Manganese

Function of Manganese

Manganese (Mn) has many important functions in plants, particularly as an activator of various enzyme systems involved in plant metabolism including chlorophyll synthesis. Cereals are susceptible to manganese deficiency and yield losses of up to 30 – 60% can occur if severe manganese deficiency is left untreated. Slight to moderate or transient deficiencies can also occur on imperfectly drained, heavier textured soils, due to poor rooting. Mn deficiency is usually induced by availability, rather than an absolute shortage (except in severely leached loamy sands) of Mn in the soil.

Deficiency risk

1. High soil pH (over liming) and high organic matter content. 
2. Restricted rooting due to impeded drainage or compaction. 
3. Loose, unconsolidated seedbeds and poor root-soil contact.
4. Low soil temperatures, poor light conditions or dry top soils.

The occurrence and severity of manganese deficiency consequently depends on the seasonal combination of these factors, as well as susceptible soil types.

High K will increase crop Mn requirement. High soil Cu will reduce Mn availability.

Mn & Soil pH

As the pH rises manganese becomes less available to the plant.  Thus, increasing the soil pH above 6.0 increases the risk of manganese deficiency when the easily reducible manganese level is less than 85 mg/kg. When the soil pH is greater than 7.0 an E.R. manganese value of less than 65 mg/kg will probably produce manganese deficiency.

Deficiency Symptoms

Deficiency Symptoms, sometimes called ‘grey speck’, first appear on older leaves as interveinal yellowing with grey or buff coloured streaks, mainly on the basal halves of affected leaves and often most severe near the margins.

The deficiency shows up as patches of pale growth and, if left untreated, affected leaves may wither.

Diagnosis & Treatment

Manganese deficiency can be diagnosed from knowledge of crop symptoms, susceptible soil types and field history. Leaf analysis will confirm a deficiency and is a cheap diagnostic test compared to the cost of Mn application. Soil analysis is a poor and not a reliable guide to diagnosis or prediction of Mn deficiency.

Foliar application – Good crop response

• Chelated products which offer advantages of much greater compatibility with other agrochemicals, better solubility and no risk of crop scorch but supply less Mn. 
• Inorganic suspensions; these proprietary products are based on Mn sulphates, carbonates, as a flowable suspension, together with stickers & wetters in a tank mixable formulations.

In Scotland, combine drilling with ammonia–N compounds has been shown to reduce the severity of Mn deficiency in spring barley, due to localized acidifying effects of the fertiliser and associated increase in Mn availability during early root growth

Spring Cereals

To maximize crop uptake and response to foliar Mn –

Split apply 

1^st 50% at GS 12 – 25

2^nd 50% at GS 31/31.

Winter Cereals

Autumn, as well as spring, Mn sprays are need on cereals (esp. oats) if deficiency symptoms develop during the autumn, as deficient crops will be prone to frost damage and winter kill. Apply foliar Mn at GS 25 in fields where moderate to severe Mn deficiency is a known problem in most years. Spring application of Mn to winter cereals should be applied by GS 31.