Tillage Update 12th May 2022
Mark Plunkett, Soil & Plant Nutrition Specialist, Teagasc, Johnstown Castle, Wexford has advice here on Spring crops and trace elements. He emphasises the importance of soil analysis before going on to discuss manganese, zinc, copper and magnesium deficiencies in detail
Recently favourable weather conditions has really provided the ingredients for rapid spring crop growth. As we move into peak plant development over the coming days and week’s nutrient demand will increase exponentially due to the good growing conditions. At this stage all crop major plant nutrient applications (N, P, K & S) may be complete. Now is a good time to monitor crops for minor nutrients such as copper, manganese and zinc.
Soil analysis
Soil test results are a very reliable indication of the soil supply of both copper (Cu) and zinc (Zn). The soil test is not as reliable for manganese supply. Where trace element deficiencies are present in a crop refer to recently taken soil sample results as it will help in identifying the trace element deficiency especially for copper and zinc, which maybe more difficult to identity compared to a manganese deficiency.
Manganese
Manganese deficiency tends to be the most wide spread trace elements that we encounter especially in spring barley crops at this time of the year. Manganese (Mn) deficiency tends to be most prevalent on sandy or lights soils, recently limed or high pH (>pH 7.0) soils, poorly consolidated seedbeds or under extremes of weather conditions such as dry and cold conditions. Where trace element deficiencies are anticipated based on soil test results (<50 mg/l) or there is a history of deficiency apply foliar manganese at 2 to 4 leaf stage and repeat depending on soil / crop symptoms. At this time of the year, both weather and soil conditions will have a large influence on soil manganese availability. For example under dry and cool conditions soil Mn availability will be reduced while improving soil temperatures and moisture will increase soil Mn availability thus plant uptake.
Manganese deficiency in barley shows Interveinal browning / necrosis on the leaf.
Zinc (Zn)
Zinc deficiency is the second most spread trace element. Soil analysis is a very reliable indicator of soil Zn supply and very useful in identifying which fields need treatment during the growing season. Where soil test results show a Zn level of <1.0 mg/l and the soil pH between 6 to 7 indicates that a Zn deficiency is likely in cereals. Zinc deficiency tends to be associated with loose unconsolidated seedbeds due to poor root to soil contact. High soil P and high soil pH reduce the availability of Zn. Zinc deficiency is also associated with continuous tillage soils withlow soil organic matter levels. Where a Zn deficiency is anticipated or present in a crop, apply a foliar Zn application between 2 to 4 leaf stage up to GS 31 (1st node).
Zinc deficiency in barley shows pale yellowing from the base of the emerging leaf.
Copper (Cu)
Copper deficiency is common in cereals but not most widespread. Copper deficiency may be due to low soil availability or low total soil copper and is problematic on light, acidic soils, low soil organic matter, granite parent materials, peaty soils and dry soil conditions. The soil test is a very reliable indicator of soil availability. On heavy textured soils Cu deficiency is not likely unless the soil Cu falls below 1 mg/l, whereas on light textured soils, a deficiency may occur in soils containing up to 2.5mg/l. Copper deficiency symptoms can go unnoticed; symptoms associated with a server deficiency are leaf twisting and white leaf tipping and tend to appear in the youngest leaf. Consult soil test results and apply a foliar Cu at the 2 to 4 leaf stage and repeat at GS 30 to 31.
Copper deficiency in spring barley shows leaf tips twisting and tipping (browning).
Magnesium (Mg)
Magnesium is a secondary nutrient and a typical spring crop requires ~ 20 to 25 kg Mg/ha/year. Magnesium deficiency is generally not an issue only on very deficient soils. Here in Ireland ~ 20% of the soils tested are low in Mg. Magnesium has an important function in plants, as it is part of the chlorophyll and is a transporter of plant assimilate. Deficiency symptoms shown in figure 4 are on a soil of know Mg deficiency (Laois) and require annual treatment. On less susceptible soil types deficiency symptoms can appear due to poor seedbeds or root growth / dry and cool weather conditions. Research would show that it could be difficult to get a yield response to foliar Mg applications. Treat crops with soil test results are < 50 mg/l (Index 1 or 2). Magnesium deficient soils can be corrected with magnesium limestone or Mg containing fertilisers. Magnesium can be foliar applied as a chelate or inorganic formulation when symptoms appear. Mg sulphate is widely used to correct a Mg deficiency due to its low cost and also adds a small quantity of sulphur.
Magnesium deficiency in spring barley shows beading of the chlorophyll and leaf yellowing.
Over the coming days and weeks assess spring crops on a regular basis for trace element deficiencies and treat crops as soon as possible with a foliar application to prevent any grain yield reduction.
Find out more information and advice from the Teagasc Crops team here. The Teagasc Crops Specialists issue an article on a topic of interest to tillage farmers every Thursday on Teagasc Daily. Find your local Teagasc office here