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Nitrogen (N) deficiency could have a negative effect on sunflower (Helianthus annuus L.) yield and grain quality. Therefore, it is necessary to adjust the optimum rate, timing, and frequency of N fertilization to improve sunflower crop nutrition. Our objective was to evaluate the effect of N fertilization rate, timing, and splitting on grain yield, and grain and oil quality. Twelve field experiments were carried out between 2016 and 2020. Treatments consisted of at least three N rates ranging from 0 to 200 kg N ha−1 applied at V2. Moreover, the 80 kg N ha−1 rate was applied at V14 (80NV14) or split between V2 and V14 (80Nsplit). Treatments were evaluated in two sunflower genotypes, high oleic (HO) and conventional (CONV). A significant grain yield response to N fertilization was observed in six out of twelve experiments, generally at rates greater than 80 kg ha−1. The mean response to fertilization was 369 kg ha−1. Fertilization increased grain protein concentration (PG) (+1.5%) at experiments E1–E3 and E9–E12 and decreased oil concentration (OG) (−2%) at experiments E1, E4, E9, E11, and E12. The maximum N rate, increased oleic and stearic acid concentration (+3%–4%), depending on the genotype (AO and CONV). Neither fertilizer timing nor splitting affected grain yield or OG. Late N fertilization (V14) increased oleic acid (+2.4%), whereas it decreased linoleic acid (+2.2%). Based on our results, N fertilization can increase yield without negatively affecting commercial grain quality (OG and fatty acids concentration), regardless of fertilization timing and frequency. Core Ideas: Nitrogen fertilization at a rate >80 kg N ha−1 maximizes sunflower yield.Increases in N rate enhance oleic and stearic concentration.N fertilization at V14 increases protein concentration.Nitrogen timing and splitting do not affect yield nor grain quality. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is one of the nutrients that most limits agricultural production. Worldwide, the Pampas region has the highest edaphic P deficits. As its existence in the soil varies from ions in solution to very stable organic and inorganic compounds, it is necessary to carry out studies at different spatial-temporal scales to survey the most affected P fractions. The objectives of the present work were: a) to evaluate different P fractions before the agriculture introduction and the long-term changes in a typical Argiudol Pergamino series under two controlled situations with 35 and 105 years of continuous agriculture and, b) to evaluate long-term changes of these P fractions in the same soil series under the agriculture performed at regional level. The following P fractions were determined: total (PT), inorganic (Pi), organic (Po), and extractable P (Pe). The P reserves of the A horizon decreased 20 and 42% (PT), 20 and 58% (Pi) and 20% (Po) with 35 and 105 years of continuous agriculture, respectively, in relation to the reserves of PT, Pi and Po of the pseudo pristine situation. For its part, agriculture practiced at regional scale decreased by 29% (PT), 33% (Pi) and 20% (Po) compared to the pseudo-pristine situation. The Po declined in the first decades of agriculture. Subsequently, it would not contribute to crop nutrition. The PT reserve continued to decrease at inorganic fraction expense, visualized in the abrupt drop in Pe (92%), which was below the range of typical values reported for the rolling pampas sub region. The prevailing cropping system puts at risk the nutritional status of soils and the productivity of agroecosystems. [ABSTRACT FROM AUTHOR]