Fluid fertilisers everyday thing in US crops

Fluid fertiliser trials. Eyre Peninsula, SA.

In recent issues Ground Cover has reported on the benefits and development of commercial fluid fertilisers in Australia. North America is well ahead in this game as Graeme Jennings reports from the farmer and adviser updates.

FLUID FERTILISERS contribute to excellent crop performance, are easy to handle, can be placed precisely in the soil in a variety of ways, and lend themselves to split nutrient applications.

They can also be applied in conjunction with crop protection chemicals such as herbicides and insecticides.

According to Larry Murphy, head of the Kansas-based Fluid Fertiliser Foundation, the agronomic differences between fluid and solid fertilisers come down to the ability to place fluids more accurately and their greater uniformity of application.

precision operation Dr Murphy was in Australia to speak at a series of GRDC-supported farmer and adviser updates across southern Australia.

Fluid fertilisers, while relatively new in Australian cropping, were pioneered in the early 1950s in the US and Canada and are now mainstream in North America, with millions of tonnes sold each year for use on a wide range of crops. Fluid fertilisers other than anhydrous ammonia make up approximately 23 per cent of total fertiliser tonnage in the US and 10 per cent in Canada.

Part of precision package

In the US market, fluid fertilisers cost more per unit of plant nutrient than solid fertilisers, but that is outweighed by their application flexibility and ease of handling, Dr Murphy said. He attributes US farmers' rapid acceptance to the products' "adaptability to precision application using variable rate technology and multiple application times".

The main fluid fertilisers in use in the US — often in combination — are urea-ammonium nitrate (UAN) solutions, containing about half urea N and half ammonium nitrate N, ammonium polyphosphate and ammonium thio-sulphate.

The primary fluid source of fluid phosphorus (P) in the US is ammonium polyphosphate (APP), a 10-15-0 fertiliser often produced at retail locations by mobile reactors combining anhydrous ammonia and superphosphoric acid.

Ammonium thiosulphate (ATS), containing 12 per cent N and 26 per cent S, is the most common fluid source of sulphur because of its relatively high analysis and positive effects on stabilisation of UAN after application. A variety of ammonium sulphate solutions (8 per cent N, 8 per cent S) are produced by manufacturers at locations across the US and Canada for particular local applications.

Potassium (K), often added as potassium chloride or through the neutralisation of phosphoric acid with potassium hydroxide, is a frequent component of mixed fluid fertilisers.

Fluid sources of micronutrients include ammoniated zinc sulphate (15 per cent N, 15 per cent Zn), ammoniated zinc chloride (10-15 per cent Zn), zinc chloride (27 per cent Zn), various Zn chelates and sequestered forms of Zn, while other micronutrient metals such as Mn, Cu and Fe are added to fluids in solid forms.

Advantage for micro-nutrient application

Fluid applications of micronutrient metals enable uniformity of distribution that .cannot be duplicated by even homogenous formulations of solids, let alone bulk blends, Dr Murphy said.

"With solid fertilisers, distribution down the row is different and puts solids at a disadvantage compared to fluids at low rates of nutrient application.

"Discontinuous distribution is simply a mathematical fact when high-analysis solids such as mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP) or micronutrients such as zinc sulphate are placed in narrow rows.

"That has been demonstrated in ongoing P work being conducted by the South Australian Research and Development Institute and the CSIRO and examined earlier in the US by researchers at the University of Nebraska and North Dakota State University."

UAN is sometimes disadvantaged through N immobilisation and possibly ammonia volatilisation when broadcast on large residues, though that problem has been diminished through the use of band placement of UAN and combining UAN and ATS to slow urea hydrolysis and lower ammonia losses, Dr Murphy said.

"Pre-plant bands have been shown to be agronomically superior to broadcast applications, particularly in terms of improved P use efficiency.

"Combinations of N and P have helped delay P fixation reactions and resulted in enhanced P uptake through the presence of ammonium nitrogen."

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