Sunflower Photosynthetic Characteristics, Nitrogen Uptake, and Nitrogen Use Efficiency under Different Soil Salinity and Nitrogen Applications

Understanding salinity and fertilizer interaction is of great importance to improve crop production use efficiency in saline areas. To evaluate the interactive effects different soil levels nitrogen (N) applications rates on sunflower photosynthetic characteristics N uptake efficiency, a two-year field experiment was conducted Hetao Irrigation District, China. The consisted three initial (IS) expressed as electrical conductivity saturated extract (ECe) (S0: 1.72–2.61 dS/m; S1: 4.73–5.90 S2: 6.85–9.04 dS/m) four (45, 90, 135, 180 kg/ha), referred N0–N3, respectively. results indicated that net rate (Pn) sunflowers treated with S0 S1 both had significant decrease bud stage, then reached their maximum at anthesis. However, during cycle, Pn S2 level only small fluctuations still remained high (>40 ?mol CO2/(m2 s)) early mature stage. When increasing IS from S1, plant (PNU) under same were decreased by less than 10% maturity, whereas decline expanded 17.2–45.7% S2. Additionally, though applying N2 could not increase PNU levels, its better those N3. Meanwhile, level, application N0 produced higher productive (NPE) (NUPE) other rates. Therefore, our study proposed recommended (S0 135 kg/ha, 45 kg/ha) for conditions.