Densidade, adubação nitrogenada e marcha nutricional em girassol de corte

Abstract

This thesis investigated the optimization of production and post-harvest quality of cut sunflower (Helianthus annuus L.), cultivar 'Vincent’s Choice', within the context of floriculture market demands. The research sought to provide information on the agronomic management and specific nutritional dynamics of this cultivar, which is distinct from those intended for grain production. The study was structured into two complementary chapters that addressed the effects of management factors and the characterization of the nutrient uptake rate. In the first chapter, the impacts of two planting densities (20 and 32 plants m⁻²) and six topdressing nitrogen fertilization doses (0, 10, 20, 30, 40, and 50 g N m⁻²) on production and post-harvest longevity were evaluated. The results evidenced a significant interaction between density and N doses on the capitulum diameter. Only the combination of low planting density (20 plants m⁻²) with the maximum nitrogen dose (50 g N m⁻²) enabled obtaining flower heads with an average diameter exceeding 60 mm, qualifying the floral stems for the commercialization standard (Veiling Holambra Standard). In contrast, stem longevity, the onset of yellowing, and the dropping of ray florets—post-harvest characteristics—were not significantly altered by the treatments, suggesting that such attributes are predominantly determined by the cultivar's genotype. The second chapter determined the dry matter accumulation and the uptake rate of macro and micronutrients in the shoot of the 'Vincent’s Choice' cultivar. Dry matter accumulation followed a sigmoid pattern, with the stem becoming the main biomass storage organ at 36 days after emergence (DAE), surpassing the leaves. Potassium (K) was the most accumulated macronutrient (2,316 g plant⁻¹), followed by nitrogen (N) (1,058 g plant⁻¹). Among the micronutrients, manganese (Mn) and zinc (Zn) showed the highest accumulations. The analysis of the Inflection Points (IP) revealed that the maximum daily absorption rate of N and K occurred, respectively, between 32.85 and 33.95 DAE, a critical period of high nutritional demand spanning the vegetative and the beginning of the reproductive stages. Additionally, the remobilization of Phosphorus (P), Magnesium (Mg), and Copper (Cu) from the leaves and stem to the capitulum was observed in the final stages of the cycle, as well as a preferential allocation of K in the stem, a fundamental factor for the rigidity and structural quality of the floral stem. The results of this thesis provide unprecedented scientific evidence for the formulation of precision fertilization programs and for the inclusion of the crop within the parameters of Floriculture 5.0. The research emphasizes the importance of adjusting planting density and synchronizing the supply of inputs with the periods of maximum physiological demand, aiming to optimize management, ensure the commercial quality of 'Vincent’s Choice' stems, and align high-performance productivity with sustainability in national floriculture.