HKDSE Geography/M5/Characteristics of Irrigation Farming in Southern California

Irrigation Schemes

Targets: Scanty rainfall

Types

Irrigation schemes in Southern California include the following:

• Dams and reservoirs store water.
• Canals (e.g. All-American Canal) and aqueducts (e.g. Los Angeles Aqueduct) transport water to farms.
• Irrigation methods are used to apply irrigation water to fields.

There are several types of irrigation methods.

• The gravity flow system involves digging a series of furrows. The irrigation water runs down these furrows, increasing soil moisture. The water can be recollected and reused.
• The sprinkler system/centre-pivot system involves a series of rotating sprinklers which distribute water in a circular way.

However, these two systems have some disadvantages:

• Leaching occurs as great amounts of water infiltrate into the soil. (See the chapter about soil in TRFs)
• Salinisation is worsened. (See the Farming Inputs)
• Much water is lost by evaporation.

The drip irrigation system is a response to these negative impacts. It involves using a tube with a series of poreholes which irrigate the root zone of the crops. The amount of water is carefully controlled, so leaching, salinsation and water loss by evaporation are minimised. It also allows for the addition of small amounts of pesticides and chemical fertilisers. However, the setup and maintenance cost is very high.

Effectiveness

Irrigation increases crop yield as the possibility of crop failure by drought is reduced. Moreover, it encourages plant growth, so yield increases.

Negative impacts

Leaching and salinisation are effects of irrigation.

The negative impacts of building large-scale water schemes are as follows:

• As water is transferred from Northern California to Southern California, discharge in the North drops. Water table drops as a result. The water and load supply to the South decreases, so less flooding occurs. The South receives fewer alluvial nutrients from flooding. Soil fertility in the lower course drops.
• Changes in the microclimate of the North and South result as reservoirs will increase condensation and precipitation. The cloud cover also narrows diurnal range of temperature and cools down the area.
• Building of dams drowns a large area upstream and may lead to earthquakes since Southern California is a tectonically unstable region near the San Andreas Fault, a notable conservative plate boundary.
• Natural habitats are destroyed.

Mechanisation

Mechanisation is carried out in Southern California, e.g. tractors.

Evidence of mechanisation

Evidence of mechanisation on a photograph is reflected by

• The regular shape of farmlands
• Sheds that store machines

Agrochemicals

Target: Pest problem, infertile soil

Types

Various agrochemicals are used in Southern California:

• Chemical fertilisers contain nutrients that improve soil fertility.
• Pesticides make plants resistant to pests.
• Insecticides make plants resistant to insects.
• Fungicides prevent fungus growth.
• Herbicides prevent weed growth.

Effectiveness

• Chemical fertilisers improve soil fertility and thus yield.
• Pesticides and insecticides reduce the chance of crop failure because of pests. Yield increases.
• Fungicides and herbicides reduce the number of plants that compete for nutrients with the crops.

Import of Labour

As Southern California is facing a labour shortage problem, workers are imported from Mexico instead.

Biotechnology

• GM crops
  • Genetically modified crops (GM crops) are plants used in agriculture, the DNA of which has been modified using genetic engineering methods. Plant genomes can be engineered by physical methods or by use of Agrobacterium for the delivery of sequences hosted in T-DNA binary vectors. In most cases, the aim is to introduce a new trait to the plant which does not occur naturally in the species. Examples in food crops include resistance to certain pests, diseases, environmental conditions, reduction of spoilage, resistance to chemical treatments (e.g. resistance to a herbicide), or improving the nutrient profile of the crop. Examples in non-food crops include production of pharmaceutical agents, biofuels, and other industrially useful goods, as well as for bioremediation.