Min Zhang

The development of controlled-release fertilizers (CRFs) has faced significant challenges due to high hydrophilicity and short release lifespan of bio-based materials, as well as non-renewable and high cost of polyester polyols (PPs). In this study, lignin-based polyols (LPs) and PPs were modified to form a cross-linked polymer film on the surface of urea through an in situ reaction. This approach effectively balanced the slow-release ability and environmental protection of controlled-release fertilizer films. A two-factor, five-level orthogonal test was designed for the mass ratio of lignin/polyester polyol and polyol/polyaryl polymethylene isocyanate (PAPI), comprising a total of 25 treatments. The results indicated that the appropriateness of lignin polyols increased the hydrogen bond content of polyurethane membrane, improved the mechanical strength of the fertilizer membrane shell, and effectively reduced friction losses during storage and transportation. Moreover, optimizing the polyol-to-PAPI ratio minimized coating porosity, produced a smoother and denser surface, and prolonged the nitrogen release period. When the lignin polyol dosage was 25% and the polyol to PAPI ratio was 1:2, the nitrogen release time of the prepared coated urea extended to 32 days, which was 3.5 times longer than that of lignin polyurethane coated urea (7 days). The incorporation of lignin and the optimal ratio of coating materials significantly improved the controlled-release efficiency of coated fertilizer, providing theoretical support for the sustainable agricultural application of biomass.

The application of a diammonium phosphate coating effectively mitigates direct contact between the phosphate fertilizer and the soil, thus minimizing phosphorus fixation. Humic acid holds a pivotal role in augmenting soil quality and activating the soil’s phosphorus reserves. Notably, when combined with humic acid, diammonium phosphate significantly enhances the utilization efficiency of phosphate fertilizer. However, there is a paucity of literature exploring the dynamics of nutrient transport in soil when humic acid is paired with coated phosphate fertilizers. To assess the impact of the combined application of coated diammonium phosphate and humic acid on wheat yield enhancement, we conducted pot experiments along with leaching and ammonia volatilization simulation tests, aiming to elucidate the effects of this combination on nutrient transport. The study explored the effects of three distinct treatments: coated diammonium phosphate (CP), coated diammonium phosphate combined with humic acid (PHA), and coated diammonium phosphate combined with humic acid (CPHA). The investigation focused on analyzing their impacts on wheat yield, ammonia volatilization, soil-available phosphorus, nitrate nitrogen, ammonium nitrogen, soil-available potassium, as well as the mobilization and transport of calcium and magnesium in the soil. (1) Compared to the P treatment, the PHA and CP treatments significantly increased grain yield by 17.2% and 13.5%, respectively. The PHA treatment also increased effective panicle number by 12.9%. Overall, the CP, PHA, and CPHA treatments improved grain yield by 13.5%, 17.2%, and 19.1% compared to the P treatment. (2) The CP and PHA treatments reduced available phosphorus by 95.6% and 49.2%, calcium by 2.0% and 67.0%, and magnesium by 11.6% and 46.1% compared to the P treatment. Ammonium nitrogen decreased by 37.0% and 64.3%, while nitrate nitrogen increased by 14.0% in CP and slightly decreased by 0.8% in PHA. In the leaching solution, PHA and CP treatments reduced available phosphorus by 96.7% and 62.5%, increased calcium by 5.0% and 78.9%, decreased ammonium nitrogen by 2.2% and 43.4%, and decreased nitrate nitrogen by 10.6% and 13.0%. The PHA and CPHA treatments increased available phosphorus in the 0–20 cm soil layer by 1.4 times and 25.8%, respectively. (3) The CP treatment reduced ammonia volatilization by 87.0% compared to the P treatment, while the CPHA treatment further reduced it by 87.5% compared to the PHA treatment. The application of coated diammonium phosphate efficiently delays nutrient release and reduces nutrient leaching in the soil. Additionally, the integration of humic acid significantly improves the availability of phosphorus in the soil, minimizing phosphorus loss. Notably, the combined application of humic acid and coated diammonium phosphate leads to a significant increase in soil phosphorus content, subsequently enhancing soil nutrient availability, conserving fertilizer, and ultimately resulting in an improved wheat yield.

Efficient use of humic acid (HA) for eco-friendly farming and environmental remediation requires further understanding of how targeted modification of HA affects the chemical structure of HA and thereby its effectiveness in enhancing soil quality. We developed novel selective modifiers (SMs) for extracting HA by codoping sodium and copper elements into the birnessite lattice. The structure of SMs was thoroughly examined, and the HAs extracted using SMs, referred to as SMHs, were subjected to a detailed evaluation of their functional groups, molecular weight, carbon composition, flocculation limits, and effectiveness in saline soil remediation. The results showed that replacing manganese with sodium and copper in SMs alters the valence state and reactive oxygen species. In contrast, SMHs exhibited increased acidic functional groups, a lower molecular weight, and transformed aliphatic carbon. Furthermore, the saline soil was improved through increased salt leaching and an optimized soil aggregate structure by SMHs. This research highlights the importance of targeted modification of HA and demonstrates the potential of these modifiers in improving soil quality for eco-friendly farming and environmental remediation.

Due to the difficult degradation and high cost of polyester polyols (PPs), their further development in controlled-release fertilizers (CRFs) has been limited. It was of great significance to partially substitute PPs with soybean oil polyols (SOPs) in the preparation of CRFs, which can adjust the proportion of substitution to balance the nutrient release period and membrane degradability. And it is possible to adjust the nitrogen release curve and prepare coated urea with different release days without changing the coating thickness. In this study, a two-factor five-level interaction experiment was designed with different SOP addition ratios (70%, 60%, 50%, 40%, and 30%) and mass ratios of polyols to PAPI (1:1.2; 1:1; 1.2:1; 1.4:1; and 1.6:1). In 25 groups of soybean-oil-modified polyester polyurethane-coated urea (SMPCU) treatments, with the increase in SOP, the thermal decomposition performance of the coated urea was improved, and the residual ash contents of the coating material was reduced. The coating surface was made smoother and denser with a reasonable ratio of polyols to PAPI, preventing the release of non-film-forming substances. When the proportion of soybean oil was 60% and the ratio of polyols to PAPI was 1.2:1, the N release days of the prepared SMPCU reached 137 days. Compared to soybean-oil polyol-coated urea (SOPCU) and polyester polyol-coated urea (PPCU), the nitrogen release days increased by 73.42% (79 days) and 234.15% (41 days), respectively. The ratio of polyols to polyaryl polymethylene isocyanate (PAPI) was explored, as well as the effect of polyol composition on coatings, and prepared SMPCUs with different nitrogen release days. According to the growth needs of crops and soil environmental characteristics, adjusting the proportion of coating materials, prolonging or shortening the nitrogen fertilizer release time, meets the nutritional needs of crops under different planting systems and provides conditions for farmers to plant different crops.

Extraction optimization is very important for the quality of humic acid (HA). In this study, actived HA (HA_b) was extracted from danty via catalytic oxidation using birnessite as a catalyst and H₂O₂ as an oxidant. Single-factor experiments and the response surface method were used to optimize the acidic functional group content of HA_b. It was found that the maximum acidic functional group content of HA_b can be achieved when danty-crushing time, H₂O₂ concentration, and birnessite dose were 105.7 min, 20, and 2%, respectively. Fourier transform infrared spectra showed that HA_b had more surface functional groups than commercial HA (HA_c) and HA extracted using the traditional method of the International Humic Substances Society (HA_I). In addition, acidic functional group titration showed that HA_b had 84.3% more acidic functional groups and 118.9% more carboxyl groups than HA_I. Additionally, HA_b had the greatest effect on promoting the dissolution of carbonate and bicarbonate, promoting the settlement of calcaline alkaline soil, and improving the germination rate of wheat seeds under saline and alkaline stress. This study provides a basis for the efficient extraction of active HA with rich functional groups and its application in agriculture and many other fields.

Exogenous application of nitrogen (N) and phosphate (P) has been demonstrated to alleviate apple replant disease (ARD). Yet, the effect of controlled-release diammonium phosphate (C-DAP), which continuously supply N and P for ARD control, is still poorly understood. Applying C-DAP markedly alleviated the typical symptoms of ARD. C-DAP maintained soil N and P at relatively high and stable levels during the entire growth period of the replanted seedlings, thus, limiting the copy number of the four key pathogenic Fusarium species that cause ARD. Particularly, continuously supplying N and P by C-DAP established a higher fungal diversity than that of conventional diammonium phosphate and induced the fungal community to be more similar to fumigated soil. The positive effect of C-DAP originated from the synergistic effects of regulating microorganisms and enhancing the resistance of the plant caused by a continuous nutrient supply. These findings provide a new perspective in the management of soil-borne diseases.

Coated diammonium phosphate (CDAP) is intended to release nutrients steadily in response to the demand of crop growth. A novel biostimulant extracted from Paecilomyces variotii has been shown to regulate gene expression in nutrient transport, enhance nitrogen (N) and phosphorus (P) uptake, and improve nutrient use efficiency. The application of CDAP combined with the Paecilomyces variotii extracts (ZNC) in maize is an efficient approach for reducing waste of resources, improving nutrient supply, and maintaining production stability. The effects of CDAP combined with ZNC on photosynthesis, enzyme activities, endogenous hormone content, maize yield, and P use efficiency (PUE) were investigated in this study. In a pot experiment, CDAP and diammonium phosphate (DAP) were tested together with P levels (1.80, 1.44 g pot–1, P2O5) and two ZNC application rates (0, 4.4 μg pot–1), which included the control treatment that had no P fertilizer added. Results showed that the key influencing elements of maize growth and yield were the soil available-P content, endogenous hormone content, and plant photosynthesis in this study. The combination of DAP and ZNC increased the soil available-P content and the auxin content in leaves at the key stage and hence increased the yield and PUE of maize, compared with DAP. The net photosynthetic rate of CDAP combined with ZNC was higher by 23.1% than that of CDAP alone, as well as by 32.0% than that of DAP combined with ZNC. Moreover, the combination of CDAP and ZNC increased the yield and PUE by 8.2% and 15.6 percentage points compared with DAP combined with ZNC while increasing the yield and PUE compared with CDAP. In conclusion, combining CDAP with ZNC as an environmentally friendly fertilizer could improve photosynthesis-related enzyme activity and enhance the net photosynthetic rate, resulting in an increase in maize yield and PUE significantly.

It has been reported that fulvic acid (FA) application improves soil structure and nutrient availability. However, the effects of combined application of urea (U) and FA solution on the photosynthesis and nitrogen metabolism in maize (Zea mays L.) have rarely been reported. In this study, pot experiments were conducted in 2017 and 2018, and the effects of combined application of urea and FA solution (U+FA) on soil available nutrient contents, maize endogenous hormone concentrations, carbon and nitrogen metabolism-related enzyme concentrations, maize yield, and nitrogen use efficiency (NUE) were researched. Compared with the U treatment, the maize yield and NUE in the U+FA treatment were significantly increased by 8.31% and 17.09 percentage points in 2017 and by 16.90% and 24.31 percentage points in 2018. At the jointing and 12-leaf (V12) stages of maize, soil NH₄⁺ content increased by 139.32% and 12.08%, separately, in the U+FA treatment. At the V12 stage, the auxin, nitrate reductase, nitrite reductase, and glutamine synthetase concentrations in maize root were increased by 42.31%, 74.17%, 16.61%, and 45.60%, respectively, and the concentrations of pyruvate phosphate dikinase and phosphoenolpyruvate carboxylase in maize leave were increased by 29.40% and 42.96%, respectively, in the U+FA treatment. The combined application of urea and FA solution significantly improved soil nutrient availability, increased the concentrations of endogenous hormones in maize, stimulated the activities of enzymes related to nitrogen metabolism, promoted the photosynthetic carbon assimilation efficiency, and ultimately improved crop yield and NUE.

In order to improve the photodegradation ability of fertilizer coating material and realize the sustainability of fertilizers, in this study, the commercially available photosensitive iron stearate (FeSt₃) was wet-ground into submicrometer FeSt₃ (SFeSt₃) particles and used in preparation of a SFeSt₃-modified bio-based polyurethane (PU)-coated controlled release urea (PU-SFe-CRU). The results showed that after 1 month photodegradation, the coating material had significant yellowing, the oxygen content of SFeSt₃-modified PU (PU-SFe) increased by 56.89%, and its structure became more porous and looser than PU. The thermal stability of PU-SFe decreased, and more intermediate products were produced after exposure to UV light. The germination experiment showed that PU-SFe before and after photodegradation (up to 60 mg/L) had no adverse effect on the seed germination and bud growth of rice. Additionally, PU-SFe had a significantly higher Cr adsorption capacity after photodegradation due to the increase of the oxygen-containing group and specific surface. This study provides a theoretical basis for the research and development of photodegradable environment-friendly controlled release urea.