Irrigation in a drier than average year- what to be aware of

This article was published in a previous edition of Top Paddock.

In the Northern Territory (NT) 90 per cent of the fresh water supply comes from groundwater. As detailed in the groundwater update, the NT Government has predicted record lows for some aquifers this year. Here are a few things to bear in mind:

Use water wisely

Being careful with water can extend its availability. Check your irrigation and fix leaks to reduce water wastage. Consider the crop water usage when planning your dry season crops.

Know how much your plants are using and which ones can have their water reduced. Mangoes have a system where partial root zone dryness sends signals to the plant to close stomata and reduce water loss. Sapindaceae (rambutan) lack this signal and do not respond the same way to soil dryness.

Know your bore

Specifically - what the groundwater level depth is in relation to where your bore screens are. Bores may start to take in sand and silt causing bore failure, make sure you clean and maintain your pump.

Watch out for salinity

When aquifer levels get low some systems (Lambells Lagoon and Middle Point) are potentially at risk of salt water intrusion into the groundwater.  If your orchard is in either of these aquifers, keep an eye on your salinity levels, the level of salt in water affects how suitable it is for irrigation. Read the Agriculture Victoria information sheet on measuring the salinity of your water and what it means in an agricultural context. Monitor the pH and electrical conductivity/salinity levels in your water and keep track of how your water quality is tracking over the dry season. There are relatively cheap hand held meters growers can buy (Hanna or Eutech Instruments) as well as pH strips (like pool shop ones).

The following table from the United Nations Food and Agriculture Organisation (FAO) crop salt tolerance data lists some generic salt tolerances for different crops that can be used as a guideline, noting that varieties, rootstocks etc can change these figures.

Crop

Threshold ECe (dS/m)

Rating

Asparagus

4.1

T

Banana

 

S

Cucumber

2.5

MS

Date

4.0

T

Eggplant

1.1

MS

Fig

 

MT

Grapefruit

1.2

S

Lemon

1.5

S

Lime

 

S

Mango

 

S

Okra

 

MS

Papaya

 

MS

Passionfruit

 

S

Peanut

3.2

MS

Pineapple

 

MT

Pumelo

 

S

Sorghum

6.8

MT

Soybean

5.0

MT

Sweet potato

1.5

MS

Tomato

2.5

MS

Watermelon

 

M

Zucchini

4.9

MT

Where T- tolerant, MT –Mildly Tolerant, MS- Mildly Susceptible, S- Susceptible,

Where can I get more information?

For agronomic advice, contact:
Matt Hall
P:
0422 938 529; E: horticulture@nt.gov.au

NT Farmers can provide advice and representation for producers, contact them on 08 8983 3233.

For Department of Environment and Natural Resources publications on water, water licencing information, or to contact the department’s Water Resources Division visit:

P: 08 8999 4455; E: waterresources@nt.gov.au

Last updated: 16 August 2019