Crop Rotation – SS2 Horticulture and Crop Production Lesson Note (Second Term)

Crop rotation is the practice of growing different crops on the same piece of land in a planned order, one after the other.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define crop rotation;
2. state the four basic principles of crop rotation;
3. explain the advantages of crop rotation;
4. distinguish crop rotation from continuous cropping;
5. read a 4-plot rotation plan and explain why maize is planted after beans.

What is crop rotation?

Crop rotation is a planned order of different crops on one piece of land that keeps the soil healthy and productive.

• Aim: keep soil fertility, control pests, diseases and weeds, and reduce erosion.
• Planned order: the farmer follows a set sequence and does not plant any crop anywhere.
• Analogy: a person who eats only white rice every day lacks nutrients. Soil that carries one crop every year also runs short of nutrients.
• Rotation cycle: the number of years before the first crop returns to the same plot. It is four years in the 4-plot plan below.
• Fallow: leaving land uncultivated for a time to rest. Some rotation plans include a fallow period.

What groups of crops are used in a rotation?

Five groups of crops are used in a rotation: legumes, cereals, root and tuber crops, vegetables and cover crops.

• Legumes: beans, groundnut and cowpea. They add nitrogen to the soil.
• Cereals: maize, guinea corn and rice. They have shallow roots and use a lot of nitrogen.
• Root and tuber crops: yam and cassava. They have deep roots and take nutrients from lower soil layers.
• Leafy vegetables: amaranth (green) and celosia (soko). They have shallow roots and mature quickly.
• Cover crops: melon and sweet potato. They spread over the ground and shade the soil.

What are the principles of crop rotation?

There are four basic principles of crop rotation: root depth, the legume rule, pest control and soil cover.

• Deep-rooted and shallow-rooted crops: follow a deep-rooted crop (yam or cassava) with a shallow-rooted crop (maize or leafy vegetables). The soil is then used at different depths.
• The legume rule: include a legume (beans, groundnut or cowpea) in the plan. Legumes add nitrogen to the soil.
• Pest control: never plant crops of the same family one after the other. Do not follow tomato with pepper, because both attract the same pests.
• Soil cover: include a crop that covers the ground well, such as melon. It shades the soil and reduces drying by the sun.

What are the advantages of crop rotation?

Crop rotation has five main advantages: better fertility, broken pest cycles, weed control, less erosion and spread risk.

1. Improves soil fertility: legumes add nitrogen, and different crops use different nutrients. The soil stays balanced, and the farmer buys less chemical fertiliser.
2. Breaks pest and disease cycles: most pests and disease organisms attack particular crops. When the crop moves to another plot, their numbers fall because their food is gone.
3. Controls weeds: crops such as melon and sweet potato spread thickly over the ground. They shade out weeds, so the farm stays cleaner.
4. Prevents soil erosion: the land is always covered by a crop, and root types alternate. The soil is held firmly and is not easily washed away by heavy rain.
5. Spreads risk: if one crop fails, the farmer still has other crops on other plots to harvest and sell.

What are the limitations of crop rotation?

The limitations of crop rotation are the extra planning and the land it needs.

• Planning and records: the farmer must keep records of what each plot carried in past years.
• Land size: the land must be divided into several plots. Very small farms find this difficult.
• Market crop: the best-selling crop cannot be grown on every plot every year.
• Knowledge: the farmer must know the needs and families of each crop.

How do we plan a crop rotation?

A rotation plan is made by dividing the land into plots and placing crops in a fixed order.

1. Divide the land into equal plots. Use as many plots as the years in the cycle.
2. Choose crops from different groups, such as a legume, a cereal and a root crop.
3. Place a legume before a crop that uses a lot of nitrogen, such as maize.
4. Alternate deep-rooted and shallow-rooted crops where possible.
5. Do not follow a crop with another crop of the same family.
6. Include a cover crop to protect the soil.
7. Move every crop to the next plot each year and keep a record.

What is an example of a 4-plot rotation?

A 4-plot rotation divides the land into four plots and moves each crop to a new plot every year.

How do we read the table?

• Across a row: shows the four crops grown in the four plots in one year.
• Down a column: shows the order of crops on one plot over four years.
• Every crop moves: each crop shifts to a new plot every year.
• Cycle repeats: in Year 5, each plot returns to the crop it carried in Year 1.

What is the difference between crop rotation and continuous cropping?

Crop rotation grows different crops on a plot in a planned order. Continuous cropping grows the same crop on the same plot year after year.

Classroom discussion and practical

Look at the 4-plot rotation table above. Why do you think we put maize (which needs a lot of nitrogen) immediately after the beans?

Answer for the teacher: The beans have just added nitrogen to the soil, so it is the best time for the maize, which uses a lot of nitrogen, to grow.

Evaluation

1. Define crop rotation.
2. Why should a farmer include a legume in a rotation plan?
3. Why should tomato not be followed by pepper?
4. State any four advantages of crop rotation.
5. In the 4-plot table, which crop is grown on Plot 3 in Year 3?

Assignment

Copy the 4-plot rotation table into your notebook and state the crop grown on Plot 2 in each of the four years. Then explain in your own words how crop rotation helps a farmer to control pests and weeds.