Soil properties currently limiting crop yields in Swedish agriculture – An analysis of 90 yield survey districts and 10 long-term field experiments
Introduction
Crop yield is of fundamental importance for food security. Yield increases must keep pace with population growth in order to provide sufficient food and avert famine (Malthus, 1798). The expansion in the global population from 1.6 billion people in 1900 to 7.8 billion today was possible through industrial synthesis of ammonia and use of inorganic fertilizers and lime leading to higher crop yields (Smil, 2000). Plant breeding has also improved the yield potential of crops and new varieties are the driving force behind current yield increases (Foulkes et al., 2007). Continuing yield increases are vital in many parts of the world due to population growth (Lobell et al., 2009; Godfray et al., 2010).
It has been observed in many European countries that yield increases are stagnating, as indicated by FAO statistics (http://faostat3.fao.org/home/E). For example, Wiesmeier et al. (2015) analyzed FAO data for three of the most important crops world-wide (wheat, barley, and maize) and found that production in both Central and Northern Europe levelled out after a breakpoint in the early 1990s. Several reasons for this have been proposed in different countries: Denmark: Regulations limiting nitrogen (N) application to crops and growing more wheat after wheat in rotations (Petersen et al., 2010). Finland: Environmental programs to reduce fertilizer inputs and nutrient emissions, compared with the modest economic incentive to increase production due to low prices for wheat (Peltonen-Sainio et al., 2009). France: Reducing N fertilizer rates, growing less legumes in rotations, experiencing high temperatures during grain filling, and drought during stem elongation (Brisson et al., 2010). Germany: Agricultural policies and economic reasons to reduce nutrient supply to crop (Laidig et al., 2014). Switzerland: Agricultural policies for adoption of extensive farming, lowering the input of mineral fertilizer (Finger, 2010). In summary, agricultural policies aiming at lowering environmental impacts by limiting nutrient input are a main reason for the stagnating yield increase in European countries.
Unlike in several other European countries, application rates of mineral fertilizer are not legally limited in Sweden, although animal manure application is limited to a maximum of 170 kg total N ha−1 in vulnerable areas (Jordbruksverket, 2015). Inputs of mineral N fertilizer have steadily increased in Sweden (SCB, 2016a), accompanied by steady yield improvements (SCB, 1982-2010). However, total crop production has been reduced due to large-scale transformation to organic farming reducing yields significantly (SCB, 2016b). Instead of N fertilizer regulations, measures to reduce discharge of nutrients from arable land to the surrounding environment have been prioritized in Sweden. These include farming more autumn-sown crops, subsidies for catch crops, creation of wetlands and buffer strips, use of N sensors and/or crop satellite images for split N application, etc. (Bergström et al., 2015). These measures have succeeded in reducing N leaching losses, as shown by long-term environmental monitoring (Fölster et al., 2012).
Short-term field trials are useful when investigating the effects of soil management, fertilizer treatments, or crop varieties on crop yields (Bootsma et al., 2005; Speirs et al., 2013). Long-term field experiments are required when analyzing soil properties requiring decades to change (Powlson et al., 2014; Ridley and Hedlin, 1980), such as SOM, pH, and plant-available phosphorus, before affecting soil functioning (Bai et al., 2018; Bünemann et al., 2018). National soil-monitoring programs and databases created from routine soil analyses by farmers and agricultural statistics are useful for assessing spatio-temporal changes in critical soil properties (Baxter et al., 2006; Lemercier et al., 2008).
In this study, data from long-term field trials and an intensive Swedish soil monitoring program, similar to the soil inventory of German arable soils (Jacobs et al., 2018), and yearly agricultural statistics were used for identification of soil properties currently limiting crop production. The objective was to identify which, and to what extent, soil properties (other than N input) limit yields of cereals, oilseeds, and root crops under various pedo-climatic conditions in Sweden. The data included physical and chemical soil properties from a detailed national soil inventory representing 90 yield survey districts, climate data and crop yield statistics, and results from long-term field experiments across the country.
To identify the most important soil properties limiting productivity and to estimate optimum soil conditions required for highest achievable yields, data on soil properties and crop yields were used to address the following research questions:
i) What general information about Swedish arable soils can be retrieved from the national soil inventory?
(ii) What type of yield response pattern in relation to soil variables (linear or breaking points) can be distinguished?
(iii) Which soil properties limit crop yields most significantly in current agriculture?
(iv) What are the critical levels of the main soil properties reducing yields?
(v) Do the data obtained in the soil inventory and yield survey districts match the outcome from long-term field experiments?
(vi) Are current agronomic recommendations appropriate, given the results of the above analysis?
An overall objective was to identify best agronomic practices in order to maintain yield increases, make best use of nutrients, and reduce negative environmental impacts so as to meet national environmental quality goals (Naturvårdsverket, 2017).
Section snippets
Soil inventory and crop yield data
Soil data were derived from the most comprehensive inventory to date of topsoil characteristics of Swedish arable land (Paulsson et al., 2015; Djodjic, 2015). This soil-monitoring program was performed in 2013 by the Swedish Board of Agriculture, in order to create a better map of Swedish arable soils. It included 12 554 topsoil samples distributed all over southern Sweden (Fig. 1), enabling site identification for specific agricultural measures. In this study, we focused on mineral soils only,
Overview of the soil inventory
Texture: The survey revealed that the dominant soil texture class was sandy loam (30 %), followed by silt loam (17 %) and loam (14 %). Fine-textured soils such silt (1%), silty clay (8%), and clay (5%) comprised of around 15 % of arable soils, while sand (2%) and loamy sand (9%) comprised around 11 % (Djodjic, 2015). The geographical distribution map revealed that clay soils were most prevalent in east-central parts of the survey area (Fig. 2), which is in good agreement with a previous texture
Why did yields respond negatively to higher soil organic matter content?
It is widely accepted that SOM is a very important indicator of soil fertility and crop productivity (Körschens et al., 2013; Lal, 2013). Meta-analyses using long-term field experiments and annual N-fertilizer trials have confirmed the positive impact of SOM on yields (Liu et al., 2014; Wang et al., 2015; Lu, 2015; Zhang et al., 2016). Positive yield responses to gradual increases in SOM have also been observed in a Swedish long-term field experiment (Henryson et al., 2018). However, negative
Conclusions
Availability of two comprehensive data sets on Swedish arable soils and regional crop yield statistics enabled us to evaluate soil variables currently limiting crop yields. Multi-variate analysis, PCA, step-wise regression, and tree partitioning analysis identified the same variables affecting yields. One main finding was that current agricultural recommendations require updating. Considering that no legislative restrictions were put on N fertilizer use in Swedish agriculture, the following
CRediT authorship contribution statement
Holger Kirchmann: Conceptualization, Writing - review & editing, Validation. Gunnar Börjesson: Data curation, Validation. Martin A. Bolinder: Data curation, Writing - review & editing. Thomas Kätterer: Methodology, Writing - review & editing. Faruk Djodjic: Data curation, Formal analysis, Writing - original draft.
Declaration of Competing Interest
This article has not be inflicted by affiliations, memberships, funding, financial holdings, interests of industries, individual companies or retailers affecting the objectivity of the data analysis.
Acknowledgements
The national data were collected by the Swedish Board of Agriculture, which is greatly acknowledged. The evaluation of data sets was sponsored by the Royal Swedish Academy of Agriculture and Forestry (KSLA), (Grant no. VX2016-0004) and the Swedish Farmers' Foundation for Agricultural Research (Grant no. O-18-23-141), which we are thankful for.
References (83)
- et al.
Effect of agricultural management practices on soil quality: a review of long-term experiments for Europe and China
Agric. Ecosyst. Environ.
(2018) - et al.
Soil acidification and liming interactions with nutrient and heavy metal transformation and bioavilability
Adv. Agron.
(2003) - et al.
Why are wheat yields stagnating in Europe? A comprehensive data analysis for France
Field Crops Res.
(2010) - et al.
Soil quality – a critical review
Soil Biol. Biochem.
(2018) - et al.
Changes in mortality of Pythium zoospores induced by calcium and calcium-modulating drugs
Mycol. Res.
(1993) Evidence of slowing yield growth - the example of Swiss cereal yields
Food Policy
(2010)Definitions and determination of crop yield, yield gaps, and of rates of change
Field Crops Res.
(2015)- et al.
The pH dependence of phosphate sorption and desorption in Swedish agricultural soils
Geoderma
(2012) - et al.
Accounting for long-term soil fertility effects when assessing the climate impact of crop cultivation
Agric. Syst.
(2018) - et al.
Yield responses of arable crops to liming - an evaluation of relationships between yields and soil pH from a long-term liming experiment
Eur. J. Agron.
(2019)
Roots contribute more to refractory soil organic matter than above-ground crop residues, as revealed by a long-term field experiment
Agric. Ecosys. Environ.
Do soil organic carbon levels affect potential yields and nitrogen use efficiency? An analysis of winter wheat and spring barley field trials
Eur. J. Agron.
Influence of soil characteristics on yield response to lime in sugar beet
Geoderma
Cereal yield trends in northern European conditions: changes in yield potential and its realisation
Field Crops Res.
Abiotic characteristics of soils suppressive to Aphanomyces root rot
Soil Biol. Biochem.
Linkages between aggregate formation, porosity and soil chemical properties
Geoderma
The role of soil organic matter for maintaining crop yields: evidence for a renewed conceptual basis
Adv. Agron.
Extent to which pH and topographic factors control soil organic carbon level in dry farming cropland soils of the mountainous region of Southwest China
Catena
Stagnating crop yields: an overlooked risk for the carbon balance of agricultural soils?
Sci. Total Environ.
Effects of enhancing soil organic carbon sequestration in the topsoil by fertilization on crop productivity and stability: evidence from long-term experiments with wheat-maize cropping systems in China
Sci. Total Environ.
The representative soil sampling scheme of England and Wales: the spatial variation of topsoil nutrient status and pH between 1971 and 2001
Soil Use Managem
Turnover and losses of phosphorus in Swedish agricultural soils: long-Term changes, leaching trends, and mitigation measures
J. Environ. Qual.
Processes of soil acidification during nitrogen cycling with emphasis on legume based pastures
Plant Soil
Potential impacts of climate change on corn, soybeans and barley yields in Atlantic Canada
Can. J. Plant Sci.
Swedish soil fertility experiments
Acta Agric. Scand. Sect. B Soil Plant Sci.
Jordartsfördelning och Växtnäringstillstånd i Svensk Åkermark – Sammanställning av Resultat från Jordbruksverkets Nationella Jordartskartering. Institutionen för vatten och miljö. Rapport 2015:11
Untersuchungen über die chemische Bodenanalyse als Grundlage für die Beurteilung des Nährstoffzustandes der Böden. II. Chemische Extraktionsmethoden zur Phoshor- und Kaliumbestimmung
Ann. Royal Agric. College Sweden
Åkermarkens matjordstyper. Naturvårdsverket. Rapport 4955
Review of beneficial uses of calcium and ammonium salts for stimulating plant growth and metabolite translocation
Comm. Soil Sci. Plant Anal.
Kväve- och Fosfortrender i Jordbruksvattendrag. Har Åtgärderna gett Effekt? Department of Water and Environment, Rapport 2012:1
Genetic progress in yield potential in wheat: recent advances and future prospects
J. Agric. Sci.
Food security: the challenge of feeding 9 billion people
Science
Soil acidification and the importance of liming agricultural soils with particular reference to the United Kingdom
Soil Use Manag.
Field Experiments With Liming of Mineral Soils to Different Base Saturation. Department of Soil Sciences, Division of Soil Fertility, Report 188
Effects of Liming and NPK Fertilization in Seven Long-term Field Experiments, 1962-1992. Department of Soil Sciences, Division of Soil Fertility, Report 198
Soil acidification induced by leguminous crops
Grass Forage Sci.
Do organic inputs matter – a meta-analysis of additional yield effects for arable crops in Europe
Plant Soil
Origins of root-mediated pH changes in the rhizosphere and their responses to environmental constraints: a review
Plant Soil
Soil Quality - Determination of Particle Size Distribution in Mineral Soil Material. Method by Sieving and Sedimentation
Landwirtschaftlich genutzte Böden in Deutschland – Ergebnisse der Bodenzustandserhebung
Föreskrifter Om Ändring I Statens Jordbruksverks Föreskrifter Och Allmänna Råd (SJVFS 2004:62) Om Miljöhänsyn I Jordbruket Vad Avser Växtnäring
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