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  • Author or Editor: Vince Lawson x
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Sweet corn (Zea mays L.) growers in the upper midwestern U.S. have used clear plastic mulch to improve early yield and advance crop maturity. Results of this practice have been inconsistent because of early season temperature variability and inadequate information on cultivar adaptation. Our objective was to improve the performance consistency by investigating earliness techniques with the early, sugary-enhancer (se) cultivar Temptation planted at two sites. Treatments were bare soil or clear plastic mulch, rowcovers or none, and direct-seeded or transplanted plants. Transplants were produced in the greenhouse in either 50-cell plastic trays or peat pot strips, 2.3 inches × 4.0 inches deep (6 × 10 cm) and were evaluated according to transplant age and cell size. In the cold springs of 1996 and 1997, the use of clear plastic mulch shortened maturity of sweet corn by 1 and 10 days, respectively, for the silt loam site; but no maturity advantage was observed for the loamy sand site. Clear plastic raised the minimum soil temperature by 3.8 to 4.0 °F (2.1 to 2.2 °C) at both sites. The 2-week-old 50-cell tray transplants matured 6 days earlier than the peat pot strip transplants or direct seeded at both locations in 1997. Marketable yield from the transplants was inconsistent by location and year. Four-week-old transplants did not withstand field stress and performed poorly regardless of type of container. Ear quality as indicated by row number, ear diameter, ear length, and tipfill was lowest with transplants.

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Undiluted tomato petiole sap from a variety by K rate experiment (48 treatment rep combinations) was used to measure K concentration via the battery operated portable Cardy meter and ICP laboratory instrumentation. Three sample 1998 dates, 16 July., 21 Aug., and 8 Sept., resulted in K sap readings by ICP of 3917, 2612, and 2297 ppm, respectively. At sap levels below 3000 ppm the linear Cardy:ICP correlation was r = 0.04, but above 3000 ppm only 0.53. From 3500 to 5000 ppm K the Cardy meter under estimated actual sap K by 200 to 900 ppm. For the years 1999 and 2001, tomato petiole sap at each sample date (4) was diluted 1:1 with deionized water. The linear regression equation describing the relationship between ICP and Cardy meter measurements was: Cardy K ppm = 0.733 * ICP + 685 (r = 0.92, n = 190). The Cardy meter error over the 2000 to 5000 ppm K range was 8 to 12%. Petiole sap K, measured by either Cardy or ICP, was highly correlated to whole leaf K concentration both years. But even though the slope of the regression lines was similar the intercepts were significantly different (P≤.01). The significant 0.32% K difference in whole leaf between years precluded the development of a common regression line to predict whole leaf K from Cardy petiole sap determinations. The Cardy meter can be reliably used for tomato petiole K determination provided the sap is diluted and the usual handling precautions are taken to prevent petiole moisture loss.

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