What deteriorates the physical, aerobic and water condition of the soil?

Soil compaction occurs when soil particles are pressed together, reducing pore space between them. Heavily compacted soils contain few large pores, less total pore volume and consequently a greater density. A compacted soil has a reduced rate of both water infiltration and drainage. This happens because large pores are more effective in moving water downward through the soil than smaller pores.

With increasing farm size, more acres need to be covered each day to conduct field operations in a timely manner. The width and weight of field equipment are increasing, and so is the horsepower of the tractors needed to pull them. The weight of tractors has increased from less than 3 tons in the 1940's to approximately 18 tons today for the big four-wheel-drive units. Wheel traffic is without a doubt the major cause of soil compaction.

Soil compaction can have both desirable and undesirable effects on plant growth. Research from North America and Europe indicates that crops respond to soil compaction. In a dry year, at very low bulk densities, yields gradually increase with an increase in soil compaction. A slightly compacted soil can speed up the rate of seed germination because it promotes good seed to soil contact. This is why corn planters have been designed specifically to provide moderate compaction with planter mounted packer wheels that follow seed placement. As soil compaction increases beyond optimum, yields begin to decline. In dry years, soil compaction can lead to stunted, drought-stressed plants due to decreased root growth. Without timely rains and well-placed fertilizers, yield reductions will occur.

With wet weather, yields are decreased with any increase in compaction. Soil compaction in wet years decreases soil aeration resulting in increased denitrification. There can also be increased risk of root diseases. All of these factors result in added stress to the crop and, ultimately, yield loss.

Soil compaction can influence plant height by preventing normal root development. This is most detrimental if it is shallow compaction (6-8 inches). If timely rains do not soften the compacted layers so roots can penetrate the soil, plants will be stunted, have fewer fine roots, and less overall root mass. Corn is most sensitive because it is one of the taller crops. By the end of the season, corn may become 6 inches to 4 feet shorter on compacted soil than on non-compacted soil.

Crop yields are reduced when soil compaction decreases crop emergence, crop growth, and nutrient uptake. Some researchers estimate soil compaction can reduce yield as much as 60%. The ranges in yield effects are broad because the outcome of compaction is variable and due to many factors, nor are compaction effects consistent across the field.


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