Author
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Lehrsch, Gary |
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Submitted to: Soil Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/7/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Soils that are frozen, then thawed repeatedly from fall through winter to spring, often are weakened and thus less able to resist erosion by wind and/or water. One to 3 freeze-thaw cycles (FTCs), however, may initially increase the stability of naturally occurring clusters of sand, silt, and clay (termed soil aggregates) when sieved in water. This experiment was designed to i) measure the stability of four agriculturally important soils from the Northwest and upper Midwest after 0, 1, 2, and 4 FTCs, and ii) identify a threshold number of FTCs up to which aggregate stability (AS) increased. Moist soil was packed into small brass cylinders, sealed in polyethylene bags, then frozen at -5 C for 48 h and then thawed at +6 deg C for 48 h for each FTC. For all four soils, AS increased, in general, with the first 1 to 2 FTCs, but changed little thereafter. For three of four soils, 2 to 3 FTCs appeared to increase AS to a threshold. Land managers should permit surface soil to freeze two or three times in the fall or alternatively, insulate the soil using crop residue from no-till or minimum tillage production systems or snow trapped by standing small-grain stubble. With the soil insulated, fewer FTCs should occur. Technical Abstract: Research has suggested that 1 to 3 freeze-thaw cycles (FTCs) may increase the stability of soil aggregates, when field-moist aggregates are wet sieved. The objectives of this laboratory experiment were to quantify aggregate stability of relatively wet aggregates from the Ap horizons of four soils when subjected to either 0, 1, 2, or 4 FTCs and, secondly, to identify a threshold number of FTCs for each soil below which aggregate stability increases. Moist soil was packed into 28-mm diam, 50-mm-tall brass cylinders by tapping to a dry bulk density of 1.15 Mg per cubic m, sealed in polyethylene bags, then slowly frozen convectively at 5 degrees C for 48 h, then thawed at +6 degrees C for 48 h for each FTC. The first 1 to 2 FTCs in general increased aggregate stability, but additional FTCs had little effect. For 3 of 4 soils, 2 to 3 FTCs appeared to increase aggregate stability to a plateau or threshold. FTCs increased aggregate stability, when averaged across the four soils, more in the 0- to 15-mm depth increment than in the 15- to 30-mm increment. |
