Effect of Organic Matter on Soil Physical Properties

September 18, 2023 Agric4Profits

Organic matter affects both the biological, chemical, and physical properties of the soil and hence its fertility and health. Some of the soil properties influenced by the organic matter are: diversity and activity of soil organisms (beneficial and harmful ones); nutrient availability; soil structure; and water holding capacity.

It also influences the effects of chemical amendments, fertilizers, pesticides ,and herbicides. Freshly added or partially decomposed plant residues and their non-humic decomposition products usually constitute labile organic matter pool.

The labile soil organic matter pool regulates the nutrient supplying power of the soil, particularly of nitrogen, whereas both the labile and stable pools affect soil physical properties, such as aggregate formation and structural stability.

When crops are harvested or residues burned, organic matter is removed from the system. However, retaining plant roots in the soil and leaving crop residues on the surface can minimize the loss.

Organic matter can also be restored to the soil through growing green manures, cuttings from agroforestry species and the addition of manures and compost. Soil organic matter is the key to soil life and the diverse functions provided by the range of soil organisms.

Organic matter influences the physical conditions of a soil in many ways. Crop residues that cover the soil surface protect the soil from sealing and crusting by the impact of raindrop thereby enhancing rainwater infiltration and reducing runoff.

Increased organic matter also contributes indirectly to soil porosity (via increased soil faunal activity). Fresh organic matter stimulates the activity of macrofauna such as earthworms, which create burrows lined with the glue-like secretion from their bodies and intermittently filled with worm cast material.

Surface infiltration depends on a number of factors including aggregation and stability, pore continuity and stability, the existence of cracks, and the soil surface condition.

Organic matter also contributes to the stability of soil aggregates and pores through the bonding or adhesion properties of organic materials, such as bacterial waste products, organic gels, fungal hyphae and worm secretions and casts.

Moreover, organic matter intimately mixed with mineral soil materials has a considerable influence in increasing water holding capacity.

In conclusion, organic matter plays an important and multi-faceted role in soil. Physically, organic matter influences soil structure and all associated properties. Chemically, soil organic matter affects the cation exchange capacity and the capacity for buffering changes in soil pH.

Biologically, organic matter acts as the nutrient and energy supply for microbial biomass and higher plants. A soil that is biologically and chemically fertile but which cannot physically support crop development will not fulfill its agronomic potential.

Soil productivity is, therefore, determined by a combination of organic matter’s influence on the physical, chemical, and biological properties of soil.