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Is magnesium (Mg) important for winter wheat yields and quality, and what’s the best course of action if a deficiency occurs?
As wheat yields have increased over the years, more Mg has been removed from the soil, raising the question as whether this impacts future yields and quality.
In wheat, Mg drives photosynthesis, protein synthesis and carbohydrate metabolism, so researchers have wanted to find out if a soil Mg deficiency could affect wheat yield and protein content. Magnesium may also help water use efficiency.
Between 2003 and 2020, New Zealand farmers’ wheat yields increased 60 per cent on average (from 7.48 t/ha to approximately 12 t/ha), due to improved cultivars and agronomic management. But as yields have increased, so too has the amount of Mg removed from the soil, and anecdotal reports of Mg deficiency.
While wheat only requires a small amount of Mg which can usually be met by soil reserves, researchers have focused their attention on the issue of low soil Mg levels due to the possible impact on yield and quality.
What the science says
For most arable crops such as wheat, a soil Quick test (QT) of Mg > 10 has traditionally been considered sufficient. However, in research on Mg on winter wheat in 2001, even when Mg soil levels were relatively low (QT Mg of 3–4) applying Mg did not increase wheat yield or quality1.
These results were echoed in a 2020 Mg trial, which assessed the timing (autumn/spring), type (slow/quick acting), and rate of Mg (0–75kg Mg/ha) on yield and quality of winter wheat on soil with an average of QT 9 Mg (still below the optimum for arable production). The various Mg fertiliser treatments once again made no significant difference to yield or quality, but applying Mg fertiliser did increase Mg concentration in herbage2.
The optimum herbage level for wheat is thought to be 0.10 to 0.16 per cent Mg, but in early spring in New Zealand it is not uncommon for Mg herbage concentrations to be below 0.10 per cent, generally due to wheat’s slow uptake of Mg during the cooler weather.
Recommendations for Mg on winter wheat
When soil QT Mg levels are maintained sufficiently for other crops or pasture grown in rotation with wheat, Mg is unlikely to limit yield or quality of wheat, as wheat appears to be more tolerant of low Mg levels.
However, if farmers are concerned about a low winter wheat herbage Mg concentration, they have two options based on previous trial work. The first is to apply 50 kg Mg/ha in spring in the form of Kieserite.
Alternatively, 25 kg Mg/ha in the form of Serpentine Super can be applied in autumn and an additional 25 kg Mg/ha in the form of Kieserite in spring. Serpentine Super is 5 per cent Mg and is a source of
phosphate and sulphur required by wheat.
Studies carried out by the Fertiliser and Lime Research Centre have shown the release characteristics of the Mg in Serpentine Super. Serpentine Super was still releasing Mg for plant uptake 30 months after application. Herbage from plots treated with Serpentine Super contained 57 per cent more Mg than herbage from control plots, indicating fertiliser Mg uptake by plants3.
Other Mg fertilisers such as dolomite could also be considered in the autumn, depending on the cost-effectiveness of the Mg, and if liming is required.
For more information, contact your local Ruralco Representative or Ballance Nutrient Specialist.
1 Craighead M 2001. Magnesium deficiency in crops and its relevance to arable farming in New Zealand - a review. Agronomy NZ 31: 2001
2 Brooker TP, Dawson AE, Field CG 2021. Does the timing and rate of magnesium fertilisers affect yield and quality of winter wheat? Agronomy New Zealand 51: 2021
3 Loganathan P, Hanly JA, Currie LD 2005. Effect of serpentine rock and its acidulated products as magnesium fertilisers for pastures, compared with magnesium oxide and Epsom salts, on a Pumice
Soil. 2. Dissolution and estimated leaching loss of fertiliser magnesium, New Zealand Journal of Agricultural Research, 48: 461–71