Soil Organic Matter

Soil Organic Matter

Introduction

Soil organic matter is the amount of the soil that consists of decomposing plant or animal tissue. Most of our productive agricultural soils contain between 3 and 6% organic matter. Soil organic matter improves soil production in a variety of ways. There are various components of organic matter, as well as the various roles organic matter plays in soil production. Over time, field management practices will help to preserve or increase soil organic matter levels.

What is Soil Organic Matter?

Soil Organic Matter is composed of several components that can be classified into 3 basic types –

1. Plant residues and microbial matter that is alive
2. Active soil organic matter, commonly known as waste
3. Stable soil organic matter, often known as humus

The microorganisms responsible for the breakdown of both plant leftovers and active soil organic materials are included in the live microbial biomass. Humus is a stable component of soil organic matter derived from degraded plant and animal tissue. It is the result of breakdown.

The first 2 categories of organic matter contribute to soil fertility because their breakdown releases plant nutrients such as nitrogen, phosphorus, potassium and so on. Because humus is the product of decomposition (hence the name “stable organic matter”), it has less influence on soil fertility. It is still significant for soil fertility management, however, because it contributes to soil structure, tilth and cation exchange capacity.

Benefits of Stable Soil Organic Matter

A relatively high stable organic matter level in agricultural soil has various advantages.

These benefits can be divided into 3 categories –

Physical Benefits

1. Increases aggregate stability, water infiltration and soil aeration, resulting in less runoff.
2. Increases water retention capacity.
3. Reduces clay soil stickiness, making it easier to till.
4. Reduces surface crusting, making seedbed preparation easier.

Chemical Benefits

1. Increases soil’s ability to deal with pH change, this is also known as buffering capacity.
2. Accelerates decomposition of soil minerals over time, making the nutrients in the minerals available for plant uptake.
3. The ability to store and supply vital nutrients such as calcium, magnesium and potassium over time.

Biological Benefits

1. Provides food for the living organisms in the soil.
2. Enhances soil microbial biodiversity and activity, which can help in the suppression of diseases and pests.
3. Enhances pore space through the actions of soil microorganisms. This helps to increase infiltration and reduce runoff.

Organic Materials

Over time, the application and incorporation of organic materials can result in an increase in stable soil organic matter levels. Sources of organic materials include –

1. Crop residues
2. Animal manure
3. Compost
4. Cover crops (Green manure)
5. Perennial grasses and legumes

The quickest increases are obtained with sources that are high in carbon such as compost or semi-solid manure material added and tillage and rotation practices, also depend on:

• Soil temperature
• Soil moisture holding capacity
• Soil type and drainage class
• Existing microbial community
• Soil fertility status and soil pH

Management Practices to Increase Soil Organic Matter

Climate, soil type, crop planted and specific management practices can all have an impact on the amount of soil organic matter. As a result, while applying practices to increase soil organic matter, local conditions should be used as a reference for comparison. Building soil organic matter takes years or decades since it involves the addition of significant plant biomass and prevention from loss over time.

Two management options for building and maintaining soil organic matter are listed below –

1. Include agricultural residues and organic materials (e.g., residue, manure, etc.) in the crop residues.
2. Conduct soil testing and use advanced crop nutrition.