February 22, 2021

Could your crops be running low on Manganese?

Applying manganese (Mn) fertilizer in the correct form (sulphate vs oxide) can be crucial to overcoming a Mn deficiency in your soil.

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Lupin crops can be particularly susceptible to Mn deficiency, resulting in split seed.

Lupin and cereal crops can both suffer from Mn deficiency and according to Geraldton based Summit Area Manager Shane Turner, it’s a nutrient issue that has made an unwanted return in recent years.

Figure 1: Geraldton Area Manager Shane Turner

Shane said Mn deficiencies can appear on a range of soils and is intensified where soil pH is alkaline (above pH 7) or has been recently limed with minimal incorporation.

“Mn deficiency in lupins is generally first seen as pale mottled young leaves or interveinal chlorosis,” he said.

“More severe deficiency can cause lupin leaves to develop brownish spots. Split seed disorder can cause yield losses of up to 70 % and is a very unfortunate outcome of Mn deficiency.

“In cereal crops, if growers see leaves that develop interveinal chlorosis or white necrotic flecks and blotches, it’s time to contact their local Summit Area Manager for proper identification.”

Soil testing for Mn is problematic in that it can be present in the soil and yet unavailable to the plant. This is because Mn in the soil can take on various forms with availability to plants dependent on oxidation state.

Manganese sulphate (as supplied in Summit MAP & Mn (figure 2) and the Legume Range) breaks down in the soil to release Mn2+ ions. Mn2+ is the only plant bio-available form of Mn, and is readily transported into root cells.

Figure 2: Summit MAP & Mn

Oxide forms are insoluble and unavailable. In any soil there will be a balance between soluble Mn2+ and insoluble Mn oxides.

In alkaline soil conditions, the oxidisation of Mn2+ to unavailable Mn oxide is favoured, which explains the lack of Mn uptake in high pH soils.

Mn is also relatively immobile in the soil, which explains why top-dressed Mn is so much less effective than when this element is placed with the sowing fertiliser below the seed.

Responding to the challenge of Mn deficiency in recent years, the Summit Field Research team has carried out field trials in lupins, wheat and barley comparing the impact of applying Mn in fertiliser in the sulphate form versus the oxide form.

Figure 3: Results from the Summit 2019 lupin Mn Eradu trial.

Supplying 3kg/ha of Mn in sulphate form roughly doubled the Mn concentration in plant stems compared with the Nil treatment or 3kg/ha of Mn in the oxide form.

7kg/ha of Mn supplied in these trials in the sulphate form was highly effective in improving Mn concentration in lupin stems and decreasing split seed occurrence in both Barlock and Jurien lupins at the trial site. Split seed is strongly correlated with Mn stem concentrations below 20mg/kg.

The results of our lupin trial at Eradu show a clear cut advantage to Mn supplied to crops in sowing fertiliser in the Mn2+ sulphate form (See figure 3). Similar trends were also seen in our wheat and barley trials.

Growers can contact their Summit Area Manager for more details on these trials or MAP & Mn based products.

Summit MAP & Mn Product Profile

  • MAP & Mn has 100% of its Mn supplied as plant available Mn sulphate.
  • An ideal cropping fertiliser, MAP & Mn can be used as a stand alone product or incorporated into blends to help alleviate soils deficient in Mn.
  • MAP & Mn is a fully compounded product formulated for superior handling and even nutrient distribution.
Figure 4: Summit cropping fertilisers that include Mn in the plant available sulphate form.

Legume, Legume Plus and Legume K are designed to supply legume crops with an ideal balance of nutrients. All fertilisers in this range are based on fully compounded Summit MAP & Mn, which is blended with other fertilisers to contain good quantities of Mn in the plant available form.