The study of cellular Biology Topics is essential to understanding the workings of all living organisms.
Manures and Fertilizers – Introduction, Activities, Differences and Advantages of Manure
The crop plants need a number of mineral elements for their growth which they get from the soil through their roots. Now, repeated growing of crops in the same field removes a lot of precious mineral elements, organic matter and other materials from the soil.
Due to this the soil becomes infertile after some time, and the crop yield decreases. So, unless the depleted plant nutrients are put back into the soil from time to time, the growth of crop would be poor. The deficiency of plant nutrients and organic matter in the soil is made up by adding manures and fertilisers to the soil.
Manure is a natural fertiliser. A manure is a natural substance obtained by the decomposition of animal wastes like cow-dung, human wastes, and plant residues, which supplies essential elements and humus to the soil and makes it more fertile. Manures are prepared from animal wastes, human wastes and plant residues by the action of micro-organisms.
In order to prepare manure, farmers dump animal wastes (animal dung, etc.) and plant wastes (like leaves, etc.) in pits at open places and allow it to decompose slowly. The decomposition is carried out by some micro-organisms. The decomposed animal and plant matter is used as organic manure.
Manures contain a mixture of various nutrient elements and a lot of organic matter (humus) recycled from bio-mass wastes (animal and plant wastes). Though manures are not very rich in plant nutrients like nitrogen, phosphorus and potassium, but they are rich in organic chemical nutrients like humus.
Thus, manures provide a lot of organic matter like humus to the soil and this humus improves the physical and chemical properties of the soil. A manure improves the soil texture for better retention of water and aeration. This is because, being porous, humus can hold more water and air in the soil. In fact, manure makes up the general deficiency of the nutrients in the soil.
A manure is, however, very bulky and voluminous due to which it is inconvenient to store and transport. Moreover, a manure is not “nutrient specific”, and hence it is not much helpful when a particular nutrient is required in the soil for a particular crop. A chemical fertiliser, on the other hand, is nutrient specific.
Manures are not able to supply the required quantities of the essential plant nutrients like nitrogen, phosphorus and potassium, etc. So, they are to be supplemented with chemical fertilisers. A chemical fertiliser is a salt or an organic compound containing the necessary plant nutrients like nitrogen, phosphorus or potassium, to make the soil more fertile.
A chemical fertiliser is rich in a particular plant nutrient (such as nitrogen, phosphorus or potassium). Some examples of fertilisers are : Urea, Ammonium sulphate, Superphosphate, Potash and NPK (N = Nitrogen; P = Phosphorus; K = Potassium).
The chemical fertilisers are nutrient specific. This means that a chemical fertiliser can provide only nitrogen, only phosphorus or only potassium to the soil, as required. The chemical fertilisers have plant nutrients in a concentrated form. So, they provide quick replenishment of plant nutrients in the soil and restore its fertility.
Chemical fertilisers have high solubility in water. So, they are easily absorbed by the plants. Chemical fertilisers are made in factories. Chemical fertilisers are easy to transport, store and handle because they come in bags (see Figure). The chemical fertilisers absorb moisture very quickly, so they are packed in air-tight bags.
The chemical fertilisers can be applied before sowing, during irrigation or sprayed on standing crops (see Figure). The use of fertilisers has helped the farmers to get better yield of crops such as wheat, paddy (rice) and maize, etc. The excessive use of fertilisers is harmful due to the following reasons :
- The excessive use of fertilisers changes the chemical nature of soil and makes the soil less fertile. For example, the excessive use of fertilisers can make the soil highly acidic or alkaline. The highly acidic or alkaline soil becomes less fertile.
- The excessive use of fertilisers causes water pollution in ponds, lakes and rivers, etc.
In order to maintain the fertility of soil, we should substitute some of the fertilisers by organic manure or leave the field fallow (uncultivated) in-between two crops. When a field is kept uncultivated for some time, its fertility is restored naturally.
To Show the Effect of Manure and Fertiliser on the Growth of Plants
Take three empty flower pots and mark them A, B and C (see Figure). Put some ordinary soil in pot A. Add some soil mixed with a little cow-dung manure in pot B. And take some soil mixed with a little urea fertiliser in pot C. Pour the same amount of water in all the three flower pots.
Now take some moong or gram seeds and germinate them. Select equal sized seedlings of moong or gram. Plant these seedlings in each of the three flower pots. Keep the flower pots in a sunny place and water them daily.
Observe the growth of seedlings in the three flower pots after 7 to 10 days. We will find that the seedlings planted in ordinary soil in pot A show the minimum growth [see Figure (a)]. The seedlings planted in soil containing manure in pot B show better growth [see Figure (b)], But the seedings planted in soil containing fertiliser in pot C show the maximum growth as well as the fastest growth [see Figure (c)]. From this activity we conclude that manure and fertilisers help the plants to grow better and faster.
Before we end this discussion, we would like to give the main differences between manures and fertilisers in tabular form.
Differences between Manures and Fertilisers
|1. A manure is a natural substance obtained by the decomposition of animal wastes like cow dung, human waste, and plant residues.||1. A fertiliser is a salt or an organic compound.|
|2. A manure is not very rich in essential plant nutrients like nitrogen, phosphorus and potassium.||2. Fertilisers are very rich in plant nutrients like nitrogen, phosphorus and potassium.|
|3. A manure provides a lot of organic matter like humus to the soil.||3. A fertiliser does not provide any humus to the soil.|
|4. A manure is absorbed slowly by the plants because it is not much soluble in water.||4. Being soluble in water, a fertiliser is readily absorbed by the plants.|
|5. Manure can be prepared in the fields.||5. Fertilisers are prepared in factories.|
Advantages of Manure
The manure is an organic material. The organic manure is considered better than fertilisers because of the following reasons :
- Manure enhances the water-holding capacity of the soil.
- Manure makes the soil porous due to which the exchange of gases becomes easy.
- Manure increases the number of useful microbes in the soil.
- Manure improves the texture of the soil.
Another method of replenishing the soil with nutrients (such as nitrogen) is through crop rotation. Before we discuss crop rotation as a means of improving the fertility of soil, we should know something about leguminous plants or leguminous crops.
The pulses, peas, beans, groundnut, gram (chana) and clover (berseem) are leguminous crops. The root nodules of leguminous plants have nitrogen-fixing bacteria (called Rhizobium bacteria) which can directly fix (or convert) the nitrogen gas present in air to form nitrogen compounds. In other words, leguminous crops have the ability to fix atmospheric nitrogen to form nitrogen compounds.
These nitrogen compounds go into the soil and improve its fertility. Some of these nitrogen compounds are used by the leguminous crop for its own growth and the rest of nitrogen compounds are left in the soil. Thus, planting a leguminous crop like pulses, peas, beans, groundnut, gram and clover, etc., in a field results in nitrogen-rich soil.
The planting of a leguminous crop in a field has the same effect as adding nitrogenous fertiliser in the field. Since leguminous crops can fix the atmospheric nitrogen themselves by using nitrogen-fixing bacteria present in their root nodules, therefore, nitrogenous fertiliser is not required for growing leguminous crops.
On the other hand, cereal crops like wheat, maize, paddy, and millet, etc., are non-leguminous crops which do not have the ability to fix (or convert) the nitrogen gas of air into nitrogen compounds. Keeping these points in mind, we will now describe crop rotation.
The fertility of soil can be improved by crop rotation. The practice in which different types of crops (leguminous crops and non-leguminous crops) are grown alternately in the same field or soil is called crop rotation. In crop rotation, the cereal crops like wheat, maize, paddy and millet are grown alternately with leguminous crops like pulses, peas, beans, groundnut and clover, etc., in the same field.
For example, when a cereal crop like maize crop is grown first, it takes away a lot of nitrogen from the soil for its growth and makes the soil nitrogen deficient. And next, when the leguminous crop like pulses or groundnut is grown in the same field, then the leguminous crop with its nitrogen fixing bacteria, enriches the soil with nitrogen compounds and increases its fertility.
And when another cereal crop like wheat is grown after that, then wheat can utilise this extra nitrogen from the soil for its growth and produce a bumper crop. In this way, rotating different crops (leguminous and non-leguminous crops) in the same field replenishes the soil with nitrogen naturally and leads to increase in the crop production. Rotation of crops has the following advantages :
- Rotation of crops improves the fertility of the soil by replenishing it with nitrogen and hence brings about an increase in the production of food grains.
- Rotation of crops saves a lot of nitrogenous fertiliser. This is because the leguminous crops grown during the rotation of crops can fix atmospheric nitrogen with the help of their nitrogen fixing bacteria, and there is no need to add nitrogenous fertiliser to the soil.