The maturation of biobased polymer synthesis process has led to the rapid adoption of biobased controlled-release fertilizers (BCRFs). Despite this progress, the loose structure, low cross-linking density, and poor water repellency of current biobased coatings result in short controlled-release periods, which do not meet the long-term nutrient demands of crops throughout their reproductive phases. Moreover, existing modifications to address these issues often involve the addition of external additives, which can increase biotoxicity and cost. In this study, castor oil-based hyperbranched polyol (COHBPs) was synthesized from castor oil (CO) using a "one-pot method." We report the development of high cross-linking density biobased hyperbranched polyurethane (COHBPPFs) as a coating for BCRFs. Gel content and SEM analysis demonstrated that COHBPPFs exhibited a high degree of cross-linking. Mechanical testing using an electronic universal testing machine, along with AFM results, highlighted the superior mechanical properties of COHBPPFs compared to traditional coatings. COHBPPFs significantly enhanced controlled release performance, with a 3% coating content providing nearly 50 days of controlled release, a marked improvement over conventional coatings. The controlled release mechanism of COHBPPFs was elucidated by modeling the cross-linking process of COHBPs with PAPI. This study offers a comprehensive examination of CRF coatings from multiple perspectives and provides valuable insights into the development of high cross-link density, environmentally friendly, and renewable biobased CRFs.

Bio-based coated controlled-release fertilizers (BCRFs) can significantly improve nutrient utilization and reduce pollution. However, challenges such as spray gun clogging, adhesion and tearing between fertilizers during the actual production of BCRFs pose a severe challenge to production chain development. In addition, the poor hydrophobicity and cross-linking properties of bio-based coatings severely affect the controlled release properties of BCRFs. Although some measures have been taken to ameliorate the above problems, the cumbersome and costly modification process is challenging to be applied on a large scale. Therefore, the primary goal of this work is to search for a more straightforward and efficient method of production and modification to address the aforementioned unresolved challenges in the field of CRFs. In this study, bio-based polyester polyol (BPP) was used as the base for polyurethane reaction, and low-viscosity castor oil (CO) was used as the modifier to reduce the viscosity of BPP. This led to the preparation of Inter-Modified Coated Controlled-Release Fertilizers (ICRFs) to prevent spray gun clogging. Building upon this, hydrophobic and dense wax-based coated fertilizer (WBCF) was prepared by modifying ICRF with Ceresin wax to alleviate the challenges associated with adhesion and tearing between fertilizer particles during the coating process. The WBCF exhibited remarkable controlled-release characteristics, with a nitrogen (N) release longevity of nearly 180 days, requiring only 3 % of the coating materials. This work provides a simple and efficient strategy for overcoming the key constraints in the development and production of CRFs and provides insights into developing green, low-cost fertilizers with excellent controlled-release properties.

Organic amendments have been widely used in coastal saline–alkali soil remediation ; however, the mechanisms involved and the interactions between organic and inorganic amendment s are still unclear. In this work, furfural residue (particulate; C/N: 51.87; O-alkyl C + di-O-alkyl C: 42.35%, aromatic C: 40.89%) and black liquor (dissolved; C/N: 3.11; O-alkyl C + di-O-alkyl C: 32.20%, aromatic C: 28.32%) were tested to examine their effects on chemical properties, water-stable aggregate fractions, chemical compositions of solid-state soil organic matter (SOM), gloaming-related soil protein contents and microbial communities of coastal saline–alkali soil under a 400-day incubation experiment. Furthermore, organic amendments mixed with mineral amendment (4:1) were employed to explore the interactions between organic and inorganic amendments. Furfural residue had stronger and more long-term effects on soil macroaggregate stability (~240 days, intense) than black liquor (~15 days, weak), and mineral amendment addition had a positive effect on the stability of microaggregates. Our results revealed that qualities (primary form, C/N, and chemical composition) of organic amendment which can change microbial communities by increasing soil C/N and effective chemical compositions of solid-state SOM, are the key factors in promoting the rapid formation and long-term stability of coastal saline–alkali soil aggregates. Moreover, inorganic amendment addition can further improve the formation and stability of microaggregates rather than those of macroaggregates. This study provided a much-needed technical basis for remediation of coastal saline–alkali soil.

Both ammonium sulfite slurry (ASS) from ammonia-based desulfurization and lignite are waste materials with low value. In this work, an innovative method was developed by applying ASS in lignite activation to produce water-soluble humic substances (WHSs) with a high bioactivity and economic value. The optimal activation method was to mix lignite and ASS at a 4:1-liquid-solid ratio by vortex blender and then oscillate it for 30 min at 25 °C. Compared with that of the unactivated lignite (UAL), the yield of WHSs from activated lignite (AL) increased by 42.72%. WHSs from AL consisted of a large number of aliphatic carbons with low molecular weight and functional groups such as amides, amines, sulfonic acid groups, C-O, and so forth. Moreover, WHSs from AL at lower concentrations (2 mg/L) has a more obvious root-elongation-promoting effect than WHSs from UAL (10 mg/L). Activation experiment with the lignite-related model compounds revealed that ASS caused the breakage of Caliph-O, Caliph-Caliph, and Carom-Caliph linkages between aromatic rings. These findings provide a theoretical basis for the development of green and sustainable technologies for the beneficial reuse of ASS and lignite in agriculture.

Controlled-release fertilizers (CRFs) could improve crop yield and fertilizer use efficiency. However, the coating materials of conventional CRFs are mainly derived from petrochemical products, which are expensive and nondegradable, bringing potential environmental pollution. Therefore, using sustainable bio-based materials is the development direction. In this study, large tablet urea (LTU) was prepared using physical extrusion technology. The economical and biodegradable liquefied apple tree branch bio-based coating material was used to coat LTU, obtaining large tablet CRFs (LTCRUs). Also, the optimum proportion of liquefaction of apple tree branches modified by castor oil was studied. The specific surface area, surface morphology, and FTIR of LTCRU were characterized. The results showed that the surface of the LTCRU was the most smooth and the LTCRU modified with 30% castor oil presented the best controlled-release characteristics. The specific surface area of LTCRU was one-third of that of traditional small-particle fertilizers, which indicated that reducing the using dosage of coating materials is economical. Overall, this work provided theoretical and technical supports for the industrialization of biocoated superlarge tablet urea, which is conducive to the green development of agriculture.

This work provides an efficient UV-curing strategy for the manufacture of energy-saving, superior performance and biopolymer-coated large tablet controlled-release fertilizers.

Bio-based slow-release fertilizers (SRFs) have drawn significant attention in resolving food scarcity issues, improving nutrient utilization efficiencies, and preventing environmental pollution. However, current SRFs still need to improve their release profile, reduce the bioresource cost, and resolve multiple environmental issues e.g., different types of soil/water contamination. In this study, we propose an original concept to fabricate double-function and environmentally friendly SRFs with a controllable fertilizer release function and strong adsorption capability of trace metals in soils. The hypothesis is that a hydrophobic nanohybrid synthesized from the low-cost lignin biowaste and clay allows the well-dispersion in the bio-based polyurethane matrix derived from readily available agriculture byproducts. The exfoliation of nanohybrid in the biopolymer membrane not only blocks the path of hydrophobic fertilizer release but also possesses cationic ions absorption function. The results show that the nanohybrid has a strong metal adsorption capability and the synthesized nanohybrid-based controlled-release fertilizers (CRFs) exhibit excellent N release longevity (more than one month). These multiple-function CRFs promote plant growth in trace-metal contaminant soil in a cherry radish matrix study. This work also provides a detailed examination of the synthesis of lignin clay hybrid biocomposite, the encapsulation of fertilizers by the biocomposite membrane, the study of the nutrient release profile, and the metal adsorption mechanism. For the first time, biobased and low-cost CRFs provide multiple functions including controllable fertilizer release, strong metal adsorption capability for soil remediation, or trace metal reutilization, which is expected to open a new door for large-scale utilization of CRFs in a nutrient contaminant soil environment.