Long-Term Effect of Organic Residues On Soil Properties In Two Loamy Soils In Denmark.

Mobilization or dispersion of soil colloids can result in breakdown of soil aggregates, and thereby soil structure, leading to a more massive soil, following the clogging of pores which can impair water transport and aeration of the soil. In addition dispersion has been shown to increase the potential risk of leaching of strongly sorbing compounds, such as PAH’s, and phosphorus to fresh water streams via tile drains and ground water reservoirs. One field pair and two fields from a long-term field-experiment were studied; the former near Fredericia (FR) and the latter near Ronhave (RH), Denmark. At RH one field had straw incorporated for the last 36 years (RH-SI), whereas the other had straw removed (RH-NS). At FR one field was organically farmed with manure application (FR-AM), whereas the other was conventionally farmed with annual cash crop and application of mineral fertilizer (FR-MF). Leaching experiments were carried out on undisturbed soil columns from all 4 four fields in order to indentify differences in soil functions/properties caused by the differences in organic carbon (OC). We measured saturated and unsaturated hydraulic conductivity, air-permeability, porosity, bulk-density and break-through of an inert tracer, tritium, as well as basic soil properties. Generally RH-SI and FR-AM had higher OC, higher porosity, higher air permeability, and higher saturated conductivity. Also RH-SI and FR-AM had slightly longer times for arrival of 5% of applied tracer suggesting a more “sponge”-like inter-connected system of smaller pores as opposed to a few larger pores. The loss of particles at end-of-experiment was remarkably similar within each field pair. With soil texture being very similar within the two field pairs, differences in soil properties and functions was related to basic properties such as OC and bulk density, but it was remarkable how little impact the long term differences in treatment had affected the soil.