Soilless agriculture

Aeroponics

Aeroponics is the process of growing plants in an air or mist environment without the use of soil or an aggregate medium (known as geoponics). Unlike hydroponice, which uses a liquid nutrient solution as a growin medium and essential minerals to sustain plant growth; or aquaponics which uses water and fish waste, aeroponics is conducted without a growing medium. 

Aquaponics

Aquaponics refers to any system that combines conventional aquaculture with hydroponics (cultivating plants in water) in a symbiotic environment. In normal aquaculture, excretions from the animals being raised can accumulate in the water, increasing toxicity. In an aquaponic system, water from an aquaculture system is fed to a hydroponic system where the by-products are broken down by nitrifying bacteria initially into nitrites and subsequently into nitrates that are utilized by the plants as nutrients. Then, the water is recirculated back to the aquaculture system.

Hydroponics

A solar hydroponic system produces vegetables by using continuously flowing water as a medium for transporting nutrients. It is made up of a greenhouse and a water reservoir that occupies the entire base of the greenhouse for the recirculation of nutrients in a closed system. It has solar pump that uses photovoltaic cells and batteries to feed the low-pressure drip-irrigation system. Solar hydroponic systems are highly efficient and require two hours of maintenance per week. Products may be envisioned for on-site consumption or to be sent to market. Plants grow on an organic-fertilizer substrate and the water reservoir may be used as a pisciculture tank.

Location

Solar hydroponic systems may be installed at any altitude. The west end of the Andean Altiplano, where soil conditions are poor, is particularly suitable. They may also be implemented in areas with a high population density and within family orchards, because they require little space. Fertile soil is not required, but a nearby water source is.

Threats and Impacts addressed

Given that solar hydroponics is a controlled system that does not require soil and that is protected by a greenhouse, production is not hindered by intense rainfall, hail, sudden temperature changes, drought or changes in rainfall patterns. This allows for a considerable increase in local productivity, food security and household income.

Implementation steps

1. Design the system (capacity, varieties to be cultivated) based on site characteristics and production objectives.
2. Prepare the site.
3. Assemble the greenhouse.
4. Place the membrane or water tank at the base of the greenhouse.
5. Prepare and assemble the hydroponic pipes.
6. Install the pumping system.
7. Set up the drip-irrigation system.
8. Put the shade mesh in place.
9. Seed the selected varieties of vegetables in an organic-fertilizer substrate on the hydroponic pipes.
10. Attend to the plants and perform system maintenance. The water in the lower deposit must be changed three or four times a year to avoid acidity and to prevent the lack of nutrients from hindering crop growth. The water resulting from the process may be used as a source of nutrients to irrigate crop fields or gardens.

Inputs and Costs

The estimated cost is for the construction of a hydroponic system 5 m long by 1.2 m high that includes: a greenhouse, shade mesh, the drip-irrigation mechanism and couplings, a pump with a 40 W photovoltaic panel with battery, a 100 l tank, geomembranes and greenhouse plastics. Three days of training are included.

Economic and Ecosystemic Benefits

A solar hydroponic system reduces the impact of agriculture on natural areas by attaining high yields in small spaces. It helps preserve soils and stimulates not only production but also the local food market. More than 300 vegetable plants per month or 30 ripe plants per square meter can be grown (UNDP, 2003). For example, the dual-level system suggested above can produce, as a conservative estimate, an average of 60 plants per square meter per month. A family’s economy can improve as a result of food production for self-consumption as well as from approximately US$ 105 per month in additional income.

Limiting Factors

The system should necessarily be installed on land with a low slope and access to a water source. The location must have direct solar incidence more than four hours a day. The system produces about 5000 l of wastewater a year that cannot be disposed of in natural streams because of the amount of nutrients it contains. Preferably it should be used to irrigate gardens or family orchards, but this requires considerable space.

Lessons Learned

The system should be easy to access, for the provision of frequent maintenance. The pump and photovoltaic equipment require little maintenance, but they must be installed by a specialized technician. It is important to ensure that the irrigation network does not become clogged with solid particles present in the water.

Additional Considerations

Solar incidence should be studied at the proposed location to determine the amount of available shade and the shade rate of the meshing. To select the species to be grown, local climate conditions and the preferences of the target market must be understood. Two variables that should be taken into account during the operation of the system are the pH and the nutrient concentration. Controlling these variables requires training and practice.

Units to Monitor Project Progress: Systems operating (number); vegetables produced per month (kg).

Units to Monitor Measure's Impact: Families with hydroponic systems (number); additional income earned (US$/month).

References

• UNDP (2003). Hidroponía familiar: cultivo de esperanzas con rendimientos de paz. Armenia, Colombia: FUDESCO Armenia.
• FAO (2003). La Huerta Hidropónica Popular: Curso audiovisual. Santiago, Chile: Manual Técnico, 3rd ed.