Spray v gran­ules study

Is fo­liar spray­ing of urea a cost-saver?

The Northern Star - Northern New South Wales Rural Weekly - - Find A -

THE ben­e­fits of ap­ply­ing fo­liar urea to pas­tures are be­ing as­sessed in a 12-month trial at the NSW De­part­ment of Pri­mary In­dus­tries in Wol­long­bar.

In the­ory, spray­ing urea onto the leaves of the grass plant di­rectly should be more ef­ficient than tra­di­tional urea gran­ules ap­plied to the soil, and in recent years there has been an in­creas­ing in­ter­est in ap­ply­ing urea or other ni­tro­gen based fer­tilis­ers this way.

Nathan Jen­nings, of North Coast Lo­cal Land Ser­vices, one of the re­search back­ers, said if it could be con­firmed that there were ben­e­fits to ap­ply­ing urea as a fo­liar spray to short-term rye­grass and kikuyu pas­tures, “it would likely have a sig­nif­i­cant re­duc­tion in on-farm fer­tiliser costs, im­prove pas­ture pro­duc­tion, and help with en­vi­ron­men­tal con­cerns over ni­tro­gen leach­ing or volatil­i­sa­tion”.

“Di­rect spray is per­ceived as more ef­ficient be­cause, with a fo­liar application, the ni­tro­gen doesn’t have to move through the soil to the plant roots be­fore it is taken up by the plant, rather the ni­tro­gen is ab­sorbed through the plant leaves.

“It is in the soil where a high pro­por­tion of the to­tal ni­tro­gen loss typ­i­cally oc­curs such as volatil­i­sa­tion to the air, leach­ing be­yond the root zone, or leach­ing un­der wa­ter­logged con­di­tions.”

Some ba­sic stud­ies over short time frames of one to three graz­ings have in­di­cated that ni­tro­gen application rates can be re­duced to 40% if ap­plied as a fo­liar spray com­pared to gran­u­lar.

Other re­sults have been more vari­able.

How­ever, all the re­search on this has been on peren­nial rye­grass which has a higher plant den­sity than short-term rye­grass, mean­ing that a short-term rye­grass pas­ture may re­sult in a lower pro­por­tion of spray ni­tro­gen be­ing taken up by the leaves.

Mr Jen­nings said a study

❝Our the­ory is that trop­i­cal grasses should be able to cap­ture even more fo­liar ni­tro­gen.

— Nathan Jen­nings

that fo­cuses on a trop­i­cal grass pas­ture such as kikuyu was im­por­tant for dairy farm­ers on the North Coast.

“Trop­i­cal grasses al­ways have a lot of green leaf or stem/stolons left af­ter graz­ing and our the­ory is that trop­i­cal grasses should be able to cap­ture even more fo­liar ni­tro­gen,” he said.

“The study will also look at the ef­fect of fo­liar ni­tro­gen application on the pas­ture plants and changes in soil ni­tro­gen lev­els by in­ten­sive grass and soil sam­pling.”

It is also likely this method of ni­tro­gen fer­tiliser application would be ap­pli­ca­ble to other trop­i­cal grass species.

Equip­ment re­quired for on-farm adop­tion al­ready ex­ists via a mod­i­fi­ca­tion of an ex­ist­ing boom spray unit and there are com­pa­nies mak­ing ma­chines tai­lored specif­i­cally for this pur­pose.

Far North Coast Dairy In­dus­try Group and Norco Foods are work­ing along­side North Coast Lo­cal Land Ser­vices on the pro­ject, which is be­ing man­aged by Mr Jen­nings (se­nior land ser­vices of­fi­cer) and Dr Bill Fulk­er­son, a re­search and devel­op­ment of­fi­cer with Norco Foods.

PHOTO: CON­TRIB­UTED

PROOF IS IN THE PAS­TURE: The trial re­sults will pro­vide sig­nif­i­cant ben­e­fits to the dairy in­dus­try.

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