Growing crops year after year in the same soil results in depletion of the various nutrients in the soil because of which the soil loses its fertility. The various practices used for the improvement of the soil in order to replenish the nutrient content are:
- Keeping the land fallow or free for sometime.
- Crop rotation.
- Multiple cropping or mixed cropping.
- Adding manure and fertilizers to the soil.
- Now let us discuss these practices one by one.
1. Field Fallow
Leaving the field free for a season so that the soil regains the list nutrients (by the action of microorganisms) are known as field fallow.
Earlier at the practice to leave the field fallow or free for a season. During the free period, soil regenerates the lost nutrients by the action of microorganisms. This makes the soil ready for supporting the next crop. Since the demand for food-grains is very great these days, so this method of keeping the land free of follow to restore the fertility of the soil in the natural way has been abandoned.
2. Crop Rotation
When same crop is grown in the same soil year, it removes particular nutrients from the soil and reduces its fertility. Growing the same crop in the same soil, year after year is referred to as monoculture. Thus, monoculture reduces the fertility of the soil.
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The fertility of soil can be restored by crop rotation. The crop rotation means growing different types of crops alternately in the same soil. In the rotation of crops, the leguminous crops like pulses, groundnuts, gram, etc., are grown in a season alternating between cereal crops such as wheat, maize, millet, etc. Now let us understand how the leguminous crops restore the fertility of soil.
We know that nitrogen is one of the elements, which are essential for plant growth, and it is required in quite large amounts by the plants. Although nitrogen is abundant in the air as nitrogen gas but most of plants are unable to utilize directly. The plants obtain their nitrogen supply from the nitrogen compounds such as nitrates and ammonium salts present in the soil. By repeatedly growing the cereal crops like wheat, maize, rice, etc. results in depletion of nitrogen content of the soil.
Although most of the plants cannot use atmospheric nitrogen directly, the leguminous plants can do so with the help of symbiotic bacteria present in their roots. These bacteria can fix the nitrogen present in the atmosphere as ammonia and proteins. Some of this ammonia is excreted by these bacteria and becomes available to the plant as nutrient. When these bacteria die (when crop is harvested), the nitrogen present in them is converted into nitrates by the action of many different kinds of bacteria.
Thus, leguminous crop plants have the ability to fix atmospheric nitrogen into nitrogen compounds. These nitrogen compounds remain in the soil and improve its fertility. Therefore, planting a legume crop like pulses, peas, beans or groundnut in a field will result in a nitrogen-rich soil. Thus, the soil becomes ready to support the next cereal crop. In this way by raising leguminous and non-leguminous crops alternately in the same field replenishes the soil in a natural way.
3. Multiple Cropping
Multiple cropping or mixed cropping can also improve the fertility of the soil. Multiple cropping involves growing of two or more different crops together in the same field. Multiple cropping helps in the following ways:
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(i) When to crops are properly chosen, the products and waste materials of one crop help in the growth in the other.
(ii) Multiple cropping helps in humus formation.
(iii) Due to different nutrient requirements of different crops, the multiple cropping avoids exhaustion of soil nutrients.
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(iv) It helps in optimum utilization of the soil.
(v) It saves time and labor of the farmer.
Maize, urd and soyabean; cotton and groundnut are grown together in multiple cropping.
4. Manures and fertilizers
The fertility of the soil can also be restored by adding manures and fertilizers to the soil. The manures and fertilizers contain necessary plant nutrients and make the soil fertile.