Week 2: Soil, plants and irrigation demand
Why water rather than sunlight decides how much of the garden is worth planting.
The obvious way to size a garden — area times days times yield — gives the wrong answer, and the reason is that it never asks where the water comes from. This week replaces it with a monthly water balance: reference evapotranspiration from FAO-56, effective rain rather than total rain, and a crop coefficient, month by month. What falls out is a deficit curve, and that curve decides how much of your growable ground is worth planting at all. Canberra leads the worked example, because it is the site where a generous growing season and a modest deficit pull in opposite directions. The deficit you compute here comes from long-term climate records, not from your client's garden: establishing what that garden actually draws is one of the things Assignment 1 will have to pay for.
This week
- Lecture, 1 March 2027
- Water is the yield limit, not sunlightWeek 2 — evapotranspiration, effective rain and the monthly deficit that decides how much of your growing area is actually productive
- Tutorial, 4 March 2027
- The irrigation demand curveWeek 2 tutorial — turn twelve rows of climate normals into a monthly irrigation demand curve, and decide on the numbers how much ground you will actually plant
- Worked example
- CanberraThe Taylors' home leads this week, because its climate makes this subsystem easy. All five homes are compared on the lecture page.
What you leave with
A twelve-row irrigation demand curve in kilolitres, and a planted area you can defend on water rather than on ambition.
You have finished the tutorial when all of this is true, and you can tell without asking anyone:
- you can compute ETo for one month by hand from Tmax, Tmin and latitude, and check it against your spreadsheet
- your twelve-row deficit table uses effective rain, not total rain
- you have chosen a planted area and can justify it against water rather than against ambition
- your monthly irrigation demand is stated in kilolitres, not millimetres
- the planted area you chose respects the retained-area constraint on your home's dossier
Assignment milestone
Tutorial checkpoint 1 of 10 (2 %) due 5 pm Friday.
Where this sits
You meet the client and work through each candidate system — garden, mushrooms, insects, fish, preservation — far enough to know what it needs and what would have to be measured before anyone spent money on it. Every calculation in these weeks is a scoping estimate on published figures, not a claim about this house.
Expected effort
About 5 hours this week: 2 h lecture and notes, 2 h tutorial, 1 h preparation and quiz. This week: Orientation and tutorial practice only; no assignment work scheduled.
A planning guide from the semester planner, not a requirement and not a measurement of anyone. Tutorial submission sits inside the tutorial hours and the quiz inside preparation; neither is counted twice.