The “emission reduction code” for maize fields in northeast China: Replacing 30% of mineral fertilizer with pig slurry cuts ammonia emissions

China is the world’s largest pork producer, with annual slaughter volume accounting for more than 40% of the global total. However, manure and slurry management from large-scale pig farming has long been a key bottleneck in green agricultural development. At present, domestic farmland remains highly dependent on mineral fertilizers, and long-term excessive fertilization has led to soil compaction and degradation of ecological functions. Direct field application of slurry also faces the challenges of high ammonia volatilization and greenhouse gas (GHG) emissions. How to safely and efficiently return livestock slurry to fields while ensuring crop yield is a barrier that must be overcome to advance the agricultural circular economy and achieve the dual-carbon goals.

Recently, the research team led by Prof. Dezhao LIU at the College of Biosystems Engineering and Food Science, Zhejiang University, published a research paper titled “Field slurry application in northeastern China for reducing greenhouse gases and ammonia emission” in ENGINEERING Agriculture (DOI: 10.15302/J-FASE-2026678). The study aimed to address the urgent issue of slurry resource utilization following the rapid scaling-up of China’s pig industry. To this end, the team conducted a field in-situ experiment in Lanxi County, Heilongjiang Province, systematically investigating the effects of the proportion of pig slurry replacing mineral fertilizers, slurry acidification pretreatment, and irrigation method on ammonia volatilization and GHG emissions in maize fields.

The team established seven treatments in a typical black calcareous soil maize field in Northeast China, covering no fertilizer (NF), raw slurry replacement (RS), acidified slurry (AS), traditional fertilization (TF), replacing 30% mineral fertilizer with pig slurry (RC30), replacing 50% mineral fertilizer with pig slurry combined with sprinkler irrigation (RC50S), and drip irrigation (RC50D). After four consecutive months of field in-situ monitoring, several key results were obtained: when pig slurry replaced 30% of mineral fertilizers (RC30), cumulative NH₃ emission was only 5.08 kg·ha⁻¹, reducing NH₃ emission by 60.4% and total GHG emission by 62% compared with full slurry substitution. In terms of slurry pretreatment, pre-acidifying pig slurry to pH 6 reduced NH₃ emission by 42.1%. In addition, compared with sprinkler irrigation, drip irrigation further reduced NH₃ emission by 38.9%–42.6%, N₂O emission by 12.4%–18.6%, and total GHG emission by 21.5%–34.7%.

Notably, the study revealed a “triggering effect” of precipitation on N₂O emission: after heavy rainfall during the topdressing period, N₂O emissions increased sharply in all treatments, indicating that climatic factors cannot be ignored in emission reduction management. At the same time, acidification did not negatively affect maize yield; the AS group had the highest yield per unit area (12,775 kg·ha⁻¹), demonstrating that emission reduction measures and stable yield goals can be achieved simultaneously.

From an economic perspective, although the initial investment in a drip irrigation system is slightly higher than that in sprinkler irrigation (with pipeline and auxiliary equipment investment accounting for 60%–80% of total cost), its emission reduction gains and water- and fertilizer-saving benefits are sufficient to cover long-term operational costs. Based on comprehensive benefits, the research team ultimately recommended the optimal combined strategy: “replacing 30% of mineral fertilizers with pre-acidified pig slurry combined with drip irrigation”. This strategy not only substantially reduced NH₃ volatilization and GHG emissions but also effectively maintained stable maize yield, providing a new path for slurry field application that balances ecological and economic benefits in the major grain-producing region of Northeast China. It has important practical guidance value for promoting the green and low-carbon transformation of agriculture.