With the concentrated dairy industry in the Shenandoah Valley of Virginia, crops there are often grown on land fertilized with liquid manure that is hauled into the fields in tanker loads. While the manure is valuable for its nutrients and organic matter, the weight of the tankers concerns those who understand the dangers of soil compaction.
Similarly, the higher clay content of Virginia soils west of the Tidewater region, combined with the need to spread liquid dairy manure, often translates into greater soil compaction.
No-tillers are not immune to the problem. Although the higher level of organic matter in no-till soils prevents some compaction, it cannot overcome the compacting forces of heavy machinery. And while earthworms, plant roots and freezing and thawing will undo some compaction, nothing avoids the problem better than conscientious management that accounts for soil moisture, heavy axle loads and traffic patterns.
Soil scientist Sjoerd Duiker of Penn State University studies compaction in Pennsylvania. He uses a penetrometer to find the depth of the compaction layer and to measure the amount of pressure needed to penetrate the soil. He says plant roots will be inhibited when the soil is tight enough to require more than 300 pounds of pressure per square inch for penetration.
In a recent field demonstration, a set of portable scales was used to measure the axle load of manure spreaders. While traditional, truck-mounted tankers with conventional highway tires had the lowest axle load, they had the highest contact pressure on the…