Surfactants affect the properties and controlled-release performance of coated fertilizers by influencing the structure of polyurethane film materials based on castor oil. This study offered a theoretical support for the practical use of surfactant-modified plant oil-based polyurethane coated urea in agriculture through a methodical examination of the properties of coated urea, surfactant-modified castor oil-based polyurethane film, and field tests.

Using surfactant modification, castor oil-based polyurethane-coated urea (BPCU) was created. The surfactant modification mechanism was examined, and FT-IR was used to corroborate the polyurethane synthesis. The effects of surfactants on the hydrophobic properties of membrane materials were investigated. In Zhaodi Village, Xinxiang, Henan Province, a field experiment was carried out using homemade slow-release fertilizer to reduce fertilizer application by 20% while using regular urea as the control. The impact of BPCU on summer maize yield was examined, and Zhongjinyu 2513 was the test crop.

By improving the compatibility of the polyurethane matrix and creating a pseudo-crosslinking effect, the surfactant could make the high hydroxyl value castor oil-based polyol and PM-200 more evenly distribution on the coating film's surface. Additionally, the cross-linking density was further enhanced by lowering the energy consumption of the interfacial reaction between the high hydroxyl value castor oil-based polyol and PM-200 to form polyurethane. The improved membrane material had a decreased residual carbon content, according to the results. The improved membrane shell's water contact angle was 105.5°, a 13.0 % increase from the unmodified membrane shell's 93.4°. The modified membrane material had a 7-day water absorption rate of 1.64%, a porosity of 1.14%, and a swelling degree of 1.18%. The 7-day water absorption rate, porosity, and swelling degree were all reduced by 76.8%, 76.7%, and 25.3%, respectively, when compared with the unmodified membrane material. The slow-release duration of BPCU was extended from 70 to 83 days at 0.5% surfactant addition, which was 18.6% longer than that of castor oil-based polyurethane-coated urea (PCU). With a 20% decrease and a 5% coating, the corn yield of the BPCU fertilizer was 11 908.1 kg·hm^-2, a 22.0% increase over the maize yield of 9 757.2 kg·hm^-2 following the application of regular urea. In contrast, the thousand-grain weight likewise rose by 16.9%. The yield and thousand-grain weight of maize were significantly impacted by the application of BPCU. It mostly influenced the thousand-grain weight of maize, which in turn impacted its yield.

It was demonstrated from aspects such as nitrogen release period and summer maize yield that the performance of BPCU was superior to that of the unmodified PCU. The application of BPCU could be regarded as an effective way to reduce fertilizer application and increase efficiency. The creation of novel coated controlled-release fertilizers was supported theoretically and technically by this study.