Direct Use Geothermal for
Agricultural Applications

Geothermal water is very useful in agriculture. Agricultural applications make direct use of geothermal water, using it to heat and water plants, to warm greenhouses, or to dry crops.

In agriculture, geothermal water is used mainly as a source of heat and moisture. Irrigation pipes can bring hot water to cold ground, making it possible to grow crops that would otherwise die. It can also be piped into greenhouses to keep them warm and to maintain humidity. As with most other uses of geothermal energy, geothermal agriculture is only practical in areas that have geothermal resources. It is possible in agriculture, however, to use geothermal water that is much too cold for power generation or even home heating.

Current uses of geothermal energy in agriculture

The main agricultural uses of geothermal water include heating and watering open fields, warming and humidifying greenhouses, and drying crops.

Open field agriculture

Geothermal water can be used to keep the soil in open fields at a steady warm temperature. Farmers run irrigation pipes under the soil to provide both water and heat to the crops. Using geothermal water for irrigation extends the growing season and keeps plants from being damaged by low air temperatures.

Geothermal water can also sterilize soil to kill pests, fungus, and diseases that can harm crops. Sterilization requires very hot water so that the steam can be applied directly to the soil. The farmers either heat the soil from pipes underneath it, or they apply the steam above the soil and cover it with a plastic sheet to keep the heat inside.

Greenhouses

Heating greenhouses with geothermal water helps maintain a constant temperature, resulting in a more reliable crop and faster-growing plants. The water in the pipes can be released into the air inside the greenhouse, raising humidity if necessary.

There are several techniques used to heat greenhouses with geothermal water. These include plastic tubes, finned pipes, finned coils, soil heaters, or unit heaters. These parts can be combined according to water temperature and the preferences of the grower and the plants. For example, a grower producing roses would want to create a heating system with good air circulation and low humidity. A grower producing tropical plants could adjust the system to create high humidity and high soil temperatures.

Chinese shiitake mushroom growers in Fujian province use geothermal heat in a greenhouse to speed production time.

Two large greenhouses at the La Carrindanga Project in Bahia Blanca, Argentina, have been using geothermal pipes to heat their facilities. These greenhouses have sliding glass side panels that can open and close to regulate humidity and heat, and misting systems to water plants and maintain moisture in the air. The geothermal water runs through pipes buried just beneath the surface of the soil, where the heat from the water easily reaches plant roots. Boxes containing dirt and seeds can sit on top of these pipes so that they receive heat from below. The beds grow vegetables, flowers, and indoor and outdoor plants from seeds and cuttings. Bahia Blanca has an unreliable climate and is not a very good location for outdoor agriculture, but its geothermally heated greenhouses are very productive and reliable.

Drying crops

The heat from geothermal water can also be used to dry crops and timber. For example, since the mid-1980s the Broadlands Lucerne Company in New Zealand has been using geothermal steam to dry alfalfa.

Benefits and drawbacks of agricultural applications

Geothermally heated greenhouses are especially useful in marginal areas where the climate is unreliable. They make plant and vegetable production more efficient, and they reduce the time it takes seeds to germinate and grow to maturity. In addition, they make it possible to grow crops in the off-season, when such plants ordinarily would not grow and when they can be sold for higher prices. Farmers can grow plants under denser and more controlled conditions. They lose fewer plants and can make more precise commitments to buyers for future deliveries of crops.

However, geothermal water is not available everywhere. Not every farming operation can make use of geothermal resources because either there are none in the region or they are too difficult to reach. Installing equipment to pipe geothermal water into a farm can be expensive and time-consuming.

Impact of agricultural applications

Using geothermal water to enhance agriculture causes few environmental problems. It does not pollute the land because only water is emitted, although if the water is contaminated with heavy metals, such as mercury, this could cause a public health concern. The use of geothermal water could potentially result in farms being constructed in areas that would otherwise not be suitable for agriculture, which could destroy natural landscape and animal habitat.

Economically, using geothermal water in agriculture can be quite inexpensive. If geothermal wells already exist, then the farmers need invest only in steel or plastic pipes to transport the steam or hot water to the field, greenhouse, or drying facility. In some places the hot water is quite shallow and inexpensive to reach. Despite this comparative lack of expense, even this level of equipment is too expensive for many individuals and businesses.

There are many regions that have geothermal resources that could be used for agriculture that have not yet been able to take advantage of them. For example, the Oserian Development Company on the shores of Lake Naivasha, Kenya, grows flowers for market. It has considered using hot water from the Olkaria Geothermal field to sterilize the soil. As of the early 2000s this plan had not been implemented because of the cost.