Innovative nutrient applications show promise

Figure 1. Wharminda wheat yields following deep ripping and subsoil nutrient application 1999-2003

High pressure injection of fluid fertilisers is showing promise in South Australian trials comparing a range of multi-nutrient fertiliser application methods with deep tillage and fertiliser placement to 40 centimetres.

The trials have been part of a GRDC-funded project by Brendan Frischke and colleagues from the South Australian Research and Development Institute"s Minnipa Centre.

Mr Frischke says five years of research in sandy soil has shown that applying nutrients to a depth of 20 to 40cm has produced the highest yield each year, in comparison to other treatments (Figure 1). In 2001 the yield increased two to three fold, and in other years it was increasing anywhere between 15 and 100 percent.

Figure 1. Wharminda wheat yields following deep ripping and subsoil nutrient application 1999-2003.

The research has also looked beyond the standard method of applying nutrients through deep ripping to systems that would allow nutrition to penetrate deep into the soil with less soil disturbance.

Mr Frischke says the trials are the first step in identifying ways to make deep placement of nutrients more practical and economic. High pressure delivery has emerged as one likely option.

The methods tested were:

Deep ripping with nutrients:
Deep rip tines working at 40cm fitted with four spray jets equally spaced down the trailing edge (Figure 2). To reduce application volume and improve practicality, speed was increased to 7.5kmh from 5kmh.

High pressure injection:
Each deep rip tine was fitted with a solid steam nozzle on the foot, and pointed down (Figure 3). This system uses a combination of shallower tillage (10 and 30cm) and the penetration of high pressure to apply fertiliser at depth. Injection pressures used were 345 bar (5000psi) and 86 bar (1250psi).

Deep coulter banding:
Large 76cm coulters fitted with a rear knife and fluid tube operating up to 30cm. Fluid fertiliser was placed in a band from a single outlet at low pressure fixed to the bottom of the knife.

Deep knife banding:
Longer knife points (225mm) were fitted to Ausplow DBS seeding tines. A fluid delivery tube was fixed to the rear of the knife, banding fluid at the working depth of the knifepoint, about 20cm below the surface.

While the research is still in its early days, high pressure application of liquid fertiliser and deep banding fluid fertiliser with extra long knifepoints both showed encouraging yield results. Grain yields for 2003 (Table 1) indicated that methods which applied nutrient the deepest, tended to produce the highest yield - a result consistent with previous work at several sites.

Table 1. Yield and protein from alternative methods of deep-placed nutrient application at Wharminda 2003.
Note: district practice received lower phosphorus, nitrogen and micronutrient inputs.

Though it is too early for absolute recommendations, Mr Frischke says growers wanting to apply these research results could opt for the deep-knife banding method first.

"I think this is the best option at this stage. It is also perhaps the most practical, being a one-pass sowing system, and it has a lower application volume," he says.

As part of the trials, high pressure injection was also tested as an option for applying nitrogen to cereal crops.

A machine developed in Canada, referred to as a root zone injector (RZI), was tested.

The RZI operates at 345 bar pressure and with an intermittent output. Special valves open several times every second to supply fertiliser solution to nozzles in short bursts.

"In practice, applying fertiliser with the RZI was very simple. Calibration procedures are similar to boom sprays. Once calibrated, driving at a constant speed is all that is required," Mr Frischke says.

The test revealed:

Mr Frischke says the tests showed that high pressure injection with the RZI looks like an effective method of nitrogen application.

However, more experience under a wider range of conditions would be required to justify its adoption.

"Protein levels in both trials indicated that nitrogen rates may have been too low to maximise yield. However, increasing up-front nitrogen beyond the levels used here, in these low rainfall environments, carries higher risk and good broadcasting opportunities can be limited."

He says the RZI"s advantages may be a broader window of opportunity to apply nitrogen; reduced risk when applying higher inputs in low rainfall areas, and; more efficient use of the nitrogen applied.

For more information:
Brendan Frischke, 08 8680 6206,

GRDC Project Code: CSO 231, program 4

GRDC Project Code CSO231, PROGRAM4