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Effect of Organic Matter on Soil Chemical Properties

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 organic matter are: the iversity 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 la abile 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 are 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.

Read Also: Role of Organic Matter in Soil Fertility

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.

Many important chemical properties of soil organic matter result from the weak acid nature of humus. The ability of organic matter to retain cations for plant use while protecting them from leaching is due to the negative charges created as hydrogen is removed from weak acids during neutralization.

Many acid-forming reactions occur continually in soils. Some of these acids are produced as a result of organic matter decomposition by microorganisms, secretion by roots, or oxidation of inorganic substances.

When acids or bases are added to the soil, organic matter reduces or buffers the change in pH. This is why it takes tones of limestone to increase the pH of a soil significantly compared with what would be needed to simply neutralize the free H present in the soil solution.

All of the free hydrogen ions in the water in a very strongly acid soil (pH 4) could be neutralized with less than 6 kg of limestone per hectare.

However, from 5 to more than 24 tones of limestone per hectare would be needed to neutralize enough acidity in that soil to enable acid-sensitive crops to grow.

Organic matter may provide nearly all of the CEC and pH buffering in soils low in clay or containing clays with low CEC. Organic matter releases many plant nutrients as it is broken down in the soil, including N, phosphorus (P), and sulphur (S).

Leguminous species are very important as part of a cereal crop rotation in view of their capacity to fix N from the atmosphere through symbiotic associations with root-dwelling bacteria.

Read Also: Effect of Organic Matter on Soil Biological Properties

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