Integrating increasing planting density with organic amendments enhances crop yield and water–nitrogen productivity: A meta-analysis

CONTEXT Agricultural intensification has increased crop yields, but improving water–nitrogen productivity remains a major challenge. Increasing planting density (IPD) and applying organic amendments (OA) are widely used strategies to address this challenge, yet their combined effects and their stability across diverse environments remain poorly quantified. OBJECTIVE This study aims to assess the agronomic benefits of integrating IPD and OA, and to quantify their combined effects and stability across diverse environments. METHODS Here, we synthesized 1086 datasets to assess the effects of integrating IPD and OA on crop yield, aboveground biomass (AB), nitrogen partial factor productivity (PFPN), and water use efficiency. To identify the dominant predictors of yield response, random forest analysis was applied across key moderating factors including climate conditions, soil properties, and management practices. RESULTS AND CONCLUSIONS Overall, IPD + OA consistently outperformed either practice alone, further increasing crop yield, AB, and PFPN by 11.15%, 10.81%, and 7.33%, respectively, compared with IPD. Compared with wheat, maize showed a stronger yield response, with the greatest benefits observed when planting density increased by 25–50%. The random forest model revealed that initial soil organic matter was the dominant predictor of yield response, with IPD + OA increasing yield by 20.14% in soils containing ≤15 g kg −1 organic matter. Management practices also influenced outcomes: manure application further increased yield by 35.13% compared with straw, while combining IPD + OA with reduced nitrogen inputs (≤150 kg ha −1 ) increased yield and AB by 28.51% and 35.67%, respectively. Favorable environmental conditions further strengthened the benefits of IPD + OA, with yield increases reaching 30.57%, 39.30%, and 33.91% when initial total nitrogen exceeded 1.0 g kg −1 , mean annual temperature exceeded 10 °C, and annual precipitation exceeded 800 mm, respectively. SIGNIFICANCE These findings highlight the importance of tailoring planting density and OA strategies to local soil, climate, and nutrient conditions, providing a scientific basis for regionally adapted management strategies that can simultaneously enhance crop yield and improve water–nitrogen productivity.