Take Home Messages
- Plant available silicon (Si) is an agronomically-essential element for healthy plants.
- Si-mediated tolerance to drought includes promoting photosynthesis and water relations.
- Si fertiliser can help sustain crop yields under stressors like drought.
Aim
To investigate the effect silicon fertilisers have on crop yields in the low to medium rainfall zone.
Background
The Mallee has a climate which features a high proportion of hot and dry growing seasons. This limits the yield potential of commonly grown crops, particularly where dry and hot conditions occur in spring when crops are starting to flower and fill grain. With climatic conditions becoming more variable, the ability to use or maintain diversified farming practices will become an important management strategy to ensure a business can cope with the uncertainty of each season.
The challenge is how this can be achieved.
Use of plant available silicon (Si) under controlled and field-based experimentation 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. Plant available Si-mediated tolerance to abiotic stressors such as water stress primarily promotes photochemical efficiency and photosynthetic enzymatic activities, and therefore improves 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 investigates whether Si fertilisers can be used to increase crop yields of wheat and barley affected by environmental stressors. The trial has a secondary aim of testing whether Si fertilisers can be used by farmers to allow greater diversity in their cropping system and grow crops that otherwise would be considered unsuitable where a drying profile and heat stress occur in spring and impact crop performance, such as winter wheats, dual purpose crops, canola and legumes.
Paddock Details
Location:
Crop year rainfall (Nov–Oct): 497mm (decile 10)
GSR (Apr–Oct): 384mm (decile 10)
Long term average rainfall (Nov–Oct): 352mm
Long term average GSR (Apr–Oct): 236mm
Soil type: Sandy Clay
Paddock history: Lentils, 2021
Trial Details
Crop type/s: Refer to Table 1
Treatments: Refer to Table 1
Target plant density: 130 plants/m² (spring wheat and barley), 100 plants/m2 (winter wheats and dual-purpose winter wheat)
Seeding equipment: Knife points, press wheels, 30cm row spacing
Sowing date: 5 May 2022
Replicates: Four
Harvest date: 17 December 2022
Trial Inputs
Fertiliser: 200kg/ha of urea was applied using a split application (100kg 3/06/2022, 100kg 11/07/2022)
Refer to Table 2 for silicic acid fertiliser application
Trial managed as per best practice for pests, weeds and disease.
Method
A replicated field trial was established at Nullawil, Victoria, on a clay loam using a randomised complete block design. Two spring varieties were grown for grain only (Table 2), while two winter varieties were used for grain only, graze and grain and received a foliar spray of the micronutrient mix, Generate. All treatments had +/- silicon to determine impacts on crop biomass, NDVI, grain yield and quality. Due to water logging, the legume trial was abandoned before harvest in 2022.
Results & Interpretation
Seasonal conditions
Growing season rainfall at Nullawil was high when compared to the long-term average, reaching decile 10. April rainfall of 44.2mm provided ideal conditions for sowing and crop establishment (Figure 1). May, June and July had lower than average rainfall, but late season rainfall in August, September and October totalled about 275mm, 176mm more than the long-term average (Figure 1). This created optimal conditions for the grain fill period, limiting the ability to test the key attributes with silicon application.
Silicon application effect on crop performance
Silicon application had no effect on NDVI readings, peak biomass or grain yields (Table 3). These results are not unexpected, as silicon plays a role in heat and moisture stress mitigation, both of which were not encountered in 2022. It highlights that silicon under ideal growing conditions has no influence on crop performance as it was not a limiting component. To test its ability to help crops cope with moisture and heat stress, it will be important to repeat this research over multiple seasons with different climatic conditions to determine if it has commercial application for the proposed use.
Performance of dual purpose (graze and grain) treatments compared to grain-only treatments.
There was no significant difference in grain yield between dual purpose treatments and grain only treatments, regardless of product application (Table 4). The 2022 growing season and soft spring provided good conditions for grazing recovery, not limiting grain production even if crops were grazed.
Winter wheat performance compared to Scepter
The winter wheat variety LTU001-092 had no significant yield difference to Scepter and yields of winter wheat varieties were not influenced by silicon application (Table 5). Seasonal conditions must be taken into account when interpreting this result. High rainfall in the last three months of the growing season (Figure 1), provided good conditions for the later maturing winter wheats to reach higher yields. Years when rainfall totals are closer to the long-term average generally favour spring wheats such as Scepter over winter wheat varieties as the season cuts off quickly during grain fill. This would be the situation in which the application of silicon could be tested, but did not apply in 2022. LTU001-39 had a significantly lower yield than Scepter and LTU001-092 regardless of silicon application (Table 5).
This suggest LTU001-39 may not be as suited to the Mallee region
Nitrogen response
An interaction between variety and nitrogen rate indicated there were different sensitivities by varieties to applied N (Figure 4).Across the nine varieties, hay yield increased as N rate increased (Figure 4). All varieties responded when N rate increased from 30 to 60kg N/ha. Hay yield was optimised for Carrolup and Koorabup at 60kg N/ha, while other varieties responded to an N rate increasing from 60 to 90kg N/ha. Largest responses to increasing N from 30 to 60kg N/ha were by Vasse, Yallara and Koorabup, and to increasing N from 60 to 90kg N/ha were Vasse, Brusher and Wintaroo.
Commercial Practice and On Farm Profitability
Role of Silicon in conventional spring wheat and barley
Moisture and heat stress can be major yield limitations in Mallee cereal crops, particularly in spring when rainfall becomes limiting and the soil profile dries as the crop is trying to fill grain. Glasshouse and field research by the University of Melbourne has shown silicon fertiliser has the potential to increase wheat yields under drought and heat stress, however 2022 provided good cereal growing conditions well into the spring grain filling period. The outcomes of this trial suggest silicon offers no additional crop benefit where environmental stressors are removed, but further research on Si fertilisers during years with greater crop stresses will provide valuable information on their fit in the system and where the biggest gains, if any, can be made.
Even if a fit is found, there are other considerations. For uptake to be feasible, there must be development in silicon fertiliser products. The labels of currently available products indicate four to six applications are required, which is unrealistic for broadacre farms.
BCG will undertake further research into the role of silicon fertilisers in 2023. This research will include work on cereals, pulses and canola
References
Porker K., 2019, 2019 BCG Season Research Results, ‘Management of flowering times and early sown slow developing wheats’ pp. 58–64.
Zhu, Y. and Gong, H., 2014, Beneficial effects of silicon on salt and drought tolerance in plants. Agronomy for Sustainable Development, 34(2), pp. 455–472
Acknowledgements
Redesigning of Broadacre Farming Systems — this project is funded by the Australian Government’s Future Drought Fund.
