Early defoliation and nitrogen fertilization: effects on maize morphophysiology and production

Abstract Early-stage defoliation represents a mechanical stress with increasing relevance in intensive cropping systems. This study investigated the morphophysiological responses and compensatory capacity of maize subjected to early defoliation and nitrogen (N) top-dressing management. The experiment was conducted under greenhouse conditions using the hybrid KWS 9668 VIP 3 grown in pots. Plants were subjected to a 5-cm shoot removal at the V4 stage, combined with N top-dressing (80 kg ha⁻¹) applied at the V4 or V6 stages, alongside non-defoliated controls. Under the evaluated conditions, defoliation at V4 transiently modified biomass accumulation and root architecture but did not impair final grain weight. These physiological adjustments were characterized by increased nitrate reductase activity and stomatal conductance, which supported recovery despite reduced water-use efficiency and biochemical limitations to photosynthesis. Nitrogen top-dressing increased final shoot and root biomass, the percentage of biomass allocated to the roots, and enhanced root surface area and volume. Furthermore, N fertilization led to higher grain weight and grain nitrogen content. These results indicate that N top-dressing is essential for optimizing morphophysiological performance and enhancing yield, acting as a primary factor in plant recovery. However, these findings are restricted to the controlled greenhouse environment and the single hybrid studied. Field-scale studies are necessary to validate these responses across diverse edaphoclimatic scenarios.