Watering the School Garden Within a Tight Budget
A Grade 9 class maintains a rectangular school garden measuring 12 m by 8 m. The soil is loamy and drains well. In July, daytime temperatures reach 33 °C and there is no rain for nine days. The class has one 200 L rain barrel, a watering can of 10 L, and a budget of 40 BAM for the month. A local shop sells mulch at 6 BAM per 30 kg bag; one bag covers about 6 m². A drip-irrigation starter kit costs 55 BAM and would need to be installed next season. Students notice that the plants near the path wilt by noon, while those near the fence stay upright until late afternoon. The caretaker says the barrel is refilled only twice a week from the mains tap.
1. Using the evidence in the setup, explain which two factors most likely cause the wilting near the path, and propose a low-cost action the class can take this month.
Read the worked answer
Factors: (1) Water loss by evaporation and transpiration is highest on exposed, sun-baked soil, and the path side receives more direct sun and reflected heat from the paving, so plants there lose water faster. (2) Limited water supply: the barrel holds 200 L and is refilled twice a week, so the class cannot simply water more - they must reduce demand.
Action: Buy mulch. The garden is 12 × 8 = 96 m², but the path strip is the priority. At 6 m² per bag, covering the 24 m² strip nearest the path needs 24 ÷ 6 = 4 bags = 4 × 6 = 24 BAM, which fits the 40 BAM budget. Mulch slows evaporation from the soil surface and keeps root-zone temperature lower, so plants wilt later. The drip kit (55 BAM) exceeds the budget and cannot be installed this season, so it is not a valid answer for this month.
2. The caretaker proposes watering only in the early morning. Evaluate this proposal using the water budget and the physics of evaporation.
Read the worked answer
Water budget: Twice-weekly refills give 2 × 200 = 400 L per week, about 57 L per day on average. Spreading this over 96 m² is roughly 0.6 L per m² per day - far below what thirsty summer crops need, so timing matters because every litre must count.
Physics: Evaporation rate depends on temperature, wind and exposed surface area. Watering at midday means much of the water evaporates before infiltrating; early morning watering lets water soak in while the soil is cool, and the surface is shaded during the hottest hours. So the proposal is sound: it reduces losses without extra cost.
Limitation: Morning watering alone does not fix the supply gap; it must be combined with mulch and possibly concentrating water on the most vulnerable plants. A complete answer notes both the benefit and the fact that timing improves efficiency rather than increasing total supply.
3. Design a simple measurement the class could use to test whether mulching actually reduces wilting, stating the variable measured and one control.
Read the worked answer
Measurement: Count the number of wilted plants (or measure the time of day when wilting first appears) in two comparable strips of equal area and plant type - one mulched, one unmulched.
Variable measured: Number of wilted plants per strip, or hours until wilting begins.
Control: Both strips receive the same volume of water at the same time, are the same distance from the path, and contain the same plant species. Only the mulch differs.
Reasoning: This is a controlled comparison, so any difference in wilting can be attributed to the mulch rather than to water amount or sun exposure. Recording results over several days reduces the effect of one unusually hot day.