Effect of moisture and freezing on some physical properties of clay soils from plough layer

Abstract

The aim of this study was to elucidate the effects of freezing on some structural properties of clay soils. The laboratory analyses were based on field observations including measurements of soil temperature and frost depth. The daily temperatures showed remarkable variations on the very soil surface both in the autumn and spring, ranging from below zero at night-time to above 10°C at daytime. The depth of soil frost was deepest in the ploughed field, whilst the straw cowers on the soil surface not only strongly reduced its depth, but also slowed up the thawing. Eight clay soil samples were analyzed in the laboratory. At the potentials of —0.001 to —0.1 bar the water retention capability of soil was reduced by freezing. Disruption of the 5 —10 mm aggregates by freezing, analyzed with wet and dry sievings and waterdrop analysis was strongly dependent on the water potential, the Water potential of 1.0 bar or lower having in general no effect. The total pore volume of aggregates Was dependent on the water potential when it exceeded —15.0 bar. Freezing had a minor effect on the pore volume of the aggregates, if they were let to thaw before drying. The freeze-dried aggregates showed a clear increase of pore volume when the water potential at freezing exceeded —1.0 bar. The movement of water due to ice formation was studied with small and big soil cylinders. It showed a great effect on the structure, if total pore volume, determined with a mercury method, is considered the standard of judgement. Thus it was concluded that the water movement even at a short freezing period is one of the most essential factors determining the structural formation of ploughed clay soil.

Reduced tillage: Influence on erosion and nutrient losses in a clayey field in southern

“…Except for very dry spring 1993, drainage flow in spring was higher in the PF in all years of the study. This reflects the water's quicker access to the drainage pipes via the ploughing furrows and the macropores (Bengtsson et al 1992) and the faster frost thawing (Kivisaari 1979) in ploughed soil. These reasons are in line with our finding that occasional drainage flow peaks detected in the PF in winter were usually not seen in the NPF.…”

“…Reduced tillage with a protective cover of crop residues left on the soil surface has many advantages over conventional cultivation. Soil with a reduced tillage is found to have higher and longer-lasting moisture (Blevins et al 1983, Kladivko et al 1986, Unger and Fulton 1990, Patni et al 1996 which, in boreal conditions is also affected by slower frost thawing (Kivisaari 1979). Additionally, because of the higher amount of organic matter in the surface soil, the stability of soil aggregates is increased and the structure of the soil improved (Jessen 1984, Kivisaari 1985.…”

Frost action in clay soils. II. Ice and water location and suction of unfrozen water in clays below 0°C

“…The action of frost on clay soils can cause clods and compact layers to be broken down to form finely-aggregated soil or frost tilth (Kivisaari, 1979). However, on freezing and thawing, the sizes of aggregates produced and the magnitude of bulk density changes vary with clay and soil type.…”

Extractability of slurry and fertilizer phosphorus in soil after repeated freezing

“…The effects of freezing on the physical properties of soil (Miller 1980) have been studied more extensively than the mechanisms affecting soil chemistry. In Finland, where most soils freeze annually, the effects of freezing on soil physics have also created interest (Sillanpää 1961, Kivisaari 1979, but hard-…”