Leveraging protein for profitability
Leveraging protein for profitability
Author: Edward Scott & Mat Clancy (CropScanAg) | Date: 17 Jul 2024
Take home messages
- Wheat grain protein concentrations of less than 11.5% generally indicate that nitrogen (N) supply was insufficient for a crop to meet its water limited yield potential.
- Reviewing grain protein and yield responses in combination can allow assessment of field performance. The protein concentration map is analogous with an ‘N adequacy’ map.
- The protein layer can be used in conjunction with targeted deep N soil sampling as a basis for site-specific N inputs to reduce both instances of yield loss due to N undersupply and adverse environmental/economic consequences associated with N oversupply.
Introduction
Nitrogen is a dynamic nutrient in the environment, and as such, grower confidence in utilising the right precision agriculture information to support variable rate (VR) decision making has been of high importance. The use of cereal grain protein mapping as part of a site-specific N fertilisation strategy has shown promising results as a valuable precision agriculture layer for improved decision making. By using grain protein as an indicator, fields can be assessed to where yield gains can be achieved through improved N fertiliser management. Results are presented from paddock scale research and on farm field examples that demonstrate real-world outcomes of utilising protein data for improved N decision making and examine relationships between soil mineral nitrogen (SMN) levels and grain protein concentration.
Theoretical background to cereal grain protein based site-specific N
For many decades, it has been recognised that a consistent relationship exists between cereal grain yield and grain protein concentration according to N supply (for example, Russell 1963). This relationship consists of increasing grain yield and protein concentrations with greater fertiliser N supply up to a certain point, after which grain yield begins to plateau while protein concentration continues to increase. At very high fertiliser N levels, a decline in yield often occurs (Holford et al. 1992).
The point at which N supply has been optimised for maximum grain yield is termed the ‘critical grain protein concentration’ and is around 11.2–12.0% in most Australian hard white wheats, determined through studies conducted in southern/central NSW (Brill et al. 2013; Sandral et al. 2018) and South Australia/Victoria (G. McDonald, review published in Unkovich et al. 2020).
While critical grain protein concentrations will vary between varieties and across seasonal conditions (Fowler 2003), a simplified ‘rule-of-thumb’ interpretation under favourable (non-drought) conditions can be summarised as:
- protein <11.5% = insufficient N supply to meet water limited yield potential
- protein 11.5–12.5% = adequate/optimum N supply to achieve water limited yield potential
- protein >12.5% = surplus N to crop requirement, possibly some yield penalty (Figure 1).
Figure 1. A generalised representation of the relationship between wheat grain yield and protein concentration with increasing fertiliser N supply. Labels refer to grades in the Australian wheat classification system.
If we apply this rule-of-thumb spatially across a management area grown to a single wheat variety, a georeferenced map of wheat grain protein concentration is analogous to an ‘N adequacy’ map, that is, it serves to distinguish areas of the paddock that had insufficient, ideal or surplus N according to their site-specific yield potentials.
Ground-truth soil testing at the start of the following season can be used to test this assumption and quantify out-of-season mineralisation. A good approach to determining the placement of soil tests is to divide the paddock into zones based on combinations of grain yield and protein results from the previous harvest. This process provides useful insights into not only N dynamics but also where non-N related constraints may warrant further investigation. These concepts are summarised in Table 1.
Table 1: Within-paddock combinations of cereal grain yield, protein attributes and their properties.
Classification | Interpretation | Residual N levels | Action |
---|---|---|---|
High Yield/ |
| Likely moderate to high, however soil test to confirm (particularly if crop N demand was higher than budgeted) | Determine N fertiliser rates based on soil test results and according to high yield potential |
High Yield/ |
| Likely low (assume post-harvest residual SMN was negligible, so levels are dependent on out-of-season N mineralisation) | Increase fertiliser N rates relative to paddock average in following season/s to support higher yields and build SMN |
Low Yield/ |
| Likely high (mining of N may be advised to reduce yield penalties associated with N oversupply) | If the constraint cannot be amended, reduce N inputs relative to paddock average permanently to match lower yield potentials |
Low Yield/ |
| Likely low | Start by increasing N to determine the non-N constrained yield potential, then manage according to results |
A major advantage of a protein-based VR N management approach over currently available alternatives (e.g. ??) is that it combines both the supply and demand elements of the N balance equation. For example, low protein areas within a paddock may occur either due to low N supply (for example, differences in carryover N, mineralisation, fertiliser inputs) or higher yield potential (for example, due to the dilution of protein by higher yield; Simmonds 1995). Regardless of which factor is responsible (or both), the management decision will involve increasing fertiliser N rates in the following season.
In this sense, the protein layer is also accounting for temporal variability of N dynamics by providing a retrospective assessment of the whole season, net N balance, rather than a ‘snapshot in time’ as occurs with data layers such as spectral indices or grid soil mapping.
Another advantage is the benefit afforded by the plant providing an indication of N adequacy according to the conditions it experienced, that is, the plant available N. This circumvents a limitation of soil testing where mineral N may be present within the profile, however the plant may not be able to access it (for example, if subsoil constraints prevent root access and/or uptake). In a similar manner, if subsoil conditions are favourable and the plant is able to access deeper SMN, this will be reflected by the plant’s protein concentration, however, it may be missed by an arbitrary soil sampling depth cut-off.
Getting started
Many growers have access to yield maps, and with an increase in growers having an on-combine grain analyser, these growers have access to quantity and quality metrics across their fields which can support subsequent crop fertiliser decision making.
A protein-based site-specific N strategy might be a good approach for a grower if they:
- are predominantly located on soil types not prone to Nitrogen losses (that is, free draining with good nutrient holding capacity) and
- have within-paddock variability in factors such as soil texture, cation exchange capacity (CEC), organic carbon (OC) %, plant available water capacity (PAWC), productivity (N removal) and/or management histories (for example, amalgamated paddocks, previous inputs).
At present, the cost of a harvester mounted grain analyser is approximately AUD $28,500–$31,000 + GST and installation (CropScanAg ‘CropScan 3300H’ and ‘CropScan 4000VT’ units). This cost will be spread over a number of seasons. There will also be costs related to data management and interpretation if the grower cannot or does not wish to do this themselves.
After completing the first harvest, a good strategy is to pick a few of the most variable paddocks to focus on. If a grower isn’t comfortable implementing a VR application straight away, they may prefer to use N-rich and/or N-poor strips to test the impact of variable N rates on their soils. If doing so, strips should be designed so they pass through several zones (for example, low/high protein, soil types, management histories). Paddocks being cropped to a second cereal crop (for example, wheat on wheat) will be of most value for reviewing the results of strip trials and/or the success of VR N applications.
Setting rates
Making sense of your own data is critical and linking back to existing N management determination strategies is key for grower and advisor confidence. Start-of-season soil sampling will remain an essential step to determining actual N rates. Soil sampling, to at least 0-60cm, will also act as a ground-truthing step to test assumptions regarding patterns of carryover SMN and to test any unusual areas.
Where consistent protein zones are present, soil sampling should cover off on each of the major protein/yield combinations (see Table 1), aiming to get an idea of the paddock average and the spread (range) of SMN values.
Over a number of seasons, implementing this strategy should reduce the spatial variability of protein concentrations, ideally converging around 11.5–12.5% if the base fertiliser N rates chosen have been appropriate. It is likely that the most ‘bang for buck’ to be gained implementing this strategy will occur in the early stages, by eliminating very low (highly constrained) and very high N zones.
It is important to remember that in paddocks where yield potential varies greatly due to factors other than N (for example, relatively fixed factors such as PAWC), a successful outcome will not be where yield becomes even, but rather where yield is optimised in all areas according to their site-specific yield potentials.
In all cases, ongoing monitoring of cereal grain protein per cent results and annual deep (0-60cm) soil sampling should serve as constant feedback to ensure N decision-making approaches are performing well.
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 author would like to thank them for their continued support.
References
Brill R, Gardner M, Graham R, Fettell N (2013) Will low protein become the new norm? GRDC Grower and Advisor Update, Coonabarabran, 25.02.2013.
Fowler DB (2003) Crop nitrogen demand and grain protein concentration of spring and winter wheat. Agronomy Journal 95(2), 260-265.
Holford ICR, Doyle AD, Leckie CC (1992) Nitrogen response characteristics of wheat protein in relation to yield responses and their interactions with phosphorus. Australian Journal of Agricultural Research 43(5), 969-986.
Hunt J, Kirkegaard J, Maddern K, Murray J (2021) Strategies for long term management of N across farming systems. GRDC Grower and Advisor Update, Wagga Wagga, 17.02.2021.
Meier EA, Hunt JR, Hochman Z (2021) Evaluation of nitrogen bank, a soil nitrogen management strategy for sustainably closing wheat yield gaps. Field Crops Research 261, 108017.
Moffitt EM (2021) Utilising new technologies to better manage within-paddock nitrogen variability and sustainably close the yield gap in southern NSW. FarmLink 2020 Research Report.
Russell JS (1963) Nitrogen content of wheat grain as an indication of potential yield response to nitrogen fertilizer. Australian Journal of Experimental Agriculture and Animal Husbandry 3(11), 319-325.
Sandral GA, Tavakkoli E, Harris F, Koetz E (2018) Improving nitrogen fertiliser use efficiency in wheat using mid-row banding. GRDC Grower and Advisor Update, Wagga Wagga, 13.02.2018.
Simmonds NW (1995) The relation between yield and protein in cereal grain. Journal of the Science of Food and Agriculture 67(3), 309-315.
Unkovich MJ, Herridge DF, Denton MD, McDonald GK, McNeill AM, Long W, Farquharson R, Malcolm B (2020) A nitrogen reference manual for the southern cropping region. GRDC publication
Contact details
Edward Scott
0403313741
ed.scott@cropscanag.com