A self-made controlled-release urea increases peanut yield and water-nitrogen use efficiency by improving the synchronization between water-nitrogen supply and crop demand

Context The peanut ridge mulching system in North China exacerbates the imbalance between water and fertilizer supply and crop demand. Combining water retaining agents (SAPs), nitrogen inhibitors (NIs), and coated urea is a promising strategy to mitigate water fertilizer conflicts. However, conventional coated fertilizers only slightly improve fertilizer use efficiency, making effective water fertilizer synergistic regulation difficult. Thus, further research on integrated application strategies is urgently needed. Objectives This study aimed to develop a novel water-retaining, efficiency-enhancing, controlled-release nitrogen fertilizer (WRSIU) and to elucidate the mechanisms by which coordinated water-nitrogen (N) regulation improves peanut yield, nitrogen use efficiency (NUE), and water use efficiency (WUE). Methods Firstly, hydroquinone (HQ) and dicyandiamide (DCD) were first sprayed onto the surface of urea granules, followed by epoxy resin coating to produce dual controlled-release urea (DCRU). Subsequently, a γ-polyglutamic acid/acrylic acid interpenetrating network copolymer (PGA/PAA-IPN) was synthesized and coated onto the surface of DCRU to obtain WRSIU. The properties of PGA/PAA-IPN and WRSIU were characterized and evaluated via laboratory experiments. Field experiments were then conducted synchronously at two sites. Six treatments were established: CK (no nitrogen fertilizer), U (regular urea), CU (epoxy resin-coated urea), DCRU, WRSBU (DCRU + PGA/PAA-IPN, physical blending), and WRSIU. Results A compact multilayer structure consisting of an inhibitor layer, epoxy resin layer, and water retaining composite layer was formed on the surface of WRSIU granules. At a coating rate of 9%, the controlled-release durations of N, HQ, and DCD were 56, 42, and 34 days, respectively. Compared with CU, ammonia volatilization and N leaching were reduced by 29.53% and 18.78%, respectively. Field results showed that WRSIU significantly increased dry matter accumulation in multiple organs at maturity. Inhibition of soil N transformation enzymes persisted until the pod setting stage, leading to increases in soil NO₃⁻-N and NH₄⁺-N contents of 7.62–29.33% and 14.67–23.27%, respectively. WRSIU significantly enhanced the coupling coordination degree ( D ) of soil water and N, particularly during the pod setting stage, with D values increasing by 44.90–63.48% compared with CU. Consequently, yield, WUE, and N fertilizer apparent utilization efficiency (NFUE) increased by 12.15–15.45%, 31.32–43.58%, and 12.46–33.73%, respectively. Economic analysis indicated that although the fertilization cost of WRSIU was 54.96 $·ha⁻¹ higher than that of CU, but net benefits rose by 584.74 and 556.52 $·ha⁻¹ in Jining and Tai’an, respectively. Conclusions WRSIU integrates three key functions-water retention, controlled N release, and nutrient loss inhibition. It synchronizes soil water and N availability with plant demand, mitigates ammonia volatilization and nitrate leaching, and enhances yield, NUE, and WUE.