Table 1_NPK quota-based fertilization: a sustainable strategy for enhancing fertilizer efficiency and mitigating paddy field acidification and environmental costs in Chongqing.docx

Widespread paddy field acidification in China has made many medium- and low-yield fields unsustainable due to excessive fertilization. This study determined optimal NPK fertilizer quotas for rice production in Chongqing by integrating yield levels with principles of matching total nitrogen (N), maintaining soil phosphorus (P), and adjusting potassium (K) to yield. Results showed recommended NPK quotas ranged from 104 to 185 kg N/ha, 44–84 kg P₂O₅/ha, and 18–35 kg K₂O/ha (lower limits) to 143–224 kg N/ha, 50–98 kg P₂O₅/ha, and 56–111 kg K₂O/ha (upper limits). Implementation of these quotas could reduce fertilizer use by 1,862 tons of N, 524 tons of P₂O₅, and 1,275 tons of K₂O, with the highest reduction potential in low-yield regions (2,109 tons N, 654 tons P₂O₅, and 268 tons K₂O). Notably, low-yield rice paddy fields exhibited significantly higher fertilizer application rates than medium- and high-yield fields. Excessive N and P use increases soil acidification, reactive nitrogen (Nr) loss, greenhouse gas (GHG) emissions, and water eutrophication, exacerbating soil degradation. To address these issues, we propose revised N and P quotas (104–141 kg N/ha and 44–60 kg P₂O₅/ha), which reduced Nr loss, GHG emissions, soil acidification potential (SAP), and water eutrophication potential (WEP) by 18, 6, 18, and 14%, respectively. This study proposes new NPK fertilizer application thresholds tailored to mitigating agricultural land degradation while improving agricultural productivity.