The practice of crop rotation is an age-long one. This is a practice where a piece of land is used for producing different crops in rotational manner. It can also be explained as the practice of growing different types of crop in the same area in sequential seasons. This practice is basically embarked on in a bid to replenish nitrogen through the use of green manure, mitigate pathogens and pest, improve soil structure and fertility, etc.
Normally, crop rotation is characterised by alternating deep-rooted crops with a shallow rooted one in the succeeding year. It can come in form of two-field, three-field, and four-field systems. Under a two-field rotation, half the land is planted in a year, while the other half lay fallow. Then, in the following year, the two fields are reversed. However, the two-field system is no longer obtainable in modern farming. Farming has now transitioned to a three-field crop rotation.
It was reported that European farmers practiced three-field rotation from the end of the middle ages until the 20th Century. By this practice, they divided the available lands into three, planting appropriate crops on the fields in their seasons, e.g. autumn (rye), winter (wheat) followed by spring (oats or barley); the second portion grew crops such as peas, lentils or beans while the third field was left to fallow. Thus the three fields were rotated in this manner.
A four-field rotation was said to have been pioneered by farmers in the region of Waasland in Belgium, in the early 16th century and popularised by the British agriculturist Charles Townshend in the 18th century. The system (wheat, barley, turnips and clover), opened up a fodder crop and grazing crop, allowing livestock to be bred year-round. The four-field crop rotation was a key development in the British Agricultural Revolution.
It has been discovered that, growing the same crop on the same soil for many years in a row leads to depletion of soil nutrient. This makes rotation necessary as it plays a complementary role in soil nutrient replacement. With crop rotation, a crop that leaches the soil of one kind of nutrient is followed, during the next growing season, by a dissimilar crop that returns that nutrient to the soil or draws a different ratio of nutrients: for example, rice followed by cotton.
It is important to note that the soil, the climate and precipitation are major factors to be considered in the choice of and sequence of rotation. Other important factors to be put into consideration include marketing and economic variables. When all these are given due considerations, crop rotation can be safe for both economic and soil fertility purposes.
The common advantages of crop rotation include:
- Crop rotation ensures continuous production on a piece of land. By this practice, the land is not left to fallow and the need for artificial fertilisers is considerably reduced.
- It encourages what is termed as “a geographic mixing of crops” which possesses the capacity to slow down the spread of pests and diseases during the growing season.
- Crop rotation allows more land to be farmed with the same amount of labour by requiring planting and harvest at different times.
- Crop rotation leads to improved nutrition through green manure.
- It reduces pest, pathogen and weed thereby saving cost.
- It leads to distribution of financial risks over diverse production of crops.
- It reduces the rate of soil erosion.
- It improves soil structure.
- Crop rotation allows for increased Soil Organic Matter (SOM), greater soil structure, and improvement of the chemical and biological soil environment for crops.
On the flip side, there are few areas of concern to be considered if maximum success would be attained in the practice of crop rotation. These are normally called disadvantages even though they are largely overshadowed by the advantages of the system. Some of these disadvantages include the requirement of more equipment since not all crops can be cultivated using one equipment; it may require the farmer to know more about many crops, especially the ones he intends planting in his fields, and the rotational system may lead to lower profit margin for the farmer. These disadvantages, however, are not enough to discourage the practice of crop rotation by farmers.