Urea-loaded nanoclay biopolymer composites integrated with beneficial microbes enhance nutrient uptake and mitigate greenhouse gas emissions

Abstract

Low nitrogen use efficiency of prilled urea contributes to substantial economic loss and environmental pollution through leaching, denitrification, and ammonia volatilization. This study evaluated urea-loaded nanoclay biopolymer composites (NCBPCs), synthesized from clay-acrylic acid + aczrylamide-based polymer composite grafted with maize flour (NCBPC-M) and mango kernel flour (NCBPC-MK), integrated with phosphorus- and zinc-solubilizing bacteria (Lactococcus lactis and Pseudomonas aeruginosa), as a sustainable alternative nitrogen source in a maize–wheat cropping system. FTIR, XRD, and SEM analyses confirmed successful polymerization and clay exfoliation. Both the composites showed high water absorption capacity (NCBPC-M: ~68 g/g; NCBPC-MK: ~62 g/g after 24 h). A field experiment (randomized complete block design) compared ten treatments, including 75% recommended nitrogen delivered via NCBPCs with or without microbial inoculants, against 100% recommended dose through conventional urea. Treatments combining NCBPCs with both phosphorus- and zinc-solubilizing cultures (T9, T10) sustained higher and more synchronized soil ammoniacal and nitrate nitrogen levels, and significantly increased grain and stover phosphorus and zinc content in both crops compared with conventional urea. These treatments also reduced cumulative N2O emissions by 17–29% in wheat and 21–24% in maize relative to full-dose urea, with the maize flour-based composite showing the greatest mitigation potential. These findings demonstrate that microbe-integrated, urea-loaded nanoclay biopolymer composites can simultaneously improve nutrient synchronization, enhance micronutrient biofortification, and mitigate greenhouse gas emissions, offering a promising climate-smart strategy for sustainable nitrogen management in cereal cropping systems.