Did You Plow Yet?
Posted: March 20, 2012
Typically the conversation that follows goes something like, I was in Lancaster and there are a lot of fields plowed out there. Then I say, “Yes, but they have well drained limestone soils compared the heavier clay soils in our area. They also farm with mules and can’t get their fields tilled as fast as farmers that use tractors.”
This spring there has been a lot more tillage done in March that what we would typically expect to see. The unseasonably warm weather and extended dry periods have dried the soil allowing for farmers to haul manure, spread fertilizer and do tillage. But, just because it hasn’t rained for a week doesn’t mean the soil is dry enough to plow.
How do you know if the soil is dry enough for plowing or tilling? Quite often if the undisturbed soil on the surface of the ground is not dry and crumbly the soil 8” below is not dry enough for tillage. If the soil is too wet for tillage the tilled ground will not crumble but rather create clods. Those clods will dry out and become hard and require repeated tillage to break them apart, which will in turn damage the soil structure.
Tilling wet soil also causes compaction. A moldboard plow exerts down pressure on the soil below the plow as it lifts and turns over the upper portion of the soil. The force will create a “plow pan” which is a compaction layer a couple inches think that restricts the movement of water through the soil profile and also limits plant rooting depth. Chisel plows, dics and roto-tillers also create “plow pans”.
Besides reducing yields, soil compaction also reduces soil health and environmental quality:
- Compacted soil is dense and has low porosity. Compaction preferentially compresses large pores, which are very important for water and air movement in the soil. Infiltration is then reduced and erosion is increased.
- Compaction causes an increase in the soil’s penetration resistance. There is little root penetration in soil above 300 psi (pounds per square inch), except if there are cracks and macropores in the soil that can be followed by plant roots.
- More energy is expended when tilling compacted soil.
- Compacted soil is a harsher environment for soil organisms, especially earthworms, to live in.
- Compaction affects nutrient uptake. Denitrification rates can increase in compacted soil due to limited aeration. Manure ammonia volatilization losses have been found to increase when liquid manure is surface applied to compacted soils because of reduced infiltration. Phosphorus and potassium uptake can be reduced if root growth is inhibited.
Even though this late winter/early spring we have experienced unseasonably warm and dry weather the soil may not be as dry it should be for tillage. Be patient for the soil to adequately dry before you start your spring tillage.
Wet spot in moldboard plowed field (notice shiny appearance, cloddy)
For more information on Soil Management visit the Penn State Agronomy Guide online at http://extension.psu.edu/agronomy-guide/cm/sec1/sec1