Microwave-Assisted Synthesis of a Novel Biochar-Based Slow-Release Nitrogen Fertilizer with Enhanced Water-Retention Capacity

Biochar-based slow-release nitrogen fertilizers (BSRFs) have been arousing a great deal of interest from researchers and academics, but many of these fertilizers do not possess water-retention capacity. In this work, a polymer matrix has been introduced into NH₄⁺-loaded biochar (N-BC), using microwave (MW) irradiation, for the purpose of acting as a superabsorbent polymer to improve soil water-retention capacity. The polymer matrix is composed of cotton stalks (CSs), acrylic acid (AA), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and bentonite (bent.). N-BC was prepared via the adsorption of NH₄⁺ onto BC, and its adsorption behavior was investigated. The structure and properties of the resulting samples were characterized using various characterization methods. Results suggest that BSRFs could significantly improve the water-holding and water-retention capacity of soil. BSRFs effectively reduced the nitrogen-release rate (69.8% of nitrogen was released after 30 days), and possessed low nitrogen-leaching-loss amounts (10.3%), low nitrogen migrate-to-surface-loss amounts (7.4%), and high nitrogen-use efficiency (64.27%), as compared to NH₄Cl and N-BC, consequently effectively promoting cotton plant growth. The soil burial degradation test of BSRFs indicated that BSRFs possessed good degradability. BSRFs may therefore have promising applications in modern, sustainable agriculture, while MW irradiation is an important strategy with which to produce BSRFs.