Functional Differences Between Conventional and Modified Organic Fertilizers in Regulating Sorghum Productivity, NH3 Loss, and Soil Quality in Coastal Saline–Alkali Soil

Saline–alkali soils are characterized by low fertility and productivity, which can be potentially improved by applying organic fertilizers. We hypothesized that conventional and modified organic fertilizers would exhibit distinct functional advantages in regulating crop performance, nitrogen (N) loss, and saline–alkali soil fertility. A soil-column experiment was conducted to compare chemical fertilizer (CF) with conventional (CF + OF), biochar-amended (CF + BOF), and functional microorganism-inoculated organic fertilizer (CF + MOF) for sorghum production, ammonia (NH3) volatilization, and soil fertility. Compared with CF, organic fertilizer treatments did not significantly increase grain yield, although CF + OF showed greater yield potential through improved leaf biomass and grain number per panicle. CF + MOF reduced N use efficiency by 43.2%, whereas organic fertilizer application altered grain quality, particularly protein and tannin contents. Cumulative NH3 volatilization decreased by 8.9–16.7% under organic fertilizer treatments, with the greatest reduction observed in CF + OF. All organic fertilizer treatments increased soil available N contents and improved soil quality index (SQI), while CF + BOF showed the strongest improvement in available phosphorus and potassium, and total N contents. Overall, different organic fertilizers exhibited distinct functional characteristics under short-term observation. CF + OF showed advantages in balancing crop production and NH3 mitigation, whereas CF + BOF mainly improved soil nutrient status. Long-term agronomic and ecological benefits require validation under multi-season field conditions.