Lixia Li

Calcium alginate is an anionic polysaccharide that forms an ionically crosslinked hydrogel network with encapsulation properties to nucleic acids and nutrients for the amelioration of osmotic stress, ion toxicity and nutrient imbalance in saline–alkali soils. Traditional soil reclamation methods, including salt leaching, incorporation of organic matter, and gypsum application, are water-intensive under a changing climate, ultimately necessitating transformative bio-based solutions for food security. Calcium alginate-based biohydrogel represents a versatile platform with a tunable macromolecular architecture, ionic crosslinking via an “egg box” mechanism and potentially promising to deliver engineered co-encapsulated nutrients and genetically modified cargoes. The mannuronic (M) and guluronic (G) acid (M/G) ratios govern ion exchange capacity, rheological behavior and release kinetics in saline- and alkali-stressed environments. Recent studies on alginate-based nutrient encapsulation showed reduced oxidative damage and a 15–50% increase in plant-available water. The irrigation intervals extended from 7 to 14 days and yield gains by 24% in wheat, with comparable improvements in maize, tomato, rice and cotton. Calcium alginate hydrogels encapsulated salt tolerance genes (HKT1, SOS1, AVP1) encoding proteins mainly involved in Na⁺ retrieval from xylem, Na⁺ extrusion from root cells and vacuolar Na⁺ sequestration, which have achieved yield gains of 40 to 75% across wheat, rice and maize. Future research should focus on optimizing mechanical strength, crosslinking chemistry and smart bioencapsulation strategies for sustainable development so that crops are capable of withstanding variable climate stresses.

Polymer coated fertilizers (PCFs) play a crucial role in the sustainable development of precision agriculture. However, conventional petroleum-based coating materials for PCFs are non-degradable and depend on non-renewable resources. Thus, biobased coatings, particularly those derived from vegetable oils, are promising alternatives. This review presents an innovative classification of vegetable oils based on their chemical structure, specifically whether they contain natural hydroxyl groups or require hydroxylation modification. By leveraging data from the Web of Science database, we systematically analyze the research progress of vegetable oil-based polyurethane coated urea from 2005 to 2024. Hydroxyl modification strategies for vegetable oils lacking natural hydroxyl groups are explored. Preparation processes and controlled-release properties of polyurethane coated urea made from both types of vegetable oils are included. Furthermore, aiming at potential coating defects, various modification strategies and their practical effects are evaluated in detail. These insights provide a systematic reference for raw material selection and formulation optimization of vegetable oil-based coated urea. While summarizing the key research achievements, this review comprehensively describes the future challenges faced by the practical application of vegetable oil-based polyurethanes in this field, and proposes potential breakthrough paths based on material innovation and process optimization.

Vegetable-oil-based polyurethane has become a promising sustainable candidate for controlled-release fertilizer based on green chemistry. The purpose of this study was to prepare a series of coatings from selective feedstocks including five vegetable oils with a high saturation degree, mono-unsaturation degree, or poly-unsaturation degree, considering that vegetable oil fatty acids played a key role in the synthesis of polyol and polyurethane. The effect of the type and proportion of fatty acids on the physicochemical properties, microstructure, and macro-properties of vegetable-oil-derived polyols and their resulting coatings was characterized and discussed. The position and number of the hydroxy groups were determined by the type and proportion of fatty acid, and polyol from linseed oil with a high poly-unsaturation degree and three carbon–carbon double bonds had a high hydroxyl value and functionality, whereas polyol from palm oil with a high saturation degree possessed the lowest hydroxyl value and functionality. The resultant coating from linseed-oil-based polyol had a good cross-linking density, and the nitrogen release longevity of coated urea was 56 days at a coating percentage of 3%, and its nitrogen use efficiency was increased by 27.15% compared with conventional urea. Although the palm-oil-based coating had good hydrophobicity, its coated urea was not ideal. Overall, this study has enriched theories of bio-based polyurethane coatings for controlled-release fertilizers; using vegetable oil with a poly-unsaturation degree, it is easy to obtain an excellent coating for controlled-release fertilizer, and this will help provide economic and environmental benefits.

To manufacture high bio-content degradable polyurethane-coated fertilizer, the co-liquefaction of corn straw and starch was carried out to convert more biomass into bio-polyol so as to substitute petroleum-based polyol. The effect of the corn straw to starch ratio on liquefaction behavior was mainly investigated by monitoring acid value, hydroxyl value, and liquefaction rate. Both chemical structures and properties of bio-polyols and their coatings were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), etc. The results indicated that adding a certain amount of starch to corn straw for co-liquefaction could contribute to a higher hydroxyl content of bio-polyol than that from sole biomass. Compared to molecular weight, the hydroxyl value was a more significant index to ensure coating quality. The incorporation of starch segments to bio-polyol led to good thermal stability, limited residual small molecules, and high crosslinking density of the coating. The controlled-release ability of coated urea prepared by co-liquefied bio-polyol was better than that of corn-straw-based bio-polyol, and the optimal ratio of corn straw to starch was 3:1. Overall, this study provides a new route to fabricate corn straw as a cost-effective and degradable coating with good controlled-release properties, which benefits solid biomass recycling.

[This corrects the article DOI: 10.1021/acsomega.2c01273.].

In this study, a spatially stratified proportional fertilizer application device was designed, which was mainly composed of a fertilizer equalization and stirring structure, fertilizer guide plate, and fertilizer plate. This was aimed at solving challenges presented by current fertilizer devices that include a poor layering effect due to untimely return of soil, excess nutrients in the early stages of plant growth, and insufficient quantities in the later stages. The "seed fertilizer + chasing fertilizer" is time-consuming and laborious; seed and fertilizer (without layering) are applied to the soil at once, which tends to cause too much nutrients for plants in the early stage and not enough nutrients in the later stage; and the layered fertilizer machines currently on the market have a poor layering effect due to untimely soil return. Through theoretical analysis and calculation, the structural parameters of the device were determined, and the main influencing factors of the movement law of fertilizer in the device were analyzed. Through simulating soil tank tests, the main factors affecting the effect of fertilizer spatial stratification were designed by quadratic regression orthogonal rotation combination designs. The optimal parameters including the length of the first fertilizer plate was 100 mm, the installation angle of the fertilizer plate was 80°, the spacing of the fertilizer port was 30 mm, and the uniform stirring speed was 650 r/min. The results of the bench test showed that the fertilizer granules could be uniformly stirred at the optimized stirring speed, with average values of 74.56, 76.56, and 105.19 g, which met the agronomic fertilizer application requirements, and the coefficient of variation of fertilizer application amount in each layer was less than 1%. The field test results showed that the stratified proportional fertilizer application device could achieve the stratified proportional application of fertilizer in the soil in ranges of 80.2-95.4, 150.3-180.2, and 230.3-250.4 mm for the upper, middle, and lower layers, respectively, with an error within 10 mm from the designed theoretical application depth. Compared with the conventional fertilizer application method, this fertilizer application method had a more obvious promotion effect on the 100-grain weight and yield of corn.