Mapping Soil Physical Structure of an Agricultural Field for Assessing Potential Leaching Risk
Translated title
Mapping Soil Physical Structure of an Agricultural Field for Assessing Potential Leaching
Author
Nørgaard, Trine
Term
10. term
Publication year
2011
Pages
88
Abstract
This thesis develops and tests a simple, field-based foundation for risk and vulnerability assessments of pesticide and contaminant leaching. As part of the Danish Pesticide Leaching Assessment Programme (PLAP), a field at Silstrup in northwestern Jutland was investigated. Undisturbed soil columns were sampled on a 15×15 m grid and irrigated at 10 mm h-1 for approximately 6.5 hours. A tracer was applied as a 10-minute impulse to characterize water transport, colloid concentrations in the effluent were monitored over time to evaluate colloid-facilitated transport, phosphorus was used as a model of a strongly sorbing compound, and soil texture was determined from bulk samples collected adjacent to the columns. A large amount of colloids leached during the first flush, and the risk of colloid-facilitated transport was enhanced by mobilized colloids and the presence of macropores. Simple leaching tests combined with texture analyses enabled identification of particularly vulnerable areas at the field scale. The highly structured Silstrup soil allowed colloid-facilitated transport, and phosphorus leaching was positively correlated with particle leaching but—contrary to other studies—not with soil clay content. Soil structure across the field could be characterized using the 5% tracer arrival time, tracer mass balance, and bulk density, indicating a practical basis for mapping and decision support at the field scale.
Dette speciale udvikler og afprøver et enkelt, feltbaseret grundlag for risiko- og sårbarhedsvurderinger af udvaskning af pesticider og andre forurenende stoffer. Som led i det danske Pesticide Leaching Assessment Programme (PLAP) undersøges en mark ved Silstrup i Nordvestjylland. Uforstyrrede jordkolonner blev udtaget i et 15×15 m gitter og gennemvandet med 10 mm h-1 i cirka 6,5 time. En tracer blev tilført som et 10 minutters impuls for at beskrive vandtransporten, kolloidkoncentrationer i afløbet blev målt over tid for at belyse kolloid-faciliteret transport, og fosfor blev anvendt som model for et stærkt sorberende stof; jordtekstur blev bestemt på bulksamples udtaget ved siden af kolonnerne. En stor mængde kolloider blev udvasket under “first flush”, og risikoen for kolloid-faciliteret transport blev øget af mobiliserede kolloider og tilstedeværelsen af makroporer. Enkle udvaskningsforsøg kombineret med teksturanalyser gjorde det muligt at identificere særligt sårbare områder på markskala. Den stærkt strukturerede jord i Silstrup tillod kolloid-faciliteret transport, og udvaskning af fosfor var positivt korreleret med partikeludvaskning, men – i modsætning til andre studier – ikke med jordens lerindhold. Jordstrukturen inden for marken kunne karakteriseres ved hjælp af 5% tracer-ankomsttid, tracer-massebalance og jordens bulk densitet, hvilket peger på et operationelt grundlag for kortlægning og beslutningsstøtte på markniveau.
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