Soil Structure

Soil Structure How the soil particles are arranged and associated with each other is called soil structure. Individual particles aggregate together, glued by attractive forces and by microbial activity plus organic matter.

If the soil simply consisted of a mass of individual particles, the spaces in-between would be very small and would seriously restrict the movement of air and water, particularly in the heavier soils.

Soil Porosity Pores exist between individual soil particles. These may be either large (macropores), medium (mesopores) or small (micropores), which is largely determined by the size of the individual particles and aggregates. Pores size is important because it determines permeability and percolation rate.

Fine textured soils, lots of micropores, some macropores Coarse textured soils, mainly macropores

Significance of Soil Structure 1.Water moves rapidly into open macropores(cracks, channels, and pores). 2.Water moves more slowly into micropores(pores between soil particles). As clay increases, so does the total porosity, but also the adhesion because pore size decreases. Soils that have a mixture of particle sizes and little porosity have restricted water movement.

Soil Percolation, Infiltration Percolation is how quickly water moves through a soil Infiltration is how quickly water moves into a soil from the surface Both depend on pore structure. Both are important considerations in water management and drainage design.

Soil Aeration Soil aeration is one of the most important factors affecting turf health. Poor aeration can lead to root death. You can improve aeration by encouraging good soil structure and by cultivation.

Soil Compaction (1) Soil compaction occurs when forces compress the soil and alter pore structure.

Soil Compaction (2) Bulk density increases, macropores decrease, infiltration decreases, aeration decreases. Compaction is most a problem when soils are wet

Soil Compaction (3) Soil Pans A compact, horizontal layer of soil in the soil profile, It is not a surface cap.

Soil Compaction (4) Soil Pans Restricts or prevents movement of water, air and plant roots down the profile. Causes: digging to same level repeatedly, layer of clay or iron in the profile

Soil Compaction Soil compaction is controlled by restricting traffic, modifying soils, and cultivation. The use of a subsoiler also reduces aeration. Use of subsoiler – info on compaction (5 mins) http://www.youtube.com/watch?v=EwG4hqtn0VA

Soil Cultivation What does cultivation do? The idea is to increase the surface area or increase the macropore space to facilitate infiltration and percolation, and to increase air diffusion into the soil.

Improving structure (1) Drainage – addition of organic matter, grit, sand or drainage systems Liming to increase organism activity & aggregration Less disturbance of soil – no dig systems Crop rotation – different root systems penetrate to different levels

Improving structure (2) Addition of OM including green manures, plant residues Addition of fertilisers Avoid capping by covering in winter with either green manures or plastic sheeting Avoid traffic on soil when wet Use of a subsoiler to break up pans & aerate the soil.

Oes cwestinau gyda chi? Neil Barry