Effect of organic-inorganic combined application on rice yield and nitrogen fate in soda saline alkali soil

In soda saline-alkali soil, long-term excessive application of inorganic nitrogen fertilizer leads to low nitrogen use efficiency, severe nitrogen loss, and aggravated soil degradation, which seriously restricts rice production and regional food security. Organic fertilizer, with its advantages of improving soil structure and providing slow-release nutrients, has potential in optimizing rice nitrogen utilization and alleviating environmental risks. This study took rice in soda saline-alkali soil as the research object, a set of 6 treatments including no nitrogen fertilization (N0), single application of chemical fertilizers (NPK), and 4 organic nitrogen substitution ratios (25%M, 50%M, 75%M, M (100%M)) with pig manure as organic fertilizer source, and measured indicators such as rice yield, dry matter accumulation, nitrogen accumulation, nitrogen use efficiency, soil inorganic nitrogen residue, and nitrogen loss (ammonia volatilization, N 2 O emission) during 2024-2025. Results showed that compared with CK (2978 kg ha -1 ), all fertilization treatments significantly increased rice yield by 77.1% - 117.9%, and organic substitution treatments (except M) increased yield by 4.3%-8.9% compared with NPK (5485 kg ha -1 ), with 50%M treatment having the highest yield (6389 kg ha -1 ). Organic substitution treatments (except M) increased rice aboveground nitrogen accumulation by 19.8%-22.9% and apparent nitrogen utilization efficiency by 10.3-12.4 percentage points compared with NPK, and 50%M treatment had the highest nitrogen accumulation (150.6 kg ha -1 ) and apparent nitrogen utilization efficiency (34.0%). Compared with NPK, organic substitution treatments reduced soil 0-100cm inorganic nitrogen residue by 11.3%-38.0% and cumulative ammonia volatilization by 12.3%-19.98%, with 50%M treatment having the lowest soil inorganic nitrogen residue (49.8-54.6 kg ha -1 ) and nitrogen loss rate (38.51%). Excessive organic substitution (M treatment) led to lower yield and nitrogen use efficiency than 50%M, with yield even not significantly different from NPK. This confirms that 50% organic nitrogen substitution with pig manure is significant for improving rice yield, nitrogen use efficiency, and reducing nitrogen loss in soda saline-alkali soil.