Optimizing foliar N-fertilization in sugarcane depends on plant genotype and nitrogen concentration

Foliar N-fertilization (FNf) has emerged as a promising approach to synchronize plant nitrogen (N) demands and application timing, reducing the N losses to the environment associated with traditional soil-based fertilization methods. However, limited information exists regarding the effectiveness of FNf in sugarcane. This study aimed to optimize FNf in sugarcane by evaluating N-fertilizer recovery by the plant (NRP) and assessing potential toxicity effects. Four sugarcane genotypes were subjected to FNf using ¹⁵ N-urea at five nitrogen concentrations. NRP was assessed at five time points for roots, stalk, old leaves, ¹⁵ N-urea-fertilized leaves (¹⁵ NL), and unexpanded leaves (UEL). Leaf scorching, indicating FNf toxicity, was analyzed using morpho-anatomical and histochemical techniques. The results showed that FNf promoted high NRP, with an average recovery of 62.3%. Surprisingly, the redistribution of ¹⁵ N-urea did not follow the nitrogen uptake rate by sugarcane leaves, with an average of 41.3% of the total-NRP. The stalk emerged as the primary sink for ¹⁵ N-urea, followed by the UEL. Genotypes differed in the leaf scorching intensity, which increased with higher concentration of ¹⁵ N-urea. Genotypes also differed in the ¹⁵ N-urea uptake rate, down-regulated by the N content in the ¹⁵ NL. These findings emphasize that by carefully choosing the appropriate genotype and nitrogen concentration, FNf can significantly enhance N-fertilizer uptake, resulting in potential environmental and economic benefits.