Greenhouses

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.

Australia enjoys a year round supply of fresh vegetables. The major vegetable crops are potatoes, tomatoes, crucifers (cabbages, cauliflower, broccoli and brussel sprouts), carrots, onions, lettuce, capsicums, peas, beans and melons. Vegetables are grown in a wide range of climate zones in Australia.

Production of high quality, high yielding crops requires optimum soil moisture conditions to be maintained throughout the entire growing season. For most vegetables and most regions this means that supplementary watering through irrigation is required.

Irrigating vegetables

Vegetable crops require continuous access to an ample supply of good quality water to achieve optimum fruit development and growth. Vegetable crops are characterised by shallow root systems, which have small soil water storage reservoirs, and plants with changing water needs, depending on their stage of development and the weather. Overwatering of vegetables can result in waterlogging, disease, leaching of nutrients, unwanted additions to groundwaters (encouraging soil salinity), increased energy use (pumping), increased labour and excess drainage water. Vegetables are very sensitive to deficiencies in available water. Inadequate irrigation of vegetable crops may result in reduced fruit quality, number, and size and increased risk of salting.

A wide variety of fruit and nut crops are produced in Australian orchards. Major crops include citrus, stone fruits and nuts. Expansion of local markets and continued growth in exports are the driving forces in the development of orchard production in Australia.

Current issues for orchard producers include international competition, a need to increase productivity, the adoption of farm best practice, and a focus on chemical-free produce and environmental sustainability. Several of these issues foster the need for sound water management. Also, with drought conditions and decreased water allocations, the availability and use of water is an issue in itself for farmers.

Irrigating orchards

High-value tree crops require precise control over the inputs of water, fertilizer, chemicals and labour to achieve high quality, high yielding fruit. Challenges faced by orchard irrigators include the need to efficiently deliver water to individual trees with high water requirements that are sometimes widely spaced, growing in difficult soils.

Precise control over the delivery of water to individual tree root zones is the most water efficient irrigation technique. Micro irrigation systems (also referred to as ‘drip’ irrigation systems) apply water to the tree root zone at frequent intervals so that soil moisture levels are maintained at optimum levels. These systems are potentially the most water efficient method.

Micro irrigation systems can save water in orchards by:

• Watering only the plant root zone;

• Reducing loss to deep drainage or percolation;

• Reducing water consumption by weeds; and

• Minimising evaporation from the soil surface.

Water-soluble fertilisers can be delivered through micro irrigation systems (fertigation systems) so that the nutrient needs of orchard crops can be supplied on a continuing basis.