Exploring optimal fertigation strategies for orange production, using soil–crop modelling

• We explored fertigation strategies for improving water and N use efficiency in orange production.
• There are strong interactions between water and N input in crop yield and N loss.
• Improving N split strategy can significantly increase crop yield and reduce N loss.
• Model simulations can provide good guidance for improving fertigation strategies.

Water and nitrogen (N) are two key limiting factors in orange (Citrus sinensis) production. The amount and the timing of water and N application are critical, but optimal strategies have not yet been well established. This study presents an analysis of 47 fertigation strategies examined by a coupled soil–crop model. The strategies include 27 main scenarios with a factorial design of 3 irrigation levels (420, 520 and 640 mm, representing 80%, 100% and 120% of water demand), 3 N input levels (100, 200 and 300 kg ha−1) and 3 main N split applications, and 20 additional scenarios testing alternative N split applications, extreme rainfall years (dry and wet) and different soil textures.The simulations showed that orange yields were strongly influenced by N input and N split applications, but not so much by irrigation. Increasing water and N input led to increased N losses (via leaching and denitrification), and there were significant positive interactions between water and N input with respect to N losses. On average, low N input (100 kg ha−1) led to relatively low N losses (16 kg ha−1) but resulted in low yield (33 t ha−1, 25% yield reduction). High N input (300 kg ha−1) produced a high yield (43 t ha−1) but led to large N losses (104 kg ha−1). Optimal N input (200 kg ha−1) significantly reduced N losses (45 kg ha‐1) without yield reduction. Importantly, with optimal N input, improving N split applications significantly increased yield by 13% and reduced N losses by 40%, compared to sub-optimal N splits.Significant interactions between water inputs, N inputs and N split applications in yield and N losses indicate that the optimization of fertigation strategies must consider these three key variables simultaneously. Our results clearly show that over-optimal water and N inputs lead to large water and N losses. Reduced irrigation (80% of water demand) and N input equal to N demand (200 kg ha−1) can significantly reduce N losses without yield reduction. The N split applications should be adjusted to the N demand of the crop during the growing season. Our study focused on a Mediterranean climate, but the methodology and results can be applied to other situations in the world.