Recent years have seen a substantial increase in durum wheat production in Australia. Durum wheat has excellent cooking qualities, which make it suited to the production of pasta. As a result, it attracts price premium over bread wheat. The development of new varieties with crown rot resistance has enabled durum wheat to be considered for production in western Victoria.
Durum requires a high protein content (13%) to ensure it delivers appropriate cooking qualities, so it is important that crops be supplied with adequate nitrogen (N). For bread wheat, the later N is applied the more it is likely to raise grain protein. This being the case, practices that allow wheat crops to take up N late in the season are advantageous.
Together with Agritech Rural (Horsham), BCG established this trial to examine durum performance in the Wimmera and to identify how to best manage its nutrition requirements.
TAKE HOME MESSAGES
- Given the price premiums of durum wheat over bread wheat, it has the potential to be a very profitable crop in the Wimmera.
- Durum wheat does not cope well with excess nitrogen in poor seasons. Smaller more frequent applications in response to seasonal conditions may be required.
- Durum has a real place in Wimmera production systems.
AIM
To determine the optimal time to apply nitrogen to durum wheat.
TRIAL DETAILS
Location: Horsham
Soil type: Wimmera grey clay with no subsoil constraints
GSR (Apr-Oct): 253mm
Crop types: Bread wheat – Derrimut Durum wheat – DB Aurora
Sowing date: 20 May
Seeding equipment: Knife points, press wheels, 30cm row spacing
Target plant density: Bread – 150 plants/m² Durum – 220 plants/m2
Harvest date: 28 November
TRIAL INPUTS
Fertiliser: Refer to Table 1
Herbicide/insecticide:
Pre-sowing: Treflan @ 1.5L/ha + Avadex @ 1.5L/ha
In-crop: Ammonium Sulfate @ 0.8kg/100L + Precept 300 @ 1.5L/ha + Lontrel Advance @ 70ml/ha + Hasten 1% v/v
Pests and diseases were controlled according to best management practice.
METHOD
A replicated field trial was established at BCG’s Horsham research site. The trial compared a range of nitrogen management approaches. Durum and bread wheat were sown in a complete randomised block design. Soil samples to 1.3m depth at the site were taken on 26 March to measure soil water and available nitrogen. Trial assessments included yield and quality parameters. All plots received consistent agronomic management with full weed and insect control, the only differences were in the treatments applied (Table 1).
Sowing treatments of fertiliser were applied by broadcasting with the seeder prior to sowing. In-crop granular fertiliser treatments were applied using garden hand spreaders.
RESULTS AND INTERPRETATION
Seasonal conditions
Soil test results from samples taken in March showed 6mm of plant available water (PAW) and 37kg N/ ha. Both values are very low.
Rainfall at the site from 26 March (soil sampling date) until late July was tracking close to Decile 5 (Figure 1). However, after 1 August very little rainfall (38.8mm) was received and at the end of the growing season the total recorded was at Decile 1. The spring rainfall at the site was the third lowest on record (114 years). The 2014 season produced the worst possible outcome for managing seasonal risk. Conditions were favourable early but were followed by one of the worst finishes on record. This low spring rainfall made responses to late applications of N unlikely.
Grain yield and protein
Given the poor finish to the season, the quantities of N applied in this trial were excessive. The control, which received no additional N, achieved a yield of 2.4t/ha which was equivalent to the late applied 2- and 3-way-split and 3-way-split-plus-zinc treatments which received an additional 140 to 150kg N/ha to the control (Figure 2).
Assuming that a wheat crop requires 40kg N/ha to produce one tonne of grain, the N supplied was adequate for a yield over 3.5t/ha. Despite this, there were significant yield and protein differences between some treatments in which lower yields were associated with earlier applications of N.
The all-up-front and the early-2 and 3-way-split and 3-way-split-plus-zinc treatments generated significantly lower yields than the Control and Late applied 2 and 3-way-split treatments.
The in-crop treatments were applied at GS30 (5 August); GS37 (5 September) and GS 65 (19 September) and respectively received 1.2, 4.2 and 1.8mm of rainfall in the 10 days following. The total rainfall from 5 August until the end of the growing season (Oct 31) was 13.4mm. With such a small amount of rain following N application, the potential for loss through volatilisation was very high. Although it is likely that this did occur with most of the N applied as part of the in-crop treatment applications, it is possible that they were not accessed by the crop and still remain in the soil.
It is evident that any treatment that accessed additional nitrogen suffered a yield penalty. Give the quantities of N used and the severity of the season finish, it is not surprising that there was some haying off.
Increases in yield due to additional N were generally accompanied by lower grain protein: the yield dilution effect (Figure 2). The Control and the Late-3-way-split treatments had lower protein concentrations than the other treatments and fell below the threshold (13%) for achieving the highest specification for bread and durum wheat.
The trial did produce a slightly higher (0.2t/ha) yield for bread wheat over the durum (Table 2). This is consistent with past experience which suggests that durum yields slightly less than bread wheat.
There were no differences in grain protein between durum and bread wheat. However, there was a significant two-way interaction between the treatment and wheat type (Figure 3). Even so, a clear pattern that would provide guidance on alternative nitrogen management for durum compared to bread wheat emerged.
Screenings and test weight
The trial did produce different screenings results for bread (2.9%) and durum (3.2%) wheat (P=0.004, LSD=0.178, CV=8.0%). However, both were below the maximum quality threshold of five per cent. Differences were also recorded for test weight between treatment and wheat type; again the test weights were well above the minimum quality threshold of 76kg/hl. It is interesting to note that even the All-up-front treatment, which could be expected to have the greatest problem with quality under these conditions, also produced grain of the highest quality.
Total nitrogen
Total grain N is a good measure of the ability of the crop to access N and remobilise that N to grain. Total mean grain N was calculated by multiplying yield with the protein percentage and applying a multiplier ([protein %]/5.7) based on the N portion of protein. The trial produced significant differences between treatments, wheat type and a two-way interaction between the two (Figure 4). It is clear that the later applications of N generated greatest N use for both the durum and bread wheat. The grain N results showed that the durum did not produce as much total grain N as the bread wheat in the All-up-front, Early-2-way-split and Early-3-way-split-plus-zinc treatments. This indicates that the bread wheat did not hay off as much as the durum in the poor finish. It is apparent from these results that providing durum with large amounts of N in a season with a poor spring is not advantageous for nitrogen usage. This suggests that if growers are to optimise nitrogen management in durum, they need to precisely match the applications of the crop requirements to the season. This may mean more frequent applications of smaller amounts, however the durum premiums should compensate for any extra expense incurred over bread wheat production.
Gross Margin
The motivation for growers to grow durum wheat is in the premium it receives. Prices used for durum and bread wheat in this article were based on the cash price at Port Adelaide on 1 December. In 2014, durum premiums were exceptional for all grades and were in excess of $220/t (Table 3), although much of the durum crop was contracted earlier in the season at somewhat lower prices. These premiums should not be expected every year. Long-term premiums are more commonly in the $100 dollar range (GRDC Farm Gross Margin and Enterprise Planning Guide, 2012).
Based on the grain classification achieved for grain protein, test weight and screenings, all treatments achieved the highest grain quality classification with two exceptions. The bread Late-3-way-split treatment did not reach the required protein to achieve H1 and the Control achieved the second highest classification for both durum (DR2) and bread wheat (H2). Based on these classifications, the partial gross margin resulting from N applications was calculated for each treatment. The cost of fertiliser and the application was subtracted from the gross return to give a partial gross margin. Spreading costs used were $6/ha.
The high durum premiums in the 2014 season meant that the partial gross margin resulting from N applications was strongly in favour of the durum treatments (Figure 5). On average, the durum ($950/ ha) generated a $420/ha margin over bread wheat ($530/ha) (P<0.001, LSD=$45.60, CV=12.2%). This margin was derived purely from income as the costs incurred were indentical.
With the exception of the Control, the treatment fertiliser costs were essentially the same. It is therefore not surprising that the partial gross margin results for the durum was consistent with the yield results where lower gross margins were associated with earlier applications of N. The All-upfront and the Early 2 and 3-way-split and the 3-way-split-plus-zinc treatments generated significantly lower partial gross margins than the Control and Late applied 2 and 3-way-split treatments. It is worth noting that the control, which did not have the highest yield and achieved a lower grade specification than all other treatments, still managed to achieve the highest gross margin as its input cost were $200/ha lower.
In the bread wheat the control was the most profitable treatment which achieved a higher partial gross margin than all treatments except the Late-2-way-split. Consistent with the yield results, the optimum N management strategy, as for the durum wheat, was where lower amounts of N were supplied.
zinc
In this trial there were no yield, quality or profitability effects resulting from the addition of zinc at sowing. In wheat, zinc is utilised in enzyme systems and is essential for growth and development. If the zinc were to create an effect, it is more likely to occur in a more favourable season with greater growth and development.
COMMERCIAL PRACTICE
In this trial, the optimal strategy was to apply no additional inputs. This was largely a consequence of the season. The trial demonstrated that durum does have a real place in Wimmera production systems. In this trial the comparable yield result of durum and bread wheat, combined with the price premium for durum, shows that it could a very profitable option. That said, there was also some evidence to suggest that providing durum with large amounts of N in a season with a poor spring is not advantageous for nitrogen usage.
Traditionally, N management in durum has been to apply very little up front and then apply high rates late in the season to increase grain protein. Durum growers should make every effort to match crop demand for N with supply in response to the season. This may add extra cost through more frequent N applications, but this trial has demonstrated the durum has the potential to compensate by means of its price premiums. While the production of durum is increasing in Australia, the market is still small. As a result it, is common practice for durum producers to secure contracts in season in order to ensure a market for their grain.
ON-FARM PROFITABILITY
In the 2014 season, which produced some of the worst conditions for making input decisions and managing seasonal risk, the Control (to which no N inputs were applied) was the most profitable option. Under the very dry conditions, the Control produced the highest partial gross margin of $1,294/ha. While this low cost approach was the most profitable in the 2014 season, this may not be the case in an average season.
ACKNOWLEDGEMENTS
This trial was funded by BCG members through their membership, in conjunction with Agritech Rural Horsham. Thanks to Dr Jason Able (University of Adelaide) for providing seed and advice on the formation of nitrogen treatments.
