Dry seeding raises fertiliser burn concern

18 May, 2018 09:44 AM
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GIVEN the high percentage of Australian broadacre farmers planting into low or no moisture, a fertiliser specialist has urged farmers to be careful with seed and fertiliser placement.

Rob Norton, a member of the Grains Research and Development southern solutions panel, said when seed was placed too close to fertiliser in dry soils there was the risk of burn.

In particular, he said farmers in low rainfall zones with lighter soils, such as the northern Wheatbelt in WA, were at particular risk.

“It is a bigger problem in dry, sandy soils,” Dr Norton said.

To combat this, he said farmers needed to make sure there was good distance between seed and fertiliser and also potentially consider dropping the fertiliser rate.

“The dry lead in to winter sowing in 2018 means last year’s strategy might not be safe this year,” he said.

Dr Norton encouraged growers to use a seed damage calculator, available at goo.gl/NT8vmB, to check how much fertiliser they can apply with seed through the same chute.

The calculator doesn’t address fertiliser placed below or to the side of seed, but Dr Norton said separation of seed and fertiliser at about 3-5 centimetres was usually enough distance to protect seed.

The severity of problems will vary from crop to crop with canola and lentils being more sensitive, while wheat and barley are relatively tolerant.

“The order of sensitivity for crop species can vary for fertiliser type, but in general, the order from most to least sensitive in major grain crops is canola, followed by lentils, peas, oats, wheat and then barley,” Dr Norton said.

Fertilisers can affect germinating seeds in at least two ways, with the first relating to salt index.

Most granular fertilisers are salts and as such, too much fertiliser salt can “burn” the seedling or stop seedlings from absorbing water.

Nitrogen and potassium fertilisers tend to have a higher salt index than phosphorus fertilisers.

Sulphate forms of popular fertilisers tend to have lower salt indexes.

Ammonia formation potential is the second consideration.

Dr Norton said free ammonia could be toxic to seed.

“Placing urea-containing fertilisers in-furrow is risky because they produce ammonia,” he said.

“A fertiliser with polymer coatings or urease inhibitors may slow the rate of ammonia production enough to protect seed, although these fertilisers are still considered risky to place near seeds.”

Dr Norton said the safe rate of fertiliser per hectare increased as row spacing narrowed.

“Closer row spacing ‘dilutes’ fertiliser over the length of row,” he said.

Machinery configuration, such as twin chuting systems which separate seed and fertiliser, can assist in protecting the seed.

Fertiliser is placed in bands to the side or below the seed bands and separation of 3-5cm is usually enough to protect seed.

Dr Norton said the more scatter there was between seed and fertiliser, the more fertiliser could be safely applied.

“The concept of seed bed utilisation (SBU) addresses this factor,’ he said.

“SBU is the proportion of row width occupied by seed row.”

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