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Carl R. Crozier, Ronnie W. Heiniger and Michael Bishop

During Summer 1997, soil compaction in agricultural fields was evaluated using a portable electronic cone penetrometer. Rather than requiring the operator to read from an analog scale, this penetrometer stores data in a digital form, which are downloaded to a personal computer for analysis. Soil strength, measured in 1-inch (2.5-cm) increments, can be stored for up to 100 25-inch (64-cm) deep soil profiles. This instrument can be operated by a single person and facilitates collecting large data sets required to characterize highly variable soil environments. Because the penetrometer was designed to measure and formulate predictions about the trafficability of wet soils, it is often incapable of measuring the higher soil resistance occurring in drier agricultural fields. If used soon after rainfall or irrigation, it is useful in detecting hardpans associated with tillage or traffic patterns.

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Charlotte Mundy, Nancy G. Creamer, L. George Wilson, Carl R. Crozier and Ronald D. Morse

Conservation tillage using residue from a cover crop grown before potato (Solanum tuberosum L.) production has been infrequently and inconclusively studied. The objectives of this study were to 1) conduct a field study to evaluate soil physical properties, and potato growth and yield, in conventional-tillage (CT), no-tillage (NT), and subsurface-tillage (SST) systems and 2) conduct a greenhouse study to evaluate the effect of soil bulk density (ρb) on potato growth and yield. Potatoes (`Atlantic') were planted into residue of sorghum-sudangrass [Sorghum bicolor (L.) Moench × S. sudanense (Piper) Staph] at two sites in eastern North Carolina—Plymouth into Portsmouth fine sandy loam and Lewiston into Norfolk sandy loam. Potatoes in the NT and SST system emerged more slowly than potatoesplanted conventionally. There were no differences in plant population or size by 8 weeks after planting at Plymouth, but plant population and size were less in NT and SST systems at Lewiston. Reducing tillage also affected soil compaction, increased soil moisture early in the season at both sites, and increased ρb at Lewiston. Yield of U.S. No. 1 potatoes planted in NT and SST systems were comparable to potatoes planted in a CT system at Plymouth, but were less than potatoes planted in a CT system at Lewiston. There were no differences in yield between potatoes planted with NT and SST. In the greenhouse study, ρb did not affect leaf area or tuber yield or tuber grade. Specific sites and soils may allow for comparable potato production with no or SST, but further research, conducted on different soil types would promote further understanding of the impacts of reducing tillage in potato production.