Nitrogen fertiliser placement in wheat and canola – effects on yield, quality and nitrogen use efficiency

Take home messages

• Field trials conducted during 2016 and 2017 showed that mid-row banding nitrogen (N) fertiliser in-season significantly increased uptake of fertiliser N by wheat compared to surface application.
• The effects of N placement on grain yield have been more variable — mid-row banding significantly increased grain yield compared to banding below the seed at sowing or top-dressed urea in-season at one out of six field trials from 2016 to 2018.
• Under drier conditions in the Mallee, mid-row banding in-season was shown to increase grain protein in wheat by 0.5%-1.6% compared with all other methods of application.
• Adoption of mid-row banding requires consideration of capital and operational costs and machinery function against potential improvements in grain yield and quality in a given farming system.

Background

Nitrogen management is a continual challenge for growers and advisers, given it is a significant expense that can be unpredictable due to variable seasons. As a result, researchers and the grains industry are constantly searching for new ways to apply N that can improve N use efficiency and productivity. The ’Four Rs’ framework is commonly used to guide improvements in management of fertilisers based on the principles of ’right rate, right time, right place and right product’. This paper outlines findings from field trials undertaken during 2018 focusing on N placement.

Placement of N fertilisers can have a variety of impacts on availability of N and the crop response. Banding N below the soil surface has been shown to influence various N loss mechanisms including ammonia volatilisation (Rochette et al. 2013) and denitrification (Drury et al. 2006). Foliar application can result in leaf uptake, but can cause leaf burn depending on rate and conditions following application, while applying high rates of fertiliser close to seed can result in toxicity and reduced crop establishment. A series of field trials commencing in 2016 investigated the effect of in-season N fertiliser placement on wheat yield, quality and N use efficiency. These trials have highlighted that mid-row banding N (where N is banded below the soil surface to every second inter-row) has the potential to increase N use efficiency and in some cases increase grain yield or protein compared to surface applications. This paper outlines findings from 2018 when mid-row banding was tested against a range of other placement methods in both wheat and canola, at sowing and in-season.

Method

Two field trials were established in 2018 testing various combinations of application method, timing and rate of N fertiliser. Sites were established at Ouyen (wheat, Kord CL Plus) and Longerenong (canola, 44Y90 CL) with N applied either at sowing or during the season (Ouyen; GS30, Longerenong; GS2.0) at rates of 25kg N/ha and 50kg N/ha in addition to the 7kg/ha applied as Granulock® Z at sowing. Urea was the N source in granular and liquid forms. Treatments included:

*            Mid-row banded at 35-50mm using a twin disc opener (granular and liquid).

*             Banded at 25mm below the seed (granular and liquid, sowing only).

*             Mid-row placement using ultra-high-pressure injection (liquid).

*             Streaming nozzle (liquid).

*             Top-dressed (granular).

Additional plots receiving further rates of 15kg and 100kg N/ha as granular urea at sowing were also added to establish the yield potential of the site. To avoid crop failure due to dry seasonal conditions (growing season rainfall (GSR): 102mm at Ouyen and 187mm at Longerenong), both sites were irrigated twice between 7 September and 5 October (coinciding with pre-flowering to early grain filling). Irrigation of 20mm was applied on each occasion and irrigation at this time was likely to be about half the efficiency of rainfall.

Results and discussion

Crop response to N placement

Both trial sites responded strongly to additional N fertiliser in 2018 despite the dry seasonal conditions experienced. At Ouyen, soil N at sowing was 56kg N/ha (1.2m depth) and wheat grain yield and protein increased by 49% and 40% at N rates of 50kg and 100kg N/ha, respectively, compared to where no additional N was applied (Figure 1). At Longerenong, soil N at sowing was 101kg/ha (1.2m depth) and applying 100kg N/ha increased canola grain yield by 25%, however, the effect on oil content was limited. Significant reductions in crop establishment and grain yield were also observed at Ouyen where 100kg N/ha was banded below the seed at sowing, demonstrating the effects of inadequate seed-fertiliser separation combined with dry soil conditions. Due to the sensitivity of canola to fertiliser toxicity, at Longerenong the 100kg N/ha rate was top-dressed.

Figure 1. Grain yield and protein/oil content response to N application rate at Ouyen and Longerenong in 2018.

At Ouyen, placement of N at sowing had a significant (P<0.05) impact on wheat yield — banding N below the seed or in a mid-row configuration significantly increased grain yield (by up to 16%) compared to mid-row placement using ultra-high-pressure injection or streaming nozzles. There was also a trend towards a significant increase (9%-10%) in grain yield compared with topdressing (Table 1). However, at Longerenong, placement of N at sowing had no significant effect on grain yield (Table 2). Given that both sites received rainfall of at least 10mm within two weeks of sowing, it is unlikely that the benefit of banded application at Ouyen was related to N loss due to ammonia volatilisation. An alternative explanation may relate to N tie-up or immobilisation — at Ouyen, stubble from the previous season was slashed prior to sowing, spreading it evenly across the soil surface compared to Longerenong where stubble remained standing. While total stubble load at both sites was similar, it is possible that by spreading stubble across the soil surface that N immobilisation may have increased at Ouyen, potentially favouring treatments where N was banded below the surface. The effect of N placement at sowing on grain protein/oil content was limited at both Ouyen and Longerenong.

Table 1. Wheat grain yield and protein response to N application method at sowing and in‑season at Ouyen in 2018. Values presented are the mean of both 25kg N/ha and 50kg N/ha rates. Superscripts indicate significant differences (P<0.05). Treatments followed by the same letter are not statistically different.

ns: not significant

Placement of fertiliser N in-season did not significantly affect grain yield at either Ouyen or Longerenong. However, similar to results at Ultima in 2017, mid-row banding N at GS30 significantly increased grain protein at Ouyen by 9%-15%, while maintaining equivalent yield to other application methods. A similar observation was made where N was applied by ultra-high-pressure injection, although the increase in grain protein was lower. This result may indicate that by applying N in between the crop rows during the growing season that crop access to the fertiliser is slowed, thereby having a greater influence on grain protein. Conversely at Longerenong, grain oil content was not affected by placement of N in-season.

Table 2. Wheat grain yield and protein response to N application method at sowing and in‑season at Longerenong in 2018. Values presented are the mean of both 25kg N/ha and 50kg N/ha rates.

ns: not significant

Granular versus liquid urea

Field trials conducted in 2016 and 2017 were undertaken using liquid urea solution except where granular urea was top-dressed, raising questions about the efficacy of liquid versus granular sources. In 2018, machinery modifications were made to allow a direct comparison of N source for the mid-row banded treatment. While it is expected that an aqueous urea solution will behave differently to a granular product in the short term following application, across both sites, times and rates of application and placement, no significant effect of urea source was found on either grain yield or protein in 2018.

Ultra-high pressure injection as an alternative method to mid-row band fertiliser

Across both sites, ultra-high-pressure injection resulted in similar grain yield or grain protein/oil content compared with other application methods including mid-row banding using a twin disc opener. However, where significant effects of application method were measured (grain yield where N was applied at sowing and grain protein where N was applied in-season at Ouyen), mid-row application by this method did not result in equivalent grain yield/protein. While applying N using ultra-high injection is practical for handling higher stubble loads and narrower row spacings, it does not necessarily result in the same placement of N as a disc opener where the fertiliser is placed in the bottom of a furrow. Instead, the liquid is used to cut through the stubble and soil, resulting in a different pattern of distribution and concentration within the soil. This effect also depends on stubble load, soil type and conditions at the time of application, potentially affecting fertiliser availability to the crop and resulting in the observed differences in grain yield and protein between the two methods of mid-row banding.

Effect of placement on N use efficiency

Studies over numerous years have shown that on average, just 44% of the N fertiliser that is applied to Australian grain crops is taken up by the crop in the year of application (Angus and Grace 2017). While fertiliser recovery results for the 2018 field trials are not available at the time of writing, results from 2016 and 2017 indicated consistent increases in crop uptake where N fertiliser was applied by mid-row banding rather than by streaming nozzles or in a mid-row surface arrangement — average crop uptake of 60% for mid-row banding compared with 41%-42% for surface applications. While these improvements in N use efficiency also resulted in reduced loss of fertiliser N, the effects on grain yield and protein have been less consistent and it will be important to find ways to more consistently link improvements in crop N-recovery to productivity and profit.

Industry application

After undertaking a total of six field trials between 2016 and 2018, it has been found that crop response to placement of N fertiliser varies with season, soil type and timing of application. At three of the six sites, mid-row banding showed potential to increase yield compared with other methods of application, however at only one of these sites was it higher yielding than the current industry practice (i.e. banded below the seed at sowing or top-dressed granular in-season). For the Mallee, under dry seasonal conditions, mid-row banding of N in-season showed potential to significantly increase grain protein (increases of 0.5%-1.6%) compared with other methods of application. These results need to be considered against the costs of shifting to mid-row banding, particularly in the case of in-season applications where the increase in capital and operational costs would be greater.

Conversely, applying mid-row banding at sowing may be less expensive in terms of capital and operational costs while offering similar yields to banding below the seed and allowing application of higher rates of N without risking fertiliser toxicity (as observed at Ouyen when 100kg N/ha was banded below the seed). While the use of ultra-high-pressure injection in a mid-row configuration was only tested in 2018, it appears able to address some of the issues with applying mid-row N using conventional ground engagement tools. However, its performance in 2018 was variable and like other methods, its commercial application would need to be considered in relation to cost and availability of equipment to apply this on a large scale.

Conclusion

Nitrogen fertiliser placement had a variable effect on grain yield and protein/oil content in 2018. At Ouyen, where conditions were drier, surface application of 25-50kg N/ha at sowing tended to reduce grain yield compared to where N was banded either below the seed or in a mid-row configuration. However, banding a high rate of N (100kg N/ha) below the seed resulted in significant reductions in emergence. In situations where the risk of fertiliser toxicity is high and high rates of N are required at sowing, mid-row banding offers the potential to improve separation between seed and fertiliser. Application of N by mid-row banding in-season at Ouyen also significantly increased grain protein compared with all other methods of application, consistent with results at Ultima in 2017. At Longerenong, however, the effect of N placement on grain yield and oil content in canola was limited in 2018. In 2016 and 2017, mid-row banding of N fertiliser in-season significantly improved N use efficiency in wheat, however, given the variable response in grain yield and quality, it is important to consider the likely changes in capital and operational costs associated with changes in method of N application.

Useful resources

Sandral, G., Tavakkoli, E., Harris, F., Koetz, E., Diffey, S., Angus, J. (2018). Improving nitrogen fertiliser use efficiency in wheat using mid-row banding.

https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2018/02/improving-nitrogen-fertiliser-use-efficiency-in-wheat-using-mid-row-banding

Wallace, A., Nuttall, J., Marsh, J. (2018). Refining nitrogen placement in cereals – mid-row banding.

https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2018/02/refining-nitrogen-placement-in-cereals-mid-row-banding

References

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

Drury CF., Reynolds WD., Tan CS., Welacky TW., Calder W., McLaughlin NB. (2006). Emissions of nitrous oxide and carbon dioxide: influence on tillage type and nitrogen placement depth. Soil Science Society of America Journal 70, 570-581.

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.

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 Jobs, Precincts and Regions, Bilateral Research Agreement. The authors also wish to acknowledge the assistance of Birchip Cropping Group and South Australian No-Till Farming Association staff in delivery of the experimental program.

Contact details

Ash Wallace
Agriculture Victoria
110 Natimuk Rd, Horsham, Vic, 3400
(03) 4344 3111
ashley.wallace@ecodev.vic.gov.au
@Ash_W_429