Project 1 — Hydroponics: Growing Plants without Soil

Every year India has more people to feed, but the amount of good farmland does not grow with them. When farmers need more land, it is often taken from forests, and cutting forests destroys the homes of countless plants and animals and adds to climate change. There is a second problem too. When the same field is cropped season after season, the soil loses its nutrients. This is called soil degradation. Farmers then pour on more chemical fertiliser, which can harm the soil further. Wind and rain wash away topsoil (erosion), factory drainage pollutes water, mining scars the land and even too much irrigation can make soil salty. Roughly a third of India's total geographical area is affected by some form of soil degradation, which means fertile land is being lost.

Scientists, engineers and nutrition experts therefore look for sustainable farming: ways of producing healthy food while doing as little harm to the environment as possible. Hydroponics is one such way. The word joins two Greek roots, hydro meaning water and ponos meaning labour, so it means 'working with water'. In hydroponics, plants grow with their roots in a nutrient-rich water solution instead of soil, sometimes held up by a little growth medium such as coco peat.

Because the grower decides exactly which nutrients go into the water and in what amount, hydroponics is called a precision farming technique. It has other strengths as well:

• Plants can be stacked in layers (vertical farming), so more food comes from less floor space.
• Water and nutrients can be recirculated and reused instead of soaking away.
• Inside a polyhouse, temperature, humidity and light can be controlled.
• It suits urban farming on rooftops, balconies and school terraces.

The Government of India promotes hydroponics and aeroponics (where roots hang in mist) under the Mission for Integrated Development of Horticulture. Hydroponics is not magic, though. It needs electricity for pumps in larger systems, careful daily checking and some money to set up, and it suits leafy and fast crops far better than large crops such as wheat or mango trees. In this project you will test those strengths and limits yourself.

You already know from Science that plants need air, water, light, a suitable temperature and humidity, carbon dioxide and nutrients. In a field, soil quietly does several of these jobs at once. Before building anything, list each need and ask: if the soil is taken away, what will do its job?

A growth medium is a loose material that holds moisture and gives roots something to cling to. Common choices are coco peat and coco coir (made from coconut husk), gravel, sand, pieces of red brick or baked clay, pebbles, rockwool and vermicompost. Coco peat is cheap and easy to find in India and holds water well, so it is a good choice for school units.

Roots also need oxygen. In soil, air fills the tiny spaces between particles. In water, roots must get oxygen that is dissolved in the water, which is why some systems use an aerator. Finally, plants are helped by microbes, organisms too small to see without a microscope. Useful microbes break complex organic matter into simple substances that roots can absorb and can help keep diseases down. In hydroponics the grower must add only helpful microbes, for example through good compost tea, and keep out harmful ones by keeping water clean.

A good habit for the whole project: whenever a plant looks unwell, go back to this list and check each need in turn. Yellow leaves may mean missing nutrients, brown roots may mean too little oxygen, and thin, pale, stretched stems usually mean too little light.

A hydroponic project is a series of builds spread over about seven weeks, so planning matters as much as building. Plants take time to grow, and a system built late will not reach harvest before the term ends.

A sample seven-week plan

• Week 1: sow microgreens; build wick bottles; build the DWC bucket.
• Week 2: observe microgreens, wick plants and DWC plants daily.
• Week 3: harvest microgreens and weigh the yield; start brewing compost tea.
• Week 4: record wick growth; build the NFT pipes; compost tea is ready.
• Weeks 5 to 7: watch DWC and NFT growth, try compost tea and pH changes, harvest and record.

Materials. Most items can be waste: flat trays and food containers for microgreens; 2-litre PET bottles and cotton strips for wick planters; a 15 to 20 litre bucket, a 10 mm styrofoam or thermocol sheet, net pots or paper cups and a small 2.5 watt aquarium aerator for DWC; a 1 metre PVC pipe of about 76 mm diameter, end caps, net pots and a small submersible pump for NFT; muslin cloth, compost and jaggery for compost tea; and pH paper with vinegar or lemon juice for pH work.

Safety rules.

• Wear gloves when using tools. Watch the demonstration before you try.
• Cut PET bottles and pipes only under a teacher's eye, cutting away from your body.
• A drill, hole saw or heat gun is used only by the teacher or a trained helper, with you watching.
• Pumps and aerators run on mains electricity. Keep plugs and sockets well away from water, never touch them with wet hands, and switch off before putting hands in the tank.
• Online, search with your teacher, do not download unknown files and never share personal details.

Field visit. Before you build, try to see a working unit: a home gardener, a commercial farm, a Krishi Vigyan Kendra (KVK) or an agricultural university. Note the date and place, and look for how they deliver nutrients, use artificial light, control water and protect plants from sun and wind. Ask the grower about advantages, disadvantages and how produce is harvested and stored. Videos from ICAR or agricultural universities are reliable when a visit is not possible.

Microgreens are very young vegetable and herb seedlings, cut when they are just 1 to 3 inches tall and carry their first few leaves. They are the quickest and easiest crop in the project: about ten days from sowing to eating. People eat them raw in salads, on sandwiches and soups, or as a garnish. They are rich in vitamins A, C, E and K and in carotenoids. Good Indian choices are methi (fenugreek), mustard, coriander, spinach, radish, beetroot, cabbage and even wheat.

Steps

• Take a flat tray, a shallow earthen pot or a used food container, roughly 10 cm by 30 cm. Make a few holes in the bottom to drain extra water.
• Fill it about 2 inches (5 cm) deep with coco peat or soil.
• Moisten the medium evenly. It should feel like a squeezed sponge, not a puddle.
• Scatter seeds evenly and thickly and cover them with a very thin layer of medium.
• Keep the tray in a moist, humid place. Seeds usually germinate in 2 to 3 days. Then give light: a bright window, or a rack under a white tube light or LED bulb.
• Harvest when the first true leaves appear, at about 5 to 7 cm height, usually around day 10. Cut just above the medium with clean scissors and rinse gently.

Seed leaves and true leaves. The first leaves that open are the seed leaves (cotyledons). They are part of the seed and carry stored food that feeds the young plant until it can make food by photosynthesis. The leaves that come after them, usually with the shape of the adult plant's leaves, are the true leaves. Their arrival is your harvest signal.

Microgreens versus sprouts. Sprouts are grown in the dark and eaten whole, roots included, after 2 to 5 days. Microgreens are grown in light, eaten without roots and take 10 to 15 days.

Record: start date, tray size, seed type and amount, medium used in grams, number of trays, days to sprouting, days to first leaves, harvest date and grams harvested per tray. Weigh the harvest on a kitchen scale; this number lets you compare seeds and trays fairly.

Microgreens stay in their tray for only a week or two. Hydroponic systems, though, are meant to grow a plant all the way to harvest. The simplest such system is a wick planter made from a used 2-litre PET (polyethylene terephthalate) bottle. It recycles waste, needs no electricity and can hang on a wall or window.

Steps

• Under your teacher's supervision, cut a 2-litre bottle around the shoulder, about 10 to 15 cm from the top. Smooth the cut edge so it does not scratch.
• Make a hole in the bottle cap with a screwdriver tip or scissors point.
• Pass a wick of waste cotton cloth or thick cotton thread through the hole so that a long piece hangs below the cap.
• Fill the bottom part with water (or nutrient water) to form the reservoir.
• Screw the cap back on, turn the top part upside down and rest it in the bottom part, wick hanging into the water.
• Fill the top part with growth medium. Once the medium is soaked from below, plant seeds or seedlings.

How it works. Water climbs up the wick into the medium by itself. This is capillary action: a liquid moves through very narrow spaces, such as the gaps between cotton fibres, without any pump and even against gravity. It is the same reason a corner of a towel dipped in water slowly gets wet all the way up. You will see the medium in the upper part turn dark and damp after some hours.

Maintenance is light because there is no pump or aerator. Top up the reservoir, check that the wick stays wet (a dry wick has lost contact with the water, or is made of a synthetic fibre that does not carry water), and remove dead or old plants. Herbs such as tulsi, mint and coriander suit wick bottles well; very thirsty or heavy plants do not, because a single wick cannot move water fast enough.

Record: number of bottles your class made, grams of medium, seeds or seedlings planted, number that survived and average height gained over 15 days. Also note three difficulties you faced and how you solved them.

In Deep Water Culture (DWC) the plant's roots hang directly in a tank of nutrient water. It is one of the easiest and most widely used hydroponic methods, and a good system for leafy vegetables such as spinach, palak, lettuce and amaranth.

Steps

• Take a clean bucket or tub of 10 to 20 litres. A used one is fine, but check that it does not leak.
• Make a lid of styrofoam, thermocol (expanded polystyrene), a plastic sheet or a thin wooden board. Styrofoam can also simply float on the water as a raft.
• Cut holes in the lid so that net pots fit firmly. Paper tea cups or plastic cups with holes or slits cut in their sides can replace net pots. Space the holes 5 to 10 cm apart so that grown plants do not crowd each other.
• Fill each cup with coco peat, coco coir or sand and put in 2 to 3 seeds or one seedling.
• Fill the tank so the water just touches the bottom of the cups.
• Put the aerator's air stone (diffuser) at the bottom of the tank, run the tube out under the lid and switch it on.

Why the aerator matters. Roots breathe. In still water, the small amount of oxygen present is quickly used up. The aerator bubbles air through the water so that oxygen from the air dissolves into it. This dissolved oxygen (DO) keeps roots healthy and also supports useful microbes. Healthy roots are white. Brown, slimy or bad-smelling roots usually mean they are starved of oxygen, so check the aerator first.

Stopping algae. If sunlight reaches the water, green algae grow, turn the water green, use up nutrients and coat the roots. A light-proof lid or a dark-coloured tank keeps the water dark. Never use a transparent tank without covering it.

Maintenance and records. Check the aerator daily, top up water, harvest leaves regularly and replace old plants with new seedlings. Record the crop, planting date, number of plants, weekly increase in height and root length, harvest date and quantity. Also fill a cost table: reservoir, cups, lid or holder, aerator, growth medium and plants, and add them for the total cost.

DWC uses floor space, and stacking heavy water tanks on top of each other is difficult. The Nutrient Film Technique (NFT) solves this. Instead of putting roots into a full tank, it brings a thin, shallow stream (a 'film') of nutrient water past the roots, then lets it return to a reservoir to be pumped round again. Less water is needed, more plants fit into the same space, and pipes can be arranged horizontally, stacked vertically, or built as an A-frame or pyramid. Because the water keeps moving and only partly covers the roots, they get plenty of air, so NFT needs no aerator.

Steps

• Take a PVC pipe about 3 inches (76 mm) in diameter and 1 metre long. Such a pipe holds about 6 to 7 plants. Several pipes can be stacked.
• Mark holes at equal intervals along the top, sized to hold net pots firmly. An adult or a local fabricator or carpenter drills them with a hole saw.
• Fit end caps on both ends. Drill an inlet hole near one end and an outlet hole near the other, push the hose in and seal with silicone glue.
• Build a frame from bamboo, wooden battens or a metal rack, giving the pipe a slight slope from inlet to outlet.
• Put a submersible pump in a bucket reservoir, connect it to the inlet and lead the outlet back into the bucket. A simple on-off timer can switch the pump at set times.

Maintenance. The water level inside the pipe should be about half the pipe's diameter. Too low and roots dangle in air and dry out; too high and water overflows from the holes. You control this mainly by adjusting the slope. Watch the leaves: a change in colour can mean disease, pests or a missing nutrient. The ICAR AI-DISC mobile app can help identify such problems.

DWC compared with NFT

Plants in hydroponics get all their nutrients from the water, so you must add them. Instead of buying chemical nutrient powders, you can make an organic liquid manure called compost tea. Compost is decayed plant material, kitchen waste or animal manure. It contains plant nutrients such as nitrogen, phosphorus, potassium (potash), magnesium and sulphur, together with useful microbes. Good compost is dark brown to black, smells pleasantly earthy like wet soil after rain and is crumbly, like tea leaves.

Steps

• Take 100 to 150 g of ready compost or vermicompost.
• Tie it loosely in a piece of muslin cloth, like a big tea bag, and place it in a 15-litre bucket with about 10 litres of water.
• Stir in about 50 g of jaggery or sugar with a wooden stick. The sugar is food for the microbes, which multiply and help release nutrients that roots can take up.
• Put an aquarium aerator in the bucket and let it bubble for 2 to 3 days. Oxygen keeps the useful microbes active and stops the mixture turning sour.
• After 2 to 3 days you have a brown liquid. Add about 1 litre of compost tea to 10 litres of hydroponic water.

How to judge your compost tea

Wash your hands after handling compost and keep the bucket covered with a cloth so that flies and mosquitoes cannot breed in it. Record the date started, amounts used, colour and smell each day, and what you changed.

Clean water with the right nutrients is still not enough if its pH is wrong. You met pH in Science: it measures how acidic or basic (alkaline) a liquid is on a scale from 0 to 14. A pH of 7 is neutral, below 7 is acidic and above 7 is basic. In hydroponics, roots take up nutrients best when the water is slightly acidic to neutral, in the range of about 6.0 to 7.0, and growers usually aim for 6.5 to 7.0. Outside this range some nutrients stay locked in the water and plants show hunger signs even though the food is there.

Testing. Dip a strip of pH paper in a sample of the tank water for a moment, take it out and at once compare its colour with the chart on the pack. Read the number and write it down with the date.

Correcting.

• If the pH is above 7, add a weak acid such as vinegar (acetic acid) or lemon juice (citric acid), a few drops or millilitres at a time, stir, wait a few minutes and test again.
• If the pH is too low (too acidic), add a mild base, for example a pinch of baking soda, in the same careful way.
• Change pH slowly. A sudden big change shocks the roots.

Professional growers sometimes use strong acids such as phosphoric acid because very small amounts are needed, but strong acids are dangerous to handle and are not for school use. Weak acids from the kitchen are safer.

A class experiment. To see what pH does, take 1 litre of tap water and test it; it is usually close to neutral. Add about 20 to 30 mL of vinegar or citric acid solution and test again until it reads about pH 4. Add this acidic water to one test unit only, keep a second unit as normal, and compare roots and leaves after 2 to 4 days. Then bring the test unit back into the 6.5 to 7.0 range. Changing just one thing, and keeping a comparison unit, is what makes this a fair test.

Other water checks used by growers include dissolved oxygen (DO), total dissolved solids (TDS: all dissolved minerals and salts), hardness (dissolved calcium and magnesium) and electrical conductivity (EC: how well the water conducts electricity, which rises with dissolved nutrients).

A hydroponic unit is a small farm, and farmers live by their records. Good records turn 'it seemed to grow well' into facts you can compare and improve.

What to record for every system

• Set-up: date, crop and variety, number of plants, growth medium used.
• Growth: plant height and root length once a week, leaf colour, any pests or disease.
• Water: date of each top-up, compost tea added, pH before and after correction.
• Harvest: date and weight in grams.
• Problems: what went wrong and what you did.

Costing. List every component and its price, even if it was free (write ₹0 and 'reused'). Add them for the set-up cost. Then compare that with the value of what you harvested: weigh the harvest and multiply by the local market price per kilogram. A first system rarely pays for itself in one crop, because equipment such as aerators and pumps is used again and again. Dividing the equipment cost over several crops gives a fairer picture.

Time log. Note the periods spent on each activity, from the field visit to the pH experiment. This teaches you how long real work takes, which is the basis of planning any job.

Reflect honestly. Which system was easiest to build? Which grew best? Was it cheaper or dearer than you expected? Is it practical to grow every crop this way? Wheat, rice and fruit trees need huge space and long seasons, so hydroponics suits leafy greens, herbs, strawberries and tomatoes far better. Note what you would do differently next time.

Going further. Take time-lapse photos of a crop growing, paint wick bottles and gift them to school guests, try different growth media in the same system, or use a weather app such as Mausam and a mobile lux-meter app to compare temperature, humidity and light inside and outside a nursery. Display your models and posters at the school's Kaushal Mela.

Careers linked to this work include hydroponic and urban farmers, gardeners, nursery managers, botanists, horticulture officers, agricultural scientists at ICAR and KVKs, and technicians who design and maintain polyhouses.