Good practice for maintaining a healthy soil structure

Soil structure is one of the most critical factors in agricultural productivity. When the structure degrades, macropores are lost, water infiltration falls, root oxygenation is reduced and fertility drops sharply.

According to INIAV, incorrect farming practices, especially excessive tillage and poor irrigation management, are among the main causes of structural degradation and soil compaction.

Organic matter

Organic matter content is a key indicator of structural quality. Values below 3.5% organic matter (≈2% organic carbon) are considered to be associated with a risk of soil structure deterioration.

Organic matter contributes to:

• The formation of stable aggregates
• Better water infiltration and retention
• Increased biological activity in the soil
• Greater resistance to erosion

Applying organic residues

Incorporating:

• crop residues
• manures
• organic composts

Increases organic matter and supplies nutrients to plants and to soil micro-organisms. Composted materials are more stable, which means longer-lasting effects on structure.

Minimising soil disturbance

Deep and frequent ploughing:

• destroys soil aggregates
• accelerates the breakdown of organic matter
• encourages compaction

The technical recommendation is to adopt conservation practices, such as:

• minimum tillage
• direct drilling
• conservation agriculture systems

Cover crops and crop residues

The use of cover crops (grasses and legumes) brings multiple benefits:

• a gradual increase in organic matter
• protection against water and wind erosion
• better soil aggregation

Crops that leave residues after harvest, such as maize, create a physical barrier against rain and wind, protecting the aggregates at the surface.

Fertilisation and soil structure

Fertilisation also influences structure. Calcium in particular promotes the flocculation of soil colloids, improving the aggregation of particles.

In addition:

• microbial activity generates humic compounds that stabilise aggregates
• earthworms and other organisms create macropores
• well-developed roots contribute to structural stability

In clay soils, applying calcium sulphate (agricultural gypsum) can improve flocculation and structure.

Source: INIAV (2022). Manual de Fertilização das Culturas. Laboratório Químico Agrícola Rebelo da Silva