Sunday, July 14, 2024
General Agriculture

Properties of Soil Organic Matter and Crop Production

The total amount and partitioning of soil organic matter in the soil is influenced by soil properties and by the quantity of annual inputs of plant and animal residues to the ecosystem.

For example, in a given soil ecosystem, the rate of decomposition and accumulation of soil organic matter is determined by such soil properties as texture, pH, temperature, moisture, aeration, clay mineralogy and soil biological activities.

A complication is that soil organic matter in turn influences or modifies many of these same soil properties. Organic matter existing on the soil surface as raw plant residues helps protect the soil from the effect of rainfall, wind and sun.

Removal, incorporation or burning of residues exposes the soil to negative climatic impacts, and removal or burning deprives the soil organisms of their primary energy source.

Properties of Soil Organic Matter

Organic matter within the soil exhibits several properties. From a practical agricultural standpoint, it is important for two main reasons:

As a “revolving nutrient fund”; and As an agent to improve soil structure, maintain tilth and minimize erosion.

As a revolving nutrient fund, organic matter serves two main functions:

As soil organic matter is derived mainly from plant residues, it contains all of the essential plant nutrients. Therefore, accumulated organic matter is a storehouse of plant nutrients.

The stable organic fraction (humus) adsorbs and holds nutrients in a plant-available form.

Organic matter releases nutrients in a plant-available form upon decomposition. In order to maintain this nutrient cycling system, the rate of organic matter addition from crop residues, manure and any other sources must equal the rate of decomposition, and take into account the rate of uptake by plants and losses by leaching and erosion.

How Organic Matter Affects Soil Properties

1. Physical Properties

1a. Soil Structure and Aggregate Stability

Soil structure stability refers to the resistance of soil to structural rearrangement of pores and particles when exposed to different stresses (e.g. cultivation, trampling/ compaction, and irrigation).

Angers and Carter (1996) noted that the amount of water – stable aggregate (WSA) was often associated with SOC content, and that labile carbon was often positively related to macro-aggregate stability.

It was reported that a minimum of 2% SOC was necessary to maintain structural stability. It has also been reported that a threshold of 3-3.5% SOC had to be attained to achieve increase in aggregate stability.

1b. Water Holding Capacity

An important indicator of soil physical fertility is the capacity of soil to store and supply water and air for plant growth.

It has been found that an increase in water content goes with increasing SOC content that an increase of 1% SOM can add 1.5% additional moisture by volume of FC.

Emerson and McGary (2003) showed that per gram of additional carbon at -10 kPa suction, a 50% increase in water content was achieved.

They suggest that the organic carbon from exudates (gel) from ectotrophic mycrorhiza would bond soil particles which would result in a change in the size of the pores and a change in water retention at -10 kPa.

1c. Soil Colour

Generally, good soil conditions are associated with dark brown colours near the soil surface; which is associated with relatively high organic matter levels, good soil aggregation and high nutrient levels.

2. Chemical Properties

2a. Cation Exchange Capacity(CEC)

A high CEC is regarded as favourable as it contributes to the capacity of soils to retain plant nutrient cations.

Functional groups of SOM have been associated with an increase in CEC and an increase in CEC goes with increase in soil organic matter.

2b. Buffer Capacity and pH

Soil buffering is considered to be an important aspect of soil health, as it assures reasonable stability in soil pH.

Buffering at intermediate pH value (5-7.5) is mainly governed by functional groups of SOM which act as sink for H+ and OHˉ.

The importance of SOM to maintain fairly stable pHvalues, despite acidifying factors, has been documented.

Read Also : Soil Organic Matter and Sources of Organic Matter

2c. Adsorption and Complexation

Adsorption of SOM on clay particles is an important mechanism for the protection of SOM from decomposition.

Complexation of inorganic materials by SOM have important ramifications for soil fertility as it may increase the availability of P by blocking potential adsorption site of Fe and Al as well as Ca.

It was reported that increase concentrations of SOM depress the concentration of heavy metals such as Cupric ions.

Properties of Soil Organic Matter

3. Biological Function of SOM

The biological function of SOM are primarily to provide a reservoir of metabolic energy that drives biological process, supply macro and micro nutrients and to ensure that both energy and nutrients are stored and released in a sustainable manner.

Importantly, biological processes in turn influence both soil chemical and soil structural properties as they greatly affect soil structure and soil redox reactions.

Baldock and Nelson (1999) stated that one of the most fundamental function of SOM is the provision of metabolic energy which drives soil biological processes

4. Soil Resilience

The resilience of a soil is really a measure of the functionality of the whole ecosystem. It is governed by the adequate performance of physical, biological and chemical functions, which in turn is to a large extent determined by the SOM content and its chemical composition.

Soil Organic Matter and Crop Production

Although there is a considerable variation in the nutrient composition of organic manures depending mainly upon the source, handling and management, the main nutrients supplied are N, P, K, Mg, Ca and a host of micro nutrients. The following were reported about organic matter and crop production;

It was reported that nutrient composition of organic manures are N, P, and S as well as micro nutrient elements as B, Cu, Mo, Zn, Mn, Fe and Cl.

Also that an average dressing of 10tonnes ha-1 of farmyard manure would supply about 50 kg N ha-1 and 50 kg K ha-1.

On crop yields, organic fertilizers have been reported to influence crops performance significantly.

Baldock and Nelson (1999) reported that poultry manure application significantly increased soybean yield over NPK fertilizer.

With or without the availability of fertilizer, it has been reported that, organic matter management remains a corner stone for successful farming in many areas of the tropics.

Organic matter within the soil exhibits several properties. From a practical agricultural standpoint, as a “revolving nutrient fund”; and as an agent to improve soil structure, maintain tilth and minimize erosion.

As soil organic matter is derived mainly from plant residues, it contains all of the essential plant nutrients. Therefore, accumulated organic matter is a storehouse of plant nutrients. The stable organic fraction (humus) adsorbs and holds nutrients in a plant-available form.

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Agric4Profits

Benadine Nonye is an agricultural consultant and a writer with several years of professional experience in the agriculture industry. - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education - PhD Student in Agricultural Economics and Environmental Policy... Visit My Websites On: 1. Agric4Profits.com - Your Comprehensive Practical Agricultural Knowledge and Farmer’s Guide Website! 2. WealthinWastes.com - For Effective Environmental Management through Proper Waste Management and Recycling Practices! Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4Profits TV and WealthInWastes TV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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