Summary

Trials were run at iron deficient sites on Yorke Peninsula to assess crop responses to iron using different application methods and forms. Iron application using current grower technology was also investigated. No crop or grain yield responses to soil or foliar iron applications were observed in any of the trials in this single season. In a season like 2023, crops grown on calcareous soils in northern YP are not iron deficient and therefore grain yield increases from iron applications are unlikely.

Background

Advancements in iron fertiliser formulations have delivered significant yield gains on calcareous soil types in South East of South Australia by correcting iron deficiency. This project investigated if iron deficiency was yield limiting on the calcareous soils of Northern Yorke Peninsula. Responses to applied iron in was investigated in both replicated and on farm demonstration trials, in paddocks identified as iron deficient by current soil testing guidelines (<10mg/kg Fe 0-10cm).

Research Aims

The core objectives of the project were to:

• Test crop responses to iron using different iron application methods and forms at two sites characterised as being iron deficient by current soil testing guidelines.
• Investigate if the current iron (Fe) soil test critical values for a 0-10cm test, for wheat and lentils are accurate.

In The Field

Current soil test guidelines suggest iron levels below 10mg/kg will impede the performance of crops. Based on this guideline, two iron deficient sites were selected on the Yorke Peninsula for field trials. Both sites were alkaline, had high phosphorus buffering index (PBI), low phosphorus and high levels of calcium carbonate.

Replicated field trials were used to assess crop responses in both wheat and lentils to different iron application methods, forms and rates in a wheat trial near Kulpara and lentil trial near Thomas Plains, SA. Iron was applied at sowing and as foliar applications at multiple timings in season.

Two demonstration sites were set up at Warooka SA on highly calcareous soil to assess iron application via farmer scale equipment. At one site, strip applications comparing two forms of iron and a trace element product were applied at seeding. At the other site, iron was applied with the fungicide at flag leaf stage to 20 hectares of an 80 hectare paddock.

Results

Replicated trials

At crop maturity, no significant response to iron applied at sowing or via foliar applications was recorded in either trial. No relationship between yield and iron was observed and no increases in grain iron concentrations were recorded. Although the finish to the 2023 season was not favourable, none of the in-season assessments such as NDVI or plant tissue analysis indicated that applying iron improved crop performance.

Demonstration trials

In the trial where iron was applied in strips at sowing, strips were scored for biomass production in-season and no visible differences between the treated strips and adjacent untreated strips were recorded. Due to logistical issues, strips were not harvested.

In the trial where iron was applied at flag leaf stage, the yield map from the paddock was analysed post-harvest and no yield improvement was evident in the treated compared to untreated areas of the paddock.