Threats to soil quality in Denmark - A review of existing knowledge in the context of the EU Soil Thematic Strategy

The EU Commission is preparing a proposal for a Soil Framework Directive with the purpose of protecting the soil resources in Europe. The proposal identifies six major threats to the sustained quality of soils in Europe. This report addresses the threats that are considered most important under the prevailing soil and climatic conditions in Denmark: compaction, soil organic matter decline, and erosion by water and tillage. For each of these threats, the relevance and damage to soil functions as well as the geographic distribution in Denmark are outlined. We suggest a procedure for identifying areas at risk. This exercise involves an explicit identification of: i) the disturbing agent (climate / management) exerting the pressures on soil, and ii) the vulnerability of the soil to those stresses. Risk reduction targets, measures required to reach these targets, and the knowledge gaps and research needs to effectively cope with each threat are discussed. Our evaluation of the threats is based on soil resilience to the imposed stresses. Subsoil compaction is considered a severe threat to Danish soils due to frequent traffic with heavy machinery in modern agriculture and forestry. The soil content of organic matter is critically low for a range of Danish soils, which should be counteracted by appropriate management options. Soil erosion by tillage, and to a lesser degree by water, adversely affects soil quality on much of the farmland because degradation rates are much higher than generation of soil

Management of phosphorus supply to Australian floricultural species

Young plants of Sticherus, waxflower (Chamelaucium) and two Caustis cultivars were grown in a soilless potting medium. The plants were fertilised at seven rates of the soluble monocalcium phosphate (MCP) fertiliser and one rate of the slightly soluble rock phosphate (RP). One group of plants was watered by a non-leaching and a second group of plants watered by a leaching method. Both Caustis cultivars (M63, B84) grown in the potting medium under the non-leaching regime did not show deficiency symptoms at no added P, but they showed P toxicity symptoms at MCP-P application rates > 11 g m-3. The critical P concentration in the shoots associated with a 10% decrease in yield from the maximum was 0.26% for Caustis M63 and 0.33% for Caustis B84. The two Caustis cultivars did not develop P toxicity symptoms or show any decline in shoot dry weight when fertilised with RP under both non-leaching and leaching regimes. Leaching reduced but did not eliminate P toxicity in both Caustis cultivars, although shoot dry weight did not differ significantly between the two watering regimes used. Waxflower grew poorly in the potting medium under the non-leaching regime at no added P or when fertilised with RP but did not develop P toxicity symptoms at any rate of P application as MCP, including the highest rate of 352 g m-3. The waxflower plants grew less well under the leaching than when grown under the non-leaching regime. The critical NaHCO3-extractable P level required for production of 90% relative dry weight of shoots of waxflower was about 46 mg kg-1 under the non-leaching and about 69 mg kg-1 medium under the leaching regime. Under the non-leaching regime the critical NaHCO3-extractable P level for toxicity of Caustis B84 was about 13 mg kg-1 while under the leaching regime this was higher at about 22 mg kg-1. Sticherus plants did not respond significantly to P application as either MCP or RP. However, Sticherus plants grew much better when grown under the leaching than when they were grown under the non-leaching regime. Although leaching conferred some advantages in the growth of Sticherus and in the reduction of P toxicity in Caustis, it also caused a considerable loss of P

Pronounced surface stratification of soil phosphorus, potassium and sulfur under pastures upstream of a eutrophic wetland and estuarine system

High concentrations of nutrients in surface soil present a risk of nutrient movement into waterways through surface water pathways and leaching. Phosphorus (P) is of particular concern because of its role in aquatic system eutrophication. We measured nutrients under annual pastures on a beef farm and a dairy farm in the Peel–Harvey catchment, Western Australia. Soils were sampled in 10-mm increments to 100mm depth in March, June and September. Plant litter contained approximately 300–550 mg kg–1 Colwell-extractable P. Extractable soil P was strongly stratified, being approximately 100–225 mg kg–1 (dairy) and 50–110 mg kg–1 (beef) in the top 10mm and 4mg g–1). We conclude that high P concentrations at the soil surface and in litter and shoots are a source of risk for movement of P from farms into waterways in the Peel–Harvey catchment

Mapping rill soil erosion in agricultural fields with UAV-borne remote sensing data

Soil erosion by water is a main form of land degradation worldwide. The problem has been addressed, among others, in the United Nations Sustainability Goals. However, for mitigation of erosion consequences and adequate management of affected areas, reliable information on the magnitude and spatial patterns of erosion is needed. Although such need is often addressed by erosion modelling, precise erosion monitoring is necessary for the calibration and validation of erosion models and to study erosion patterns in landscapes. Conventional methods for quantification of rill erosion are based on labour-intensive field measurements. In contrast, remote sensing techniques promise fast, non-invasive, systematic and larger-scale surveying. Thus, the main objective of this study was to develop and evaluate automated and transferable methodologies for mapping the spatial extent of erosion rills from a single acquisition of remote sensing data. Data collected by an uncrewed aerial vehicle was used to deliver a highly detailed digital elevation model (DEM) of the analysed area. Rills were classified by two methods with different settings. One approach was based on a series of decision rules applied on DEM-derived geomorphological terrain attributes. The second approach utilized the random forest machine learning algorithm. The methods were tested on three agricultural fields representing different erosion patterns and vegetation covers. Our study showed that the proposed methods can ensure recognition of rills with accuracies between 80 and 90% depending on rill characteristics. In some cases, however, the methods were sensitive to very small rill incisions and to similar geometry of rills to other features. Additionally, their performance was influenced by the vegetation structure and cover. Besides these challenges, the introduced approach was capable of mapping rills fully automatically at the field scale and can, therefore, support a fast and flexible assessment of erosion magnitudes

Drawn to nature: Young children learning about nature through drawing

Today children in the developed world have less experience of the natural environment than any previous generation, due to a range of environmental and social factors that have changed how children live their lives. Many observers are concerned that children are missing out on the benefits of engaging with nature, which impacts on physical and psychological health, play and development, and the possible cultivation of future environmentalists. Reconnecting children with nature has become a focus for many people in the developed world. This visual ethnographic study had a two-fold purpose: to engage a group of young children, aged 3 to 5 years, in studying nature in their immediate environment of the preschool playspace, and to document how they made meaning from their observations and ideas using drawing. As background to the study I explored the reasons for the erosion of children's contact with the natural world. I also examined the changes in theories of children's drawing development from stage theory to repertoires, intentionality, multi-modality and meaning making. My study documented the children engaging in dialogue and drawing subsequent to their explorations of the outdoor playspace. I focused on how the children used drawing to document, communicate, explore and experiment with their understandings of the natural world. The children's learning was analysed within a Vygotskian social constructionist framework, as well as in the light of other contemporary theorists. I demonstrated that drawing acted as a mediator between perceptions and thought, and functioned as a tool for learning (Vygotsky, 1962)

Pløjefri dyrkning: effekter på jordens frugtbarhed

Interessen for pløjefri dyrkning er steget voldsomt gennem de seneste år. Fokus har primært været på de kortsigtede økonomiske gevinster som følge af mindsket tidsforbrug og lavere maskinomkostninger og i langt mindre grad på de langsigtede gavnlige effekter af pløjefri dyrkning på jordens frugtbarhed. Forskellen er slående i forhold til Nordamerika, hvor den udbredte brug af pløjefri dyrkning i høj grad er båret af et ønske om en langsigtet sikring af jordens frugtbarhed (jfr. betegnelsen ”conservation tillage” anvendt for pløjefri jordbearbejdning. I Nordamerika har man især været optaget af pløjefri dyrkning, som et middel til bekæmpelse af vind- og vanderosion. Pløjefri dyrkning er også et anvendeligt redskab til at begrænse pakningen i dybden og den omfattende jordflytning ved jordbearbejdning – såkaldt jordbearbejdsningserosion. De danske erfaringer med pløjefri dyrkning i 1970 og 80’erne var brogede. Der var problemer med håndtering af planterester og i mange tilfælde fandtes skadelig pakning af overjorden. Nyt effektivt udstyr til snitning og fordeling af halm og avner kan afhjælpe problemerne med planterester, mens problemet med skadelig pakning af overjorden fortsat eksisterer. Til løsning af pakning i overjorden anbefales ikke-vendende jordløsning til den behovsbestemte dybde, der sikrer at jorden ikke opblandes og en skånsom påvirkning af regnorme m.v. Genpakning af jorden er dog et problem, der skal tages højde for ligegyldigt hvilken strategi og hvilket redskab, der vælges til ikke-vendende løsning. Forebyggelse er det bedste middel imod pakning af overjorden, hvilket kan ske ved kontrolleret trafik i spor, der anvendes år efter år. Mindsket afhængighed af ukrudtsmidler og optimeret gødningsudnyttelse bør også være centrale elementer i fremtidige pløjefri dyrkningssystemer

Combining Laser-Induced Breakdown Spectroscopy (LIBS) and Visible Near-Infrared Spectroscopy (Vis–NIRS) for Soil Phosphorus Determination

Conventional wet chemical methods for the determination of soil phosphorus (P) pools, relevant for environmental and agronomic purposes, are labor-intensive. Therefore, alternative techniques are needed, and a combination of the spectroscopic techniques—in this case, laser-induced breakdown spectroscopy (LIBS)—and visible near-infrared spectroscopy (vis-NIRS) could be relevant. We aimed at exploring LIBS, vis-NIRS and their combination for soil P estimation. We analyzed 147 Danish agricultural soils with LIBS and vis-NIRS. As reference measurements, we analyzed water-extractable P (Pwater), Olsen P (Polsen), oxalate-extractable P (Pox) and total P (TP) by conventional wet chemical protocols, as proxies for respectively leachable, plant-available, adsorbed inorganic P, and TP in soil. Partial least squares regression (PLSR) models combined with interval partial least squares (iPLS) and competitive adaptive reweighted sampling (CARS) variable selection methods were tested, and the relevant wavelengths for soil P determination were identified. LIBS exhibited better results compared to vis-NIRS for all P models, except for Pwater, for which results were comparable. Model performance for both the LIBS and vis-NIRS techniques as well as the combined LIBS-vis-NIR approach was significantly improved when variable selection was applied. CARS performed better than iPLS in almost all cases. Combined LIBS and vis-NIRS models with variable selection showed the best results for all four P pools, except for Pox where the results were comparable to using the LIBS model with CARS. Merging LIBS and vis-NIRS with variable selection showed potential for improving soil P determinations, but larger and independent validation datasets should be tested in future studies

Transit times – the link between hydrology and water quality at the catchment scale

In spite of trying to understand processes in the same spatial domain, the catchment hydrology and water quality scientific communities are relatively disconnected and so are their respective models. This is emphasized by an inadequate representation of transport processes, in both catchment-scale hydrological and water quality models. While many hydrological models at the catchment scale only account for pressure propagation and not for mass transfer, catchment scale water quality models are typically limited by overly simplistic representations of flow processes. With the objective of raising awareness for this issue and outlining potential ways forward we provide a non-technical overview of (1) the importance of hydrology-controlled transport through catchment systems as the link between hydrology and water quality; (2) the limitations of current generation catchment-scale hydrological and water quality models; (3) the concept of transit times as tools to quantify transport and (4) the benefits of transit time based formulations of solute transport for catchment-scale hydrological and water quality models. There is emerging evidence that an explicit formulation of transport processes, based on the concept of transit times has the potential to improve the understanding of the integrated system dynamics of catchments and to provide a stronger link between catchment-scale hydrological and water quality models