In agriculture, hydrogels can be addressed for effective operation of water and controlled-release fertilizers. Hydrogels have a significant ability for retaining water and improving nutrient availability in soil, enhancing plant growth while reducing water and fertilizer usage. This work aimed to prepare a hydrogel composite based on microalgae and biopolymers including chitosan and starch for use as a soil conditioner. The hydrogel composite was characterized by FTIR, XRD, and SEM. All hydrogel properties were studied including swelling degree, biodegradability, water-holding capacity, water retention, and re-swelling capacity in soil and water. The urea fertilizer loading and releasing behavior of the prepared hydrogels were investigated. The results revealed that the range of the maximal urea loading was between 99 and 440%, and the kinetics of loading was fitted with Freundlich model. The urea release % exhibited 78-95%, after 30 days, and the kinetics of release was fitted with zero-order, Higuchi, and Korsmeyer-Peppas models. Furthermore, the prepared hydrogels obtained a significant water-holding capacity, after blending soil (50 g) with small amount of hydrogels (1 g), the capacity increased in the range of 99.4-101.5%. In sum, the prepared hydrogels have the potential to be applied as a soil conditioner.

This study is to examine zinc exchanged montmorillonite (Zn-MMT) as a potential slow release nanofertilizer for rice crop. The effective intercalation of zinc within the montmorillonite inter layers was firmly established via analytical techniques including Zeta potential, FE-SEM (Field Emission Scanning Electron Microscopy) with Energy Dispersive X-ray Analysis (EDAX), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR). The efficacy of Zn-MMT was examined by evaluating its ability to facilitate controlled zinc release, as confirmed through an incubation study. Subsequently, the kinetics of zinc release was analyzed by different mathematical models such as Zero-order kinetics, First-order kinetics, the Higuchi model, and the Korsmeyer-Peppas model. From the pot culture study spanning 90 days the results indicated that Zn-MMT had significantly high plant height, Leaf Area Index (LAI), Dry Matter Production (DMP), number of tillers per hill, panicles length, increased grain and straw yield, in comparison with conventional zinc sulphate (ZnSO4). Total phenol, total protein and total chlorophyll content were significantly at higher levels with Zn-MMT treated rice crops as compared to conventional fertilizers and control. A similar trend was seen with phytochemicals such as Indole Acetic Acid (IAA), Superoxide Dismutase (SOD) and Carbonic Anhydrase (CA). Notably, rice grains harvested from Zn-MMTtreated crops exhibited significantly higher zinc content than those using other treatments. This Zn-MMT can be confirmed as a better alternative to conventional zinc sulphate fertilizers owing to its slow-release of nutrient into the soil and thus increased zinc use efficiency.

The urgent concerns of controlling water body eutrophication and the alleviating phosphorus shortage have led to an urgent need for action. The removal of phosphate from polluted waters and its reuse are essential for the prevention of eutrophication and for the sustainable utilization of phosphate resources. In this study, modified attapulgite with different Ca:Mg molar ratios was synthesized to facilitate the recovery of phosphate, with subsequent use of soil fertilizer. Ca-Mg modified attapulgite with the optimal ratio (ACM-5:3) exhibited an exceptional adsorption quality, achieving a maximum adsorption capacity of 63.2 mg/g. The pseudo-second-order model and Langmuir model could well describe the adsorption kinetics and isotherms, respectively. The adsorption mechanism analyses suggested that the interaction between ACM-5:3 and phosphate depended mainly on ion exchange and electrostatic attraction. Moreover, phosphate-laden-ACM-5:3 demonstrated a significant potential as a phosphorus-releasing fertilizer. It could promote corn growth by ensuring a continuous supply of phosphorus and minimizing phosphorus runoff losses. The above results suggested that ACM-5:3 was a potential adsorbent for efficient phosphate removal and recovery.

Recently, replacing chemical fertilizers with straw returning and new fertilizers has received considerable attention in the agricultural sector, as it is believed to increase rice yield and improve soil properties. However, less is known about rice growth and soil properties in paddy fields with the addition of different fertilizers. Thus, in this paper, we investigated the effects of different fertilizer treatments, including no fertilization (CK), optimized fertilization based on the medium yield recommended fertilizer amount (OF), 4.50 Mg ha-1 straw returning with chemical fertilizers (SF), 0.59 Mg ha-1 slow-release fertilizer with chemical fertilizers (SRF), and 0.60 Mg ha-1 water-soluble fertilizer with chemical fertilizers (WSF), on rice growth, yield, and soil properties through a field experiment. The results show that compared with the OF treatment, the new SF, SRF, and WSF treatments increased plant height, main root length, tiller number, leaf area index, chlorophyll content, and aboveground dry weight. The SF, SRF, and WSF treatments improved rice grain yield by 30.65-32.51% and 0.24-1.66% compared to the CK and OF treatments, respectively. The SRF treatment increased nitrogen (N) and phosphorus (P) uptake by 18.78% and 28.68%, the harvest indexes of N and P by 1.75% and 0.59%, and the partial productivity of N and P by 2.64% and 2.63%, respectively, compared with the OF treatment. However, fertilization did not significantly affect the average yield, harvest indexes of N and P, and partial productivity of N and P. The contents of TN, AN, SOM, TP, AP, and AK across all the treatments decreased significantly with increasing soil depth, while soil pH increased with soil depth. The SF treatment could more effectively increase soil pH and NH4+-N content compared to the SRF and WSF treatments, while the SRF treatment could greatly enhance other soil nutrients and enzyme activities compared to the SF and WSF treatments. A correlation analysis showed that rice yield was significantly positively associated with tiller number, leaf area index, chlorophyll, soil NO3--N, NH4+-N, SOM, TP, AK, and soil enzyme activity. The experimental results indicate that SRF was the best fertilization method to improve rice growth and yield and enhance soil properties, followed by the SF, WSF, and OF treatments. Hence, the results provide useful information for better fertilization management in the Chaohu Lake region of China.

To solve the problem of shortage of agricultural water resources and low utilization rate of fertilizer, a slow-release fertilizer based on chitosan modified water retention function was developed. Solution polymerization and semi-interpenetrating network technology were used to load urea aldehyde into carboxymethyl chitosan superabsorbent resin network. This technology realizes the simultaneous slow release of nutrients and water by using modified chitosan, which has important implications for the application of chitosan in agriculture to regulate the soil water and fertilizer conditions. The optimal preparation conditions were: MBA 0.07 %, KPS 0.8 %, AM to AA mass ratio of 0.3:1, CMC content of 10 %, AA neutralization degree 85 %, UF 20 %, AA+AM mass sum of 10 g, reaction temperature 70 °C and reaction time 2 h. The maximum water absorption rate of the optimized NC reached 172.3 g/g. The cumulative release of nitrogen in 30 days was 83.67 %. The application of NC in sandy soil promoted seed germination and growth. The comprehensive results indicate that NC has broad application prospects in arid areas based on its excellent water retention and nutrient release performance.

A new adsorbent called iron-magnesium oxide coupled lignite (CIMBC) was developed to address the challenges of recovering high concentrations of ammonia nitrogen and phosphate in livestock farm wastewater and improving the inefficient use of lignite (BC) with low calorific value. CIMBC was synthesized using the modified ferromagnesium salt double-coating method. The experiments demonstrated that Fe2O3 and MgO could be effectively loaded onto the surface of BC at a Fe/Mg molar ratio of 1:2 and pyrolysis temperature of 500 °C. The optimal conditions for adsorption were determined to be an N/P concentration ratio of 2:1, adsorbent dosage of 1 g/L, and pH of 7. The presence of coexisting cations (Ca2+ and Mg2+) inhibited the removal of ammonia nitrogen but enhanced the removal of phosphate. Likewise, the presence of coexisting anions (CO32- and SO42-) hindered the removal of both ammonia nitrogen and phosphate. The adsorption behavior followed the pseudo-second-order model and the Langmuir model, with a maximum adsorption capacity of 95.69 mg N/g for ammonia nitrogen and 101.32 mg P/g for phosphate. The adsorption process was a spontaneous endothermic process controlled by multiple levels. The main mechanisms of adsorption involved electrostatic attraction, intra-particle diffusion, ion exchange, chemical precipitation, and coordination exchange. After 5 times of adsorption-desorption, the recovery rate of CIMBC is less than 50%, and the removal rate of phosphate is less than 40%. Although the RCIMBC exhibited low reusability, but also it showed potential in removing heavy metals (Pb) from wastewater and for use as a slow-release fertilizer. CIMBC is a promising new adsorbent, which can realize resource utilization of lignite with low calorific value while removing nitrogen and phosphorus.

The development of alginate-based composites in agriculture to combat nutrient loss and drought for sustainable development has drawn increasing attention in the scientific community. Existing studies are however scattered, and the retention and slow-release mechanisms of alginate-based composites are not well understood. This paper systematically reviews the current literature on the preparation, characterization, and agricultural applications of various alginate-based composites. The synthesis methods of alginate-based composites are firstly summarized, followed by a review of available analytical techniques to characterize alginate-based composites for the attainment of their desired performance. Secondly, the performance and controlling factors for agricultural applications of alginate-based composites are discussed, including aquasorb, slow-release fertilizer, soil amendment, microbial inoculants, and controlled release of pesticides for pest management. Finally, suggestions and future perspectives are proposed to expand the applications of alginate-based composites for sustainable agriculture.

To simplify the process of the application of fertilizers and herbicides for farmers, a slow-release fertilizer containing cyhalofop-butyl (SFC) was developed to prolong the combined effect of the herbicide-fertilizer and achieve a synergistic effect on weeding and reducing N2O emissions. A greenhouse pot experiment was conducted using five treatments: CK (no fertilizer), CF (compound fertilizers), FC (fertilizers combined with cyhalofop-butyl), FF (film-coated compound fertilizers), and SFC (a slow-release fertilizer containing cyhalofop-butyl). The findings indicated that SFC exhibited the lowest N2O emissions, the highest paddy yield, and the highest nitrogen utilization rate among all the treatments. When compared to CF, the nitrogen release was notably delayed, leading to a significant reduction in cumulative N2O emissions under FF and SFC. When compared to CF, N2O emissions under FC were significantly decreased, suggesting that cyhalofop-butyl exerted a reduction role in N2O emissions. The SFC-treated nirK abundance was significantly lower than FF and FC, suggesting that the cyhalofop-butyl of SFC interacted with film of SFC inhibited the denitrification process in the paddy soil. Thus, the SFC reduced N2O emissions by slowing nitrogen release and down-regulating the relative abundance of nirK.

Magnesium-functionalized Magnolia grandiflora Linn leaf-derived biochar (MBC) capable of efficiently reclaiming phosphorus from urine was synthesized by slow co-pyrolysis. Four adsorption kinetic and seven adsorption isotherm models were fitted to the batch adsorption and desorption experimental data, and it was found that pseudo-first-order kinetic model and multilayer model with saturation best described the phosphate-phosphorus (PO43--P) adsorption process by MBC. MBC and phosphorus-saturated MBC (P-MBC) were found to offer outstanding phosphorus adsorption and slow release properties, respectively. Based on material characterization, statistical physics, adsorption energy distribution and statistical thermodynamics, a multi-ionic, inclined orientation, entropy-driven spontaneous endothermic process of MBC on PO43--P was proposed, involving physicochemical interactions (porous filling, electrostatic attraction, ligand exchange and surface precipitation). Further, seed germination and early seedling growth experiments proved that P-MBC can be used as a slow-release fertilizer. Overall, MBC offers prospective applications as an efficient phosphorus adsorbent and then as a slow-release fertilizer.

Zinc (Zn) deficiency has caused nutritional disorders in 17% of the world\'s population; thus, producing Zn-enriched plants as a dietary source is necessary. Recently, nanofertilizers have gained much attention as a substitute for conventional fertilizers; however, soil application of polymer-coated Zn-based nanofertilizer has not been explored much. The present study depicts the green synthesis of ZnO nanoparticles using Melia azedarach L. leaf extract, whose phytoconstituents have reducing abilities. The synthesized nanoparticles were combined with gum acacia (GA) to form a ZnOGA nanocomposite. The structural and morphological properties of ZnOGA were studied using XRD, FTIR, FESEM, and EDX. A pot experiment study was carried out with Spinacia oleracea L. at various doses (3, 5, and 10 mg/kg) of the synthesized ZnOGA to evaluate its effectiveness as a slow-release fertilizer and was compared with a commercial Zn fertilizer. The plant growth studies revealed a significant increase in the phyto-morphological traits of the plants fertilized with ZnOGA compared to commercial fertilizer. The plants also displayed significantly higher contents of protein (17-47%), phenols (25-60%), proline (82-94%), total soluble sugar (20-31%), DPPH activity (70-72%), and Zn uptake (91-106%). The doses of ZnOGA played an imperative role in determining the growth and productivity of the plant. Soil column studies showed that ZnOGA reduces Zn leaching by 52% compared to commercial Zn fertilizer. This study signifies the potential of ZnOGA to be applied as an eco-friendly and sustainable substitute for conventional Zn fertilizer minimizing Zn losses and Zn deficiency-related health problems in human populations.