Lucerne lowers watertable at Mannum
After several seeps formed on their Mannum, South Australia, property, Mallee grower Kevin Bond and his brothers planted lucerne to use more water on deep and non-wetting sands and improve control of the seeps.
Kevin suspects the seeps formed after they implemented practices including summer weed control, which improved water use efficiency, leaving more water available to recharge the watertable.
“When we bought the property it was a good paddock but, as time went by, several soak areas started to appear,” he says.
Kevin decided to plant lucerne on the dune to use more water and hopefully return a profit through hay production.
“In 2015 we planted 19 hectares of lucerne. I didn’t plant all the way down to the seep, as lucerne doesn’t like wet feet, but instead planted a trial of sulla, which is supposed to be more tolerant of salt.”
Kevin planted a winter-dormant lucerne using side-banding, keeping the fertiliser at a depth of 6 to 7.5 centimetres, separate from the seed, with 45 kilograms/ha of monoammonium phosphate (MAP).
In his first year, Kevin has had good success with the lucerne. A wet start to the 2015 season helped it establish well, and after one cut for hay in spring the crop was already developing significant biomass by the end of summer.
“We have planted the lucerne up the hill as a bit of a trial to determine where it grows the best. We intend to plant across the hill at that level, so we can get the most value out of the crop and intercept as much water as possible,” he says.
“So far we’ve seen that the crop is thinner at the top of the hill in the really non-wetting sand, but there are still enough plants there for it to recover. The sulla is also looking good: it has persisted over summer, although it didn’t germinate as well in the non-wetting sand.
“There’s also signs that the lucerne is helping to control the watertable,” he says.
“There’s one spot on the swale where I dug a hole to monitor the watertable level. Before we planted the lucerne the water was at the surface. Since we planted the lucerne it is now about 1.5 metres lower.”
Chris McDonough, from Insight Extension for Agriculture, has monitored Kevin’s lucerne performance through soil moisture probes and agrees that, so far, the lucerne is working.
“Compared to the adjoining wheat crop, the lucerne used less water up until the end of October, but has drawn much more water over the summer and has dragged the moisture content right down,” Mr McDonough says.
“With no significant summer rainfall, we didn’t see any leaching from the wheat crop, but if there had been more summer rain, there definitely could have been a situation where water gets through to the keeper in the wheat crop, whereas the lucerne had much more available capacity to use summer rainfall and prevent the seep recharging.”
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