The application of fertilizer is necessary for the growth and yield of crops, especially for paddy rice. Precision application is important for the fertilizer utilization rate and sustainable development of agriculture. However, the crushing of fertilizer grains will reduce the quality of fertilization, for the decrease in the size and mass of the fertilizer particles and the degree of crushing mainly depend on the physical and mechanical properties of the fertilizer grains. In this study, the compression strength and critical impact speed of four typical commonly used fertilizer grains, a compound fertilizer of nitrogen, phosphorus, and potassium (NPK compound fertilizer), organic fertilizer, large granular urea, and small granular urea, were measured and analyzed. The static compression test was carried out using a TMS-Pro texture analyzer and the results show that the four kinds of fertilizer grains are brittle materials, and their elastic moduli are 208 MPa, 233 MPa, 140 MPa, and 107 MPa, respectively; the theoretical impact model of fertilizer granules is established based on the compression test result and Hertz elastic contact theory, the theoretical formula for the critical impact speed of fertilizer grains is derived, and the theoretical critical impact strength and speed are worked out. An image capture system for the impact process of fertilizer grains was developed, and the impact test was conducted. The results show that the critical impact speed of the four kinds of fertilizer grains decreases with the increase in granule size, while the variance analysis shows that the effect is not significant. The comparison of the experimental results with the theoretical values shows that the theoretical formula could be used to predict the trends of the critical impact speed of fertilizer grains. The model was optimized with the MATLAB 2018 function fitting tool based on the test and analysis. The goodness of fit of the formula is 0.824, which is 13.43% greater than that of the original theoretical formula, indicating that the modified formula based on the compression test data might estimate the critical impact speed of the granular fertilizer with brittle material properties more accurately. The results may provide a reference for the parameter design of a precision fertilization machine.

Previous studies have demonstrated that slightly acidic electrolyzed water (SAEW) treatment can enhance rice seed growth and promote the accumulation of γ-aminobutyric acid (GABA), a bioactive compound. However, the underlying mechanisms remain unexplored. This study systematically investigated the effects of pH and available chlorine concentration (ACC) of SAEW on rice seed germination and GABA biosynthesis. The changing trends were monitored within 7 days. The results revealed that the treatment group with moderate pH (S2, pH 5.74 ± 0.04) showed significantly higher GABA accumulation (71.27 ± 0.45 mg/100 g) compared with S1 (pH 5.04 ± 0.03) and S3 (pH 6.38 ± 0.04) (p < 0.05). Furthermore, a positive correlation was observed between ACC levels and GABA accumulation, suggesting that ACC plays a crucial regulatory role in rice seed germination. These findings were further substantiated by monitoring the enzymatic activity of glutamate decarboxylase (GAD) throughout the germination process. Notably, while higher ACCs negatively impacted rice seed growth, pH variations within the tested range showed no adverse effects on seed development. The results show that optimal SAEW parameters, considering both pH and ACC, should be carefully determined for practical applications in rice seed production.

Supplemental fertilizer application is critical for improving rice yield. Pneumatic deep fertilization effectively improves fertilizer utilization, but high-speed airflow may disturb the soil and affect the location of the fertilizer particles. An air–fertilizer separator was developed in this study to separate the fertilizer from the airflow before the two-phase flow rushes into the soil, and the airflow is directed away from the surface of the paddy soil. The structural and operating parameters of the air–fertilizer separator are determined in this paper. A quadratic orthogonal rotation combination experiment was conducted, taking structural parameters of the device as variables, and fertilizer injection speed, separation loss rate, and outlet airflow speed as performance indicators, to optimize the design parameters of the air–fertilizer separator. The variance analysis and surface response analysis of the experimental data are conducted, and the mathematical models between the indicators and the influencing factors are established. The optimal parameters were determined using multi-objective optimization, and the experimental verification was carried out. The optimal parameters for the air–fertilizer separator were obtained as an arc radius of the AFAST of 380 mm, central angle of arc trough of 45°, and depth of primary separation arc-trough of 12.5 mm. The validation experimental results show that the fertilizer injection speed is 21.45 m/s, the fertilizer separation loss rate is 10.22%, and the outlet airflow speed is 42.54 m/s. The experimental values are close to the predicted values, with errors of 1.2%, 1.7%, and 1.3%. The results of the study may provide a reference for the development of an air–fertilizer separator for pneumatic deep fertilization in paddy fields.

Conventional underwater vehicles, which are typically equipped with oscillating fins or standard propellers, are incapable of effective locomotion within the viscous, high-resistance environment of muddy substrates common in agricultural ponds. To address this operational limitation, this paper presents a compact dual-screw propelled robot capable of traversing both the water column and soft substrate layers. The robot’s locomotion is driven by two optimized helical screw propellers, while depth control and roll stability are actively managed by a control fin. A dynamic model of the robot–fluid interaction was developed to optimize the screw configuration that achieves a maximum theoretical thrust of 40 N with a calculated 16% slippage rate in mud. Computational fluid dynamics simulations were employed to determine the optimal angle for the control fin, which was found to be 9°, maximizing the lift-to-drag ratio at 12.09 for efficient depth maneuvering. A cable-free remote control system with a response time of less than 0.5 s governs all operations. Experimental validation in a controlled tank environment confirmed the robot’s performance, demonstrating stable locomotion at 0.4 m/s in water and 0.3 m/s in a simulated mud substrate. This dual-screw propelled robot represents a promising technological solution for comprehensive monitoring and operational tasks in agricultural pond environments.

Primary flight feather shafts, a critical structural component of avian flight, exhibit excellent mechanical properties. The cross-sectional and medullary foam internal cavity structures of the feather shaft exhibit a gradual variation along the shaft; however, the mechanism by which this gradual variation influences the mechanical properties of the shaft remains unclear. In this study, the structural characteristics of a primary flight feather shaft were analyzed. Subsequently, the effects of gradual variations in the cross-sectional shape and medullary foam internal cavity structure along the shaft on its buckling resistance, torsional stiffness, and bending behavior were investigated. The experimental results showed that, along the length of the primary flight feather shaft, its cross-sectional shape transitions progressively from circular to approximately pentagonal and finally to quadrilateral, while its medullary foam cavity structure gradually changes from a circular to an inverted triangular shape. Feather shafts with an approximately pentagonal cross-section and an elliptical medullary foam cavity structure exhibit excellent buckling resistance, torsional resistance, and bending stability. Finally, based on the structural characteristics of the feather shaft, bionic samples with different cross-sectional shapes and medullary foam cavity structures were fabricated using fused deposition modeling (FDM), and their bending properties were assessed through three-point bending tests. The experimental results demonstrated that the bioinspired prototype, featuring an approximately pentagonal cross-section and an elliptical medullary foam cavity structure exhibited optimal bending properties, achieving a maximum specific load-bearing capacity of 102.64±1.66 N/g. This study provides bio-inspired insights into the design of lightweight structures.