|Agricultural field planting operations encounter great spatial and temporal variability. Research has shown that seeding depth and soil loading, produced by planting equipment, affect early crop growth as well as crop yield. For these reasons, control system development for seeding depth, planter down force, and press wheel force provides an opportunity to maximize crop yield potential by achieving greater precision in planting depth and more uniform soil loading.
Effective feedback control of these systems requires an improved knowledge of soil-planter interaction forces and how the force distribution changes with planting depth. An experiment was conducted in an indoor soil bin at the United States Department of Agriculture National Soil Dynamics Laboratory in Auburn, Alabama to determine the force distribution due to soil-planter interaction forces on a John Deere MaxEmerge™ Plus agricultural field planter row unit. The experimental design included two factors, planter configuration and planting depth setting, and four replications, which were run in a uniformly prepared Norfolk Sandy Loam soil. Data were collected for four-bar link angle, gauge wheel arm angle, vertical force on the gauge wheels, planting furrow depth, gauge wheel rut depth, and press wheel rut depth, as well as draft and vertical forces acting on the toolbar.
An analysis of variance with mixed effect models was conducted on the response variables previously mentioned. A change in target planting depth from 2.54 cm to 7.62 cm produced a 112% decrease in the gauge wheel rut depth. The same change in planting depth setting produced an increase of 80% and 273% in press wheel rut depths referencing the undisturbed soil surface and gauge wheel rut depth respectively. Across planting depths, vertical force on the double disc opener was not significantly affected; however, a trend of increased force with increased depth was observed. Vertical force decreased on gauge wheels by 48% and increased on press wheels by 55% as planting depth increased. While a significant change in the distribution of total vertical load supported by the planter was not observed for every component interacting with the soil, the percentage supported by the gauge wheels was significantly decreased.
Two linear regression models were produced to estimate planting furrow depth. The first model utilized rut depth measurements and included gauge wheel arm angle (GWAS), an indicator of planting depth setting, and press wheel rut depth referencing the undisturbed soil surface. The model resulted in an adjusted R2=0.82. The second model used resultant forces on planter components interacting with the soil. Stepwise elimination of variables resulted in a model including only GWAS with an adjusted R2=0.78. It is not expected that this model will accurately estimate planting furrow depth for soil conditions outside those present during the experimental data collection, and highly uniform conditions within the soil bin may have contributed to the elimination of variables that would be present in models predicting planting furrow depth for in-field operations.
The response of soil-planter interaction forces, soil rut depths, and planting furrow depth observed during this experiment clearly demonstrated that a redistribution of forces occurred as planting depth setting adjustments were made. The data also indicated that planting depth setting adjustments and actual planting furrow depth are not a one-to-one relationship. Changes to any planter setting adjustment or force input to the system affected not only the component adjusted but also the balance of forces acting on the remainder of the planter row unit components. Results from this experiment and those previously conducted indicate that actual planting furrow depth is a function of planting depth setting and the distribution of forces acting on the planter. For this reason, maximizing crop emergence and yield through improved seeding depth and soil conditions around the seed will likely require feedback control of all planter adjustment settings working in conjunction with as opposed to independently controlled systems.