US contractor makes more efficient use of nitrogen

Getting the most from every ounce of fertiliser has become a priority for farmers all over the world as prices continue to rise and the environmental impacts of liberal nitrogen applications come under closer scrutiny than ever.

For the most forward-thinking growers, it has meant reconsidering spreading methods. Many have opted to vary nitrogen rates based on crop conditions and soil types, while others are looking to apply products at a little-and-often rate to feed the plants exactly when they need a boost.

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That has been the case for a growing number of farmers across the rolling plains of Minnesota, in the USA’s Midwest, where nitrogen can all too easily be lost through leaching and volatilisation.

Throwing granular urea, spraying ammonium nitrate and injecting anhydrous nitrogen remain popular ways of getting a vital farming ingredient into crops. But between-row application during the growing season is becoming a more common sight for maize growers across North America.

Big benefits

On paper at least, there are stacks of benefits. Although liquid nitrogen works out slightly more expensive per unit compared with urea, side-dressing is far more accurate than a blanket approach on the soil surface, and injecting it straight into the plant’s root zone makes it more readily available to the crop, too.

Miller and Hagie are two of the big US-based manufacturers building toolbars that attach to the front of the sprayer. Miller is particularly vociferous in its support for side-dressing, suggesting that without the necessary rain, top-dressed crops can be left in a “yield-robbing state of nitrogen deficiency”.

Studies suggest the company has a point. Up to 30% of ground-applied nitrogen can be lost to volatilisation within two weeks of application without sufficient rain, and nutrients can be tied up in surface residue, too. Well-timed nitrogen injections can also minimise the environmental risks associated with leaching and eliminate the risk of burnt crops due to fertiliser and plant leaves coming into contact.

What about wheat?

Although most of the current machines are designed with maize in mind, side-dressing could equally be applied to cereal and brassica crops.

With the widest European wheat rows out at 13cm, and some oilseed rape drilled at 60cm, it could give growers the chance to spread autumn fertiliser in areas vulnerable to nitrate leaching where applications are currently restricted.

A blanket approach to urea application is still useful – nitrogen can move laterally in the soil until it reaches the crop’s rooting zone – but it also feeds the persistent weeds that grow between the rows. This wastes fertiliser and harms yields, which will both affect the crop’s profitability.

Hover over the white information button to learn more about Brooks Torke. 

How does it work?

The toolbar is designed to work between rows of knee-high crops maize crops, injecting liquid nitrogen directly into the rooting zone for maximum efficiency at the six- to eight-leaf stage and at tasselling when the crop is at its hungriest.

Mr Torke reckons a 24.7kg/ha (10kg/acre) dose of extra late-season nitrogen helps the crop mature quicker and bulks up the grains, and the results seem to back up his claims. Customers have seen yield increases worth $24.7/ha ($10/acre) (£20/ha, £8/acre) and, on average, crops are harvested 1% drier, which saves money further down the line, too.

The Miller injector works alongside a Case 3520 self-propelled fertiliser spreader, but half of Mr Torke’s 30 regular customers have now swapped post-emergence urea for injected ammonium nitrate – a number he expects to grow as more customers take an interest in splitting their nitrogen applications.

Fitting the toolbar

The 13.4m-wide (44ft) injection toolbar is carried on the sprayer’s front linkage and plumbs in through two double-acting valves. It floats hydraulically as it leans on four guide wheels, with shock absorbers and springs fitted on each of the coulters to provide 544kg (1,200lb) of downward pressure.

Fluted discs of 508mm (20in) diameter are fitted at the base of each 1.5m-long (5ft) leg, with their height adjusted by a hole-and-pin arrangement. The wavy-shaped discs slice a 25-50mm (1-2in) groove ready for the ammonium nitrate to be fired into the channel through a stainless-steel pipe.

See also: Variable fertiliser approach raises dry-land maize yields

The liquid is pumped from the 4,542-litre (1,200gal) tank through 5cm (2in) pipework. It is held along the boom section at 2-2.8bar (30-40psi) before being fired through a 1.3cm (1/2in) hose to the disc. High pressure is vital in keeping the dust at bay, so normal spray nozzles simply wouldn’t work. Even then, the jets need cleaning off every 162ha (400 acres).

One of the big appeals for contractors like Mr Torke is the option of adjusting row spacing to suit different customers. He can run at 508mm (20in), 558mm (22in) or 762mm (30in) and is also looking to add a variable rate system to the toolbar this year – a system he is already running on the spreader.

On the job

Miller’s power is provided by a gravelly 350hp Cummins block wound up to 2,600rpm for the 16kph (10mph) toolbar work. The relatively narrow working width and steadier pace means daily averages are around the 12.1ha/hour (30 acres/hour) mark, though filling in the field using a tanker can up output closer to 20ha/hour (50 acres/hour). In comparison, the standard sprayer will cover closer to 24.3ha/hour (60 acres/hour).

It’s possible to control the toolbar as two halves – a crude section shut-off – and Mr Torke has the rig paired with a Raven guidance system to turn the jets on/off and keep the sprayer on the straight and narrow.

About Miller
Sprayer specialist Miller was bought by CNH in late 2014. Early on the company was a dealer for McCormick-Deering. It wasn’t until the 1980s that Miller began manufacturing machinery, starting with forage boxes, rotary rakes and trailed sprayers. A decade later, the firm focused its attention on front-boom self-propelled sprayers. The most recent additions to the line-up are the Nitro-5000 and Condor GC mechanical drive sprayers.

Miller’s sprayer mode

For a large chunk of the season, the Miller Nitro is reverted to standard spraying mode. Here, nozzles are spaced at 381mm (15in) and the machine works at a brisker 22.5kph (14mph), which means it can cover 405ha/day (1,000 acres/day) on pre-emergence sprays.

Five section auto shut-off helps maintain relative accuracy at such speeds, as does an auto-boom system that uses nodes to sense the boom height and lifts things up if they’re getting too close.

Wind is a major problem in Minnesota, so drift retardant sprays and nozzles are the only way of getting on the ground in 24.1kph (15mph) winds.