Making the soil bucket larger

Increasing the size of the bucket


Zoe Creelman, Southern Farming Systems research and extension officer, says increasing soil permeability is the best way to increase water holding capacity in high rainfall zones, reducing the risk of both waterlogging and drought.

Zoe Creelman, Southern Farming Systems research and extension officer, says increasing soil permeability is the best way to increase water holding capacity in high rainfall zones, reducing the risk of both waterlogging and drought.

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THE KEY to unlocking yield potential in high rainfall zones (HRZs) will be increasing the moisture holding capacity of the soil.

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THE KEY to unlocking yield potential in high rainfall zones (HRZs) will be increasing the moisture holding capacity of the soil, according to a Southern Farming Systems (SFS) researcher.

Speaking at the SFS Agri Focus field day last week at Lake Bolac, Ms Creelman said farmers in HRZs had an advantage in terms of reliable rainfall but added they had to manage both water excesses and deficits at various times.

“At the end of winter, most years our ‘soil bucket’ of plant available water is above capacity, but equally we can quickly run out of water in the spring,” she said.

The major issue is the amount of water that can be stored, generally between 160-200mm in most parts of Victoria’s Western District, a typical HRZ.

“It all depends on the soil type but that is a typical figure,” she said.

Ms Creelman said at peak times plants could use up to 8.5mm of water a day in years with high temperatures in the spring.

“If you only can store 166mm of rain in the soil profile then that vanishes pretty quickly under those conditions, you can quickly drain your moisture profile.”

And she said the problem became more pronounced again when you consider the subsoil constraints prevalent in many HRZ areas.

“In many parts where Agriculture Victoria has put down the moisture probes so we can assess the ‘bucket size’ in terms of soil moisture holding capacity there is a bleaching layer in the soil at around 90cm.

“This means plant roots will not push below this depth, obviously meaning they miss out on any moisture below this level.”

Ms Creelman said studies were assessing the effectiveness of treatments such as subsoil amelioration.

“There is a project deep banding animal manure to try and open up the soil and break down that bleaching layer.”

“Improving the soil type is the major factor in making the bucket bigger and thus improving our water use efficiency.”

She said she believed research into early sowing of wheat was also showing potential.

“We are seeing wheat that goes in early and starts making use of early season moisture is particularly effective.

“It seems as though it is better able to withstand late winter wetness as the plant is better established.”

While there has been much talk about the gradual delay of the autumn break, Ms Creelman said data showed there was still a 71pc chance of a break by Anzac Day in the Western District annually.

“This is early enough to get crops up and going before the slowdown in growth kicks in with the winter.”

“Plants are then hardier and able to deal with the wet.”

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