Find out the reasons why sulphur is important for your crops and pastures

Yet some early 2000s trials did not show much of a sulphur response in canola. It became a nutrient not of the highest priority for many agronomists and farmers. What is the full story?

A recent analysis of 76,000 soil and tissue tests conducted over three years by Incites Pivot confirms widespread sulphur deficiency.

A total of 30 per cent of soil samples were low, below six mg/kg (KCl40 soil test), and 90pc of tissue tests were below the normal sulphur range for canola.

This data, based on an enormous sample size, has recently been documented by Incitec Pivot Technical agronomist Clint Sheather.

He points out that tissue testing for in-crop analysis, and soil testing, mainly for pre-sowing fertiliser decision-making, is a verifiable and well-documented way of assessing likely sulphur deficiency, especially vital for crops like canola as well as for pasture legumes.

Mr Sheather notes sulphur is vital for plant growth.

In many areas, he stresses that three years of big crop removal via high yields means it is not a given that sulphur levels are in the optimum range.

Especially vulnerable, he stresses, are soils with low soil organic levels and lighter textured soils.

These soils tend to be naturally low in sulphur in both the top as well as in their subsoils.

Many heavier soils may naturally be on the low side for sulphur in the topsoil but often have good subsoil levels.

Compared to cereals, where documented sulphur fertiliser responses have been few for many cropping areas, canola has a far bigger sulphur requirement, and deficiencies are far more widespread and common.

Hence it is entirely possible sulphur fertiliser may not be required for a cereal crop but could well be for a canola crop.

Also important for all crops and pastures is if sulphur fertiliser programs are ignored, far more widespread and common deficiencies will occur.

Years ago, superphosphate was commonly used in pasture phases, and this explained the lack of response in many canola-growing situations.

With 11pc sulphur, superphosphate commonly left soils higher in sulphur after the pasture phase, with sufficient sulphur for cereals as well as for canola.

However, today many rotations no longer contain a pasture phase, hence no excess fertiliser sulphur for the cropping phase.

Secondly, most farmers are mainly using a combination of fertilisers like MAP, DAP and urea.

These have no (urea) or very little sulphur in them.

A third factor is that for many paddocks, yields have been high the last three years, with possibly another high one for southern areas in 2023.

And overall, crop yields tend to be far higher now than they were 20 to 30 years ago.

Widespread research by NSW DPI district agronomists and research agronomists during the 1980s and 1990s identified almost universal sulphur deficiencies in pastures where none to very little previous sulphur fertiliser had been added.

Where sulphur deficiencies are not addressed in pastures, plus other elements like phosphorus, legume growth is poor, and their ability to build soil nitrogen is poor, hence low-quality grasses, as well as commonly lower-performing grasses.

There are many options available for adding sulphur via fertilisers to crops and pastures.

For example, the old Starter 15, now marketed by Incitec Pivot as Croplift 15, contains 14.6pc nitrogen, 12pc phosphorus and 11.6pc sulphur.

Other companies have similar product choices.

Sulphate ammonia has 22pc nitrogen and 24pc sulphur.

DAP and MAP have less than 2pc sulphur.

Well before sowing crops like canola, as well as when assessing pastures, it is worth undertaking soil tests from a representative range of areas.

For cropping, it is also worth undertaking some deeper soil sampling to assess what level of sulphur (as well as elements like phosphorus and nitrogen) are in the subsoil.

Next week: Crown rot biggest 2023 cereal disease. Future control strategies.