Foliar Nanoparticulate Sulphur and Amino Acids Modulate Wheat Yield Components and Seed Quality Across Contrasting Environments

Wheat productivity and seed quality are often constrained by nutrient imbalances and environmental stress, which can be mitigated through biostimulants and nanofertilisers. This study evaluated the effects of foliar applications of nanoparticulate sulphur (SNP) and hydrolysed amino acids (AAs) on wheat agronomic performance and seed quality under contrasting environmental conditions in Paraná, Brazil, during the 2022 and 2023 growing seasons. The experiment was conducted in four environments, using a randomised block design, with a 5 × 2 factorial scheme and four replications. Parameters included grain yield, yield components, and physiological and nutritional seed traits. SNP positively influenced the number of grains per ear and spikes per metre, with quadratic responses peaking at 1.048 kg ha^-1 for SNP and 0.347 kg ha^-1 for S, respectively. However, AAs showed no significant effects, likely due to favourable climatic conditions and high soil fertility. Regarding seed quality, a positive response in seed vigour was observed at 2 kg ha^-1 SNP in one environment, while other parameters showed no consistent improvement. Principal component analysis indicated that environment and soil fertility were the main sources of variation in yield and seed quality. Overall, foliar SNP and AA applications did not markedly enhance wheat performance under non-stressful conditions.