Agriculture • Grade 7

Compost Pit: 21-Day Organic Waste Recycling Project

Transform kitchen vegetable peels, dry leaves, and paper into nutrient-rich soil conditioner. A complete 21-day guided project with daily observation logs, turning schedule, and full SBA rubric. Zero cost, maximum learning.

Finished compost pit showing dark brown crumbly compost material

SBA Rubric Included Grade 7 Zero Cost Updated: May 2026

21 dayscomplete cycle

2-3 turnsmixing schedule

20 pointsSBA max score

Why build a compost pit?

Composting is nature's way of recycling. Every day, Kenyan households throw away vegetable peels, tea leaves, eggshells, and other organic waste that ends up in landfills. This project teaches you to turn that waste into valuable fertilizer for your school garden or kitchen garden. Compost improves soil structure, adds nutrients, and reduces the need for chemical fertilizers.

Agricultural Science Fact: Compost contains millions of beneficial microorganisms that break down organic matter. These microbes also help plant roots absorb nutrients more efficiently. A single teaspoon of healthy compost can contain up to one billion bacteria!

Important Note: This is a 21-day project. You must commit to daily observation (5 minutes per day) and three turning sessions (on days 7, 14, and 18). Plan your start date so that Day 21 does not fall during a school holiday unless you can still access the pit.

KNEC SBA connection: This project covers Agriculture Strand 2: Soil Conservation and Management. Your evidence will include daily logs, temperature readings (optional), before/after photos, and a final report.

Materials needed (all free or recycled)

Brown materials (carbon-rich) - collect these first:

Dry leaves (collected from under trees) - about 2 large buckets
Small dry twigs (for aeration layer at bottom) - handful
Shredded paper (newspaper, exercise book scraps) - 1 small bag
Cardboard pieces (torn into small squares) - optional

Green materials (nitrogen-rich) - collect daily for 7 days:

Vegetable peels (potato, carrot, cabbage, tomato) - do not use diseased plants
Fruit peels (banana, orange, mango, pawpaw) - cut into small pieces
Tea leaves and coffee grounds - excellent nitrogen source
Crushed eggshells (adds calcium) - rinse and crush
Grass clippings (if available) - thin layer only

Tools and equipment:

Small garden trowel or strong stick (for turning/mixing)
Watering can with rose (or small bucket for sprinkling water)
Gloves (optional but recommended)
Notebook for daily observations (or printed log sheet)
Measuring ruler (to check temperature depth - optional)
Plastic sheet or cardboard to cover the pit (retains moisture)

Total cost: 0 KES (all items are household waste or naturally available).

What NOT to add to your compost pit: Meat, fish, bones, dairy products (cheese, milk), oily foods, cooked food with salt, diseased plants, weeds with seeds, or pet droppings. These attract pests, create bad odours, and may introduce harmful pathogens.

Step-by-step construction and maintenance guide

Follow these 8 steps carefully. Take timestamped photos at each stage for your SBA portfolio. A complete observation log is provided after the steps.

Choose and prepare the pit location

Select a shaded spot in your school compound or home garden, away from direct afternoon sunlight (which dries the compost). The area should have good drainage (not a place where water pools). Mark a rectangular area approximately 50cm wide by 50cm long. Dig a shallow pit about 30cm deep. Keep the excavated soil nearby - you will use it to cover the pit later.

Shallow rectangular pit dug in shaded garden area

Layer 1: Aeration base (twigs and small branches)

Spread a 5cm layer of small dry twigs and coarse plant material at the bottom of the pit. This creates air pockets that allow oxygen to reach the composting microbes. Good airflow prevents bad smells and speeds up decomposition. Do not pack this layer tightly - keep it loose.

Layer of small dry twigs at bottom of pit

Layer 2: Brown materials (carbon layer)

Add a 10cm layer of dry leaves, shredded paper, and small cardboard pieces. This is your "brown" layer. Brown materials provide carbon, which is food for the decomposer organisms. Lightly moisten this layer with a watering can - it should feel like a wrung-out sponge, not dripping wet.

Brown layer of dry leaves and paper inside pit

Layer 3: Green materials (nitrogen layer)

Add a 5cm layer of fresh kitchen vegetable peels, fruit scraps, and crushed eggshells. Cut or tear larger pieces into smaller chunks (2-3cm) - smaller pieces decompose faster. Spread this green layer evenly over the brown layer. Green materials provide nitrogen, which fuels microbial growth.

Green layer of vegetable peels and fruit scraps

Add a thin soil layer and water

Sprinkle a 1-2cm layer of the excavated soil over the green materials. Soil introduces local decomposing microorganisms (bacteria and fungi) that will accelerate the process. Lightly water the entire pile. Insert your finger into the pile - it should feel moist but not soggy. If water drips out when you squeeze a handful, it is too wet.

Thin soil layer sprinkled over green materials

Repeat layers until pit is full

Continue adding alternating brown and green layers (brown, green, soil, water) until the pile rises about 15cm above ground level. Always end with a brown layer on top (dry leaves or paper) to reduce smells and deter flies. The final height should be a rounded mound. Cover the pile with a plastic sheet, old sack, or cardboard to retain moisture and heat.

Completed layered compost pile covered with plastic sheet

Turning schedule: Days 7, 14, and 18

Turning (mixing) adds oxygen, which speeds decomposition and prevents bad smells. Use a garden fork or strong stick to turn the pile:

Day 7 (first turn): Move materials from the outside to the inside, and from the bottom to the top. Add water if the pile feels dry.
Day 14 (second turn): Mix thoroughly. The pile should feel warm inside (30-40°C) - this is normal microbial activity.
Day 18 (third turn): Final mixing. Check moisture. The pile should now have an earthy smell, not ammonia or rotten egg odour.

Student turning compost pile with garden fork

Day 21: Harvest and use your compost

On Day 21, your compost is ready. It should look like dark, crumbly soil with an earthy smell. You should not be able to recognize the original vegetable peels or leaves. Use a sieve (optional) to separate any large unfinished pieces - return those to the pit. Apply the finished compost to your school vegetable garden or potted plants by mixing it into the top 5cm of soil.

Dark crumbly finished compost being harvested

Daily Observation Log (Days 1 to 21)

Copy this table into your notebook or print it. Record observations every day at the same time (e.g., 5:00 PM). Take a photo of your completed log on Day 21 for SBA evidence.

Day	Date	Temperature Feel	Moisture Level	Smell	Visible Changes	Action Taken
1	_____	_____	_____	_____	_____	Built pile, watered
2	_____	_____	_____	_____	_____	Observed
3	_____	_____	_____	_____	_____	Observed
4	_____	_____	_____	_____	_____	Observed
5	_____	_____	_____	_____	_____	Observed
6	_____	_____	_____	_____	_____	Observed
7	_____	Warm/Neutral	_____	Earthy/None	_____	First turn + water
8-13	_____	_____	_____	_____	_____	Daily observe
14	_____	Warm	_____	Earthy	_____	Second turn
15-17	_____	Cooling	_____	Earthy	_____	Observed
18	_____	Cool	_____	Earthy	_____	Third turn
19-20	_____	Cool	_____	Earthy	_____	Observed
21	_____	Ambient	Dry/Moist	Fresh earth	Dark crumbly	Harvested compost

KNEC SBA Rubric – Compost Pit Project

Your teacher will assess using this rubric. Maximum score: 20 points. Read the "Exceeds" column carefully to aim for the highest grade.

Criteria	Exceeds (5)	Meets (4)	Approaching (3)	Below (2-1)
Site selection & pit construction	Shaded, well-drained location. Pit dimensions accurate (50x50x30cm). Aeration layer properly placed.	Good location, pit depth within 5cm of required. Aeration layer present.	Location partly shaded, pit depth off by more than 10cm. Thin aeration layer.	Poor location (full sun or waterlogged). No aeration layer.
Layering & material balance	Alternating brown/green layers with correct thickness ratios (2:1 brown to green). Soil sprinkled between layers. No forbidden items.	Alternating layers present, ratio approximately correct. No major forbidden items.	Layers mixed together or ratio wrong. One or two forbidden items present.	No layering, mostly one type of material, or several forbidden items.
Maintenance (turning & moisture)	All three turns completed on correct days. Moisture consistently at "wrung sponge" level. Pile covered properly.	Two turns completed, moisture generally adequate.	One turn completed OR pile too dry/wet for several days.	No turns, pile dried out or waterlogged.
Observation log & evidence	Daily log complete (21 entries) with detailed descriptions. Minimum 4 timestamped photos (Day 1, Day 7 during turn, Day 14, Day 21 final product). Written conclusion paragraph.	15-20 log entries, 3 photos, basic conclusion.	10-14 entries, 1-2 photos, no conclusion.	Fewer than 10 entries, no photos.

To achieve "Exceeds" (20/20):

Measure and record internal pile temperature on Days 1, 7, 14, and 21 using a soil thermometer (or touch test with description).
Take a "before and after" photo of the same handful of material - show identifiable vegetable peel on Day 1 vs dark crumbly texture on Day 21.
Write a one-paragraph application: describe where you will use the compost and how it improves soil health.
Have a parent or teacher sign your observation log to verify authenticity.

Project Gallery – add your own images

Use these slots to document your complete composting journey from start to finish.

Extension activity (bonus marks)

Build a second compost pit using the same materials but do not turn it at all (no mixing for 21 days). Compare the two results on Day 21 by answering these questions:

Which pile decomposed faster? Why?
Which pile had more earthworms? (Check the bottom of each pit)
Which pile had a stronger smell?

Present your findings as a short report (one page) with comparison photos. This demonstrates scientific inquiry and can push your score higher.

Print or save as PDF

Take this guide outdoors. Print the observation log and rubric to fill in by hand.