Harvesting of Field Crops – SS1 Horticulture and Crop Production Lesson Note (Third Term)

Harvesting is the gathering of mature crops from the farm. For field crops such as maize, rice, cassava and yam, it is done when the crop is fully mature, using hand tools or machines.

Behavioural objectives

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

1. define harvesting and state why it is important;
2. list the signs that show a field crop is mature;
3. name the tools used to harvest field crops;
4. describe manual and mechanical harvesting;
5. explain threshing, winnowing, drying and bagging.

What is harvesting?

Harvesting is the process of gathering mature crops from the field.

• Field crops: crops grown on large areas of land, such as maize, rice, cassava and yam.
• Difference from vegetables: field crops are usually left to mature and dry before they are moved.
• Position in farming: it comes after land clearing, planting, weeding and pest control.

Why is harvesting important?

• End of production: it marks the end of the production cycle for the season.
• Quality: correct harvesting gives good-quality food to eat or sell.
• Income: a good harvest brings the farmer money from sales.
• Loss: poor harvesting or wrong timing can waste the work of the whole season.

How do we know a field crop is ready to harvest?

A field crop is ready when it shows signs of full maturity, such as a change in colour, hard grains and drying leaves.

What happens if a crop is harvested at the wrong time?

• Too early: the seeds are watery and soft, and they rot easily.
• Too late: birds eat the grain, and dry pods may burst open and spill the seeds on the ground.

What are the signs of maturity in field crops?

1. Change in colour: maize husks turn from green to brown or white. Rice stems and grains turn golden yellow.
2. Hardness of grains: the seeds become hard. A maize grain that you can still dent with your fingernail is not yet dry enough.
3. Drying of leaves: yam and cassava leaves turn yellow and wither. This shows the plant has finished storing food in the tubers.
4. The snap test: pods of beans and cowpea feel dry and crackle or snap when touched.

What tools are used to harvest field crops?

Harvesting tools are either simple hand tools or machines.

• Small-scale farmers: most harvest by hand with simple tools.
• Large-scale farmers: they use machines to save time and labour.

What are the common hand tools?

• Sickle: a curved blade for cutting cereals like rice and wheat at the base of the stem.
• Cutlass (machete): the most common tool in Nigeria, used for cutting maize stalks or clearing the way to reach tubers.
• Harvesting knife: a small, very sharp knife for cutting cocoa pods or oil palm bunches.
• Garden fork or digging mattock: lifts root crops such as yam, cassava and sweet potato out of the ground without breaking them.
• Hoe: loosens the soil around tubers so they can be pulled out.

What are the mechanical tools?

• Combine harvester: a large machine that cuts the crop, threshes it (removes the seeds) and cleans the grain in one operation.

What are the methods of harvesting?

There are two methods of harvesting: manual harvesting and mechanical harvesting.

• Choice of method: it depends on the type of crop, the size of the farm and the money available to the farmer.

What is manual harvesting?

Manual harvesting is the gathering of crops by hand or with simple hand tools.

• Pulling or digging: a fork or hoe lifts root crops such as yam and cassava from the soil.
• Plucking: maize cobs are pulled off the stalk by hand.
• Cutting: a sickle cuts the stalks of rice or millet.
• Use: common on small farms and in school gardens.

What is mechanical harvesting?

Mechanical harvesting is the gathering of crops with machines such as the combine harvester.

• Use: done on very large farms.
• Speed: it is much faster than hand harvesting.
• Cost: the machines are expensive and need fuel and trained operators.

What is the difference between manual and mechanical harvesting?

What are the rules for good harvesting?

• Be gentle: a yam bruised by a hoe gets a wound that lets rot enter, and it will not last in the barn.
• Harvest on time: wait for the signs of maturity.
• Use sharp, clean tools: they give clean cuts and cause less damage.
• Harvest in dry weather: wet crops spoil faster.

What care does a crop need after harvest?

Post-harvest care is the work done on the crop after it is cut, to keep it in good condition.

The steps for grains are:

1. Threshing: beat the dry stalks or pods to release the seeds, as with rice and cowpea.
2. Winnowing: use the wind to blow away the light chaff (dust and dry husks) from the heavy seeds.
3. Drying: spread the grains on a clean mat in the sun until completely dry.
4. Bagging: put the dry grains into jute bags and store them in a cool, dry place away from rats and weevils.

What is the difference between threshing and winnowing?

• Threshing: the removal of seeds from the dry stalks, pods or heads of the crop.
• Winnowing: the separation of light chaff from the heavy seeds using moving air.

How are root crops treated after harvest?

• Yam: tubers are handled gently and stored in a yam barn, not in bags.
• Cassava: tubers spoil quickly, so they are usually processed soon after harvest, for example into gari.

What are the harvest time and tools for common crops?

Evaluation

1. Define harvesting.
2. State three signs that a field crop is ready to harvest.
3. Name two hand tools used for harvesting and say what each is used for.
4. What is the difference between threshing and winnowing?
5. Why must farmers be gentle when harvesting yam?

Assignment

Choose any two crops from the table of harvest time and tools. For each one, state the sign that shows it is ready to harvest and the tool used to harvest it. Then list the four post-harvest steps for grains in the correct order.