Preparation and characterization of biochar-based slow-release nitrogen fertilizer and its effect on maize growth

Biochar (BC) is often used to prepare carbon-based slow-release fertilizers, but the slow-release performance of traditional biochar-based fertilizers is still low and needs to be further improved. In addition, the slow-release mechanisms, such as physical encapsulation, adsorption, functional group action, etc., of specific biochar-based slow-release nitrogen fertilizers (BSRNFs) are unclear. In this study, six BSRNFs were synthesized and their nitrogen release patterns and mechanisms were investigated. Soil column leaching experiments demonstrated that BSRNFs significantly slowed down the release of nitrogen. The release performance of sodium alginate coated BSRNFs with carbon fertilizer ratio of 2: 1 (BUS2) was the optimal; and the cumulative nitrogen release of BUS2 was 65.91% within 74 days, which was 28.56% lower than that of urea. The maize pot experiment showed that the maize yield of BUS2 treatment group was 7.51% higher than that of ordinary sulfur coated urea treatment group. The samples of BUS2 before and after sustained release were characterized., it was confirmed that BUS2 captured nitrogen by physical encapsulation, physical adsorption, hydrogen bonding and functional group action, so as to play the role of slow release. Moreover, the production cost of BUS2 was 29.32% lower than that of urea fertilizer. In conclusion, the newly-developed BUS2 is proven to be easily-synthesized and low cost, while possessing excellent slow-release nitrogen performance and increasing crop yield. Mass production and application of BUS2 in field are promising to contribute to the green agricultural development.