Although　controlled-release　fertilizer　(CRF)　is　a　safer　and　more　efficient　strategy　to　administer　nutrients　for　plant　growth,　it　is　still　a　daunting　task　to　reduce　the　cost　and　improve　the　degradability　of　the　synthetic　resin　coatings.　In　this　paper,　an　inorganic/organic　composite　coating　for　urea　fertilizer　was　prepared　from　a　biodegradable　castor　oil-based　polyurethane　(PU)　filled　with　the　layered　Na-bentonite　(Na-BT),　which　was　ultrasonically　treated　by　a　series　of　green　PEG　surfactants.　Synergistically　influenced　by　various　intercalation　ability,　cation-hosting　ability　and　hydrophilicity　of　the　PEGs,　the　porous　structures　of　the　modified　Na-BT　(MBT)　fillers　were　simply　tuned　by　varying　the　Mn　molecular　weights　of　the　PEGs,　resulting　in　the　adjustable　water　swelling　and　me-chanical　properties　of　the　MBT/PU　composites.　Moreover,　it　was　confirmed　that　the　water　swelling　property　played　a　critical　role　in　controlling　the　early　stage　of　nutrient　release,　and　the　mechanical　properties　were　important　for　the　longevity　of　nutrient　release　from　the　CRFs.　The　best　MBT/PU　composite　supported　a　CRF　with　a　long-term　release　of　75　%　in　38　days,　which　was　much　longer　than　the　one　based　on　pure　PU　(20　days).