Making the most of water in dry region

Northern Victorian farmers making the most of water in dry region

Business Management
FAMILY: The Tyler family on their fair farm in Tongala, Vic.

FAMILY: The Tyler family on their fair farm in Tongala, Vic.

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Northern Victorian irrigators Andrew and James Tyler are using soil moisture monitoring to get the best return for every drop of water this season.

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Northern Victorian irrigators Andrew and James Tyler are using soil moisture monitoring to get the best return for every drop of water this season.

The Tylers, who farm at Tongala, grow maize under flood irrigation with plans to sow about 60ha this year.

Maize silage forms an important part of their herd's diet, accounting for around 15 to 25 per cent of their daily feed requirements throughout the year. Despite the cost of water this season, for the Tylers it stacks up economically to grow their own maize.

For the first time, they last year installed two moisture probes in their maize crop to assist with irrigation scheduling. As a result, they had more confidence in their irrigation decisions and felt they used water more efficiently, especially in starting up and finishing the crop.

Soil moisture monitoring provides real-time data to track soil moisture and crop water use to identify irrigation requirements. Using soil moisture monitoring last season, the Tylers worked with their agronomist to fine-tune the timing, frequency and quantity of water applications to correlate with crop water needs.

Maize is a significant investment and requires water and nutrients at critical stages through the growing cycle. The growth of maize slows as soon as the plant becomes water stressed or waterlogged, having a direct impact on crop development and yield potential.

"The benefit of having the probes in last year was that even in extreme heat, when the plant appeared to shut down, you could be confident that there was moisture in the soil," Andrew said.

"In the past, we looked at the visible signs in the plant but now, with the probes in, we can see what's really there."

In the past, we looked at the visible signs in the plant but now, with the probes in, we can see what's really there. - Andrew Tyler

Unlike pastures which have a fairly consistent water demand, the water requirement for maize increases rapidly from about two weeks prior to tassel and ear appearance until about two weeks after full silk, before dropping off. Soil moisture probes can be used to track the crop's root development and water demand.

In conjunction with climate indicators and crop monitoring, data from their probes enabled the Tylers to make timely responses to changes in plant water requirements.

"We used the probes to monitor water levels and let the soils dry out towards harvest when plant water needs really drop off," Andrew said.

"Having too much water on the site can delay the harvest, especially if you get rain."

The Tylers had probes installed on two different soil types - a sandy loam and a clay soil - so they could effectively manage different sites. Soil moisture probes are only useful if they are located in a representative soil type and area of crop.

FIGURE 1: Water requirements of maize (dry weight gain) taken from Pioneer Seeds Corn Growers Guide.

FIGURE 1: Water requirements of maize (dry weight gain) taken from Pioneer Seeds Corn Growers Guide.

Soil moisture probes, generally installed 80 centimetres to one metre deep for maize and providing measurements in increments of 10cm, can be used to track plant root development and see how the plant is extracting water from different depths of the soil.

Andrew said the probes provided the information they needed to strategically reduce plant-available moisture in the early stages of crop development to encourage roots to extend deeper into the soil profile.

"We wanted the roots of the plant to get down to chase moisture," he said.

"By encouraging the plant roots and the moisture to move down the profile, it helps to reduce hard panning on the soil surface, which we often get with flood irrigation.

"Using the probes gave us more confidence to spread the irrigations. Given that water's so expensive, we don't want to irrigate when we don't have to."

Soil moisture chart example

This soil moisture chart was taken from a demonstration site in southern NSW where maize was grown under flood irrigation. It shows the weighted average soil moisture content to a depth of 50 centimetres. The vertical axis of the chart is representative of the percentage of moisture in the profile, with near-saturation (80 per cent) at the top and near-depletion (25pc) at the bottom.

The coloured zones are indicators of moisture availability, blue representing 'excess', green representing 'good', and pink representing 'stress'.

This example shows three irrigations, indicated by the spikes in the trendline. Soil moisture depletion between irrigations is represented by the dips in the curve. The flattening of the curve is indicative of the slowdown in water use.

This example shows crop water use slowing significantly once the soil moisture falls below the refill point, generally the level at which irrigation is applied. The subsequent irrigation occurred earlier, reducing water stress on the plant as it came into critical development stages.

The chart also shows that the third irrigation didn't fill the profile to the same level as the previous two irrigations. This could be due to the sealing of the soil which was observed on the surface.

Access resources 

Conditions remain variable across the country, with high farmgate milk prices challenged by ongoing cost pressures and a dry weather outlook.

Dairy Australia has created a range of resources to assist farmers to make the most of the current season, no matter their farm circumstances.

Visit feed.dairyaustralia.com.au to access tailored information around effective feed and management options to help inform on-farm decisions.

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