Declining Soil Sulphur: A Hidden Threat to Cereal Yield and Protein Quality

Over the past five decades, cereal production has increased largely through fertilizer-driven yield gains to meet rising global food demand. Sulphur (S) is an essential macronutrient required for plant growth and development, although its role in crop production has often been underemphasized compared with other major nutrients. Unintentional sulfur accumulation from atmospheric deposition has traditionally been sufficient for most crops, but recent trends indicate a steady decline in soil sulfur levels worldwide. This decline is largely attributable to reductions in atmospheric sulfur deposition, the widespread use of sulfur-free high-NPK fertilizers, and increased sulfur uptake by high-yielding crop varieties. Despite increasing yield losses associated with sulfur deficiency, sulfur fertilization remains inadequately adopted in many crop production systems. In cereals, sulfur deficiency not only reduces growth and yield but also alters the synthesis of sulfur-containing amino acids and storage proteins, thereby weakening grain processing, baking, and nutritional quality. Additionally, sulfur deficiency in cereal grains has emerged as a notable health concern. Nevertheless, sulfur fertilization alone may not effectively mitigate these challenges, as optimal sulfur uptake, distribution, and assimilation depend on precise synchronization with plant developmental stages through complex physiological processes. Further research on the genetic regulation of these physiological mechanisms is critical to enhancing sulfur use efficiency and sustaining cereal crop production systems in the coming years.