David Owens, Extension Entomologist, owensd@udel.edu and Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Congratulations to Will Carlisle for correctly answering soil compaction. Will will receive a sweep net and be entered along with all correct guessers for the end of season raffle. Unfortunately, this is one case where a sweep net is not going to do much to alleviate the problem, unless you put a shovel or soil corer on the end of the handle.
This from Gordon Johnson:
Peas do not perform well in soils that are worked when they are too wet. Compaction will lead to poor emergence and reduced growth. Wet soil conditions, compaction, and poor drainage are also associated with higher rates of infection of root rots in peas such as Aphanomyces root rot, or common root rot. Soil compaction limits root development and root function and will reduce yield potential in vegetable crops such as peas.
There are two processes at play when soils are compacted by equipment. The first is destruction of soil structure. In most Delaware soils, our surface soil structure is granular or crumb in nature and consists of small aggregates. It takes considerable time and good cropping practices to build up soil structure. When compacted by equipment, structure is destroyed, making soils denser. Excessive tillage also destroys soil structure.
A second compaction process is the compression of soil particles, pushing them closer together. This happens with equipment traffic across fields. The heavier the loads carried by equipment passing over soils, the more the compaction. With large equipment and heavy axle loads, significant soil compaction is expected; the heavier the weight on an axle, the more the compaction. Other equipment factors affecting compaction include tire size, tire pressure and operating speeds. Wider tires or dual tires will distribute weight over larger areas, reducing deep compaction but increasing the amount of area with shallow compaction. Higher tire pressures will result in more deep soil compaction and slower speeds will also result in more compaction.
In wet soil, there is less resistance to soil particle movement and soil is more “plastic”. This means that potential for compaction is greater in wet soils than dry soils. It is important to wait until soil conditions are favorable for tillage. Waiting a day or two for soils to dry will improve yield potential by reducing compaction.
Subsoiling in the fall is a short-term solution to deep compaction. The use of forage radish cover crops has shown great potential to reduce shallow and deep compaction. Research in Delaware has shown that peas can be no-tilled after a winter-killed radish cover crop successfully with equivalent or better yields than conventionally tilled peas.