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Planting time is the last opportunity to alter the physical environment in soils to provide optimal conditions for seed germination and early growth. Placing seeds at a required depth consistently, seed by seed, and row by row, requires proper down force management during planting.
Each crop has an optimum seeding depth that helps foster uniform germination, optimum growth, and maximum yields. Shallow planted seed is subject to feeding by animals and birds and can result in lodging and rootless corn syndrome. Planting too deep extends time to emergence which can predispose seeds/seedlings to pests and diseases. Excessive down pressure can cause compaction zones and lower actual seeding depth as well as limit root growth later in the growing season.1 Planting seeds at the required depth consistently, seed by seed, and row by row, requires proper down force management. Due to the wide textural variability and different residue conditions in most fields, improper down force management may result in too much down force in some areas and not enough in others.
Down force is the one thing operators have the least amount of control over once in the cab. It is unlikely that one setting would be the best for all conditions. Down force settings should be re-evaluated after each planting rainout because the level of soil moisture may change what is the best setting for a field.
Springs, air bags, air force, and DeltaForce® hydraulic cylinders are down force management platforms available for farmers. Automated down force automatically provides the appropriate pressure for each seed throughout the entire field. The benefits of automatic down force systems would likely be more evident in fields where greater variability in soil physical properties are encountered at planting. Working with a trusted equipment dealer, growers can set a base pressure for auto mode to fit field conditions. The automated down force system then provides the most consistent and dependable management adjusting for field variability.
Using appropriate amounts of down force at planting can improve yield potential compared to excessive or inadequate down force. In both corn and soybean, a yield penalty has been observed when down pressures are greater than a static pressure of 125 psi.2 Early stand counts of corn taken at V4 stage may decrease as down force increases beyond static 125 psi. Static down force settings can be considered those systems that use spring or air bags set for field-wide, planter pass or planter sections. In a Learning Center trial at Huxley, Iowa the static 0 psi treatment showed loss of ground contact; a defect that could add up in large fields (Figure 2).2 Yield potential can be negatively affected when this loss is coupled with less-than-ideal growing conditions.
Figure 2. Field layout of down force management treatments in Iowa corn trials. Blue coloring indicates loss of ground contact.
Planters can be adjusted to improve early plant growth. A 2010 study in Iowa researched corn plant emergence with different load levels of depth-gauge planter wheels on the soil surface. These researchers determined the rate of corn emergence was affected by load level and soil moisture. Loads of 40 to 110 lbs caused more rapid emergence in wet soil conditions. However, corn emergence was more rapid with heavy loads (>200 lb) in dry soil conditions.3
In summary, yield potential may be greatest for fields with optimized planter performance. Seed depth placement is directly related to the pressure of depth-gauge wheels- increased pressure causes deeper seed placement. Seed trench environment is also affected by wheel pressure. The rapidness of plant emergence is affected by down-pressure and soil moisture conditions.
1 Gratton, J., Chen, Y., and Tessier, S. 2003. Design of a spring-loaded downforce system for a no-till seed opener. Canadian Biosystems Engineering. Vol. 45: 229-235.
2 Down force management and its effect on corn and soybean establishment and yield. Demonstration Report. North America Knowledge Transfer. 151215150158.
3 Hanna, H.M., Steward, B.L., and Aldinger, L. 2010. Soil loading effects of planter depth-gauge wheels on early corn growth. Applied Engineering in Agriculture. American Society of Agricultural and Biological Engineers. Vol. 26. 551-556. 180414004711