With more than 60% of the land farmed, with vulnerable freshwater and marine environments, and with one of the most intensive, export-oriented livestock sectors in the world, the nitrogen (N) ...pollution pressure from Danish agriculture is severe. Consequently, a series of policy action plans have been implemented since the mid 1980s with significant effects on the surplus, efficiency and environmental loadings of N. This paper reviews the policies and actions taken and their ability to mitigate effects of reactive N (Nr) while maintaining agricultural production. In summary, the average N-surplus has been reduced from approximately 170 kg N ha−1 yr−1 to below 100 kg N ha−1 yr−1 during the past 30 yrs, while the overall N-efficiency for the agricultural sector (crop + livestock farming) has increased from around 20-30% to 40-45%, the N-leaching from the field root zone has been halved, and N losses to the aquatic and atmospheric environment have been significantly reduced. This has been achieved through a combination of approaches and measures (ranging from command and control legislation, over market-based regulation and governmental expenditure to information and voluntary action), with specific measures addressing the whole N cascade, in order to improve the quality of ground- and surface waters, and to reduce the deposition to terrestrial natural ecosystems. However, there is still a major challenge in complying with the EU Water Framework and Habitats Directives, calling for new approaches, measures and technologies to mitigate agricultural N losses and control N flows.
Adaptation to climate change is given increasing international attention as the confidence in climate change projections is getting higher. Developing countries have specific needs for adaptation due ...to high vulnerabilities, and they will in this way carry a great part of the global costs of climate change although the rising atmospheric greenhouse gas concentrations are mainly the responsibility of industrialized countries. This article provides a status of climate change adaptation in developing countries. An overview of observed and projected climate change is given, and recent literature on impacts, vulnerability, and adaptation are reviewed, including the emerging focus on mainstreaming of climate change and adaptation in development plans and programs. The article also serves as an introduction to the seven research articles of this special issue on climate change adaptation in developing countries. It is concluded that although many useful steps have been taken in the direction of ensuring adequate adaptation in developing countries, much work still remains to fully understand the drivers of past adaptation efforts, the need for future adaptation, and how to mainstream climate into general development policies.
► Grain yields of spring cereals were significantly improved by growing catch crops. ► Yield benefits from catch crops were higher for spring oats than for spring barley. ► Mean estimates of N ...recovery from catch crops were 69% for oats and 46% for barley. ► N uptake in undersown catch crops was affected by competition with main crops.
Catch crops can contribute to nitrogen supply of following crops through uptake of excess soil mineral nitrogen (N) and through biological N fixation. The contribution of catch crops to the ecological intensification of organic arable systems was investigated using data of a 12-year field experiment carried out at three sites in Denmark. This study focused on the yields of spring oats and spring barley in systems with and without manure in two different cropping systems (O2 and O4) that differed in the proportion of legume-based catch crops (O2 lower and O4 higher) and in the rotation composition (grass–clover green manure in O2 and pulse crops in O4). Three consecutive four-year crop cycles were established at three locations representative of different soil types (loamy sand, sandy loam and coarse sand) and climatic conditions. Crop management and soil operations were performed following common practices in organic farming. Measurements of dry matter (DM) and N content of grain cereals at harvest, above-ground biomass in catch crops and green manure crops in autumn and of the green manure crop at the first cutting were performed. The effect of catch crops on grain yield varied with cereal and catch crop species, soil and rotation type, and the application of N in manure. Higher yield increases from previous catch crops were obtained for spring oat than for spring barley with mean estimates of the apparent N recovery efficiency of N in above-ground catch crops of 69% and 46%, respectively. However, lower autumn N in catch crops undersown in high yielding cash crop was also observed. For spring oats mean grain yield benefits of including catch crops varied from 0.2 to 2.4MgDMha−1 depending on location, manure use and cycle of the rotation. In spring barley mean grain yield benefits from catch crops varied from 0.1 to 1.5MgDMha−1. There was a tendency for the effect of catch crop on grain yield to increase over time. These results indicate that in Nordic climates catch crops can contribute to the ecological intensification of spring cereals, not only by reducing the nitrate leaching and increasing N retention, but also by improving yields. Management practices in relation to catch crops must be adapted to the specific soil and cropping systems.
Climate change may have profound effects on phosphorus (P) transport in streams and on lake eutrophication. Phosphorus loading from land to streams is expected to increase in northern temperate ...coastal regions due to higher winter rainfall and to a decline in warm temperate and arid climates. Model results suggest a 3.3 to 16.5% increase within the next 100 yr in the P loading of Danish streams depending on soil type and region. In lakes, higher eutrophication can be expected, reinforced by temperature-mediated higher P release from the sediment. Furthermore, a shift in fish community structure toward small and abundant plankti-benthivorous fish enhances predator control of zooplankton, resulting in higher phytoplankton biomass. Data from Danish lakes indicate increased chlorophyll a and phytoplankton biomass, higher dominance of dinophytes and cyanobacteria (most notably of nitrogen fixing forms), but lower abundance of diatoms and chrysophytes, reduced size of copepods and cladocerans, and a tendency to reduced zooplankton biomass and zooplankton:phytoplankton biomass ratio when lakes warm. Higher P concentrations are also seen in warm arid lakes despite reduced external loading due to increased evapotranspiration and reduced inflow. Therefore, the critical loading for good ecological state in lakes has to be lowered in a future warmer climate. This calls for adaptation measures, which in the northern temperate zone should include improved P cycling in agriculture, reduced loading from point sources, and (re)-establishment of wetlands and riparian buffer zones. In the arid Southern Europe, restrictions on human use of water are also needed, not least on irrigation.
Aims
Cover crops (CC) have been widely used to improve soil quality and sustain agricultural productivity. However, the turnover of carbon (C) and nitrogen (N) from different species and parts of CCs ...incorporated into the soil under Northern European conditions remains unclear.
Methods
In this study, we examined mineralization of C and N from isolated shoots and roots of two leguminous and two non-leguminous CCs labeled with
15
N tracers in a 100-day incubation experiment at 10 °C.
Results
After 100 days incubation, the average net N mineralization was 33% from the leguminous CCs and 20% from the non-legumes. Net N mineralization from shoots was 1–15% (% of the N input) higher than that from the corresponding roots, and the net C mineralization accounted for 53–62% and 18–39% of the total C applied with CC shoots and roots, respectively. The C/N ratio of plant residues was a good predictor for net N mineralization, while the lignin concentration was a good predictor for C mineralization from both roots and shoots. Roots of both legume and non-legume CCs caused net immobilization of (unlabeled) soil N, whereas no significant soil N immobilization occurred from shoots with low C/N ratios.
Conclusions
Our results indicate that different CC characteristics (C/N ratio and lignin) control the turnover of residue N and C, respectively, in the soil. Our results further showed very limited interactions with soil N turnover (no priming effects) when materials with low C/N ratios were applied to soil.
Crop residue incorporation is a common practice to increase or restore organic matter stocks in agricultural soils. However, this practice often increases emissions of the powerful greenhouse gas ...nitrous oxide (N2O). Previous meta-analyses have linked various biochemical properties of crop residues to N2O emissions, but the relationships between these properties have been overlooked, hampering our ability to predict N2O emissions from specific residues. Here we combine comprehensive databases for N2O emissions from crop residues and crop residue biochemical characteristics with a random-meta-forest approach, to develop a predictive framework of crop residue effects on N2O emissions. On average, crop residue incorporation increased soil N2O emissions by 43% compared to residue removal, however crop residues led to both increases and reductions in N2O emissions. Crop residue effects on N2O emissions were best predicted by easily degradable fractions (i.e. water soluble carbon, soluble Van Soest fraction (NDS)), structural fractions and N returned with crop residues. The relationship between these biochemical properties and N2O emissions differed widely in terms of form and direction. However, due to the strong correlations among these properties, we were able to develop a simplified classification for crop residues based on the stage of physiological maturity of the plant at which the residue was generated. This maturity criteria provided the most robust and yet simple approach to categorize crop residues according to their potential to regulate N2O emissions. Immature residues (high water soluble carbon, soluble NDS and total N concentration, low relative cellulose, hemicellulose, lignin fractions, and low C:N ratio) strongly stimulated N2O emissions, whereas mature residues with opposite characteristics had marginal effects on N2O. The most important crop types belonging to the immature residue group – cover crops, grasslands and vegetables – are important for the delivery of multiple ecosystem services. Thus, these residues should be managed properly to avoid their potentially high N2O emissions.
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•Meta-analysis to identify best predictors of crop residue N2O emissions•Nitrogen returned with residues and residue characteristics were good predictors.•The predictive power of individual residue characteristics was limited.•Using correlations between chemical characteristics, we developed a maturity class.•Immature residues stimulate N2O emissions, mature residues have marginal effects.
Nutrient loadings of nitrogen (N) and phosphorus (P) to aquatic environments are of increasing concern globally for managing ecosystems, drinking water supply and food production. There are often ...multiple sources of these nutrients in the landscape, and the different hydrological flow patterns within stream or river catchments have considerable influence on nutrient transport, transformation and retention processes that all eventually affect loadings to vulnerable aquatic environments. Therefore, in order to address options to reduce nutrient loadings, quantitative assessment of their effects in real catchments need to be undertaken. This involves setting up scenarios of the possible nutrient load reduction measures and quantifying their impacts via modelling. Over the recent two decades there has been a great increase in the use of scenario-based analyses of strategies to combat excessive nutrient loadings. Here we review 130 published papers extracted from Web of Science for 1995 to 2014 that have applied models to analyse scenarios of agricultural impacts on nutrients loadings at catchment scale. The review shows that scenario studies have been performed over a broad range of climatic conditions, with a large focus on measures targeting land cover/use and land management for reducing the source load of N and P in the landscape. Some of the studies considered how to manage the flows of nutrients, or how changes in the landscape may be used to influence both flows and transformation processes. Few studies have considered spatially targeting measures in the landscape, and such studies are more recent. Spatially differentiated options include land cover/use modification and application of different land management options based on catchments characteristics, cropping conditions and climatic conditions. Most of the studies used existing catchment models such as SWAT and INCA, and the choice of the models may also have influenced the setup of the scenarios. The use of stakeholders for designing scenarios and for communication of results does not seem to be a widespread practice, and it would be recommendable for future scenario studies to have a more in-depth involvement of stakeholders for the elaboration and interpretation of scenarios, in particular to enhance their relevance for farm and catchment management and to foster better policies and incentives.
•The most widely applied measures in scenarios are changes in land use and agricultural land management.•None of the reviewed papers considered spatial differentiated measures due to variation in groundwater reduction of nitrogen.•Scenario evaluation was carried out with a limited set of models.•All scenario studies have limitations as well as technical and conceptual uncertainties.•Scenario building should better consider spatial information and the use of participatory approaches.
Many current organic arable agriculture systems are challenged by a dependency on imported livestock manure from conventional agriculture. At the same time organic agriculture aims at being climate ...friendly. A life cycle assessment is used in this paper to compare the carbon footprints of different organic arable crop rotations with different sources of N supply. Data from long-term field experiments at three different locations in Denmark were used to analyse three different organic cropping systems (‘Slurry’, ‘Biogas’ and ‘Mulching’), one conventional cropping system (‘Conventional’) and a “No input” system as reference systems. The ‘Slurry’ and ‘Conventional’ rotations received slurry and mineral fertilizer, respectively, whereas the ‘No input’ was unfertilized. The ‘Mulching’ and ‘Biogas’ rotations had one year of grass-clover instead of a faba bean crop. The grass-clover biomass was incorporated in the soil in the ‘Mulching’ rotation and removed and used for biogas production in the ‘Biogas’ rotation (and residues from biogas production were simulated to be returned to the field).
A method was suggested for allocating effects of fertility building crops in life cycle assessments. The results showed significantly lower carbon footprint of the crops from the ‘Biogas’ rotation (assuming that biogas replaces fossil gas) whereas the remaining crop rotations had comparable carbon footprints per kg cash crop. The study showed considerable contributions caused by the green manure crop (grass-clover) and highlights the importance of analysing the whole crop rotation and including soil carbon changes when estimating carbon footprints of organic crops especially where green manure crops are included.
•Carbon footprints of crops from organic and conventional crop rotations were assessed.•The contributions caused by the green manure crop were considerable.•Highlights the importance of analysing the whole crop rotation and to include soil carbon changes.•Carbon footprint of organic compared to conventional varied depending on production practice.•Indicates a potential for improving the carbon footprint of organic produce.
Decline in climate resilience of European wheat Kahiluoto, Helena; Kaseva, Janne; Balek, Jan ...
Proceedings of the National Academy of Sciences - PNAS,
01/2019, Volume:
116, Issue:
1
Journal Article
Peer reviewed
Open access
Food security relies on the resilience of staple food crops to climatic variability and extremes, but the climate resilience of European wheat is unknown. A diversity of responses to disturbance is ...considered a key determinant of resilience. The capacity of a sole crop genotype to perform well under climatic variability is limited; therefore, a set of cultivars with diverse responses to weather conditions critical to crop yield is required. Here, we show a decline in the response diversity of wheat in farmers’ fields in most European countries after 2002–2009 based on 101,000 cultivar yield observations. Similar responses to weather were identified in cultivar trials among central European countries and southern European countries. A response diversity hotspot appeared in the trials in Slovakia, while response diversity “deserts” were identified in Czechia and Germany and for durum wheat in southern Europe. Positive responses to abundant precipitation were lacking. This assessment suggests that current breeding programs and cultivar selection practices do not sufficiently prepare for climatic uncertainty and variability. Consequently, the demand for climate resilience of staple food crops such as wheat must be better articulated. Assessments and communication of response diversity enable collective learning across supply chains. Increased awareness could foster governance of resilience through research and breeding programs, incentives, and regulation.
Increased human‐derived nitrogen (N) deposition to terrestrial ecosystems has resulted in widespread phosphorus (P) limitation of net primary productivity. However, it remains unclear if and how ...N‐induced P limitation varies over time. Soil extracellular phosphatases catalyze the hydrolysis of P from soil organic matter, an important adaptive mechanism for ecosystems to cope with N‐induced P limitation. Here we show, using a meta‐analysis of 140 studies and 668 observations worldwide, that N stimulation of soil phosphatase activity diminishes over time. Whereas short‐term N loading (≤5 years) significantly increased soil phosphatase activity by 28%, long‐term N loading had no significant effect. Nitrogen loading did not affect soil available P and total P content in either short‐ or long‐term studies. Together, these results suggest that N‐induced P limitation in ecosystems is alleviated in the long‐term through the initial stimulation of soil phosphatase activity, thereby securing P supply to support plant growth. Our results suggest that increases in terrestrial carbon uptake due to ongoing anthropogenic N loading may be greater than previously thought.
Current Earth System Models predict strong P limitation of plant productivity, based on the assumption that anthropogenic N enrichment shifts plant growth from N to P limitation. However, empirical evidence for P limitation following prolonged N additions is equivocal, and temporal variations in P limitation have not been systematically assessed. Using soil phosphatase activity as an indicator of P limitation, we show that N‐induced P limitation acclimates to long‐term N addition. This finding highlights the importance of plant and microbial adaptation strategies to control P availability. Absence of these strategies in models underestimates the potential of vegetation to slow climate change.
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