The Innovation Team of Fertilizer and Fertilization Technology of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) combined temperature-sensitive materials with controlled-release technology to develop a temperature-sensitive polyurethane-coated fertilizer that releases nutrients in response to environmental temperature.

The nutrients' release of this intelligent controlled release fertilizer in response to temperature changes can provide a theoretical basis for achieving precise release of fertilizers, improve the fertilizer use efficiency, reduce the fertilizer input amount and increase the grain yield; Meanwhile, it also provide ideas for the creation of new fertilizers. Relevant research results were published in Materials Today Chemistry, a TOP journal in the field of materials chemistry.

In order to achieve the goal of carbon peaking before 2030, China is steadily launching a new green fertilizer research and development plan in which the precise and intelligent release of chemical fertilizers is a new hot spot.

Utilizing the specific relationship by which crop growth is affected by environmental factors such as soil temperature and pH value, the development of temperature and pH-responsive intelligent controlled-release fertilizers can match the nutrient release rate of controlled-release fertilizers with changes in environmental factors to achieve precise release.

Thermosensitive polyurethane (TSPU) is a common thermosensitive polymer widely used in drug delivery systems to control drug release. However, the work of directly using it to prepare coated controlled-release fertilizers and artificially regulating the nutrient release rate has not previously been reported.

In this study, biodegradable polycaprolactone diol (PCL), which is widely used as a raw material for temperature-sensitive polyurethane (PU), was used as the coating material. And the temperature-sensitive controlled-release fertilizers coated using the PU films synthesized by reacting the polyether polyol (PPG)/PCL blends and methylene diphenyl diisocyanate (MDI) were prepared in a fluidized bed device by in-situ reaction method. and was mixed with polypropylene glycol (PPG) in a certain proportion and then fluidized by an in-situ reaction method. A temperature-sensitive polyurethane-coated controlled-release fertilizer was prepared on a bed.

The varied temperature experiment shows that the nutrient release rate of this kind of temperature-sensitive coated controlled-release fertilizer switches suddenly at 33°C, and the nutrient release rate per hour increases by 22.3 times, which is 1.4 times higher than that of ordinary polyurethane-coated controlled-release fertilizers. In addition,  the nutrient release period can reach more than 30 days, which meets the ISO international standard for controlled release fertilizers (ISO 18644).

PCL is a biodegradable material. The creation of this intelligent temperature-sensitive coated controlled-release fertilizer provides a new process plan for the development of biodegradable controlled-release fertilizers. Besides, the temperature-sensitive intelligent controlled-release fertilizers for crop growth and ground temperature changes in different regions can be developed by adjusting the crystallization peak of the temperature-sensitive composite film, which performs prospects of industrial development and farmland application value.

Associate researcher Li Juan and Qiao Dan, master student of the IARRP, are the co-first authors of this paper, and associate researcher Yang Xiangdong and researcher Zhang Shuqing are its corresponding authors. This research was supported by the National Natural Science Foundation of China, the Chinese Academy of Agricultural Sciences Scientific and technological innovation projects and other project funding.

Paper link: https://www.sciencedirect.com/science/article/pii/S2468519422004785