Catchment information

Catchment name
Mallee

Map of catchment area

Overview of region

• The Mallee region covers approximately 3.9 million hectares of the northwest corner of Victoria - almost one-fifth of Victoria.
• The regional population is approximately 65,000 people with the major urban centre being Mildura. Smaller towns in the region include Ouyen, Red Cliffs, Merbein, Irymple, Murrayville, Hopetoun, Rainbow, Birchip, Sea Lake, Robinvale and Nyah.
• The region is characterised by diverse land systems and unique vegetation types.
• The Mallee region is agriculturally diverse, covering key irrigation areas and extensive dryland cropping and grazing areas. The irrigated area around Mildura is one of the richest agricultural areas in Australia, producing wine, dried fruits, olives, citrus fruits and vegetables.

Horticulture industry in region

• The Mallee’s irrigated areas, especially along the Murray River, support a significant amount of the state’s agriculture.
• A large proportion of Victoria's grapes, almonds and fruit for drying is produced in the region.
• A wide range of produce is grown including:
• table grapes (in addition to wine and dried fruit)
• nuts (almonds and pistachios)
• vegetables (including asparagus, mushrooms, avocados, potatoes and carrots)
• fruit (including watermelons, citrus, pome fruit and stonefruit)
• Producers range from smaller holdings growing traditional crops such as grapes and stonefruit to those growing vegetables under large-scale broadacre conditions.
• Local horticultural growers produce high quality product for the fresh and processed product markets. Some products such as carrots and potatoes can be grown year round.

Incentives for region
None identified in region

Case study of horticulture in the Malle region

Project title / summary
HAL NRM Initiative – Final Report

Project authors

• RMCG, Consultants for Business, Communities and Environment

Objectives of project

• Through the use of farm data, this project aimed to:
  • Provide a link between farm and catchment nutrient/salt exports;
  • Consider on-farm benchmarks and influence of practices; and
  • Have data to build and improve the existing relationships between industry organisations and the Mallee CMA.
• As a result, the information collected for this project can be used to inform the development of future nutrient and salinity Resource Condition Targets (RCTs).

Methodology
Field Sampling

• Irrigation drainage and saturated soil water extracts were monitored from November 2005 to April 2006.
• Measurements were taken from five farms including two producing citrus with overhead irrigation, two producing dried grapes with under-vine sprinklers and one with drip irrigated avocados.
• The crop site samples were collected using full stops set at either 30cm and 60cm, 30cm and 90cm or 20cm and 40cm depths.
• Salinity and nitrate readings were taken from the full stop samples using an EC meter and nitrate test strips, respectively.
• Information was also collected from the growers regarding the amount of water applied during irrigation and the application rate. The level of nitrogen applied to crops and the timing of applications was also recorded.

Key finding's

• Based on the results of this project, benchmarks for the irrigation drainage nitrate levels associated with the different crops are suggested below (Table 5.1).
  
  Table 5.1 – Nitrate benchmarks for the different crops
  

• Nitrate leaching risk is a function of fertiliser application, cover crop legumes and crop requirements. It is also a greater risk on light soils.
• Citrus and avocados are often located on lighter soils and are at a greater risk of nutrient leaching.
• The salinity readings taken in this project are consistent with the salinity readings from regional drains. There is not expected to be any relationship between crop types and drain salinity.
• Drain salinity is a function of irrigation efficiency and leaching.
• Nitrate concentrations vary greatly depending on fertiliser practices. Spikes in drainage concentrations can occur if fertiliser levels are not matched to plant requirements and some nitrate is leached.
• Soils also play a role in the level of nitrate leaching associated with different crops.
• Salt concentrations in irrigation drainage are strongly influenced by irrigation practices and the level of leaching through the soil column.
• In this study dried grapes had a relatively higher salt concentration in the drainage water, which may be attributed to less leaching of salt through the heavier soils. However, low leaching of salt is not an issue unless salt concentration exceeds safe levels for production.
• Given the influence of fertiliser practices on nitrate levels in irrigation drainage, it is essential that fertiliser applications are monitored and implemented according to crop requirements. There are numerous fertigation strategies including continuous injection, pulsing and split applications.

Recommendations

• There are a range of high and low total nitrogen load targets which seem inconsistent with current drainage monitoring data.
• It is therefore recommended that the Mallee CMA review their total nitrogen targets for irrigation drainage water quality.
• The very small data set cannot hope to challenge the current salt load targets, which are based on decades of monitoring and analysis.
• It is therefore recommended the current salt load targets are retained by the Mallee CMA.
• There is currently limited information on nutrient levels associated with farm irrigation drainage in the region. It is recommended that further investigations be carried out concerning the nutrient levels associated with irrigation drainage from different crop systems, irrigation systems and soil types.
• This will allow key areas for nutrient management to be identified in the region, so that ultimately nutrient loads to the Murray River can be reduced.