High yielding wheat and sorghum for the Northern Region
Many locally adapted wheat and sorghum hybrids with great yield potential have been released over the past few years. However, that yield potential has been determined in breeders’ plots and may overestimate what is achievable through best agronomic practice due to local soil and climatic limitations, price ratios, seasonal outlooks, and farmers’ investment capacity and risk preference.
Present wheat yield gaps in the Northern Region are on average ca. 1.9t/ha (Z Hochman 2014, personal communication) showing large potential for improvement. For sorghum, trends in yield increase across the Northern Region show a large spatial variability. This is likely to be driven by the impact of technology adoption under different levels of farmers’ investment and skills across the region. Therefore crop selection and rotations influence the cause and magnitude of yield gaps.
This is particularly important in the northern region, as we move from a predominantly wheat production systems in the south, where sorghum was a secondary crop, to the more summer dominant cropping systems in the north where we find the sorghum specialists (Rodriguez and Sadras, 2007; Rodriguez et al., 2012). Across the northern region grower’s target yields may also be highly contrasting as investment decisions on intensification practices are influenced by regional soils and climates, price ratios, mix of grain and production systems, and markets, in addition to perceived levels of climate risk.
Depending on farmers’ present level of performance and investment there are three basic steps farmers could use to approach the full potential of the available genetic resources. Step 1: the agronomic performance of average growers needs to be improved; Step 2, convince already good growers that the benefits from increased investment levels, needed to achieve higher yields, justifies the higher risk exposure; and Step 3: support leading farmers to explore new and more innovative practices that increase returns with minimal additional risk i.e. identify new production frontiers.
In this project we are addressing Step 2 working with growers, input suppliers, grower groups and seed companies to: (i) quantify the difference between the yield that is potentially achievable i.e. determined by agro-ecological conditions (i.e. climate and soils), and farmers’ yields; (ii) quantify under what environments and seasonal conditions the benefits from increasing investments compensate for the increase in risks; (iii) demonstrate that there is a best practice target yield that is smaller than the potentially achievable yield, as farmers determine their preferred target yield after considering normative (i.e. price ratios, and climatic risks) and behavioral (i.e. risk preference) factors; and (iv) deliver project outputs to at least 250 farmers from Darling Downs and Central Queensland through a collaboration with Conservation Farmers Inc. (CFI), Pacific Seeds, Du Pont Pioneer, DAFF and QAAFI.
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In 2014, with support from CSIRO and GRDC as part of our project Higher yielding wheat and sorghum for the Northern Region (UQ00074), we collected data from 75 sorghum crops grown over the last four years on farmers' fields in the Darling Downs. As expected, crop performance varied widely. Average yield in the lowest 50% of fields was 3882 kg/ha. The same value for the top 50% was 7112 kg/ha. That's an 83% difference in yield. So, the objective of this study was to understand what was the role of management in explaining such a variability.
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To answer the question above we used classification methods to identify the main variables that linked field performance, in terms of water use efficiency, yield and gross margin and management. The results showed that sowing date was the most important factor in determining sorghum performance. Top performing fields were sown early (i.e. by early-October); other factors included sowing on a full soil profile, applying at least 80 kg N/ha, and obviously, high in-crop rainfall.
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Most northern growers understand that sorghum can be sown once soil temperatures reach 16° C. We looked at historical data from Dalby provided by the Bureau of Meteorology and found this temperature is typically reached by the 4th of September. Our analysis of frost risk at all farm sites from the study indicated little to no risk of frost occurrence after the 6-leaf stage even when sowing in September. These results suggest early sowing could be a viable option for farmers receiving those early rains, and that earlier sowing would greatly increase their chances of higher WUE, yield and profit.
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Given higher N fertiliser was such an important driver of higher yield, we looked at why some farmers weren’t applying much N to their fields. We found that high debt levels, from our data this is above $1525 / ha, were associated with lower levels of investment in N, leading to poorer yields and lower gross margins.
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In summary, best performing fields were sown early, farmers used higher levels of N, and were found on farms having lower levels of farm debt. These factors alone won’t guarantee success, but they appear to be the key difference between higher and lower performing fields across the Darling Downs in Queensland.