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Fluid Journal : Fluid Journal 1993-1995
3 Fluid Journal Late Spring 1993 occurred in the uncompacted treatment, whereas response in the compacted treatment was 0.28 ton/A. While this effect was not significant at other cuttings, a similar trend was observed, suggesting that alfalfa is more responsive to K fertility on compacted soils. Recognize that even though yield was increased at higher soil test K levels, yield was considerably lower than yield measured in the uncompacted treatment at low soil test K. It should be obvious that compaction should be avoided. The effect of compaction on forage K concentration is shown in Table 3. Compaction consistently reduced K concentration in the forage, except in cases where dry conditions limited growth (second cut each year). This is interesting to note in light of the fact that soil test K was apparently increased by compaction and that less dry matter (which would dilute tissue K) was produced in compacted treatments. This finding is consistent with other research, which demonstrated that inadequate soil aeration from reduced soil porosity caused by compaction reduced plant uptake of monovalent cations, such as rubidium and potassium. Bulk density measurements were taken each season from the main plots with a 1.3-inch diameter probe, spaced at six-inch increments to a depth of 24 inches. Yield measurements were taken with a three-foot flail mower mounted on a small tractor. A subsample of the harvested material was taken to determine dry matter and nutrient content. Surface soil samples were taken to a depth of six inches following the second harvest. Stand counts (three per plot) were also taken following the second cut. Plant tissue and soil analyses were conducted by the UW Soil and Plant Analysis Laboratory, according to standard procedures. Data were analyzed using SAS statistical procedures (SAS Institute. Cary, NC). Significance is expressed as the probability that tabular value is greater than that determined by the analysis of variance (Pr>F). Traffic main culprit Soil compaction long has been recognized as a yield limiting factor in crop production. Researchers have described the causes of soil compaction and its negative effects on crop production. Most compaction research has been on row crops, with relatively little reported on the relationship between soil compaction and legume forage production. The most significant cause of soil compaction is the use of heavy equipment, with little regard to controlling traffic patterns on wet soils. Negative effects include: reduced porosity and aeration, increased resistance to root penetration, reduced nutrient uptake and yield reductions. In perennial crops, such as alfalfa, compaction problems may exist before stand establishment or develop after seeding because the soil is subjected to many traffic passes (e.g., topdressing, cutting, raking, baling, or chopping). Yield stand and loss may also be caused by physical damage to the alfalfa crown from wheel traffic. Researchers in California have shown a 26 percent reduction in alfalfa, related to both situations. Researchers in Wisconsin found that preplant compaction consistently reduced K concentration in alfalfa, but inconsistently affected yield. Over several years of this study, the volume of soil having an increased penetration resistance decreased, suggesting that long-term forage production may ameliorate compaction effects. Dr. Wolkowski is extension soil specialist and Dr. Bundy is professor in the Department of Soil Science at the University of Wisconsin, Madison. J Acknowledgment: The Fluid Fertilizer Foundation and PPI provided partial funding for this research as a grant.
Fluid Journal 1996-1998