Refining nitrogen placement in cereals – mid row banding

Take home messages

• Mid-row banding significantly increased recovery of nitrogen (N) fertiliser by wheat in 2016, improving N use efficiency.
• The impact of mid-row banding on yield and protein has been more variable, but may improve in situations that are more N deficient.
• Adoption of mid-row banding in-season will require consideration of factors including speed of operation, capital requirement and cost of operation and the ability to apply N inter-row to established crops in a given farming system.

Background

Managing nitrogen (N) fertilisers in dryland cropping is a continual challenge for growers and advisers. Matching N rate to crop demand is complicated by a range of factors, not least of which is the relatively poor predictability of seasonal conditions during autumn. As a result, there has been a trend towards tactical, in-season management of N where possible. The challenge, however, with in‑season N application, such as topdressing urea, is that it can result in loss of N due to volatilisation of ammonia depending on conditions following application. One option to reduce this risk is to apply N below the soil surface (Rochette et al.2013), however, until the advent of high accuracy GPS guidance, in-season banding was not a practical option.

Mid-row banding, where N fertiliser is applied below the soil surface to every second inter-row, has been tested both internationally and within Australia for N application at sowing (Angus et al. 2014, Campbell et al. 1991). Aside from the potential reductions in loss as ammonia compared to surface application, concentrating N into narrow bands can also slow the nitrification of ammonium (Wetselaar et al. 1972). By restricting the conversion of N to nitrate, this may reduce other losses (such as denitrification) and slow movement of N below the depth of application.

High concentrations of ammonium have also been shown to restrict root growth within the fertiliser band. As a result, roots have been shown to proliferate in the surrounding area, eventually encapsulating the fertiliser band over time (Passioura and Wetselaar, 1972). By increasing root growth surrounding the fertiliser band, this may help to improve crop uptake of applied N. The purpose of this research was to test the potential benefits of mid-row banding as opposed to other options for in-season application of N fertiliser.

Method

A series of four field trials were undertaken during 2016 and 2017 testing a range of different methods for in-season application of N fertiliser. Sites were at Longerenong and Quambatook in 2016 and Longerenong and Ultima in 2017. All sites were sown to Mace wheat except Ultima in 2017 (Kord CL Plus) on 300mm row spacing and received a starter amount of N at sowing (6kg to 7kg N/ha).

Fertiliser was applied as urea in solution or granular (top-dressed only) at rates of 25kg and 50kg N/ha on two occasions at each site between late tillering and second node growth stages. Application methods tested were:

• Mid-row banded: N placed at 35mm to 50mm depth into every second inter-row using a twin disc opener.
• Mid-row surface: N placed on the surface of every second inter-row.
• Streaming spray: N applied using streaming nozzles spaced evenly across the plot.
• Flat fan spray: N applied using air induction nozzles to produce extra coarse droplets.
• Top-dressed granular.

The purpose of multiple applications at each site was to observe the effect of rainfall following application on the relative response of each method. This was based on the assumption that volatilisation risk should be higher where N is applied in front of a dry forecast and therefore, mid‑row banding may offer the opportunity to apply N when it suits the grower rather than ‘chasing rain fronts’. As a result, the timing of each application was designed to be relatively close together to minimise differences in response due to growth stage. Additional rates of top‑dressed N were also applied (15kg to 100kg N/ha) to identify the overall N response curve for each site, as well as unfertilised controls, including unfertilised, banded plots to measure the effect of the banding operation on crop growth. Key measurements included soil characterisation at sowing, grain yield and quality and recovery of fertiliser by the crop using ¹⁵N ‘labelled’ fertiliser.

Results and discussion

Crop response to N application method

All sites with the exception of Longerenong in 2017 showed a strong yield response to the addition of N (Figure 1). At both sites in 2016, grain yield continued to increase up to rates of 90kg N/ha, while at Ultima in 2017, yields were more moderate due to a drier season, however N response continued up to a rate of 50kg N/ha. Grain protein also increased significantly with N rate at all sites. In general, protein levels were lower in 2016 (7% to 9%) compared with 2017 (8% to 12%).

Figure 1. Yield response to rate of N applied as top-dressed urea on the first day of application at each site.

Yield response to the method of N application varied across sites and in some cases, the time and rate of application. In 2016, mid-row banding produced the highest average yield at both sites, however this was only significant (P<0.05) in comparison to mid-row surface application at Longerenong (Table 1). In 2017 at Ultima, the mid-row surface and flat fan treatments resulted in significant yield reductions — in absolute terms approximately 0.1t/ha. At Longerenong in 2017, the streaming spray treatment was significantly higher yielding than mid-row banding and flat fan applications even though the site showed a low overall N response. While the flat fan treatment resulted in the lowest yields in 2017, visual symptoms of leaf burn in response to application were limited across all sites and years despite relatively high rates of N application.

Table 1. Yield and protein response to N application method at each site, averaged across rate and time of application. Superscripts indicate significant differences (P<0.05). Treatments followed by the same letter are not statistically different.

The effect of application method on grain protein also varied with site. At Longerenong in both 2016 and 2017, no significant differences were observed. However at Quambatook in 2016, application by streaming sprays significantly reduced protein compared with topdressing or mid-row banding. Meanwhile at Ultima in 2017, mid-row banding produced significantly higher protein compared to all treatments, increasing protein by 0.5% to 1%. If mid-row banding is delaying crop access to applied N, this may further complicate the effect on grain protein. It is generally accepted that later applications of N tend to shift crop response from increasing yield to increasing protein. Therefore, depending on how long it takes for the crop to access applied N and how N deficient the crop is, this may shift the effect of application between yield and protein response.

Does banding damage the crop?

At a row spacing of 300mm, the impact of the banding operation was negligible when comparing unfertilised plots. Across all four sites, the biggest difference in yield and protein between unfertilised controls and unfertilised-banded plots was 0.13t/ha and 0.14%. However, this was where stubble loads were moderate, row spacing relatively wide, soil throw was controlled and the accuracy of guidance was good. The impact of banding in-season could vary in circumstances where these factors or crop growth stage are different.

Effect of application method on N use efficiency

Recovery of fertiliser in the crop and soil at harvest

Studies over numerous years have shown that on average, Australian grain crops take up just 44% of the N fertiliser that is applied in a given year (Angus and Grace, 2017). Results from 2016 indicated that mid-row banding in-season has the potential to increase crop uptake of fertiliser N well beyond typical rates. At Quambatook, crop uptake increased from approximately 42% of the N applied to 63%, and at Longerenong this figure increased from approximately 54% to 78% when comparing mid-row banding to mid‑row surface or streaming applications (Figure 2). By improving crop uptake of applied N, this also resulted in a significant reduction in N ‘lost’ to the environment — shown by the proportion of applied N not present either in the crop or soil at harvest.

Figure 2. Recovery of applied N in grain, straw and soil (0-20cm) at harvest for a range of application methods at Quambatook and Longerenong in 2016 based on ¹⁵N mass balance. Data is the average of two application times at a rate of 50kg N/ha. (Wallace et al. 2017).

Effect of rainfall following N application

One of the reasons that growers might look to adopt mid-row banding in-season is the potential to reduce loss of N as volatilised ammonia in situations where rainfall following application is limited. By applying N on two occasions at each site, it is possible to compare the benefit of mid-row banding with varying amounts of rainfall after application.

In 2016, at Quambatook, rainfall in the 10 days following the first application was 14.2mm compared with 4.6mm for the second application. At Longerenong, a total of 5.6mm was received following the first application and 75.2mm following the second. Table 4 shows that where follow-up rainfall was lower at each site, the relative benefit of mid-row banding (measured by recovery of fertiliser N in grain) compared to other application methods was greater.

Table 4. Recovery of applied N in grain at harvest for a range of methods and times of application at Quambatook and Longerenong in 2016 based on ¹⁵N mass balance. Superscripts indicate significant differences (P<0.05). Treatments followed by the same letter are not statistically different (Wallace et al. 2017)

What about mid-row banding at sowing?

Mid-row banding has been tested both locally and overseas for N application at sowing. Most recently this has been undertaken by a group led by Graeme Sandral at NSW DPI in Wagga Wagga — a link to their work from 2016 is listed under useful resources. In this situation, they have observed that mid-row banding at N rates of 95kg to 135kg/ha conserved significant amounts of N as ammonium in the top 20cm of soil and encouraged root growth around the fertiliser band resulting in improved N use efficiency.

In addition to the potential benefits of mid-row banding presented here, applying N using mid-row banding at sowing may offer the additional benefits of:

• Reduced risk of fertiliser toxicity, allowing higher rates of N to be applied at sowing.
• Restricting crop access to N early in the season thus reducing the risk of hay-off.
• Ability to apply N by mid-row banding where narrow row spacings or poor trafficability restrict the ability to band N in-season.

Conclusion

The effect of mid-row banding N fertiliser in-season compared with other application methods varied across sites and years. In 2016, mid-row banding resulted in the highest average yields, but in 2017, the effects were more mixed. In 2016, mid-row banding was also shown to significantly improve crop uptake of fertiliser N. It is possible that in more N deficient situations than those tested, the potential benefit of mid-row banding may increase. Further testing is also required in conditions where rainfall following N application is lower to better test the potential to reduce N loss to volatilisation.

Adoption of mid-row banding in-season will require careful consideration of a range of practical and economic factors including the ability to accurately apply N inter-row at a given row spacing and stubble load, speed of operation, cost of capital and ongoing operating costs plus unforeseen impacts such as the potential for increased weed germination following inter-row soil disturbance. However, initial indications for improving N use efficiency are positive and similar research will continue in 2018.

Useful resources

Wallace A., Nuttall J., Henry F., Clarke G and Marsh J. (2017). Mid-row banding nitrogen fertiliser in-season: Improving nitrogen use efficiency of cropping systems of southern Australia.

Sandral G., Tavakkoli E., Harris F., Koetz E. (2017). A test of nitrogen fertiliser use efficiency in wheat using mid row banding.

References

Angus JF., Gupta VVSR., Pitson GD., Good AJ. (2014). Effects of banded ammonia and urea fertiliser on soil properties and the growth and yield of wheat. Crop and Pasture Science, 65, 337-352.

Angus JF., Grace PR. (2017). Nitrogen balance in Australia and nitrogen use efficiency on Australian farms. Soil Research, 55,435-450.

Campbell CA., Selles F., Nuttall W., Wright T., Ukrainetz H. (1991). Effect of nitrogen source, placement and time of application on winter wheat production in Saskatchewan. Canadian Journal of Soil Science, 71, 177-187.

Passioura JB., Wetselaar R. (1972). Consequences of banding nitrogen fertilizers in soil II. Effects on the growth of wheat roots. Plant and Soil, 36, 461-473.

Rochette P., Angers DA., Chantigny MH., Gasser M-O., MacDonald JD., Pelster DE., Bertrand N. (2013). Ammonia Volatilization and Nitrogen Retention: How Deep to Incorporate Urea? Journal of Environmental Quality, 42, 1635-1642.

Wetselaar R., Passioura JB., Singh BR. (1972). Consequences of banding nitrogen fertilizers in soil I. Effects on nitrification. Plant and Soil, 36, 159-175.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC — the authors would like to thank them for their continued support. This work was funded by the ‘Improving practices and adoption through strengthening D&E capability and delivery in the southern region’, Regional Research Agronomists program (DAV00143) as part of the GRDC and Department of Economic Development, Jobs, Transport and Resources, Bilateral Research Agreement. The authors also wish to acknowledge the assistance of Birchip Cropping Group staff in delivery of the experimental program.

Contact details

Ash Wallace
Agriculture Victoria
110 Natimuk Rd, Horsham, Vic, 3400
0429 935 400
ashley.wallace@ecodev.vic.gov.au
@Ash_W_429