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Modulating wheat seeding rate for site specific crop management
Abstract
Site Specific Crop Management is a technique by which agricultural inputs such as seed, fertilizer and herbicides are adjusted to match the requirements of specific field areas. Agricultural machines must apply the correct application rate at each field location. One possibility is to add a controller to obtain variable rate capability from conventional metering mechanisms for uniform application. Two control systems for variable rate capability with conventional grain drills were evaluated in this study. Both were operator controlled open loop systems. One system used a set of rate switches. An electric linear actuator moved the meter adjustment lever and contacted limit switches for each rate setting of external fluted wheel meters. The other system used a rheostat to control the speed of an electric motor driving internal fluted wheel meters. Seeding rate and rate change response were determined by operating the drills over a course of artificial turf mats. A four-parameter sigmoid model described the distribution profile. The linear actuator system response time averaged 5.6 s for a 20 kg/ha rate increase. The response time varied considerably for a 10 kg/ha increase and was inconsistent for decreased rates. For rotary actuation, response times varied from 3 to 9 s depending upon the rate change magnitude. This control system performed well for rate increases and decreases. Finally, theoretical guidelines were developed to characterize the transition area accompanying a change from one application rate to another. Response time was divided into (1) actuation lag and (2) actuator mechanical response. Actuation lag was greater for the linear actuator. Generally, the mechanical response was longer for decreasing rates. For a 10 kg/ha rate change, the 68% confidence interval lower limit of the final rate overlapped the 68% confidence interval upper limit of the initial rate. With a 20 kg/ha change, no rate overlap occurred. More variability was associated with the estimation of the inflection point of the sigmoid curve for 10 kg/ha than for 20 kg/ha. This indicates that the metering systems were less suitable for smaller rate changes.
Subject Area
Agricultural engineering|Agronomy
Recommended Citation
Bahri, Abdeljabar, "Modulating wheat seeding rate for site specific crop management" (1995). ETD collection for University of Nebraska-Lincoln. AAI9611039.
https://digitalcommons.unl.edu/dissertations/AAI9611039