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Root System, Phenology and Yield of Sunflower in Relation to Nitrogen and Phosphorus

Abstract Sunflower is a crop of world interest that is acquiring economic importance in Mexico. The aim of this study was to determine the effect of nitrogen (N) and phosphorus (P) on the growth of the root system and its relationship with the canopy dry matter and yield and its components of sunflower (Helianthus annuus L.). The planting of cv. Victoria was conducted in Montecillo Mex., of temperate climate in a vertisol under conditions of seasonal rainfall on 16 May, with population density of 5 plants per m2. Treatments consisted in supply 0–200 kg ha−1 of N and P. The time to phenological stages was similar between treatment. The N and in minor degree the P increased grain yield (GY) and oil yield (OY) by increases in the grains number (GN), capitulum area (CA), canopy dry matter (CDM) and radical area (RA). In contrast, the P increase RDM but decrease the CDM/RDM relation. The effect of the interaction N * P on GY, OY indicates it is necessary to seek the best combination of N and P for increased the production of sunflower. The size grain and oil content in the grain did not change with N and P. The growth cycle was 122 days, with a seasonal ETc of 207 mm and 1,369°C d (Heat unit, HU).