Back to basics on soil

Published date29 September 2022
Please visit waikatoregion.govt.nz/public-events for the details and to RSVP

Environmental and economic performance and sustainability of our agriculture, including forestry, can be greatly influenced by soil quality.

Soil physical condition — commonly referred to as ‘soil structure’ — has an important influence on farm economics and environment.

Soil structure determines the porosity, strength and stability of a soil. For all practical purposes, these are the most important soil physical properties because they influence the movement and storage of water in the soil, the ability of roots to penetrate and grow in the soil and withdraw water and nutrients, and finally the ability of a soil to resist erosion.

A well-structured soil has many stable aggregates with a wide range of sizes. It contains a large number of pores, both within and between those aggregates, which maintain the correct balance of air and water in the soil and also allows easy emergence of seedlings and growth of plant roots.

Poorly structured soil either does not have aggregates of many different sizes or the aggregates are packed tightly together with few pores. Poor structure in a light textured soil results in unstable aggregates and the soil appears fine and powdery. Poor soil structure can markedly increase the risk of wind erosion.

Soil porosity and water holding capacity Over half the total soil volume consists of pores in a well-structured soil. About 40 per cent of these pores are very small and nearly always filled with water held so tightly that plant roots cannot withdraw it.

The proportions of sand, silt, clay and organic matter determine volumes of these small pores.

Medium size pores retain water, which can be taken up by the roots. The volume of these pores determines the water holding capacity of a soil and therefore its susceptibility to drought.

Large pores (macropores) are the structural soil pores, and are important for infiltration of...

To continue reading

Request your trial

VLEX uses login cookies to provide you with a better browsing experience. If you click on 'Accept' or continue browsing this site we consider that you accept our cookie policy. ACCEPT