Preparation and characteristics of urea coated with water-based copolymer-biochar composite film material

Objectives Biochar could be used as a support material to enhance the properties of coated materials and deliver plant nutrients. A novel slow-release fertilizer was developed using biochar and water-based copolymer of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) as coating materials. A further study was conducted on the properties of water based polymer-biochar composite coating materials and the surface microstructure, slow release effects of coated urea . Finally, the optimal proportion of water-based copolymer-biocar film materials, which are widely sourced, environmentally friendly and relatively inexpensive, was obtained. This study help provide a theoretical basis for the development and application of environmentally friendly, nutrient sustained-release fertilizer.

Methods The water based copolymer-biochar composite film materials were prepared from polyvinyl alcohol, polyvinylpyrrolidone and biochar. Through the analysis of its water absorption, permeability, and biological degradation, the suitable ratio of coating materials and slow release effects of coated urea were screened out and its surface microstructure characteristic was further studied. A field trial was conducted on the effects on yield and yield components of maize when the rate of nitrogen was reduced by 20%.

Results The water absorbency of A₁B₁C₁, A₁B₂C₂, A₃B₂C₁ were 35.3%, 37.3%, 26.7% lower than those of corresponding non-biochar copolymer. However, there was no difference among the three treatments. Among A₁B₁C₁, A₁B₂C₂, and A₃B₂C₁, A₁B₁C₁ had lower NH₄⁺ permeability and water permeability, and early stage mass loss, but higher mass loss later (after 45 days) at copolymer concentration of 6.0%, biochar 3.0% and the particle size 0.250–0.150 mm . Scanning electron microscopy (SEM) showed that the surface of the water based polymer-biachor composite coating material was rougher after burying, and the tissue was looser. While there were different sizes of pores in the coating layer, the coating material penetrated into the gaps on the surface of the urea particles. Meanwhile, coated urea prepared under this condition had better slow release properties with nitrogen leaching of 67.19% after 22 d. With a reduction of 20% of coated urea-N, the yield was increased by 1.45%, along with improvement in ear diameter, grain number of row, and 100-grain weight.

Conclusions The water based copolymer-biocarbon composite film materials prepared under the experimental conditions was a new environment-friendly coating material.