Replenishment of Nutrients in Soil: Methods, Soil Fertility & Depletion

Soil is the uppermost layer of the Earth’s crust. Good soil is composed of mineral nutrients, humus, water, air, and microorganisms. Soil supplies a variety of nutrients to life forms. Plants utilise several nutrients found in the soil for the purpose of high yield, growth, development, photosynthesis and other metabolic activities. The utilisation of nutrients by the plants results in the depletion of soil fertility. To maintain the fertility and quality of the soil, the replenishment of nutrients in soil is essential. Let’s read this article to enhance the knowledge about soil fertility, soil nutrients, and replenishment of nutrients in soil.

Replenishment of Nutrients in Soil

Let us first look at what is soil fertility and how it plays a role in Replenishment of Nutrients in Soil:

Soil Fertility

Definition: The capacity of the soil to sustain plant life with required nutrients is called soil fertility. A fertile soil results in a high yield of crops. The soil loses its fertility when the nutritional content of the soil is used extensively without being replaced.

Factors Affecting Soil Fertility: There are several physical, chemical, and biological factors that affect the fertility of the soil. These are discussed as follows:

1. Soil Texture: Relative proportions of different types of particles (clay, sand, and humus) determines the texture of the soil. Soil texture influences the water-holding capacity and aeration of the soil. It also affects the ability of roots to penetrate deeper into the soil.
I. Sandy Soil is considered to be poor due to the least water-holding capacity.
II. On the other hand, the water holding capacity of clay soil is very high and can cause waterlogging.
III. Loamy Soil is the best soil for growing plants, as it contains sand, slit, humus and clay particles in appropriate proportion. The sand particles make it capable of holding air, and clay particles retain their water-holding capacity, therefore allowing the deeper penetration of roots in the soil. In contrast, the slit particles facilitate air circulation and water retention.

2. Soil pH: pH is the measurement of alkalinity and acidity of the matter. Most of the mineral nutrients are available to plants in the soil, having pH ranges between 5.5-7.5 (neutral).

3. Organic Matter: The organic matter of the soil is derived from dead and decaying parts of plants and animals. These dead remains of living beings are converted into organic matter called humus by the action of microorganisms. Humus is a dark brown or black colour mass that is formed by the decomposition of dead organic matter. Humus plays the following roles:
I. Increases soil fertility.
II. It forms many organic acids, which serve as solvents for soil materials and that can be easily absorbed by plant roots.
III. Humus has a high water-retaining capacity and increases the aeration of the soil.

Fig: Factors Affecting Soil Fertility

Methods of Replenishment of Nutrients in Soil

When the plants are grown, they absorb quality nutrients from the soil that causes a fall in the nutrient content of the soil and ultimately, the soil becomes nutrient deficient due to the repetitive cultivation of crops. To overcome such adverse conditions, the replenishment of nutrients in the soil is one of the necessary steps to be taken.

Definition: Replenishment of nutrients in the soil is defined as the addition of mineral nutrients in the soil after a certain period of time to enrich the soil and to maintain its fertility. The following methods can be applied for the replenishment of nutrients in the soil:

1. Adding Manures: Manure is an organic material that is used as organic fertiliser in agriculture. The manures are of three types:
I. Compost: Compost is used to improve the soil structure by the addition of inorganic and available nutrients that are formed by slow and gradual decomposition of organic matter (animal excreta and leftovers of plants).
Besides this, it is a source of other mineral nutrients such as nitrogen, phosphorus, sulphur, etc.
Compost binds the clusters of soil particles which provide good soil structure and increase the water-holding capacity of the soil.
II. Vermicompost: Worms (earthworm and red wigglers) that inhabit the soil decompose organic wastes and excrete the macronutrients like carbon, hydrogen, and oxygen in the soil along with other micronutrients, therefore contribute to the replenishment of soil.
III. Green Manure: Green manure is the key to organic gardening. It is the cover crop that is grown to maintain the fertility and structure of the soil. Alfalfa, buckwheat, cowpea, fenugreek, etc., are examples of green manures. They serve a number of different purposes that contribute to soil enrichment. Green manure is the major source of nitrogen and phosphorus in the soil. These also contribute to the improvement of soil structure, prevention of soil erosion, and inhibit the growth of weeds.

2. Adding Fertilisers: Fertilisers are the chemical substances that increase the yield of crops. Urea and NPK are the two main fertilisers that are most commonly used.
I. Nitrogen is widely used by crops for the purpose of growth and development
II. NPK is a combination of Nitrogen, Phosphorus, and Potassium and replenishes the soil with these three main mineral nutrients. Nitrogen is essential for plant growth, phosphorus is essential for root development, and potassium focuses on the quality of the plant and offers resistance to microbial diseases.

Fig: Adding Fertilisers

3. Growing Leguminous Plants: Air constitutes a large amount of nitrogen, but unlike oxygen and carbon dioxide, plants cannot directly absorb the atmospheric nitrogen. Plants utilise nitrogen in the form of water-soluble compounds. The conversion of atmospheric nitrogen into ammonia is called nitrogen fixation.
I. Nitrogen fixation is biologically carried by the bacterium that inhabits leguminous plants like peas, beans, etc.
II. Rhizobium is a bacterium that shows a symbiotic relationship with legumes.  It lives in the root nodules of the legume plants and fixes the atmospheric nitrogen into water-soluble ammonia.
III. These nitrogen compounds are captured in the soil water and replenish the soil with nitrogen whenever required and make the nitrogen available for plant use.

Fig: Nitrogen-Fixation by the Bacterium

4. Cropping Patterns: Different cropping patterns are used to maintain the soil fertility and nutrient content of soil without any artificial inputs. The three main methods are crop rotation (growing different crops one after another on the same field), intercropping (growing two or more crops in a definite pattern), and mixed cropping (seeds of two or more crops are intermixed and spread in the field). There are the following purposes of different cropping patterns that are subjected to soil fertility and nutrient replenishment in the soil:
I. Plants not only obtain nutrients from the soil but also add some essential components that are the results of their metabolic activities.
II. Since different crops have different and specific nutrient requirements, therefore the metabolic wastes of one crop could serve as key nutrients for another crop.
III. Moreover, by growing different types of crops alternatively or simultaneously maintain a balance of mineral nutrients in the soil. Neither the element will be excessive nor depleted.

Fig: Cropping Patterns

Depletion of Soil

Soil depletion occurs when the soil nutrients are exhausted by continuous use and are not replaced. Soil depletion leads to the overall degradation of soil. There are the following main reasons for soil depletion:

1. Soil Erosion: The uppermost layer of the soil is fertile and contains humus. The removal of the uppermost fertile layer of the Earth’s crust is called soil erosion. Cutting trees is the main reason for soil erosion.

2. Removal of Vegetation Cover: Vegetation cover that serves as green manure is added to the soil to maintain fertility. The removal of cover crops leads to the depletion of nutrients in the soil and hence significantly reduces the fertility of the soil.

3. Growing the Same Crop on a Particular Land Repeatedly: The repeated cultivation of the same crop for a longer and repeated period makes the soil deficient in some of the specific nutrients that ultimately leads to the sterility of the soil.

4. Excessive Use of Chemical Fertilisers: Chemical fertilisers may increase the fertility rate, but in the long course of time, they prove to be harmful to the soil because they adversely affect the pH of the soil.

5. Growth of Weeds: Weeds are undesired plants that often grow with the main crop. Weeds are capable of absorbing the soil nutrients faster and relatively in larger amounts than the main crop. This does not disturb the soil structure and quality but also adversely affects the growth and quality of the main crop.

Summary: Replenishment of Nutrients in Soil

Soil is one of the most important natural resources on Earth. Like water and air, soil also plays a critical role in supporting life. Soil is a house of several mineral nutrients that are required by plants and other living organisms for their growth, development, and physiological activities. Crops absorb certain elements stored in the soil, such as water, minerals in the form of ions, etc., for better yield. Extensive use of soil nutrients by the crops can cause the depletion of soil nutrients.

Hence along with their usage, replenishment of nutrients in soil is also necessary. Soil replenishment can be brought about by adding manure and fertilisers, growing legumes, and applying different cropping patterns.

FAQs on Replenishment of Nutrients in Soil

Here we have provided answers to the most frequently asked questions about Replenishment of Nutrients in Soil:

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