Monitor spring crops for trace element deficiencies
Weather conditions over the past 10 days have really provided the ingredients for rapid spring crop growth.
With longer sunny days and improving air temperatures, there has been an exponential increase in demand for major and minor nutrients, explains Mark Plunkett, Teagasc Soil and Plant Nutrition Specialist.
At this stage, all crop major plant nutrient applications (N, P, K & S) maybe complete. Now is a good time to monitor crops for minor nutrients such as copper, manganese and zinc and put a plan in place where known deficiencies exist. Where spring crops were not rolled after sowing, aim to roll now to firm up seedbeds and improve nutrient supply.
Spring barley tends to be the most sensitive crop when it comes to nutrient deficiencies, as its rapid growth habit demands nutrients quite fast when favourable conditions arrive.
Soil test results are a very reliable indication of the soil supply of both copper (Cu), zinc (Zn) and magnesium (Mg). The soil test is not as reliable for manganese (Mn) supply; other factors have a greater influence on the soil’s supply such as soil, seedbed and weather conditions. Visual symptoms of nutrient deficiencies may appear and it can be difficult to identify in field deficiencies. Recent soil test results will help in identifying specific nutrient deficiencies - especially for copper, zinc and magnesium - which maybe more difficult to identity compared to a manganese deficiency.
Manganese deficiency tends to be the most wide spread trace element that we encounter, especially in spring barley crops, at this time of the year. Manganese 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 the 2 to 4 leaf stage and repeat depending on soil/crop symptoms. It may be necessary to repeat depending on the intensity of the deficiency.
At this time of the year, both weather and seedbed 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.
Figure 1: Manganese deficiency in barley shows interveinal browning / necrosis on the leaf
Zinc (Zn) 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 and 7, this 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 have been reported to reduce the availability of Zn. Zinc deficiency is also associated with continuous tillage soils, with low soil organic matter levels and can be quite difficult to identify (see Figure 2). 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).
Figure 2: Zinc deficiency in barley shows pale yellowing from the base of the emerging leaf
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. However, 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 (see Figure 3). Consult soil test results and apply a foliar Cu at the 2 to 4 leaf stage and repeat at GS 30 to 31.
Figure 3: Copper deficiency in spring barley shows leaf tips twisting and tipping (browning)
Magnesium is a secondary nutrient and a typical spring crop requires ~ 20-25 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.
Figure 4: 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.
The Teagasc Tillage team provides regular updates on crop management in the weekly Tillage Edge podcast. You can access the podcast here.