Summary

Detailed field trials showed mobility of sulphur from recent applications can be quite high and is influenced by soil profile characteristics. Growers should not assume that available sulphur forms applied in the previous season are still accessible, as in certain seasons or soil profiles, sulphur could have moved out of reach of root systems.

Background

Growers need more information on immediate and longer-term sulphur management options in various soil profiles and growing conditions. This project investigated the mobility and availability of different sulphur forms in sand compared to loam soil profiles to improve growers’ understanding of sulphur dynamics and budgeting.

Research Aims

The core objectives of the project were to:

• Compare different forms of sulphur fertilisers for mobility and availability within soil profiles with detailed profile sampling.
• Examine the impact of two different crop types in sulphur accessibility due to varying rooting depths.

In The Field

Two replicated trials were conducted in collaboration with Trengove Consulting – one trial on a predominantly loam soil profile and the other on a sand soil profile. Season 2022 was a decile 8-9 season and 2023 a decile 5 season which provided the opportunity to examine sulphur mobility across seasons at the two contrasting sites.

In 2022, both sites were sown to wheat and elemental sulphur, sulphate of ammonia (SOA) or gypsum were applied at increasing rates. In 2023, both sites were sown to barley with both fresh applications and residual treatments implemented. Detailed soil sampling was conducted before and after each trial in each season.

Results

No significant increase in NDVI or plant sulphur concentrations that could be attributed to sulphur were recorded in 2022 or 2023. No significant treatment effects on grain yield were recorded despite the high yields meaning a reasonable demand for soil sulphur in relatively low background soil sulphur profiles, particularly at the sand site. The treatment x sulphur rate interaction was significant at the loam site, but this was attributed to the negative effects of the two highest rates of SOA. The treatment x sulphur rate was not significant at either site in 2023 with grain yields still high.

No significant increase in grain sulphur concentrations was recorded with any sulphur treatment and there were no differences in overall sulphur uptake or removal from the paddock.

SOA and gypsum sulphur forms were both highly mobile and moved freely through the soil profile in the moderate to high rainfall received during 2022 and 2023. The majority of SOA applied in the 2022 season moved to the 60-80cm layer at the sand site and to the 20-40cm layer at the loam site. At the end of the 2023 season, the sulphur had moved beyond 1m of the profile at the sand site and reached 40-60cm in the loam site. No significant increases in profile sulphur levels were recorded with elemental sulphur.