Abstract
Abstract: Current variable-rate fertilizer applicator generally drives all the fertilizer distributers through the same drive shaft at a fixed working width. Most fields are in an irregular shape during the operation of fertilization, particularly unsuitable for an integer multiple of working width. Severe overlap of working areas normally occurs at the edge of the field, resulting in a large amount of waste of fertilizer at the boundary. In addition, the cross-regional or cross-prescription raster operations are still lacking in the current fertilizer applicator. In this study, a bivariate fertilizer control system was designed to implement the independent control of fertilizer discharging unit in a modified applicator for corn fertilizing. The whole machine was composed mainly of a real-time kinematic (RTK) and global navigation satellite system (GNSS) positioning, a bivariate fertilization control system, and an executing device. Firstly, a calibration test was conducted at different active-feed roll lengths and rotational speeds of the drive shaft. A quadratic polynomial fitting was then used to obtain the bivariate control model for the distributing monomer of fertilizer. Specifically, the coefficient of determination reached 0.9992 in the fitting equation, indicating a high level of fitting. Secondly, an in-depth analysis was conducted for the positioning of each fertilization unit. Thirdly, the hardware and software of the control system were developed using the CAN bus communication to realize the collection, analysis and storage of GNSS information, the operation parameter setting, and the independent control of discharging unit. The hardware was composed of a GNSS navigation device, an industrial personal computer, a servo/stepping motor, a micro-controller, and an electronic ruler. The software was performed on a VS2012 platform with SQL2008 database using C# language. Three function modules were included: the communication, setting of working parameters, and working control in the manual and automatic mode. Finally, a systematic evaluation was completed on the comprehensive performance of the bivariate fertilizer control system, including the consistency of fertilizer discharge in each row, the accuracy of fertilization rate at different vehicle speeds, and independent control performance in each row. The results showed that the maximum coefficient of variation (CV) was 5.37% at the driving speed of 10 r/min within the range of 10-60 r/min of fertilizer shaft speed, as the speed of the driving shaft increased. The minimum CV of each row dropped to 2.99% at the driving speed of 55 r/min, indicating the average CV of consistency was 3.35%. At the target fertilizer rate of 350 kg/hm2, the accuracies of fertilization control were 93.2%, 96.75%, and 97.60% under the working speed of 3, 5, and 7 km/h, respectively. The operating speed was generally around 4-12 km/h in the variable rate fertilizer applicator, meeting the national standard accuracy of fertilizer application. Three experiments were conducted on the road fertilization with irregular boundary shapes, such as the concave y, convex and S boundary. The lag distance change rate fertilization correlated to the working width was less than 15% on average, indicating no influence by the shape of fertilization boundary. More specifically, the variation ratios of lag distance were 10%, 14%, and 13% at the concave, convex and S boundary, respectively. This applicator can be expected to well simulate the fertilization boundary shape, due to its high stability of fertilization, and control accuracy. The bivariate fertilizer applicator with independent control of fertilization monomer can realize the independent control of each row, suitable for the shape of complex fertilization boundary, while reducing fertilizer wastes at the boundary of the furrow. The finding can provide a potential technical reference for the innovative development of variable-rate equipment for basal fertilizer in corn production.
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