losses through nitrous oxide emission (−27%), ammonia volatilization (−18%), and N leaching (−24%), reducing the crop environmental footprint by decreasing the global warming, acidification, and eutrophication potential by 8%–13%, 4%–9%, and 8%–22%, respectively. Furthermore, the use of BU increased economic benefits and EEB by reducing agricultural (N fertilizer; labour) and ecological costs. Compared to CU, BU improved the EEB by 68%, 39%, 29%, and 25% at N rates of 90, 180, 270, and 360 kg N ha−1, respectively. These results demonstrated that replacement of CU with BU at the N rate of 180 kg N ha−1 is an effective strategy to improve sustainability of maize production in subtropical regions of China.

Identifying the main crops and key factors determining the carbon footprint of crop production in China, 2001–2018

Agriculture affects climate change and contributes directly and indirectly to greenhouse gas (GHG) emissions. However, no reports have fully quantified the GHG emissions from different crop systems in China. In this study, the carbon emission and carbon sequestration inventories and the carbon footprint (CF) of 16 major crop systems in China from 2001 to 2018 were analyzed with a cradle-to-farm gate life cycle analysis approach for the first time. The results showed that the largest farm CF and product CF were vegetables (11.9 t CO2 eq ha−1) and tea (4.6 t CO2 eq t−1), respectively. From the perspective of crop emissions and processes, the main crop systems influencing the national total net carbon emissions (NTCE) from crop production are rice, maize, wheat, fruits and vegetables, accounting for 87.3–90.4%; the key emission processes for NTCE are fertilization and irrigation, accounting for 73.7–76.8%. The NTCE has increased by 410.4 Mt CO2 eq from 2001 to 2018, of which maize, fruits and vegetables were the main crops that explained 99.0%, while fertilization and irrigation were the key factors and explained 91.9% of these increases. Scenario analysis indicated that increasing the straw return rate and partially replacing chemical fertilizers with manure have a minimal impact on NTCE. In contrast, reducing the loss of reactive nitrogen is the most effective single strategy to alleviate agricultural GHG emissions in the future. Our results will provide a fresh perspective for the development of more effective GHG emission reduction strategies for agricultural green development.

Long-term straw return with N addition alters reactive nitrogen runoff loss and the bacterial community during rice growth stages

Crop residue return is an effective, eco-friendly tillage method for decreasing reactive nitrogen (Nr) losses via surface runoff. However, the associated variation in Nr characteristics and its prospective mechanisms are not well understood. We systematically evaluated the response of Nr runoff loss and N variation in standing water to the abiotic and biotic parameters of soil in a paddy field after 6 years of straw return. Five experimental treatments of different fertilization strategies in combination with straw return were tested during the rice growth season. The results indicated that under equivalent fertilizer input, long-term straw return significantly reduced Nr runoff loss by 11.5% (P < 0.05), even though the loss increased with N fertilizer addition. We report that variations in abiotic soil properties (P < 0.05) and bacterial communities (P < 0.01) were both responsible for Nr loss differences between the rice growth stages and among the tested fertilizing patterns. Soil inorganic nitrogen (r = 0.18) had a significant positive influence on Nr runoff loss, but this effect was surpassed by the overall negative influence of soil organic carbon (r = −0.43), soil pH, (r = −0.40), and bacterial community composition (r = −0.14), which was especially apparent during the tillering stage. Our results emphasize the importance of jointly considering biotic and abiotic factors in soil and standing water when characterizing the effects of long-term straw return and N addition on Nr runoff loss, which will aid in mitigating N-based agricultural non-point pollution.

Hotspots of reactive nitrogen loss in China: Production, consumption, spatiotemporal trend and reduction responsibility

Effective and fair mitigation measures hinge on the identification of hotspots and tracking provenance on reactive nitrogen (Nr) loss at a high spatial resolution. We assessed the Nr loss intensity in China at 1 km spatial resolution from 1980 to 2015. The total Nr loss increased from 20.2 to 54.5 Tg N yr−1, with hotspots (>100 kg N ha−1 yr−1) concentrated in the North China Plain, the Middle and Lower Yangtze River and the Sichuan Basin. The Nr loss hotspots covered less than 20% of the Chinese territory but contributed more than 90% of total Nr loss since 1990. Geographical disparity in Nr loss has increased and calls for a fair regional policy synergy. Compared to managing Nr loss based only on production, we demonstrate that the estimation of Nr loss responsibility driven by consumption has greater potential to allocate a fair share of responsibility for reducing Nr loss.

Ammonia, nitrous oxide, carbon dioxide, and water vapor fluxes after green manuring of faba bean under Mediterranean climate

Green manuring of legume crops has increased in interest in recent years because of environmental and economic costs of synthetic fertilizers and need of sustainable cropping systems. Climatic conditions can reduce the agronomic and environmental effectiveness of green manuring promoting reactive nitrogen losses, or fostering soil heterotrophic respiration. This study aims to quantify ammonia and nitrous oxide losses, as well as carbon dioxide exchanges following green manuring of faba bean (Vicia faba spp. minor L.) under semi-arid climate conditions, typical of the Mediterranean basin. Ammonia emissions were measured by means of an aerodynamic gradient approach equipped with a multi-channel wet-denuder system (ROSAA), alongside with a concentration-based inverse dispersion modelling assessment. Nitrous oxide losses were measured with an automated chamber system, whereas carbon dioxide and water vapor exchanges were monitored jointly by means of eddy covariance technique. Ammonia volatilization lasted for three weeks and was triggered by the increase of soil water content due to rainfall, occurring 5 days after green manuring. Total emissions were 0.31% of the nitrogen supplied by green manuring (230 kg N ha−1). Nitrous oxide emissions from soil were of low intensity during the measurement period and were directly corelated to the water filled pore space. The biogeochemical model CERES-EGC was validated with the measurements of nitrous oxide, then used to reproduce the dynamic until the sowing of the succeeding crop. Cumulated emissions of nitrous oxide were 1% of the total nitrogen supplied. Soil became a net source both of carbon dioxide and water vapor soon after green manuring, with an emission of 900 kg C-CO2 ha−1 by heterotrophic respiration (23% of added carbon). In terms of water balance, 19 mm of water evaporated from soil surface, originated from the addition of fresh biomass. Green manuring proved to be a significant agronomic strategy to improve soil fertility, limiting reactive nitrogen and carbon losses to the atmosphere.

A National Nitrogen Target for Germany

The anthropogenic nitrogen cycle is characterized by a high complexity. Different reactive nitrogen species (NH3, NH4+, NO, NO2, NO3−, and N2O) are set free by a large variety of anthropogenic activities and cause numerous negative impacts on the environment. The complex nature of the nitrogen cycle hampers public awareness of the nitrogen problem. To overcome this issue and to enhance the sensitivity for policy action, we developed a new, impact-based integrated national target for nitrogen (INTN) for Germany. It is based on six impact indicators, for which we derived the maximum amount of nitrogen losses allowed in each environmental sector to reach related state indicators on a spatial average for Germany. The resulting target sets a limit of nitrogen emissions in Germany of 1053 Gg N yr−1. It could serve as a similar means on the national level as the planetary boundary for reactive nitrogen or the 1.5 °C target of the climate community on the global level. Taking related uncertainties into account, the resulting integrated nitrogen target of 1053 Gg N yr−1 suggests a comprehensible INTN of 1000 Gg N yr−1 for Germany. Compared to the current situation, the overall annual loss of reactive nitrogen in Germany would have to be reduced by approximately one-third.

Carbon and nitrogen footprints accounting of peanut and peanut oil production in China

The peanut sector has significant potential for decreasing greenhouse gas (GHG) emissions and reactive nitrogen (Nr) loss from agricultural production activity in China. This study calculated the carbon (C) and nitrgen (N) emissions of the peanut sector in China by jointly using the carbon footprint (CF) and nitrogen footprint (NF) methods based on the national statistical data from 2008 to 2017. The results showed that the average area-based CF (CFa) and NF (NFa) of peanut cropping in China were 1912.58 kg CO2-eq ha−1 and 41.19 kg N-eq ha−1, respectively. The average yield-based CF (CFy) and NF (NFy) of peanut oil reached 1.38 kg CO2-eq kg−1 and 28.23 g N-eq kg−1, respectively. The CFa of the peanut cropping subsystem in China increased from 2008 to 2017, while the NFa presented a reduction feature during 2009–2011 and during 2015–2017. Based on the results above, the total GHG emissions and Nr losses caused by the peanut sector in China were estimated to reach average values of 8.33 million tons (Mt) CO2-eq year−1 and 0.15 Mt N-eq year−1, respectively, during 2009–2017. Moreover, peanut cropping in Fujian showed the highest CF and NF, while that in Anhui and Chongqing presented the lowest CF and NF, implying that optimizing peanut layout in China would be of significant importance to developing the peanut sector with fewer environmental consequences. Fertilizer production and application were continuously the largest sources of CF and NF in the peanut sector in China, which should be given more attention for reducing the environmental consequences in the future. This study provides policy guidance for clean production in peanut industrial chain in the China.

Cutting environmental footprints of maize systems in China through Nutrient Expert management

Excessive fertilizer consumption, poor management, and intense pollution currently restrict sustainable agriculture in China. To address these problems, two 9-year experiments involving typical maize production systems in Northcentral China (summer maize) and Northeast China (spring maize) were conducted to evaluate the effectiveness of Nutrient Expert (NE) management, a Nutrient Decision Support System which combines 4 R nutrient management with improved varieties and optimized plant density, on reducing carbon (C) and nitrogen (N) footprints. The mean grain yields under NE were 7.4 and 11.5 tons ha−1, which were 3.9% and 6.9% higher than those of local farmers’ practices (FP) in the summer and spring maize systems, respectively; the N-derived (affected by N fertilization) yield accounted for 21.7% and 73.5% of the total yield under NE, respectively. Compared with FP, NE achieved 21.8% and 16.0% lower reactive nitrogen (Nr) losses, 18.4% and 20.9% lower greenhouse gas (GHG) emissions, 24.8% and 21.4% smaller N footprints (9.1 and 2.3 kg N ton−1 grain), and 21.5% and 26.0% smaller C footprints (436 and 206 kg CO2 eq ton−1 grain) in summer and spring maize, respectively. NE reduced the N-derived N and C footprints by 30.3% and 27.2% in summer maize and 22.9% and 28.0% in spring maize, respectively, as a result of greater yields and optimal N management. Moreover, compared with summer maize, spring maize showed significantly smaller N-derived N (12.6-fold) and C (7.2-fold) footprints. The results demonstrated the ability of long-term NE management to sustain maize yields, reduce Nr losses and GHG emissions, and cut C and N footprints, indicating its potential suitability as an alternative management for sustainable agriculture. Moreover, the summer maize system still had considerable potential for environmental footprints reduction even when current NE management practices were adopted.

The Warming Climate Aggravates Atmospheric Nitrogen Pollution in Australia.

Australia is a warm country with well-developed agriculture and a highly urbanized population. How these specific features impact the nitrogen cycle, emissions, and consequently affect environmental and human health is not well understood. Here, we find that the ratio of reactive nitrogen (Nr) losses to air over losses to water in Australia is 1.6 as compared to values less than 1.1 in the USA, the European Union, and China. Australian Nr emissions to air increased by more than 70% between 1961 and 2013, from 1.2 Tg N yr−1 to 2.1 Tg N yr−1. Previous emissions were substantially underestimated mainly due to neglecting the warming climate. The estimated health cost from atmospheric Nr emissions in Australia is 4.6 billion US dollars per year. Emissions of Nr to the environment are closely correlated with economic growth, and reduction of Nr losses to air is a priority for sustainable development in Australia.

Nitric and nitrous oxide fluxes from intensifying crop agriculture in the seasonally dry tropical Amazon–Cerrado border region

AbstractRapid expansion and intensification of crop agriculture in the tropics may accelerate ecosystem losses of reactive nitrogen (N). We quantified emissions of nitric oxide (NO) and nitrous oxide (N2O) in forest, single‐cropped soybean [Glycine max (L.) Merr.], and N‐fertilized double‐cropped soybean–maize (Zea mays L.) at three N fertilizer levels within the largest area of recent cropland expansion on earth, in the Amazon and Cerrado biomes in Brazil. The NO emissions were 2.1 kg N ha‒1 yr‒1 in forest, 0.6 kg N ha‒1 yr‒1 in soybean, and 1.3 kg N ha‒1 yr‒1 in soybean–maize. The N2O fluxes were &lt;1.1 kg N ha‒1 yr‒1 across all land uses. As fertilization levels increased from 80 to 160 kg N ha−1 yr‒1 in soybean–maize double‐cropped sites, NO emissions increased from 0.6 to 6.7 kg N ha−1 mo‒1 in the month immediately after fertilization, but N2O emissions only increased from 0.6 to 1.8 kg N ha−1 mo‒1. These results indicate that NO emissions do not increase when forests are converted to croplands under current fertilization levels, and that NO will respond more strongly than N2O fluxes to increases in fertilizer applications. Our findings suggest that if N fertilization rates in the region were increased, NO fluxes could increase rapidly.

160 Effects of cow-calf management strategies on environmental footprints of beef cattle production in the United States

Abstract As baseline environmental footprints of beef cattle production are established, mitigation strategies through cow-calf dietary and production management can be evaluated. Our objective was to quantify environmental benefits obtained by beef cattle production through implementation of cow-calf management strategies. Ten cow-calf management strategies were identified related to animal performance, feed management, or pasture management. Each strategy was incorporated into 20 representative beef cattle production systems and simulated with the Integrated Farm System Model (IFSM) using local soil and climate data. A combined strategy was identified based upon the results of individual strategies, which was also simulated with IFSM. Farm-gate life cycle assessment was used to estimate carbon (C) footprint, fossil energy use, blue water use, and total reactive nitrogen (N) loss for all production systems and strategy combinations. Averages of each environmental metric for the cow-calf sector were based on weighted averages of regional cow inventory data. National estimates of environmental impacts were based upon number of cattle represented by each production system. Feed efficiency, terminal cross sires, and reduced cow body size strategies had greatest effect on C footprint (reductions of 1.31, 1.15, and 0.71 kg CO2e/kg CW, respectively from a baseline of 16.34 kg CO2e/kg CW). Calving season, reduced cow body size, and improved fiber digestion increased fossil energy use (7.8%), while improved feed efficiency and calf implant use reduced fossil energy use (7.4%). Blue water use was reduced by a greater extent from improved feed efficiency (4.6%) and reduced cow body size (5.3%) compared to other strategies (0.6%). Total reactive N loss was reduced by 7.0 and 6.9% through improved feed efficiency and reduced cow body size, respectively. Combining strategies reduced C footprint (18.2%), fossil energy use (18.6%), blue water use (18.9%), and reactive N loss (16.2%).

161 Effects of management strategies on environmental footprints of cow-calf production in the United States

Abstract Estimates of beef cattle production’s national and regional cradle to farm grate environmental impacts have been quantified. As baseline footprints are now established, cow-calf dietary and production management strategies can be evaluated for their capacity to reduce environmental impacts. Accordingly, our objective was to quantify environmental changes from implementing management strategies in cow-calf production. Ten management strategies were identified, with each related to animal performance, feed management, or pasture management. Each strategy was incorporated into a representative cow-calf operation for each of 6 major regions of beef production in the United States and simulated with the Integrated Farm System Model (IFSM) using local soil and climate data. A combined strategy was also identified based on results of the individual strategies, which was simulated with IFSM. Farm-gate life cycle assessment was used to estimate carbon (C) footprint, fossil energy use, blue water use, and total reactive nitrogen (N) loss for all production systems and strategy combinations. Averages of each environmental metric for the cow-calf sector were based on weighted averages of regional cow inventory data. Averaged across all strategies, the reduction in C footprint was 4.1% and fossil energy use was reduced 3.5% for the cow-calf sector. Improved feed efficiency (8.0%) and terminal cross (7.1%) strategies reduced C footprint to a greater extent than other strategies simulated (2.0%). Fossil energy use was reduced by 8.3, and 6.5% from improved feed efficiency and terminal cross strategies, respectively. Early weaning increased C footprint, fossil energy use, blue water use, and reactive N loss by 13.8, 17.8, 20.2, and 12.7%, respectively. The combined strategy, including improved feed efficiency, improved fiber digestion, calf implant use, increased weaning rate, reduced cow body weight, and terminal cross strategies, reduced C footprint (18%), fossil fuel use (18%), blue water use (23%), and reactive N loss (15%).

Combined applications of organic and synthetic nitrogen fertilizers for improving crop yield and reducing reactive nitrogen losses from China's vegetable systems: A meta-analysis.

The combined application of organic and synthetic nitrogen (N) fertilizers is being widely recommended in China's vegetable systems to reduce reliance on synthetic N fertilizer. However, the effect of substituting synthetic fertilizer with organic fertilizer on vegetable productivity (yield, N uptake and nitrogen use efficiency) and reactive nitrogen (Nr) losses (N2O emission, N leaching and NH3 volatilization) remains unclear. A meta-analysis was performed using peer-reviewed papers published from 2000 to 2019 to comprehensively assess the effects of combined application of organic and synthetic N fertilizers. The results indicate that overall, the vegetable yield, N2O emission and NH3 volatilization were not significantly changed, whereas N leaching was reduced by 44.6% and soil organic carbon (SOC) concentration increased by 12.5% compared to synthetic N fertilizer alone. Specifically, when synthetic N substitution rates (SRs) were ≤70%, vegetable yields and SOC concentration were increased by 5.5%-5.6% and 13.1-18.0%, and N leaching was reduced by 41.6%-48.1%. At the high substitution rate (SR>70%), vegetable yield was reduced by 13.6%, N2O emission was reduced by 14.3%, and SOC concentration increased by 16.4%. Mixed animal-plant sources of organic N preferentially increased vegetable yield and SOC concentration, and reduced N2O emission and N leaching compared with single sources of organic-N. Greenhouse gas (GHG) emission was decreased by 28.4%-34.9% by combined applications of organic and synthetic N sources, relative to synthetic N fertilizer alone. We conclude that appropriate rates (SR≤70%) of combined applications of organic and synthetic N fertilizers could improve vegetable yields, decrease Nr and GHG emission, and facilitate sustainable development of coupled vegetable-livestock systems.

Comprehensive assessment of the effects of nitrification inhibitor application on reactive nitrogen loss in intensive vegetable production systems

Previous studies regarding environmental impacts of nitrification inhibitors (NIs) in intensive vegetable production systems mainly focused on the fate of individual nitrogen (N) compounds. Due to the influence of various N-dynamic pathways on one another, systematic observations, taking into account all key component processes, must be carried out to achieve practically useful recommendations. As well, the mechanisms of how NI application leads to increasing vegetable yields are not well understood. Therefore, we conducted a field experiment with three leading vegetable crops (lettuce, celery, and tomato), and two urea N input rates, without (N1, N2) or with a nitrification inhibitor, 2-chloro-6-(trichloromethyl)-pyridine (CP) (N1 + CP, N2 + CP), to evaluate the comprehensive effects of CP on reactive-N emission in these intensive vegetable production systems, with a focus on leaching, ammonia (NH3) volatilization, and nitrous oxide (N2O) emission, and to clarify the possible mechanisms by which CP affects vegetable yield. The results show that CP application significantly decreased (p < 0.05) N leaching by 36.9, 26.9, and 28.4 %, soil residual NO3-N contents by 34.1, 43.7, and 43.9 %, N2O emission by 46.4, 77.2, and 36.9 %, and significantly increased (p < 0.05) NH3 volatilization by 33.5, 56.3, and 308.1 % in the lettuce, celery, and tomato seasons, respectively, while having no significant effect on yield at the typical N-application rate (N2). Under 60 % of the typical N-application rate (N1), CP addition significantly increased (p < 0.05) yield and N-use efficiency (NUE) over the three-season period by 23.9 and 55.1 %, respectively, significantly reduced (p < 0.05) N2O emission by 43.5 %, while having no significant effect on the other three observed N processes. In a lettuce-celery-tomato rotation, compared with the typical N-application rate (N2), 60 % of the typical N-application rate with CP addition (N1 + CP) significantly increased (p < 0.05) yield and NUE by 37.1 and 214 %, and decreased (p < 0.05) soil residual NO3-N contents, N leaching, and N2O emission by 70.9, 51.1, and 69.6 %, respectively, and had no significant effect on NH3 volatilization. Furthermore, the distribution analysis of N derived from 15N-labeled urea in tomato aboveground suggested that CP application significantly decreased (p < 0.05) N allocation to stems and leaves by 12.1 and 9.7 %, and significantly increased (p < 0.05) N allocation to fruits by 31.2 %, averaged over 60 % and 100 % N treatments. Application of CP increased N storage in fruits and benefited yield.