Organic fertilizer substitution enhances maize yield and quality under reduced irrigation

Ensuring an adequate and nutritious food supply for the global population is a significant challenge in agricultural production practice. Water and fertilizer are the main limiting factors in improving crop yield and quality. However, it remains unclear whether the substitution of a portion of chemical nitrogen fertilizer with organic fertilizer, combined with reduced irrigation, can increase maize yield and quality through improvements in photo-physiological traits and nitrogen transportation. A split-plot field experiment of maize was established in an arid area of northwestern China from 2021 to 2023. Two irrigation levels formed the main plot: local conventional irrigation (I2, 4,050 m³ ha⁻¹) and reduced by 20% (I1, 3,240 m³ ha⁻¹). Five equivalent nitrogen substitution ratios of chemical nitrogen with organic fertilizers formed a split plot, including sole chemical nitrogen fertilizer (F1), organic fertilizer substituting for 25% (F2), 50% (F3), 75% (F4), and 100% (F5) of chemical nitrogen fertilizer. This study investigated the effects of combining organic and chemical nitrogen fertilizers under reduced irrigation on maize yield, quality, photo-physiological traits, and nitrogen transportation. The results showed that reduced irrigation decreased maize yield and quality. However, organic fertilizer substitution for 25% of chemical nitrogen increased maize yield and quality, with this effect greater than that observed with other equivalent nitrogen substitution ratios of chemical fertilizer with organic fertilizer. A 20% reduction in irrigation combined with organic fertilizer substitution for 25% of chemical nitrogen (I1F2) increased maize grain yield and biomass by 13.0 and 8.9%, respectively, compared to local conventional irrigation and sole chemical nitrogen fertilizer (I2F1). Meanwhile, I1F2 improved grain protein content by 10.0%, enhanced amino acid and vitamin B contents by 60.4 and 30.6%, and raised straw crude fat and crude protein contents by 23.1 and 5.6% compared to I2F1 in maize, respectively. The reason for improving maize yield and quality with I1F2 was attributed to (1) improving leaf area index and leaf area duration at the blister (R2)−dough (R4) stage by 6.2 and 4.1%, increasing net photosynthetic rate by 43.8%, and enhancing pyruvate phosphate dikinase, phosphoenolpyruvate carboxykinase, and Rubisco activities by 9.8, 9.7, and 10.5%, respectively; (2) promoting nitrogen uptake and nitrogen accumulation after the R1 stage by 5.6 and 5.4% while maintaining nitrogen transportation quantity before the R1 stage. Therefore, reducing irrigation by 20% combined with organic fertilizer substitution for 25% of chemical nitrogen can improve maize yield and quality via improving photo-physiological traits and nitrogen transportation in arid irrigation areas.