Bio and chemical fertilizers integration supplemented by biostimulants a sustainable way to reduce chemical inputs in rainfed wheat systems

A sustainable solution to reduce chemical inputs in rainfed wheat systems is to replace part of the chemical fertilizers with biofertilizers, combined with foliar application. During 2023-2024, a field experiment was conducted at two sites at research farms in Javanroud and Dehgolan, Iran. Five integrated fertilizer levels [100% chemical fertilizer (CF100), 75% CF + biofertilizers (CF75 + BF), 50% CF + BF (CF50 + BF), 25% CF + BF (CF25 + BF), and 0% CF + BF (CF0 + BF)] with three foliar applications (control, seaweed, and amino acids) were tested. A complementary pot experiment was conducted to assess treatment effects on root growth parameters specifically. Overall, in comparison to other treatments, CF75 + BF and CF100 improved root growth, physiological attributes, and grain yield and quality parameters. In all fertilizer integration strategies, foliar application of seaweed extracts and amino acids improved plant performance indicators. The CF75 + BF treatment, supplemented with seaweed foliar application, achieved maximum chlorophyll levels (2.35 mg g^{─ 1} FW), membrane stability index (82.69%), relative water content (84.50%), peroxidase activity (0.307 unit mg^{─ 1} protein), biological yield (10,183.7 kg ha^{─ 1}), grain yield (3,343.4 kg ha^{─ 1}), and grain Zn content (36.43 g g^{─ 1}), as well as minimum malondialdehyde (1.72 g g^{─ 1} FW) and H₂O₂ (141.4 nmol g^─1 FW). Furthermore, the greatest root length (91.90 cm), root dry mass (4.86 g pot^{─ 1}), grain Fe content (43.34 µg g^{─ 1}), and grain phosphorus content (3.27%) were obtained for CF75 + BF. Based on the results, a 25% reduced chemical fertilizer dose, combined with biofertilizers and foliar seaweed extract application, appears to be the optimal approach.