Factors Affecting the Decomposition of Organic Matter in Soil

September 10, 2023 Agric4Profits

Favorable conditions for microbial growth and activity have to be ensured before the rate of decomposition can move fast and consequently maximize the use of organic fertilizer.

The conditions favorable for organic matter decomposition include:

Composition and Particle Size of the Organic Material

The smaller or finer the organic matter particles, especially due to the composition of soil macro-organisms on organic matter, the greater the surface area exposed for decomposition, consequently the faster the rate of decomposition.

Making the plant material smaller in size as in the case of grinding, exposes a lot of surface area to enzymes of micro-organisms in the soil and thereby accelerating the decomposition process.

Succulent organic materials get degraded rapidly; and as the plants mature, higher contents of hemicellulose, cellulose, and lignin decrease the rate of decomposition.

The quality of the organic material in terms of its nitrogen content compared to its carbon content also affects the rate of decomposition.

The higher the nitrogen content, and therefore the lower the carbon/nitrogen ratio, the faster the rate of decomposition. A separate discussion on the effect of the carbon/nitrogen ratio on organic matter decomposition is given below:

Carbon: Nitrogen Ration

The carbon: nitrogen ratio of the organic matter affects the rate of its decomposition. The microorganisms require nitrogen for tissue or bodybuilding.

The organic matter must contain a reasonably high quantity of nitrogen for micro-organisms to obtain enough for rapid multiplication and accelerated activity.

Otherwise, the organic material remains in the soil undecomposed. The alternative is that the micro-organisms may make use of the native nitrogen in the soil.

Soil Reaction (pH)

The different groups of soil organisms have specific ranges of soil acidity under which they exhibit maximum activity.

Thus, bacteria and protozoa are most active under the soil pH range of 6-7 or under a neutral range of soil acidity, fungi strive best when soil pH is low or soil is acidic while actinomycetes have an optimum pH range of 6-8.0.

Since the bulk of organic matter decomposition is affected by soil bacteria, it follows that decomposition is higher in the neutral range than under acid and alkaline conditions. Liming acid soils will accelerate the rate of organic matter decomposition.

Aeration

Decomposition of organic matter is oxidation and respiratory process mediated by microbial enzymes and it is similar to burning or digestion of food.

Experiments with incubated soil samples had shown that maximum decomposition and subsequent nitrification occur when the percentage of oxygen reaches about 20 which tallies with the percent concentration of oxygen in the atmosphere.

During cultivation, it is important to maintain the rapid diffusion of gases into and out of the soil. Tillage helps the aeration of the soil and hastens decomposition. Resisted aeration through zero or minimum tillage and excess water favor organic matter accumulation.

There is usually a significant effect of aeration on organic matter decomposition at an oxygen level below 1% of the partial pressure of oxygen in the atmosphere.

Temperature

It is a generally established fact that increasing temperature stimulates microbial activities and therefore decomposition processes. As a chemical reaction, decomposition processes should follow the rule of Q10 which states that the rate of chemical reactions doubles for every 100C rise in temperature. The optimum temperature is generally quoted as between 20 and 40⁰C.

In a dry season in northern Nigeria, Wild (1972) reported low numbers of autotropic organisms because the temperature at a soil depth of 5cm reached a daily maximum which averaged between 38 and 40⁰C.

Not much information has been reported in the literature about the effect of temperature on decomposition in Nigerian soils, but it is widely believed to be very rapid. This is due, in part to the generally high temperatures which range between 20 and 35⁰C with an annual mean of about 25⁰C.

These temperatures are most favorable to most microorganisms responsible for organic matter decomposition. The prevalent high temperatures and humidity encourage microbial growth and action, and therefore, leads to a high rate of organic matter decomposition and subsequent loss from the soil.

Although the biomass turnover is high in Nigeria, it does not meet the organic matter requirement of the soils. Therefore, the organic contents of Nigerian soils are relatively lower than soils in colder regions.

Factors Affecting the Decomposition of Organic Matter in Soil

Soil Moisture

There is a cyclic pattern of soil microbial activity and the availability of soil nutrients (such as N, P, and S) to crops mainly due to the alteration of wet and dry seasons.

Microorganisms involved

Microbes are in constant competition for organic and inorganic nutrients and for oxygen in the soil. At any point in time, a certain group of microbes dominates but does not remain for too long before another group takes over. When the organic matter decomposing bacteria dominate the decomposition process is fast.