The production of horticultural crops in greenhouses has increased significantly in Australia in recent years because the capacity to produce high quality fruit and vegetables under controlled environmental and production conditions is attractive to many growers.
The majority of greenhouses in Australia are in Victoria and NSW. The main crops are vegetables (tomatoes, capsicums, cucumbers), cut flowers (roses, carnations, gerberas and lisianthis) and nursery crops. Many greenhouses have been constructed with hydroponic production facilities. In hydroponic production crops are grown without soil, either in a medium (such as peat, sawdust or rockwool) or in a solution (no medium). The production solution incorporates both the water for irrigation and the nutrients. Such systems can be arranged to recirculate the solution instead of allowing it to run to waste.
Irrigating greenhouse crops
A prime requirement of greenhouse crops is uniformity of irrigation application- every plant must receive sufficient water and no plant should be over-watered. The purpose of greenhouse production is to optimise all factors that affect plant growth including both the aerial environment (sunlight, air temperature and relative humidity) and the root environment (soil moisture, nutrient availability and soil temperature). As a greenhouse is covered, all plant water requirements need to be met by the irrigation system.
The irrigation methods available for greenhouses include:
• Overhead sprinklers;
• Travelling sprinkler boom;
• Drip irrigation; and
• Subsurface irrigation techniques, such as ebb and flow, and capillary.
Internal greenhouse structure and layout can present special challenges in achieving high uniformity and efficiency with overhead sprinklers and sprays.
Subsurface irrigation methods deliver water automatically to each container and also allow drainage water to be readily recycled. These methods provide the greatest opportunity for high water use efficiency. Though the initial instalment cost is slightly higher than that of other systems, the eventual water savings and increased productivity make the installation of subsurface systems a worthwhile investment.
The ability to automatically deliver nutrients to plants in precise amounts through a fertigation system is a major advantage of greenhouse micro irrigation systems. This technique also reduces the likelihood of nutrient-rich leachate draining from the greenhouse site.