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Fluid Journal : Fluid Journal 1999-2001
2 Fluid Journal Winter 2001 problems such as phosphate deficiency or herbicide carryover. Compaction reduces availability of nutrients, causing stunted growth and discoloration. Uneven growth. This is especially noticeable in corn and is usually caused by wheel tracks and hard pans. Shallow root systems in a compact soil grow sideways and become malformed because of the hard pan. In uncompacted soil, roots grow in a diagonal downward direction. Slow- or non-emergence. Severe crusting may cause the plant to leaf out underground. Once that happens, tiny plants may not emerge. Some corn and soybean varieties have more pushing power than others. Dry weather stress results where compaction causes shallow root systems. Wilting and firing of plants occur. Crusted soil is one of the most obvious characteristics of a compacted soil. Crust can form under the weight of equipment or develop naturally. Remember, a wind-driven raindrop has enough energy to shatter soil particles. Crust is most common on soils with high silt and clay content, but can develop on sandy soils. Cracks in wheel marks, which run parallel to rows, most commonly occur in fine-textured soils. Subsurface compaction or hard pans develop after using a disk or moldboard plow. Standing water collects when rain or irrigation water does not rapidly enter soil due to crust or compacted conditions. It pools on surface or runs off to another site. Excessive soil erosion from water may also occur. Increased pull or horsepower is needed to pull tillage equipment through dense, compacted ground, compared to loose, uncompacted ground. Slower decomposition of residue is caused by an inadequate supply of oxygen. Occurs when soil is compacted or waterlogged. Nitrogen deficiency results in compacted soils from gaseous loss of nitrogen caused by denitrification. Herbicide carryover is common in compacted soils because microbial activity is reduced, causing poor herbicide performance. Causes Causes Causes Causes Causes Though equipment tires are generally blamed, there are other causes as well. Soil type. Low organic matter soils have a tendency to compact more than high organic soils. In some soils very fine materials are washed from the surface or fill subsoil pores. This results in greater compaction. In other soils the tremendous weight of glacial ice has been a natural compacting force. Excessive tillage. Back in the '40s, a three-ton tractor plowing eight inches deep caused little compaction. Today, 4-wheel drive tractors that weigh up to 20 tons, combined with shallower tillage, produce more compaction than ever. Working wet soil. In the spring, working the soil even a half to a full day too early can cause compaction. Check moisture level at the depth you plan to till. The first trip is the most important. Up to 80 percent of compaction can be caused by the first tillage. Overusing disk. The disk is a compacting tool. The edges of the blades exert tremendous pressure on the subsoil at their point of contact. Slow speeds. Higher speed equals less compaction. The faster a vehicle travels, the less compression is exerted under the tires. Yield-bu/A No compaction Severe compaction 90 Year 1 55% loss Year2 25% loss Year 3 12% loss 110 130 150 170 190 210 Table 1. Effects of different tillage on soil compaction, as measured in soil strength that inhibits root growth. Soil strength-lbs/in2 Moldboard Chisel Spring N o-till plow plow disk Surface 80 90 180 210 4 inches 110 150 280 260 8 inches 100 180 260 210 12 inches 140 200 240 205 16 inches 190 200 230 205 Figure 3. Yield losses due to compaction.
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