Take Home Messages
- Foliar and granular application of silicon had no effect on flowering biomass and grain yield for all crop types and varieties in the 2023 season.
- Silicon has been shown to improve tolerance to heat and moisture stress in glasshouse experiments.
Aim
To assess the role of silicon fertilisers in increasing crop drought resilience and to determine whether it can also be used as a tool to allow for more marginal farming practices to be expanded across the low rainfall zone. In addition, silicon fertilisers were tested as a stress mitigation solution to increase species diversity cultivated on farm, with specific focus on legume crops such as chickpea and faba bean, which are not commonly grown in the Mallee region.
Background
Tough conditions, including hot and dry growing seasons, are common in the Mallee. Many areas receive consistently low rainfall on soils with poor water holding capacity. These conditions limit the yield potential of commonly grown crops, particularly when a dry spring occurs and crops are flowering and starting to fill grain. With climatic conditions becoming more variable, the ability to use or maintain diversity in our farming systems will become an important management strategy to ensure businesses can minimise economic risk.
Use of plant available silicon (Si) under glasshouse experiments at the University of Melbourne Dookie campus has shown positive effects on plant performance under moisture and heat stress for a range of cereal and legume crops, allowing them to better maintain yield (Ashfaq 2023). Plant available Si-mediated tolerance to abiotic stressors such as water stress primarily promotes photochemical efficiency and photosynthetic enzymatic activities, improving photosynthetic rate. Results have also shown improved water relations through higher water uptake by roots – simultaneously reducing water loss from leaves – and improving antioxidant defence through scavenging of reactive oxygen species (ROS) produced as a stress response by plants. While this has been shown in controlled environments, application in field situations has been limited.
This trial investigated whether Si fertilisers delivered via foliar sprays or soil amendment can sustain the yield of cereals, canola and pulses under low rainfall conditions. The first year of this trial was in 2022, where crops (wheat, canola and four pulses: faba bean, lentil, chickpea and vetch) were tested in the field under rainfed conditions with the application of plant-available silicon (PAS) applied as a foliar spray at key growth stages. The replicated experiment was hosted at the BCGs Nullawil site. The first year results indicated Si fertiliser had no effect on wheat varieties. Data on pulses was not available as the experiment was lost due to flash flooding. This second year of the trial, conducted in the 2023 cropping season, was conducted with similar aims. An extra Si fertiliser treatment was added for the 2023 cropping season: granular Si applied as soil amendment at the time of sowing.
Paddock Details
Location: Kinnabulla
Crop year rainfall (Nov–Oct): 276mm
GSR (Apr–Oct): 187mm
Soil type: Sandy clay loam
Paddock history: Lentil brown manure
Trial Details
Crop type/s: Refer to Table 1
Treatments: Refer to Table 2
Target plant density: Refer to Table 1
Seeding equipment: Knife points, press wheels, 30cm row spacing
Sowing date: Canola: 24 April 2023 Cereals and Pulse: 5 May 2023
Replicates: Eight
Trial Inputs
Trials managed as best practice for pests, weeds and disease.
Method
Three replicated field trials were established at Kinnabulla. Commonly grown canola, pulse and cereal varieties were sown, as well as more marginal practices such as graze and grain winter wheats and marginal LRZ pulses (faba beans, chickpeas and long season vetch). All varieties, apart from canola, had +/- foliar silicon or granular silicon applied at sowing and were assessed for crop biomass at flowering, grain yield and quality.
Results & Interpretation
Seasonal conditions
Growing season rainfall at Kinnabulla was below average when compared to the long-term average, only reaching decile 3. However, water stress conditions were not seen in 2023, as the soil profile was full of moisture from high rainfall in the spring of 2022. A high starting plant available water along with consistent rainfall made optimal conditions for crop growth. Moisture stress conditions looked likely in September as soil moisture started to run out for pulses, but crops were able to hold on until rain in October.
Silicon application effect on crop performance
Neither foliar nor granular application of silicon affected flowering biomass (data not presented) or grain yield for all crop types and varieties in the 2023 season (Table 3 and Table 4). Protein and test weight were also unaffected (data not presented). These results are not unexpected as silicon has been shown to improve tolerance to heat and moisture stress which was rarely seen in 2023. This was consistent with results seen in 2022.
Performance of dual-purpose winter wheats compared to grain-only treatments
Both winter wheat varieties performed slightly poorer when grazed, with Mowhawk displaying a 0.2t/ha yield decrease (p-value <0.001, LSD 0.120, CV% 4.1) and Kittyhawk a 0.3t/ha yield decrease (p-value <0.001, LSD 0.135, CV% 5.4). Although these results are significant, a dual-purpose system did allow for 750kg/ha of early feed with only a slight yield decrease. Generate (micronutrient formulation) helped grazing recovery slightly, with Kittyhawk gaining 150kg/ha (p-value 0.02, LSD 0.105, CV% 3.6) and and Mowhawk 125kg/ha (p-value 0.023, LSD 0.128, CV% 5.2) in grain yield when applied after grazing. Although these results are significant, due to the small yield difference and the extra costs, applying Generate would not have been practical. Silicon application did not affect grazing recovery.
Marginal and common practices
Scepter was the best performing cereal in the trial, with an average yield of 5.5t/ha followed by Mowhawk at 5.1t/ha (Table 3). Mowhawk is a new, quicker winter wheat that may have a fit in a Mallee system for growers with a large program, as it can be sown early and yielded well in 2023. Yields of faba beans and chickpeas were low at the site (Table 4). Moisture was removed from these crops due to their poor ability to complete against weeds. Silicon fertilisers did not mitigate the risk of abiotic stress for these crops in 2023. Benetas vetch hay yielded 4.1t/ha whereas commonly-grown Morava vetch hay yielded 3.3t/ha (p-value <0.001, LSD 0.310, cv% 19.3). Benetas is a very long season variety suited to higher rainfall areas. With high levels of soil moisture and good growing conditions, Benetas can achieve high biomass. It is important to keep in mind however, hay cut timing for Benetas can often overlap with the grain harvest period. Canola was also not affected by the application of silicon fertiliser and on average yielded 2.3t/ha (p-value=NS).
Commercial Practice and On Farm Profitability
Moisture and heat stress can be a major yield limitation in the Mallee on all crop types, particularly during the grain fill stage in spring. These conditions, however were not seen in 2023 and crops were able to fill grain without heat stress. Silicon fertiliser has been proven to increase crop yields in drought conditions through glasshouse trials by the University of Melbourne (Gupta 2022). Further long-term trials under low rain fall field conditions with complementary controlled environment experiments are needed to provide evidence of the effects of such products. In addition, the mechanism of delivery (foliar sprays or soil amendment) also requires further investigation from agronomic and economic perspectives to determine the usefulness of such products to farmers and primary growers. It is also unclear if these products are compatible with chemicals such as herbicides, fungicides and insecticides. Granular fertiliser could be a potential fix for this issue, but more trials are required to determine the effectiveness of silicon granular fertiliser. In addition, further testing of the crops grown with this treatment is needed to evaluate how the fertiliser might alter the nutritional composition of the crops.
References
Ashfaq W., Brodie G., Fuentes S. et al., 2023, Plant Soil, ‘Silicon improves root system and canopy physiology in wheat under drought stress’ https://doi.org/10.1007/s11104-023-06202-4 Ashfaq W., Fuentes S., Brodie G., and Gupta D., 2022, Frontiers in Plant Science ‘The role of silicon in regulating physiological and biochemical mechanisms of contrasting bread wheat cultivars under terminal drought and heat stress environments’. 13:955490. doi: 10.3389/fpls.2022.955490
Acknowledgements
This trial is part of the project ‘Redesigning of Broadacre Farming Systems in South East Australia’. This project received funding from the Australian Government’s Future Drought Fund. This project is led by the University of Melbourne with partners BCG, Riverine Plains Inc, Gap Flat Track – Native Foods, Black Duck Foods, Goulburn Broken Catchment Management Authority.
