Steering wheel angle is an important and essential parameter of the navigation control of autonomous wheeled vehicles. At present, the combination of rotary angle sensors and four-link mechanisms is the main sensing approach for steering wheel angle with high measurement accuracy, which is widely adopted in autonomous agriculture vehicles. However, in a complex and challenging farmland environment, there are a series of prominent problems such as complicated installation and debugging, spattered mud blocking the parallel four-bar mechanism, breakage of the sensor wire during operation, and separate calibrations for different vehicles. To avoid the above problems, a novel dynamic measurement method for steering wheel angle is presented based on vehicle attitude information and a non-contact attitude sensor. First, the working principle of the proposed measurement method and the effect of zero position error on measurement accuracy and path tracking are analyzed. Then, an optimization algorithm for zero position error of steering wheel angle is proposed. The experimental platform is assembled based on a 2ZG-6DM rice transplanter by software design and hardware modification. Finally, comparative tests are conducted to demonstrate the effectiveness and priority of the proposed dynamic sensing method. Experimental results show that the average absolute error of the straight path is 0.057° and the corresponding standard deviation of the error is 0.483°. The average absolute error of the turning path is 0.686° and the standard deviation of the error is 0.931°. This implies the proposed dynamic sensing method can accurately realize the collection of the steering wheel angle. Compared to the traditional measurement method, the proposed dynamic sensing method greatly improves the measurement reliability of the steering wheel angle and avoids complicated installation and debugging of different vehicles. The separate calibrations for different vehicles are not needed since the proposed measurement method is not dependent on the kinematic models of the vehicles. Given that the attitude sensor can be installed at a higher position on the wheel, sensor damage from mud blocking and the sensor wire breaking is also avoided.

To obtain a more consistent droplet distribution and reduce spray drift, it is necessary to keep the entire spray boom parallel to the crop canopy or ground and maintain a certain distance from the spray nozzles to the crop canopy or ground. A high-performance boom active control system was developed for boom trapezoid suspension. The hydraulic system and hardware circuit of the boom control system were designed based on analyzing the configuration of active trapezoid suspension. The mathematical models of valve-controlled hydraulic cylinders and active boom suspensions were developed. Step response and frequency domain response analysis of passive suspension were conducted by Simulink simulations, and then key parameters of the boom suspension and hydraulic system were determined. A feedforward proportion integration differentiation (FPID) control algorithm was proposed to improve the tracking performance. The designed control system was assembled on a 24 m boom with trapezoid suspension. The response characteristic of the active boom control system was tested by the step signal and the sinusoidal signal from a six-degree-of-freedom hydraulic motion platform. Firstly, the tracking performance of the active balance control system for the PID (proportion integration differentiation) and FPID control algorithms was compared for a given 0.2 Hz sine signal. Then, for the ground-following control system, the response characteristics in challenging terrain and tracking performance in less challenging terrain were tested. Field experiment results indicate that the maximum rolling angle of the chassis was $3.896°$ while the maximum inclination angle of the boom was $0.453°$. The results show that the designed boom adjustment and control system can effectively adjust the boom motion in real time and meet the requirements of field operation.

Except for transpired water, the intracellular water stored in leaves accounts for only 1–3% of the water absorbed by roots. Understanding water transport and use, as well as the related photosynthetic response, helps with determining plant water status and improving the revegetation efficiency in fragile karst habitats. In this study, we conducted experiments on 8 year old naturally growing plants of Coriaria nepalensis Wall., Broussonetia papyrifera (L.) Vent., and Elaeocarpus decipiens Hemsl. in karst areas. We determined the diurnal variations in leaf electrophysiology, water potential, gas exchange, and chlorophyll fluorescence parameters. The results indicated that C. nepalensis plants maintained a high photosynthetic rate, with a high root water uptake ability and leaf intracellular water-holding capacity (LIWHC). The stomata quickly closed to conserve water within cells and protect the photosynthetic structure. B. papyrifera maintained stable intracellular water transport rate (LIWTR), and the photosynthetic efficiency was increased with increasing intracellular water-use efficiency (LIWUE). B. papyrifera also maintained its photosynthesis by efficiently using the transpired water when the LIWHC was increased. The inter- and intracellular water in the leaves of E. decipiens remained stable, which could be attributed to the leathery leaves and its high water-holding capacity. The photosynthesis of E. decipiens was low and stable. Compared with the high photosynthesis, high transpiration, and low instantaneous water-use efficiency (WUE_i) pattern in C. nepalensis plants, E. decipiens plants exhibited low photosynthesis, low transpiration, and low WUE_i, whereas B. papyrifera plants presented high photosynthesis, low transpiration, and high WUE_i. Plants in karst regions change their transport and use of intracellular leaf water to regulate the photosynthetic performance, which differs among different plant species.

Orychophragmus violaceus (L.) O. E. Schulz adapts to karst environments through a variety of adaptability mechanisms. However, the leaf intracellular water translocation and utilization mechanism is still unknown. This study hypothesizes that plants adapt to dehydration by synergistically adjusting the leaf anatomy, cell elasticity and intracellular water translocation. Leaf structure, elastic modulus (Em), physiological capacitance (CP), impedance (Z), water potential (Ψ_L), leaf tensity (LT) and chlorophyll fluorescence parameters of the detached leaves in plants of O. violaceus and Brassica napus L. were measured at each water loss time (0, 1, 2, 3, 4 and 5 h). The uniform leaves were randomly selected from five different plants for each species. The cell vacuole volume and translocation resistance of intracellular water could be represented by the electrophysiological parameters, such as CP and Z. The results indicated that timely shrinkage of O. violaceus leaves and mesophyll cells together with the increased water translocation resistance retained the intracellular water and maintained the turgor pressure. Water within sponge parenchyma could also be translocated into palisade parenchyma. The PSII reaction center was kept stable, and the photosynthetic activity of O. violaceus was clearly inhibited at 3 h. Palisade parenchyma of B. napus leaves increased quickly to improve the intercellular water translocation due to the strong cell stiffness. Gradually increasing intracellular water translocation resistance and recovery of the cell elasticity slowed down the leaf water loss, which, however, could not timely stop the damage on the PSII reaction center and the photochemical efficiency. The photochemical efficiency was seriously inhibited at 4 h and 5 h. The response mechanism of intracellular water to dehydration can be investigated with the help of leaf electrophysiological traits. However, the direct determination of plant drought resistance using electrophysiological information can still not be realized at present and needs further research.

High-voltage electrostatic fields (HVEFs) can increase the nitrogen uptake of plants. An ammonium cation inhibitor, tetraethylammonium chloride, and a nitrate ion inhibitor, 5-nitro-2-(3-phenylpropylamino)benzoate, were added to ammonium and nitrate growing solutions with and without exposure to HVEFs to investigate the effects of these fields on tomato seedlings. The seedlings were exposed to HVEFs with field intensities of 2.25 and 2.5 kV cm(-1), respectively, for 8 h and the dynamic absorption of nitrogen ions was comparatively analyzed. The seedlings exposed to HVEFs were planted in a greenhouse, the diameter and length of their stems were measured after a 20-d growth period, and their fruit yield was recorded after harvest. Results demonstrated that HVEFs with field intensities of 2.25 and 2.5 kV cm(-1) could respectively improve the dynamic absorption of NH4+ and NO3- by the hydroponically grown tomato seedlings. Many channel proteins were also activated by HVEFs as nitrogen uptake increased. HVEF treatment in the seedling stage is a potential mechanism to enhance nitrogen uptake, cultivate shorter and stockier seedlings, and increase yield.

Conventional mat-type seedlings are still widely used in autonomous rice transplanters and automatically supplying seedling devices suited to conventional mat-type seedlings is difficult to develop. Thus, an autonomous rice transplanter carries at least one person to load the seedling pieces into the seedling box, which has led to an increase in the labor force and low operational efficiency. To solve this problem from another point of view, a machine vision-based system for the real-time monitoring of the seedling amount in a seedling box is developed. This system aims to achieve the monitoring of the fault of seedlings and seedling amount in the seedling box. According to the real-time and accuracy requirements of the image, the image acquisition platform is designed based on a previously developed autonomous rice transplanter. A camera model was developed and camera parameters for correcting the image distortion is obtained. The image processing method and segment method of seedling rows are presented. The algorithms for fault diagnosis and the calculation of the number of remaining seedlings are proposed by image analysis. The software is developed for seedling box fault diagnosis and monitoring the remaining number of seedlings. Field experiments are carried out to test the effectiveness of the developed monitoring system. The experimental results show that the image processing time is less than 1.5 s and the relative error of the seedling amount is below 3%, which indicates that the designed monitoring system can accurately realize the fault diagnosis of the seedling pieces and monitor for the remaining amount of each row. By combining the navigation information, the developed monitoring system can predict the distance from which the remaining seedlings in the seedling box can be planted, which can guarantee remaining seedlings in a seedling box are enough for transplanting until the rice transplanter returns to the supplying seedling site. This implies that one person can provide seedlings for multiple autonomous rice transplanters. This study was limited to supplying the seedling when the rice transplanter passed through the place of the seedling storage situated at the headland. In the future, we decide to conduct a study on path planning of breakpoint endurance so that the rice transplanter can automatically return to the supplying seedling place when the seedling amount in the seedling box is not enough.