Reduction in Nitrogen Rate and Improvement of Nitrogen Use Efficiency without Loss of Peanut Yield by Regional Mean Optimal Rate of Chemical Fertilizer Based on a Multi-Site Field Experiment in the North China Plain

**Background:** China is the world's largest peanut producer, accounting for over 40% of global production. However, smallholder farmers in China often apply excessive chemical fertilizer, leading to increased costs, reduced fertilizer use efficiency (FUE), and environmental pollution. Existing precision fertilization methods (soil testing, plant analysis, yield-response modeling) are often too time-consuming, labor-intensive, and expensive for widespread adoption in regions with small, scattered fields and limited technical infrastructure. The regional mean optimal rate (RMOR) method — using the average optimal fertilizer rate from multi-site trials as a single regional recommendation — has shown promise for rice, wheat, and oilseed rape, but its effectiveness for nitrogen-fixing crops like peanut and for phosphorus and potassium management was unknown.

**Methods:** A two-year (2020–2021) multi-site field experiment was conducted across 13 field sites (8 in 2020, 5 in 2021) in Zhengyang County, Henan Province, in the North China Plain — the largest peanut-growing county in China. The soil type was Alfisol with clay texture and low pH. Each site compared two treatments: farmer practice (FP), where fertilizer rates were determined by individual farmers, and optimal fertilization (OPT) based on RMOR. The RMOR was determined from 46 prior field trials using yield–fertilizer rate response modeling (quadratic equation), with rates adjusted by nutrient experts. The OPT rates were 181.5 kg N/ha, 39.3 kg P/ha, and 93.4 kg K/ha. Each treatment had three replicates in plots >100 m². At maturity, 2 m² samples were taken per plot for yield measurement (adjusted to 8% moisture), and five representative plants were collected for dry matter and nutrient analysis. N and P were determined using a flow injection analyzer, and K by flame photometer. Statistical analysis used one-way ANOVA at p < 0.05.

**Key Results:** Pod yield ranged from 1958 to 6915 kg/ha (mean 4879 kg/ha). OPT significantly increased yield at 6 of 13 sites, with an average increase of 10.9% over FP. Dry matter increased by an average of 6.6%. The harvest index averaged 54.0% and was not significantly different between treatments. Total NPK uptake averaged 214.3 kg N/ha, 23.3 kg P/ha, and 78.4 kg K/ha. OPT increased N uptake by 19.3%, P uptake by 7.3%, and K uptake by 11.0% compared to FP. Nutrient harvest indices averaged 76.0% for N, 59.8% for P, and 41.4% for K, with no significant treatment effect. The reciprocal internal efficiency (nutrient required per 1000 kg pods) was 42.0 kg N, 4.6 kg P, and 15.3 kg K. OPT significantly improved N partial factor productivity (PFPₙ) by 15.1% in 2020 and 29.8% in 2021, and N uptake efficiency (NUpE) by 19.3% in 2020 and 45.2% in 2021. However, K partial factor productivity decreased by 23.7% in 2020 and 31.5% in 2021, and K uptake efficiency decreased by 25.5% and 32.2%, respectively. Fatty acid composition (oleic 42.1%, linoleic 36.7%, palmitic 10.7%, stearic 5.0%) was not significantly affected by treatment.

**Clinical Implications:** This study demonstrates that the RMOR method is a feasible, simple, and scalable approach for optimizing NPK fertilizer recommendations in peanut farming across regions dominated by smallholder farms. By reducing N and P fertilizer inputs while maintaining or improving yield and N use efficiency, the RMOR approach can lower production costs and reduce environmental pollution from excess fertilizer. The quantified nutrient requirements (42.0 kg N, 4.6 kg P, 15.3 kg K per 1000 kg pods) provide a practical benchmark for regional fertilization guidelines. Limitations include significant site-to-site variability in yield and nutrient response, meaning some individual farmers may experience yield reductions. The authors recommend combining RMOR with local adjustments based on soil fertility, organic fertilizer use, and previous crop stubble to minimize adverse effects at the field level.