Crop performance: It’s not all about nitrogen, phosphate and potash

Nitrogen, phosphate, and potash are well-known nutrients that play a crucial role in crop performance and yield. However, relying solely on these three elements can lead to missed opportunities for maximizing productivity, especially in modern agricultural systems where every unit of fertilizer must deliver a return. A closer look reveals that other nutrients, such as sulphur (S), magnesium (Mg), and manganese (Mn), also play significant roles in crop health and yield.

Sulphur (S) is increasingly important in contemporary farming practices, particularly on light soils, continuous tillage rotations, and fields with low organic matter. Its deficiency can be subtle, manifesting as a slight yellowing of the youngest leaves without necrosis. To address this, Teagasc recommends applying 15-20kg S/ha as part of a compound fertiliser between the GS 28–31 growth stages, ideally alongside nitrogen. This approach not only helps maximize nitrogen use efficiency but also enhances overall yield response.

Magnesium (Mg) deficiency, while less common, can occur on soils with low Mg levels (<50 mg/l), especially where soil pH is high or potassium levels are elevated. Light soils, compaction, and poor soil structure can further limit magnesium availability. Symptoms of magnesium deficiency include interveinal chlorosis on older leaves and the characteristic “beading” of chlorophyll. Deficiency can often be temporary, appearing early in the season when root growth is restricted and easing as roots develop.

In cases where liming is necessary, magnesium limestone is the most effective long-term solution. For soils not requiring lime, magnesium can be maintained through Mg-containing fertilisers every 3–4 years. When deficiencies occur in-season, magnesium sulphate (Epsom salts) or Mg chelates can be applied as a foliar spray. Magnesium sulphate is commonly used due to its low cost and added sulphur benefit.

Manganese (Mn) deficiency is one of the most widespread issues in cereals, particularly in areas with acidic soils or where manganese levels are naturally low. This deficiency can lead to stunted growth, poor grain filling, and reduced resistance to diseases and pests. To mitigate manganese deficiency, farmers can apply manganese-containing fertilisers, particularly in soils with a pH below 5.5. In some cases, soil amendments such as lime or dolomite can help improve manganese availability.

Overlooking these nutrients can quietly limit yield potential, particularly when fertiliser costs are high and every unit applied must deliver a return. As agricultural systems become more intensive and reliant on efficient nutrient use, it is essential for farmers to consider the role of sulphur, magnesium, and manganese in addition to the traditional trio of nitrogen, phosphate, and potash. By doing so, they can unlock the full potential of their crops and ensure sustainable, profitable farming practices.

In conclusion, while nitrogen, phosphate, and potash are undeniably vital for crop performance, it is crucial to recognize the importance of other nutrients such as sulphur, magnesium, and manganese. By addressing these elements, farmers can optimize their crop yields, reduce fertiliser costs, and promote sustainable agricultural practices. As the demand for food continues to grow, understanding the complex interplay of nutrients will be key to meeting the challenges of modern farming.