Agriculture & Future Food Systems · Article
Inputs, Organisms and Harvested Outputs
Follow water, nutrients, carbon and energy through a growing or food-production system, and learn what a harvest number can—and cannot—tell you.
Preparation and related reading
Shared Foundations
This article helps you
- Distinguish material inputs, energy supplies, living organisms and supporting infrastructure.
- Choose a clear production boundary and account for outputs and changes in stored materials.
- Compare cultivation and microbial production without hiding their upstream requirements.
- Recognise why harvest mass, food quality and resource efficiency answer different questions.
Begin with a harvest you can follow
Imagine a small greenhouse producing lettuce. At harvest, a tray of leaves looks like the result of seeds, watering and patient care. But the leaves also contain carbon that entered from the air, minerals supplied to roots and water retained in their tissues. Light supported the reactions that built plant material. A harvest becomes easier to understand when you follow these contributions separately.
Now imagine a food producer growing yeast in a vessel. Its carbon may arrive in a sugar solution rather than through photosynthesis. The same questions remain useful: what enters, what the organism transforms, what leaves, and what keeps production working? They connect a garden with a bioreactor while preserving their different needs and products.
This article builds that account. The shared Foundations records Systems, Conservation and Metabolism provide the underlying ideas; here we apply them to food production.
Separate materials, energy and support
Material inputs supply matter: water, carbon sources, nutrients, seeds or starter cultures. Energy supplies support transformations and work: sunlight, electricity or chemical energy in substrates. Categories can overlap. Sugar provides carbon and chemical energy to a microorganism; electricity provides energy but cannot supply the nitrogen atoms needed for proteins.
The organism carries out the biological transformations. A lettuce plant obtains carbon through photosynthesis and takes up water and mineral nutrients through its roots. Growing roots, leaves and other tissues requires coordinated metabolism. Supplying more of one input cannot automatically replace another missing requirement.
Conditions and infrastructure make transformations possible. Temperature, root-zone aeration and light affect cultivation; equipment, clean water and people support production. Buildings are not consumed like nutrients, but their construction, maintenance and operation matter when the comparison boundary includes them.
| Role | Examples | Question to record |
|---|---|---|
| Materials | Water, seeds, mineral nutrients, carbon dioxide | What enters, in what amount and form? |
| Energy | Sunlight; electricity for any pumps or lights | What powers growth and operation? |
| Living transformation | Plants and their metabolism | Which organism makes the intended product? |
| Operating support | Containers, greenhouse, controls and labour | What must stay available and reliable? |
| Outputs and storage | Harvest, drainage, vapour and remaining materials | Where does each tracked material go? |
Choose the boundary before counting
A system boundary identifies the activities in your account. A growing batch might start with plants entering a greenhouse and finish at harvest. State the period and starting inventory: water, plants and materials already inside. Omitting earlier inputs can make an output appear to come from nothing.
For any conserved material, the basic account is: amount entering minus amount leaving equals the change in the amount stored inside. You can track water, nitrogen or carbon separately. Do not add litres of water to kilowatt-hours of electricity: they are different quantities. Total mass accounting also requires gases and other flows that a simple irrigation log may miss.
A narrow boundary can answer how much irrigation entered a greenhouse. A wider boundary may include input preparation, electricity generation, buildings, transport or cooling. Choose according to the question and write it down, so another reader can tell what the result includes.
Follow one material all the way through
Consider an invented greenhouse batch receiving 100 litres of irrigation water. Our simplified water account assigns 80 litres to evaporation and transpiration, 15 litres to collected drainage and 2 litres to water carried out in harvested leaves. Water remaining inside increases by 3 litres. The account closes because 80 + 15 + 2 + 3 = 100.
These are teaching numbers, not measured data or crop targets. Assume no rain, no unrecorded supply and negligible net chemical transformation of water. Stored water includes plants, growing medium and reservoirs. Evaporation leaves surfaces; transpiration transfers water from plants to air. The diagram and table describe the same batch.
The 2 litres in the harvest are not the total water needed to produce it. Most supplied water took other routes. Nor does 15 litres of drainage automatically mean 15 litres wasted: it may be collected and reused, but that requires checking its quality and counting it consistently.
| Flow or storage change | Amount | Position in the account |
|---|---|---|
| Irrigation received | 100 | Input across the boundary |
| Evaporation and transpiration | 80 | Output to the air |
| Collected drainage | 15 | Output from this boundary |
| Water in harvested leaves | 2 | Output with the product |
| Increase in water remaining inside | 3 | Storage change, not an output |
One batch: where the water goes
Read the diagram as text
A simplified illustrative water account shows 100 L entering a greenhouse batch, 97 L leaving by three routes and a 3 L increase in water remaining inside.
Parts
- 100 L irrigation
- New water entering during this batch
- Greenhouse batch
- Plants, growing medium and reservoirs inside the boundary
- 80 L to the air
- Evaporation and plant transpiration
- 15 L collected drainage
- Leaves this boundary; reuse needs its own account
- 2 L in harvested leaves
- Water carried out with the product
- +3 L remaining inside
- Increase in stored water, not an outgoing flow
Connections
- 100 L irrigation → Greenhouse batch: input
- Greenhouse batch → 80 L to the air: vapour output
- Greenhouse batch → 15 L collected drainage: liquid output
- Greenhouse batch → 2 L in harvested leaves: product water
- Greenhouse batch → +3 L remaining inside: storage change
Follow the actual organism and feedstock
Cultivation combines organisms with fields, orchards, gardens, greenhouses or other growing environments. Microbial production uses selected bacteria, yeast or fungi to make biomass or ingredients; precision fermentation targets specific products. Each mechanism needs an account suited to its actual process.
If a microbial process uses sugar from a crop, the farm has moved upstream; it has not disappeared from the system. Record that sugar's origin, along with water, nitrogen, minerals and any required aeration or temperature control. The word fermentation is also used broadly in industry, so the name alone does not establish whether oxygen is required. Details belong in the relevant process chapter.
A useful combination might connect cultivated plant materials with microbial ingredient production, followed by food formulation. That is an option to investigate rather than a guaranteed improvement. Safety, feedstock suitability and real operating evidence determine which connections are practical. Alternative-carbon routes need their own evidence and will be examined separately.
A useful output is more than a weight
Name the output: fresh leaves, stored grain, mushrooms, microbial biomass or a purified ingredient. Record its condition when weighed. Fresh mass includes water; dried material uses another basis. Equal masses of different products are not automatically nutritionally or functionally equivalent.
Also ask which part is usable, safe and acceptable for its intended purpose. A damaged harvest may weigh the same as an intact one but have a different usable life. A recovered stream can be a useful co-product, an input to another process or material requiring treatment. Its name does not settle its safety or value.
To compare resource demand, specify a common output and the same boundary. Electricity per kilogram answers an electricity question; it does not by itself establish sustainability, affordability or food quality. A complete decision may also need water, nutrients, land, waste, infrastructure, operating skills and the cost of delivering suitable food.
Make the account useful for the next decision
Begin with a question small enough to answer: where did this batch's water go, which input limited the process, or why did two production records differ? Identify the organism, product, boundary, period and units. Keep measured values separate from estimates and clearly label missing flows.
If the account does not close, investigate omitted flows, changed inventories, inconsistent timing or measurement uncertainty. Do not force the difference into a convenient category. Once the account is understandable, test a change against the outcome you care about.
Worked examples
Close the illustrative water account
A batch receives 100 L. Vapour, drainage and harvested water total 97 L. What storage change makes the account consistent?
- Keep all quantities in litres and use the same batch period.
- Add the outgoing flows: 80 + 15 + 2 = 97 L.
- Calculate the storage change: 100 - 97 = 3 L.
- Check that remaining water increased by 3 L; this is an assumed teaching inventory, not a measurement.
The account requires a 3 L increase in stored water. A measured discrepancy would still need investigation rather than being automatically assigned to storage.
See how the boundary changes a comparison
Two invented processes each deliver 1 kg of the same ingredient at agreed quality. A uses 6 kWh on site and 10 kWh for input preparation; B uses 12 kWh on site and 2 kWh for input preparation. Which uses less electricity?
- Within the site boundary, A uses less: 6 kWh compared with 12 kWh.
- Include the specified input-preparation step: A uses 6 + 10 = 16 kWh.
- On that wider boundary, B uses 12 + 2 = 14 kWh.
- Keep the conclusion limited to these hypothetical electricity demands; other energy, infrastructure and impacts remain outside the example.
A uses less on-site electricity, while B uses less within the stated wider boundary. The changed ranking shows why comparisons must state what they include.
Check your understanding
A growing system has abundant electricity but lacks an essential mineral nutrient. Can more electricity replace the missing nutrient?
Show answer and reasoning
No.
Electricity supplies energy. It does not supply the required element's atoms, although powered equipment may help deliver an available nutrient input.
A pump circulates 40 L through roots twice while the whole system receives only 5 L of new water. Should external water input be recorded as 80 L?
Show answer and reasoning
No. External input is 5 L for that boundary and period.
The 80 L describes internal circulation. Counting it again as external input would count reused water repeatedly.
A producer describes a sugar-fed microbial ingredient as independent of cultivation. What evidence would you request first?
Show answer and reasoning
The actual sugar source and an input account that includes its production.
If the sugar came from cultivated crops, cultivation remains an upstream component. Other carbon routes require their own verified feedstock and process evidence.
Key ideas
- Trace materials and energy separately, alongside organisms and operating support.
- State the boundary, period, units and changes in starting and ending inventories.
- Internal reuse is different from a new external input.
- Compare products on an agreed usable output basis and preserve their upstream requirements.
- A resource account supports a decision; it does not automatically prove sustainability or affordability.
References
Sources supporting the explanations and examples in this article.