Sustainable Nitrogen Management Research Articles

Nitrogen and the food system

To stave off world hunger, humanity manipulated and unbalanced the nitrogen cycle. Today’s excess fixed nitrogen is a global pollutant, of which our food system is a primary driver. Yet, food insecurity remains a global concern. In this Voices, food-system experts offer insights into the challenge of the sustainable management of nitrogen.

Alkaline air: changing perspectives on nitrogen and air pollution in an ammonia-rich world.

Ammonia and ammonium have received less attention than other forms of air pollution, with limited progress in controlling emissions at UK, European and global scales. By contrast, these compounds have been of significant past interest to science and society, the recollection of which can inform future strategies. Sal ammoniac (nūshādir, nao sha) is found to have been extremely valuable in long-distance trade (ca AD 600–1150) from Egypt and China, where 6–8 kg N could purchase a human life, while air pollution associated with nūshādir collection was attributed to this nitrogen form. Ammonia was one of the keys to alchemy—seen as an early experimental mesocosm to understand the world—and later became of interest as ‘alkaline air’ within the eighteenth century development of pneumatic chemistry. The same economic, chemical and environmental properties are found to make ammonia and ammonium of huge relevance today. Successful control of acidifying SO2 and NOx emissions leaves atmospheric NH3 in excess in many areas, contributing to particulate matter (PM2.5) formation, while leading to a new significance of alkaline air, with adverse impacts on natural ecosystems. Investigations of epiphytic lichens and bog ecosystems show how the alkalinity effect of NH3 may explain its having three to five times the adverse effect of ammonium and nitrate, respectively. It is concluded that future air pollution policy should no longer neglect ammonia. Progress is likely to be mobilized by emphasizing the lost economic value of global N emissions ($200 billion yr−1), as part of developing the circular economy for sustainable nitrogen management.This article is part of a discussion meeting issue ‘Air quality, past present and future’.

Nitrogen challenges in global livestock systems

One-third of human-induced reactive nitrogen emissions can be traced to livestock supply chains. Highly variable nitrogen use efficiencies along these chains uncover opportunities for more sustainable nitrogen management.

Potassium fertilization as a driver of sustainable management of nitrogen in potato (Solanum tuberosum L.)

The objectives of the present study were to assess and demonstrate the role of potassium fertilizer management on nitrogen use efficiency (NUE), and to select the most suitable set of NUE indicators. A series of six field experiments was conducted during 2009-2014. A principal trial factor was crop rotation (CR), potatoes - winter wheat - winter barley (1st CR/ lupine – cover crop/2nd CR). The experimental design was composed of four K rates (0, 80, 160, 240 kg K2O ha-1) and two N rates (120, 160 kg N ha-1). The marketable yield (MY) ranged from 20 to 49 Mg ha-1. The amount of K in tubers at harvest (Ka) was significantly associated with the MY. Ka, largely governed by the interaction between CR and K rate, was also linked to Partial Factor Productivity of fertilizer nitrogen (PFPN) and Agronomic Nitrogen Efficiency (ANE). The results suggest that the K rate should be oriented to the realization of a specific production strategy, depending on environmental factors (water shortage), and N use efficiency. It was documented that increased Ka might be a crucial factor for controlling N productivity, subsequently decreasing its rates. At the optimum K fertilizer rate, N rates can be significantly reduced.

Challenges for Global Sustainable Nitrogen Management in Agricultural Systems.

Nitrogen (N) losses from agricultural production contribute to detrimental impacts on water, soil, air, and human health. However, it is still lacking in evaluating global N budgets in agricultural systems. Hence, we conducted a global analysis on the current status of the N flows in the agricultural systems, explored the possible mitigation measures and challenges, and investigated the existing regulations on controlling N pollution. Globally, agricultural soils received a total of 73 kg of N ha-1 year-1 on average, including N fertilizer plus manure (61%), atmospheric N deposition (10%), and N litters and fixation (29%). The estimated global NH3 loss to total N inputs was 17%, which led to a loss of $15 billion year-1. The N use efficiency (NUE) in Eastern China (33%) was much lower than that in the Eastern United States (65%) or Western Europe (61%), leaving much room to enhance the NUE to increase agricultural food production. Meanwhile, higher NH3 losses from N fertilizers and manure were found in Eastern China (22%) than the Eastern United States (17%) and Western Europe (17%). We highlight the urgency to improve the NUE and decrease NH3 loss with lower environmental consequences. Our results showed high potentials to mitigate NH3 volatilization and enhance the NUE by various measures, such as substituting manure N for chemical fertilizer N, applying controlled release fertilizers, and urease inhibitors. These measures should be implemented in combination with the transfer of knowledge to farmers with new technologies and increasing the farm size to enhance the efficiency of agricultural production in the future.

Toward a Generic Analytical Framework for Sustainable Nitrogen Management: Application for China.

Managing reactive nitrogen (Nr) to achieve a sustainable balance between production of food, feed and fiber, and environmental protection is a grand challenge in the context of an increasingly affluent society. Here, we propose a novel framework for national nitrogen (N) assessments enabling a more consistent comparison of the uses, losses and impacts of Nr between countries, and improvement of Nr management for sustainable development at national and regional scales. This framework includes four key components: national scale N budgets, validation of N fluxes, cost-benefit analysis and Nr management strategies. We identify four critical factors for Nr management to achieve the sustainable development goals: N use efficiency (NUE), Nr recycling ratio (e.g., ratio of livestock excretion applied to cropland), human dietary patterns and food waste ratio. This framework was partly adopted from the European Nitrogen Assessment and now is successfully applied to China, where it contributed to trigger policy interventions toward improvements for future sustainable use of Nr. We demonstrate how other countries can also benefit from the application our framework, in order to include sustainable Nr management under future challenges of growing population, hence contributing to the achievement of some key sustainable development goals (SDGs).

Groundwater nitrate response to sustainable nitrogen management

Throughout the world, nitrogen (N) losses from intensive agricultural production may end up as undesirably high concentrations of nitrate in groundwater with a long-term impact on groundwater quality. This has human and environmental health consequences, due to the use of groundwater as a drinking water resource, and causes eutrophication of groundwater-dependent ecosystems such as wetlands, rivers and near-coastal areas. At national scale, the measured nitrate concentrations and trends in Danish oxic groundwater in the last 70 years correlate well with the annual agricultural N surpluses. We also show that the N use efficiency of agriculture is related to the groundwater nitrate concentrations. We demonstrate an inverted U-shape of annual nitrate concentrations as a function of economic growth from 1948 to 2014. Our analyses evidence a clear trend of a reversal at the beginning of the 1980s towards a more sustainable agricultural N management. This appears to be primarily driven by societal demand for groundwater protection linked to economic prosperity and an increased environmental awareness. However, the environmental and human health thresholds are still exceeded in many locations. Groundwater protection is of fundamental global importance, and this calls for further development of environmentally and economically sustainable N management in agriculture worldwide.

La gestion de la matière organique du sol, un enjeu important pour limiter la lixiviation du nitrate vers les eaux souterraines

Description du sujet. La concentration en nitrate dans la moitié des masses d’eau souterraine de la région wallonne (Belgique) a justifié le classement de celles-ci en zone vulnérable, en application de la Directive Nitrates (DN). Cette zone vulnérable présente une diversité de contextes agro-pédologiques. Ainsi, le contenu en azote des sols agricoles peut localement varier d’un facteur 4. Objectifs. L’étude consiste à établir si la teneur en carbone organique total (COT) d’un sol constitue un facteur de risque significatif quant à la lixiviation du nitrate vers les eaux souterraines. Méthode. L’article s’appuie sur des mesures COT et de reliquat d’azote nitrique dans le sol en début de période de lixiviation (APL – Azote Potentiellement Lessivable), réalisées en 2012 dans 1 500 parcelles lors d’un contrôle organisé en application du Programme de Gestion Durable de l’Azote, transposition de la DN en région wallonne. Résultats. L’examen des résultats illustre d’une part que l’APL est positivement corrélé au COT et que les parcelles qualifiées de « non conformes » présentent une concentration moyenne en COT significativement supérieure aux autres résultats. Conclusions. L’APL étant un indicateur environnemental du risque de lixiviation du nitrate, il apparait que le contenu COT est généralement de nature à constituer un risque de contamination des eaux souterraines par le nitrate. Il convient dès lors d’une part, d’améliorer la prise en compte de ce paramètre dans les conseils de fertilisation azotée et, d’autre part, dans le cas de récolte estivale, de gérer au mieux le sol par une mise en place efficiente de cultures pièges à nitrate.

Sustainable nitrogen management in rice based cropping system

Sustainable nitrogen management in rice based cropping system

Climatic risk assessment to improve nitrogen fertilisation recommendations: A strategic crop model-based approach

Within the context of nitrogen (N) management, since 1950, with the rapid intensification of agriculture, farmers have often applied much larger fertiliser quantities than what was required to reach the yield potential. However, to prevent pollution of surface and groundwater induced by nitrates, The European Community launched The European Nitrates Directive 91/6/76/EEC. In 2002, in Wallonia (Belgium), the Nitrates Directive has been transposed under the Sustainable Nitrogen Management in Agriculture Program (PGDA), with the aim of maintaining productivity and revenue for the country’s farmers, while reducing the environmental impact of excessive N application.A feasible approach for addressing climatic uncertainty lies in the use of crop models such as the one commonly known as STICS (simulateur multidisciplinaire pour les cultures standard). These models allow the impact on crops of the interaction between cropping systems and climatic records to be assessed. Comprehensive historical climatic records are rare, however, and therefore the yield distribution values obtained using such an approach can be discontinuous. In order to obtain better and more detailed yield distribution information, the use of a high number of stochastically generated climate time series was proposed, relying on the LARS-Weather Generator. The study focused on the interactions between varying N practices and climatic conditions. Historically and currently, Belgian farmers apply 180kgNha−1, split into three equal fractions applied at the tillering, stem elongation and flag-leaf stages. This study analysed the effectiveness of this treatment in detail, comparing it to similar practices where only the N rates applied at the flag-leaf stage were modified.Three types of farmer decision-making were analysed. The first related to the choice of N strategy for maximising yield, the second to obtaining the highest net revenue, and the third to reduce the environmental impact of potential N leaching, which carries the likelihood of taxation if inappropriate N rates are applied.The results showed reduced discontinuity in the yield distribution values thus obtained. In general, the modulation of N levels to accord with current farmer practices showed considerable asymmetry. In other words, these practices maximised the probability of achieving yields that were at least superior to the mean of the distribution values, thus reducing risk for the farmers.The practice based on applying the highest amounts (60–60–100kgNha−1) produced the best yield distribution results. When simple economical criteria were computed, the 60–60–80kgNha−1 protocol was found to be optimal for 80–90% of the time. There were no statistical differences, however, between this practice and Belgian farmers’ current practice. When the taxation linked to a high level of potentially leachable N remaining in the soil after harvest was considered, this methodology clearly showed that, in 3 years out of 4, 30kgNha−1 could systematically be saved in comparison with the usual practice.

Alleviation of salt-induced ionic, osmotic and oxidative stresses in Cajanus cajan nodules by AM inoculation

Legume-Rhizobium symbiotic nitrogen (N2) fixation plays a critical role in sustainable nitrogen management in agriculture. The nitrogen fixed by the root nodules not only affects the nitrogen cycle of nature, but is also of great economic importance. A number of physiological and biochemical processes in the nodules are affected by salt stress. The objective of this study was to evaluate the role of arbuscular mycorrhiza (AM) in moderating toxic effects of salt stress on nodular metabolism in Cajanus cajan (L.) Millspaugh (pigeonpea) cv. Manak. Exposure of plants to salinity stress (4, 6 and 8 dSm−1) caused ionic imbalance, which resulted in increased Na+ and reduced K+ and Ca2+ contents in the nodules. Salinity induced increased synthesis and accumulation of proline and glycine betaine. Salt stress significantly increased the antioxidant enzyme activities in the nodules of all plants. Nodular growth suffered remarkably and a marked decline in nodule biomass was observed under salt stress. Leghemoglobin content and acetylene reduction activity (ARA) also declined under saline conditions. AM could significantly improve nodule dry mass, leghemoglobin content and nitrogenase activity, and phosphorus content under salt stress. Activities of antioxidant enzymes increased markedly in nodules of mycorrhizal-stressed plants. This study suggested a correlation between improved functional efficiency of nodules and higher osmolyte accumulation and enhanced antioxidant enzyme activities of AM plants under stressed conditions relative to the nodules of uninoculated plants.

Nitrogen Supplying Capacity of Brown Forest Soil under Different Cropping Practices and 0.01 M CaCl2 Soluble Organic Nitrogen

The best known and most remarkable example of continuous production in Hungary is the Westsik’s crop rotation experiment, which was established in 1929, and is still in use to study the effects of organic manure treatment, to develop models, and predict the likely effects of different cropping systems on soil properties and crop yields. In this respect, Westsik’s crop rotation experiment provides data of immediate value to farmers concerning the applications of green, straw and farmyard manure, as well as data sets for scientific research.Although commonly ignored, the release of nitrogen by root and green manure crops has a significant impact on soil organic matter turnover. The design of sustainable nitrogen management strategies requires a better understanding of the processes influencing nitrogen supplying capacity, as the effects of soil organic matter on soil productivity and crop yield are still very uncertain and require further research. In the treatments of Westsik’s crop rotation experiment, nutrients removed from soil through plant growth and harvesting are replaced either by fertilisers and/or organic manure. Data can be used to study the nitrogen supplying capacity of soil under different cropping systems and its effect on the 0.01 M CaCl2 soluble organic nitrogen content of soil.The aim of this paper is to present data on the nitrogen supplying capacity of brown forest soil from Westsik’s crop rotation experiment and to study its correlation with hundredth molar calcium-chloride soluble organic nitrogen. The main objective is to determine the effects of root and green manure crops on the nitrogen supplying capacity of soil under different cropping systems. The nitrogen supplying capacity was calculated as a difference of plant uptake, organic manure and fertiliser supply.The 0.01 M CaCl2 soluble organic nitrogen test has proved reliable for determining the nitrogen supplying capacity of soils. Brown forest soils are low in organic matter and in the F-1 fallow-rye-potato rotation, the nitrogen supplying capacity was 15.6 kg/ha/year. 0.01 M CaCl2 soluble organic nitrogen content was as low as 1.73 mg/kg soil. Roots and green manure increased the nitrogen supplying capacity of soil by more than 100%. This increase is caused by lupine, a legumes crop, which is very well adapted to the acidic soil conditions of the Nyírség region, and cultivated as a green or root manure crop to increase soil fertility.

Recruitment of novel calcium-binding proteins for root nodule symbiosis in Medicago truncatula.

Legume rhizobia symbiotic nitrogen (N2) fixation plays a critical role in sustainable nitrogen management in agriculture and in the Earth's nitrogen cycle. Signaling between rhizobia and legumes initiates development of a unique plant organ, the root nodule, where bacteria undergo endocytosis and become surrounded by a plant membrane to form a symbiosome. Between this membrane and the encased bacteria exists a matrix-filled space (the symbiosome space) that is thought to contain a mixture of plant- and bacteria-derived proteins. Maintenance of the symbiosis state requires continuous communication between the plant and bacterial partners. Here, we show in the model legume Medicago truncatula that a novel family of six calmodulin-like proteins (CaMLs), expressed specifically in root nodules, are localized within the symbiosome space. All six nodule-specific CaML genes are clustered in the M. truncatula genome, along with two other nodule-specific genes, nodulin-22 and nodulin-25. Sequence comparisons and phylogenetic analysis suggest that an unequal recombination event occurred between nodulin-25 and a nearby calmodulin, which gave rise to the first CaML, and the gene family evolved by tandem duplication and divergence. The data provide striking evidence for the recruitment of a ubiquitous Ca(2+)-binding gene for symbiotic purposes.

Sustainable Management of Nitrogen in East Africa

ABSTRACT Most soils in Africa are low in both total and plant-available nitrogen (N) and hence the balance of N in most of the cropping systems is negative. The main sources of N inflow to agricultural systems are commercial fertilizer, farmyard manure, atmospheric deposition and biological N fixation. Nitrogen is lost through crop removal, leaching, erosion and gaseous losses. In this paper gains and losses are estimated for East Africa based on available data to assess the sustainability of N management. Data show that the removal of N through crop harvest (5–17 kg ha− y−) and through the processes of soil erosion (2–13 kg ha− y−), leaching (2–3 kg ha− y−) and gaseous losses (4–5 kg ha− y−) far exceeds the amounts added through fertilizers (2–10 kg ha− y−), organic manure (<1 kg ha− y−), atmospheric deposition (1–3 kg ha− y−) and N fixation (1–4 kg ha− y−). The total depletion (input-output) of N in Tanzania was found to be several fold higher than that in Zambia. Lower rates of N application through fertilizers and greater losses of N through soil erosion have contributed to higher depletion rates in Tanzania as compared to Zambia. Alternative source of N and some strategies for sustainable management in East Africa are suggested.