Assessment of nitrogen diagnosis methods in sunflower

Nitrogen deficiency can severely limit sunflower (Helianthus annuus L.) grain yield and quality. Our objective was to evaluate N diagnosis methods based on: (a) pre-plant soil nitrate-nitrogen (NO3––N) test (PPSNT) mineralized in short-term anaerobic incubation (Nan), (b) Greenness index (GI) the normalized difference vegetation (NDVI) measured at 6 (V6) 12 (V12) leaves, (c) nitrogen concentration (Nc). Seventeen experiments were carried out between 2010 2019 Argentina, evaluating nine rates (0, 30, 40, 60, 80, 90, 120, 150, 160 kg ha–1). The GI, NDVI, sufficiency relative (NDVIr) determined V6 V12 growth stages. On average, response 492 ha–1 Nc 0.25% 9 11 responsive experiments, respectively. inclusion of Nan improved PPSNT method. critical availability (PPSNT + fertilizer N) threshold 115 for with low (<60 mg kg–1), 90 high (>60 kg–1). NDVIr allowed monitoring crop status a 0.95 threshold. adequately diagnosed deficiencies 2.26%. Also, predicted from ratio (R2 = .39). results would allow better estimate recommend adequate aiming optimize quality, minimize economic environmental cost fertilization.