DSE Geography | Farming Systems and Food Supply Tutor Prep Guide

DSE Geography | Farming Systems and Food Supply Tutor Prep Guide | How many people one farm feeds

2026-11-03

Tutor lesson-prep guides · Secondary Geography

Students label fertiliser as an output and think intensive means large. This lesson locks farming into a three-column table of inputs, processes and outputs, then uses yield per hectare and consumption per person to count how many people a farm feeds.

Objectives — Students can: (1) split a farm into inputs, processes and outputs, separating natural from human inputs; (2) distinguish intensive from extensive farming using labour density, for example 6 workers on 2 hectares giving 3 per hectare against 6 on 400 hectares giving 0.015 per hectare; (3) calculate that 120 hectares at 4.5 tonnes per hectare give 540 tonnes, 432 tonnes after 20 per cent loss, feeding 2,880 people at 0.15 tonnes each per year; (4) explain that local Hong Kong farming is small-scale vegetables and flowers while most food is imported.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Physical environment	Three natural factors affecting crops	Temperature, rainfall, soil
Population density	How is population density calculated?	Population divided by area
Land use	What do land use conflicts usually involve?	Different uses and interests on the same land
Sustainable development	Name the three pillars	Economic, social and environmental

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Opening question	How many steps from field to bowl of rice?	Name at least three stages
8-20 min	Three columns	Sort a farm example into inputs, processes, outputs	Separate natural and human inputs
20-32 min	Intensive and extensive	Compare 6 workers on 2 hectares with 6 on 400	Compute labour density
32-44 min	Yield and food	120 hectares, 4.5 tonnes per hectare, 20 per cent loss	Compute net output and people fed
44-52 min	Hong Kong and sustainability	Local vegetables, hydroponics, aquaponics	Explain the import share
52-60 min	Independent practice	Three questions in eight minutes	Check and label errors

03 Teaching script (read it out)

Scene 1: The three-column table is the foundation, so classify before explaining

Inputs are natural, such as temperature, rainfall, sunshine and soil, or human, such as labour, capital, fertiliser, pesticides, machinery, subsidies and market demand. Processes are ploughing, sowing, irrigation, fertilising, harvesting, processing and transport. Outputs are crops, income, and also waste and pollution. Students most often put fertiliser in the output column because a harvest follows it; make them state that fertiliser is bought and applied, while the crop is what the field produces.

Ask which column holds pesticide and which holds rice, and why.

Scene 2: Intensive is not large, it is input per hectare

Six workers on 2 hectares give 3 per hectare, while six on 400 hectares give 0.015 per hectare, so the first is intensive and the second extensive even though it is a hundred times larger. Judge by inputs per hectare, never by total area. Market gardens in Hong Kong and greenhouses in the Netherlands are intensive, while wheat belts in inland Australia and the Canadian prairies are extensive. Compare with one formula rather than with adjectives.

Ask whether 6 workers on 400 hectares is intensive, and require the numbers in the answer.

Scene 3: Food supply compares net output with consumption per person

120 hectares at 4.5 tonnes per hectare give 540 tonnes, and a 20 per cent loss in storage, transport and processing leaves 432 tonnes. At 0.15 tonnes per person per year that feeds 2,880 people. Dividing 540 directly gives 3,600 and overstates the reach by 25 per cent. Answers must state that net output is used and must carry units through every step: hectares, tonnes and people.

Ask why 540 tonnes cannot simply be divided by consumption per person.

04 Question types and worked steps

Type	Example	Steps	Answer
Classify inputs and outputs	Data from a vegetable farm	Draw three columns, split natural from human, put waste in outputs	Fertiliser is input, cabbages are output
Intensive or extensive	6 workers on 2 hectares against 6 on 400	Compute workers per hectare, compare, apply the definition	Intensive then extensive
Yield and carrying capacity	120 hectares, 4.5 tonnes per hectare, 20 per cent loss	Gross output, multiply by 0.8, divide by consumption	432 tonnes, 2,880 people
Sustainable measures	Organic farming, hydroponics, aquaponics	Name the measure, say which impact falls, state the limit	Less fertiliser and transport emissions but higher cost

Sanity check (teach this): Order check: labour on an intensive farm is a single-figure number of people per hectare, while an extensive farm gives a few hundredths, so the two differ by two orders of magnitude; answers of similar size mean the divisor is wrong. A net 432 tonnes is exactly 80 per cent of 540 and can never exceed the gross figure. Feeding 2,880 people is a village, so an answer of 288,000 means tonnes and kilograms were mixed.

05 Independent practice (3 questions)

Question	Answer	What to watch
80 hectares at 3.5 tonnes per hectare with 15 per cent loss	238 tonnes	Did you multiply by 0.85
5 workers on 2 hectares and 8 on 320 hectares	2.5 and 0.025 workers per hectare	Did you use totals instead of density
200 kg of nitrogen per hectare over 120 hectares	24,000 kg or 24 tonnes	Did you convert kilograms to tonnes
Main local farm products in Hong Kong	Vegetables and flowers	Did you answer rice

06 Common mistakes and what to say

Mistake	Student writes	Say this
Calling fertiliser an output	Farm outputs include fertiliser and vegetables	Fertiliser is bought and put into the field, so it is an input; putting it in outputs confuses cost with revenue.
Equating intensive with large	400 hectares must be intensive because it is big	Intensity is input per hectare; 6 workers on 400 hectares is 0.015 per hectare, which is extensive.
Dividing gross output by consumption	540 tonnes feeds 3,600 people	Two tenths of the harvest is lost in storage and processing, so dividing the gross figure assumes no waste.
Saying Hong Kong has no farming left	There is no agriculture in Hong Kong now	Small vegetable, flower and hydroponic farms remain; their share of total supply is low and most food is imported.

07 Homework (paper, section and question numbers)

Geography chapter index — Revise river management and water resources, then questions 1 and 2
Industry and manufacturing — Question 3 compares farming with industrial location factors
Sustainable tourism — Do the sustainability section only to revise the three pillars

08 Exit check (last 5 minutes)

Question	Answer	Decision
Which column holds fertiliser	Inputs, human	Error: treated as output
Farm type for 6 workers on 400 hectares	Extensive	Error: judged by area
Net output of 120 hectares at 4.5 tonnes per hectare with 20 per cent loss	432 tonnes	Error: loss ignored
Main local farm products in Hong Kong	Vegetables and flowers	Error: answered rice or no farming

09 Tutor FAQ

Why separate natural from human inputs?

They differ in how far they can be managed: natural inputs follow site choice, human inputs follow capital and policy, and answers must target the right group.

Is hydroponics always greener?

It saves water, land and pesticide but depends on electricity and nutrient solutions, so the carbon result depends on the power source.

Does food security mean self-sufficiency?

No. Food security is stable and affordable supply, built on local production, diverse imports and reserves together.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.