Deep banding nitrogen in high rainfall cropping

The aim of the trial was to investigate whether deep banding reduced the amount of nitrogen loss through denitrification, volatilization and leaching.

Project Overview

• Funding received from DELWP via the Victoria Climate Change Innovation Grant, allowing trials research to be conducted into minimising nitrogen emission over 2018-19 and 2019-2020 growing seasons.
• The plot trial was replicated at 3 sites across the Southern Victorian cropping zone at; Bradvale (Grampians), Inverleigh (Barwon) and Toongabbie (Gippsland).

By Stephen O’Connor (Agriculture Victoria & GRDC) & Jon Midwood (SFS)

Background

Deep banding is deep placement of a fertiliser, in this case urea, directly below the seed. For these trials, this operation was completed in one pass, placing varying rates of urea under the seed with a standard rate of MAP (100 kg/ha) at 2.5 cm below soil surface.

The aim of the trial was to investigate whether deep banding reduce the amount of nitrogen loss through denitrification (NH4 gaseous loss occurring from waterlogging), volatilization (NH4 gaseous loss from UV rays) and leaching (NO3 particle loss in ground water movement).

The theory is that deep banding nitrogen at sowing creates a tight band in a zone of high alkalinity below the seed bed, which cause a slow release effect to occur. As the plant grows it slowly starts to access the nitrogen as ammonium and then as nitrate. The nitrogen is expected to be retained in the tight band as it is placed in a low oxygen zone which slow its release.

Ideally, some of the nitrogen required during the season is deep banded to maintain crop nitrogen source until waterlogging has subsided during winter and once the soil dries out, only one top up of nitrogen will be required during the growing season (GS 35).

In these trials, urea was banded at three depths (2, 7 and 12 cm) below the seed, and compared to broadcasting at emergence.

Three rates of urea (50, 100 and 150 kg/ha) were used along with a nil to further investigate how responsive the site was to nitrogen application. Beaufort wheat was chosen for these trials because it is a high yielding feed variety in the HRZ.

General observations

Pre-season soil nitrogen testing (0-90 cm) indicated that the Toongabbie and Inverleigh trial sites had low background nitrogen ( ~ 125 kg N/ha) and would most likely response to applied nitrogen, while the Bradvale site had a large reserve of nitrogen (300 kg N/ha +) and most likely not responsive, as it the second year in crop after 20 years of pasture.

A second soil nitrogen test was completed in-season (June), to reassess whether there was enough nitrogen to meet yield targets of 5 t/ha at Toongabbie and, 8 t/ha at both Inverleigh and Bradvale. It was concluded that enough urea was applied at sowing and hence no further nitrogen was warranted to be broadcasted.

One of the main comments about up front nitrogen application is that it can cause haying off and lodging of the crop, however this was not observed in the trials. High screenings and low test weights which are associated with haying off also did not occur. The slow release effect that occurs from deep banding will have also reduced the haying off, as incremental amount of nitrogen will become available to the crop.

Both Inverleigh and Bradvale showed no significant difference in yield and protein between rates of urea. Therefore, results are not included.
Toongabbie

The results from Toongabbie are displayed in Table 1, below. Significant differences were seen within the grain yield, but not grain protein. Screenings and test weight also had no significant difference between treatments (not included).

The nitrogen applied contributed to an increase of yield and protein when considering the absolute values. The 7cm depth deep banded treatment @150 kg/ha urea yielding the highest (4.9 t/ha) with above average protein (12.1 %).

Although there was no clear benefit to deep banding nitrogen in 2018, a below average rainfall year, it is likely that in a year with average or above rainfall deep banding would be more beneficial. As 2018 was a dry year, it is expected that residue nitrogen will be retained for next season crop, resulting in a higher economic return.

A gross return for each treatment as been calculated based on the absolute values of grain yield.

The gross return gives a realistic take on each practice comparing costs and returns. As Beaufort wheat is classed as a feed wheat, there is no premium received for protein. This maybe the case at the sample stand but may provide an advantage in the open market. Grain protein is a good indicator, albeit retrospectively, of how close to producing the optimum yield the nitrogen supplied to the crop was, for the respective season.

A grain protein of around 11% to 11.5% would imply yield was optimised for that crop assuming no very late N was applied. Only applications of 100 or 150 kg/ha of urea supplied the correct amount of N to influence yield and grain protein. Although this isn’t as important in a feed variety it could be critical had the variety been a milling wheat.

Table 1 show 7cm depth @150 kg/ha returning the most $/ha, an increase of $27 over 0 cm (GS1) @ 50 kg/ha broadcast. Depending on the level of risk and work the farmer is happy to accept is likely to determine their gross return.

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