To reduce the preparation cost of superabsorbent and improve the N release rate at the same time, a novel low-cost superabsorbent (SA) with the function of N slow release was prepared by chemical synthesis with neutralized acrylic acid (AA), urea, potassium persulfate (KPS), and N, N'-methylenebis(acrylamide) (MBA). The order of influence factors on the water absorbency property was determined by an orthogonal L(3) experiment. On the basis of the optimization results of the orthogonal experiment, the effects of a single factor on the water absorption were investigated, and the highest water absorbency (909 g/g) was achieved for the conditions of 1.0 mol urea/mol AA ratio, 100% of AA neutralized, K, 1.5% KPS to AA mass fraction, 0.02% MBA to AA mass fraction, 45 °C reaction temperature, and 4.0 h reaction time. The optimal sample was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Swelling behaviors of the superabsorbent were investigated in distilled water and various soil and salt solutions. The water-release kinetics of SA in different negative pressures and soils were systematically investigated. Additionally, the maize seed germination in various types of soil with different amounts of SA was proposed, and the N could release 3.71% after being incubated in distilled water for 40 days. After 192 h, the relative water content of SA-treated sandy loam, loam, and paddy soil were 42, 56, and 45%, respectively. All of the results in this work showed that SA had good water retention and slow N-release properties, which are expected to have potential applications in sustainable modern agriculture.

The effects of newly developed controlled release urea (CRU) and its placement method on the N use efficiency and nutritional quality of winter wheat (Triticum aestivum L.) grown on a loam soil were investigated during 2 yr. The winter wheat was grown on a loam soil. The CRU was applied at 0, 75, 150, and 225 kg N ha−1 and the urea was applied at 225 kg N ha−1 The CRU was applied with wheat seeds during sowing while the urea treatment was split into two applications: two‐thirds applied during sowing and one‐third at the 5‐tiller stage (Z25). Results showed that N release rates of CRU fit N requirements of wheat and the placement of wheat seeds with CRU improved wheat's apparent N uptake efficiency by 28.5% compared to urea treatment. Although the CRU treatment at 150 kg N ha−1 had one‐third less supplied N than that of conventional urea treatment (225 kg N ha−1), the wheat with CRU at 150 kg N ha−1 produced 6.5% more grain. In addition, at the same or one‐third reduced amount of N compared with the conventional urea treatment, CRU significantly increased the contents of Fe and Mn, providing additional nutrition and quality to the wheat grain.

Although commercialized slow-release fertilizers coated with petrochemical polymers have revolutionarily promoted agricultural production, more research should be devoted to developing superhydrophobic biopolymer coatings with superb slow-release ability from sustainable and ecofriendly biomaterials. To inform the development of the superhydrophobic biopolymer-coated slow-release fertilizers (SBSF), the slow-release mechanism of SBSF needs to be clarified. Here, the SBSF with superior slow-release performance, water tolerance, and good feasibility for large-scale production was self-assembly fabricated using a simple, solvent-free process. The superhydrophobic surfaces of SBSF with uniformly dispersed Fe3O4 superhydrophobic magnetic-sensitive nanoparticles (SMNs) were self-assembly constructed with the spontaneous migration of Fe3O4 SMNs toward the outermost surface of the liquid coating materials (i.e., pig fat based polyol and polymethylene polyphenylene isocyanate in a mass ratio 1.2:1) in a magnetic field during the reaction-curing process. The results revealed that SBSF showed longer slow-release longevity (more than 100 days) than those of unmodified biopolymer-coated slow-release fertilizers and excellent durable properties under various external environment conditions. The governing slow-release mechanism of SBSF was clarified by directly observing the atmosphere cushion on the superhydrophobic biopolymer coating using the synchrotron radiation-based X-ray phase-contrast imaging technique. Liquid water only contacts the top of the bulges of the solid surface (10.9%), and air pockets are trapped underneath the liquid (89.1%). The atmosphere cushion allows the slow diffusion of water vapor into the internal urea core of SBSF, which can decrease the nutrient release and enhance the slow-release ability. This self-assembly synthesis of SBSF through the magnetic interaction provides a strategy to fabricate not only ecofriendly biobased slow-release fertilizers but also other superhydrophobic materials for various applications.

Soil, air, and water pollution caused by lignite is considered a serious environmental problem. Activation methods thus have been developed to extract humic acid from lignite to support the agricultural production as the soil amendment or fertilizer synergist. The traditional activation methods of humic acid from lignite, however, are not environmentally friendly. As the first study, this work developed a novel solid-phase activation method with a Pd/CeO2 nanocatalyst for lignite-derived humic acid. This study analyzed the morphology and structures of the as-synthesized Pd/CeO2 nanocatalyst with various characterization tools. The mechanisms of the Pd/CeO2 nanocatalyst for lignite activation were determined. The Pd/CeO2 catalyst effectively promoted the production of water-soluble humic acids from lignite via KOH solid-phase activation at room temperature. It increased the amount of small molecular active groups and the corresponding small molecules of humic acid. The existence of a strong synergistic effect at the interface sites between Pd/CeO2 nanoparticles and lignite was one of the key factors for the outstanding catalytic performance. In conclusion, this study has great application perspectives for reducing lignite pollution and increasing humic acid utilization by crops, which can improve the sustainability of the environment and agricultural systems.

In this work, lignite, a low-grade coal, was modified using the solid-phase activation method with the aid of a Pd/CeO nanoparticle catalyst to improve its pore structure and nutrient absorption. Results indicate that the adsorption ability of the activated lignite to NO, NH, HPO, and K was significantly higher than that of raw lignite. The activated lignite was successfully combined with the polymeric slow-release fertilizer, which exhibits typical slow-release behavior, to prepare the super large granular activated lignite slow-release fertilizer (SAF). In addition to the slow-release ability, the SAF showed excellent water-retention capabilities. Soil column leaching experiments further confirmed the slow-release characteristics of the SAF with fertilizer nutrient loss greatly reduced in comparison to traditional and slow-release fertilizers. Furthermore, field tests of the SAF in an orchard showed that the novel SAF was better than other tested fertilizers in improve the growth of young apple trees. Findings from this study suggest that the newly developed SAF has great potential to be used in apple cultivation and production systems in the future.

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To improve fertilizer use efficiency, reduce irrigation requirement, and minimize negative environmental impact, a novel large-grained-activated-lignite-slow-release fertilizer (LAF) with good water retention was developed by mechanical extrusion of activated lignite and conventional fertilizer. A 3D molybdate-sulfur hierarchical hollow nanosphere (3D-MoS2–HN) catalyst was successfully fabricated via a simple route, and the lignite was activated by 3D-MoS2–HN to increase its water-soluble humic acid content and nutrient adsorption ability. After activation, the amounts of small molecular active groups and water-soluble humic acid of activated lignite were significantly higher than those of raw lignite. The activation also increased adsorption ability of the activated lignite for nutrients. LAF prepared from the activated lignite had a preferable slow-release property and good water-holding capacity in soil. Moreover, a pot trial further demonstrated that LAF effectively improved the growth of an apple plant. With outstanding water-retention and slow-release capacities, this new fertilizer is economical and eco-friendly, and thus is promising in field applications.

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