Optimizing nitrogen management in the food system for sustainable development: a case study of Quzhou County

Nitrogen(N) is an essential nutrient for food production. The rapid increase in population requires high inputs of N to meet the growing food demand. If not managed well, the substantial loss of N from the food system has multiple impacts on grain yield, air and water pollution, and the economic benefits of agricultural. Multi-objective(food security, environmental sustainability and economic sustainability) synergistic consideration of N management in the food system is still lacking. This study employed strategies for optimizing N management in the food system, using Quzhou County as a typical example on the North China Plain. Firstly, a food chain approach was adopted to understand drivers and reasons behind N losses from the food system.Secondly, a top-down approach was used to define multi-objective N management, taking into consideration food security, environmental sustainability and economic sustainability. Multi-objective N management aims to reduce N losses to the environment and increase N use efficiencies,while simultaneously increasing yields and economic benefits. Thirdly, 3R(reduce-retain-recycle) N management strategies were identified for specific crops and animals through a bottom-up approach and then analyzed the potential of these strategies to achieve the multi-objectives. Finally, there is a discussion of how to engage different stakeholders to promote the technologies implementation. This study provides new insights into the synergistic achievement of multi-objective N management in the food system and the development of environmentally-friendly agriculture.

HOTSPOTS OF NUTRIENT LOSSES TO AIR AND WATER:AN INTEGRATED MODELING APPROACH FOR EUROPEAN RIVER BASINS

Nutrient pollution of air and water is a persistent problem in Europe.However,the pollution sources are often analyzed separately,preventingthe formulation of integrative solutions.This study aimed to quantify the contribution of agriculture to air,river and coastal water pollution by nutrients.A new MARINA-Nutrients model was developed for Europe to calculate inputs of nitrogen(N)and phosphorus(P)to land and rivers,N emissions to air,and nutrient export to seas by river basins.Under current practice,inputs of N and P to land were 34.4 and 1.8 Tg.yr^(-1),respectively.However,only 12%of N and 3%of P reached the rivers.Agriculture was responsible for 55%of N and sewage for 67%of P in rivers.Reactive N emissions to air from agriculture were calculated at 4.0 Tg.yr^(-1).Almost twofifths of N emissions to air were from animal housing and storage.Nearly a third of the basin area was considered as pollution hotspots and generated over half of N emissions to air and nutrient pollution in rivers.Over 25%of river export of N ended up in the Atlantic Ocean and of P in the Mediterranean Sea.These results could support environmental policies to reduce both air and water pollution simultaneously,and avoid pollution swapping.

WATER POLLUTION AND AGRICULTURE:MULTI-POLLUTANT PERSPECTIVES

Agriculture is an important cause of multiple pollutants in water.With population growth and increasing food demand,more nutrients,plastics,pesticides,pathogens and antibiotics are expected to enter water systems in the 21st century.As a result,water science has been shifting from singlepollutant to multi-pollutant perspectives for large-scale water quality assessments.This perspective paper summarizes and discusses four main highlights related to water pollution and agriculture from the multi-pollutant perspective.These highlights reveal the spatial and temporal distribution and main sources of multiple pollutants in waters.Based on the highlights,a scientific agenda is proposed to prioritize solutions for sustainable agriculture(UN Sustainable Development Goal 2)and clean water(UN Sustainable Development Goals 6 and 14).This agenda points out that when formulating solutions for water pollution,it is essential to take into account multiple pollutants and their interactions beyond biogeochemistry.

不同利用模式下内蒙古自治区草地生态系统服务供给的对比分析（英文）

Although several previous studies in Inner Mongolia examined the effects of ecological conservation on the delivery of ecosystem services, they were often limited in scope（few ecosystem services were assessed） and often suffered from confounding by spatial variation. In this study, we examined the impact of conservation measures（changes in grassland utilization patterns） on the provision of selected ecosystem services in three types of grasslands（meadow steppe in Hulun Buir, typical steppe in Xilin Gol, and semi-desert steppe in Ordos） in Inner Mongolia. We examined five utilization patterns： no use（natural grasslands）, light use, moderate use, intensive use, and recovery sites（degraded sites protected from further use）. Through household surveys and vegetation and soil surveys, we measured the differences in ecosystem services among the different grassland utilization patterns. We also identified spatial factors that confounded the quantification of ecosystem services in different types of grasslands. We found that light use generally provided high levels of ecosystem services in meadow steppe and typical steppe, with the main differences in the supporting ecosystem services. Surprisingly, we found no consistently positive impacts of strict conservation activities across the sites, since the results varied spatially and with respect to differences in the land-use patterns. Our study suggests that appropriate grassland utilization patterns can enhance the supply of ecosystem services and reduce negative effects on both household livelihoods and the environment.

ECOLOGICAL EFFECTS OF NITROGEN DEPOSITION ON URBAN FORESTS: AN OVERVIEW

The global urban area is expanding continuously,resulting in unprecedented emissions and deposition of reactive nitrogen(N)in urban environments.However,large knowledge gaps remain in the ecological effects of N deposition on urban forests that provide key ecosystem services for an increasing majority of city dwellers.The current understanding of the spatial patterns and ecological effects of N deposition in urban forests was synthesized based on a literature review of observational and experimental studies.Nitrogen deposition generally increases closer to cities,resulting in an urban hotspot phenomenon.Chemical components of N deposition also shift across urban-suburban-rural gradients,showing higher ratios of ammonium to nitrate in and around urban areas.The ecological effects of N deposition on urban forest ecosystems are overviewed with a special focus on ecosystem N cycling,soil acidification,nutrient imbalances,soil greenhouse gas emissions,tree growth and forest productivity,and plant and soil microbial diversity.The distinct effects of unprecedented N deposition on urban forests are discussed in comparison with the common effects in natural forests.Despite the existing research efforts,several key research needs are highlighted to fill the knowledge gaps in the ecological effects of N deposition on urban forests.

Modelling impacts of acid deposition and groundwater level on habitat quality and plant species diversity

Introduction:We quantified the effects of the site factors pH and nitrate(NO_(3))concentration in soil solution and groundwater level on the vegetation of terrestrial ecosystems for the Netherlands in response to changes in atmospheric nitrogen(N)and sulphur(S)deposition and groundwater level over the period 1990-2030.The assessment was made with the SMART2 model,a simple one-layer model including geochemical buffer processes,element cycling by litterfall,mineralisation and uptake,nitrogen transformation processes and element input through deposition,weathering and upward seepage.Methods:To assess the effects of changes in abiotic site factors on the vegetation,we developed a simple plant diversity indicator for grassland,heathland and forest,based on the occurrence of target plant species and competing species.Species occurrence was calculated from the preferred ranges of each species for the NO_(3) concentration and pH in soil solution and mean spring groundwater level.Changes in the plant diversity indicator were assessed from effects of changes in the occurrence of target and competing plant species in response to changes in mean spring groundwater level and in pH and NO_(3) concentration,as calculated with SMART2.Calculations were made for combinations of five vegetation structure types(three forest types,semi-natural grassland and heathland)and seven soil types(three sandy soils,two clay soils,peat and loess soils)using a 250×250 m grid.We used data for atmospheric deposition and groundwater level in the past to assess trends between 1990 and 2010 and evaluated two future scenarios for the period 2010-2030:a Business as Usual and an Improved Environment scenario.Results:Comparison of model predictions on pH and NO_(3) with measured soil solution concentrations for forest showed a reasonable to good agreement for pH but rather poor for NO_(3).The largest impacts were found for the combination of the two Improved Environment scenarios.Conclusions:Reductions in N and S deposition and an increase in groundwater level between 1990 and 2030 hardly caused changes in soil pH and only relatively small reductions in NO_(3) concentration(11-13%).Nevertheless,those changes caused a significant increase in plant diversity indicator.

A NEW APPROACH TO HOLISTIC NITROGEN MANAGEMENT IN CHINA

Since the 1980s,the widespread use of N fertilizer has not only resulted in a strong increase in agricultural productivity but also caused a number of environmental problems,induced by excess reactive N emissions.A range of approaches to improve N management for increased agricultural production together with reduced environmental impacts has been proposed.The 4R principles(right product,right amount,right time and right place)for N fertilizer application have been essential for improving crop productivity and N use efficiency while reducing N losses.For example,site-specific N management(as part of 4R practice)reduced N fertilizer use by 32%and increased yield by 5%in China.However,it has not been enough to overcome the challenge of producing more food with reduced impact on the environment and health.This paper proposes a new framework of food-chainnitrogen-management(FCNM).This involves good N management including the recycling of organic manures,optimized crop and animal production and improved human diets,with the aim of maximizing resource use efficiency and minimizing environmental emissions.FCNM could meet future challenges for food demand,resource sustainability and environmental safety,key issues for green agricultural transformation in China and other countries.

SUSTAINABLE NITROGEN MANAGEMENT INDEX: DEFINITION, GLOBAL ASSESSMENT AND POTENTIAL IMPROVEMENTS

To represent the sustainability of nitrogen management in the Sustainable Development Goals indicator framework,this paper proposes a sustainable nitrogen management index(SNMI).This index combines the performance in N crop yield and N use efficiency(NUE),thereby accounting for the need for both food production and environmental protection.Applying SNMI to countries around the world,the results showed improvement in the overall sustainability of crop N management over the past four decades,but this improvement has been mainly achieved by crop yield increase,while global NUE has improved only slightly.SNMI values vary largely among countries,and this variation has increased since the 1970s,implying different levels of success,even failure,in improving N management for countries around the world.In the standard SNMI assessment,the reference NUE was defined as 1.0(considered an ideal NUE)and the reference yield was defined as 90 kg·ha^(−1)·yr^(−1) N(considering a globally averaged yield target for meeting food demand in 2050).A sensitivity test that replaced the reference NUE of 1.0 with more realistic NUE targets of 0.8 or 0.9 showed overall reduction in SNMI values(i.e.,improved performance),but little change in the ranking among countries.In another test that replaced the universal reference yield with region-specific attainable yield,SNMI values declined(i.e.,improved performance)for most countries in Africa and West Asia,whereas they increased for many countries in Europe and South America.The index can be improved by further investigation of approaches for setting region-specific yield targets and high-quality data on crop yield potentials.Overall,SNMI offers promise for a simple and transparent approach to assess progress of countries toward sustainable N management with a single indicator.