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Henry G. Taber

Black, clear, and wavelength-selective IRT 76 plastic mulches with or without clear, slitted, hooped rowcovers were evaluated for early muskmelon production in 1991 and 1992. Clear and IRT 76 plastic mulches tripled early yield, compared with bare ground, 130 and 45 cwt/acre, respectively. Highest yields both years were from the combination of rowcover with either clear plastic or IRT 76 mulch-181 cwt/acre in 1991 and 379 cwt/acre in 1992. Yield from clear plastic was superior to that from IRT 76 by 41 cwt/acre in 1991, but not in 1992. The minimum soil temperature for IRT 76 compared with clear plastic was +0. 5F and -2F for 1991 and 1992, respectively. Crop rotation and herbicides were used to provide adequate weed control both years. The best cost-effective early muskmelon production system tested involved clear plastic, rowcovers, and trickle irrigation.

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Henry G. Taber

Tomato transplants were set mid-May 1998, 1999, and 2001, with black plastic mulch and a single line source drip irrigation system. The soil type was a well-drained, central Iowa loam (prairie developed on glacial till) with 2.4% organic matter, 13.1 CEC, and a pH of 6.8. The soil test level of 89 kg·ha-1 of K was considered low for field corn and would require 121 kg·ha-1 of K for optimum yield. The experimental design was a factorial, split-plot, randomized complete block with four replications. The whole unit was K rates (0 to 372 kg·ha-1 of K as KCl). The subunit was cultivar, either `Mtn. Spring' (a determinate) or `Jet Star' (an indeterminate). Fruit harvest began the first week of August and continued weekly for 5 to 8 weeks. As expected, `Jet Star' produced from 12% to 35% more total fruit than `Mtn. Spring'. The K response was best described by a quadratic function. Total maximum yield occurred from 325 to 372 kg·ha-1 of K, depending on the production year. Cullage was high, mostly as a result of ripening disorders, and `Jet Star' consistently produced more culls than `Mtn. Spring', 10% to 11%. Increasing soil K rate did not reduce the percentage of culls. For 2001, increasing K rate to 300 kg·ha-1 of K enhanced `Mtn. Spring' marketable fruit size 18%, from 258 g to 305 g each, but not `Jet Star', which remained at 258 g. There was a difference (P< 0.01) between the varieties for leaf K; `Mtn. Spring' consistently had higher K concentrations, from 0.2% to 0.4%. The leaf K sufficiency range at the rapid flowering and vegetative growth stage was determined to be 3.10% to 3.25% with the corresponding petiole leaf sap K (using a dilution of 1 sap: 1 water) of 5000 mg·kg-1, for the same time period. The correlation between the Cardy meter petiole sap K values and whole leaf K was r= 0.83.

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Henry G. Taber*, Vince Lawson and Diane Shogren

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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Henry G. Taber and D.F. Cox

Three trials, beginning June, July, and September 1991, examined the breakdown of photodegradable plastic bags. The plastic contained a light-sensitive compound dissolved in the polymer to hasten degradation. The bags were placed in east-west rows on bare ground. Other factors studied included turning the bags over either every 3 or 7 days and either filling the bags with fresh grass clippings or leaving them empty. Strength loss was determined with a hand-held puncture tester. Strength increased initially by 36%, 32%, and 63% in the three trials, respectively. The bags took 33, 35, and 64 days to reach brittleness (puncture strength of 180 g) in the three trials, respectively. Once degradation began, all trials showed similar rates of decline. However, the degradation began 7 days after exposure in the first two trials, but not until 14 days after exposure in the September trial. The addition of grass clippings to the bags increased the initial strength and delayed the onset of degradation. Turning the bags every 3 days rather than every 7 did not affect degradation.

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Kimberly A. Klock and Henry G. Taber

Three bone products (meat and bone meal, steamed bone meal, and bone chips) were compared to a water-soluble P source (monocalcium phosphate) for P availability and enhancement of tomato shoot growth. All bone products were finely ground to pass through a 40-mesh sieve. The products were added to a phosphorus-deficient greenhouse growing medium based on their P concentration with P at 50, 100, 200, and 400 mg·kg−1. Meat and bone meal produced the least shoot growth in 1992, but all products were similar in 1993. Growth peaked with P at 111 mg·kg−1 in 1992, but in 1993, P at 50 mg·kg−1 was sufficient. Shoot P uptake was in direct proportion to P availability in the soil mix, monocalcium phosphate having the highest shoot P content. Although bone products affected N, Ca, Zn, and Mn content in shoots, the magnitudes of differences were minor and inconsistent from 1992 to 1993. Major consideration for using a bone product are its relative cost of P, fineness of grind, and CaCO3 equivalent.

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Gail R. Nonnecke and Henry G. Taber

The purpose of this project was to investigate the use of evapotranspiration (ET) as a guideline for trickle irrigation timing in field-grown day-neutral `Tristar' strawberry. Proper management of trickle irrigation would allow optimum yields and quality with minimum water inputs. A randomized complete block field design with four replications was used at the ISU Horticulture Station in central Iowa. Irrigation treatments were based on % of ET and number of applications per week. The four treatments included: 30, 60, and 90 % of ET applied once per week (1X) and 30% of ET applied 3 times per week (3X). Total yield data (kg of fruit per season) indicated the 30% of ET (3X) treated plants yielded 15% more fruit than the 30% of ET (1X) plants. Berry number was 14% greater from plants receiving the 30% of ET (3X) treatment than from those receiving the 30% of ET (1X) treatment. Average berry weights for the entire growing season were similar among all treatments.

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Joseph Aguyoh, Henry G. Taber and Vince Lawson

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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Roy H. Peterson and Henry G. Taber

Five polyethylene rowcover treatments (none, slitted white, slitted clear, chimney, and perforated) were combined factorially with four tomato [Lycopersicon esculentum (Mill)] cultivars (`PikRed', `Jetstar', `Supersonic B', and `Heinz 1810') in a 2-year experiment. Clear or white rowcovers more than doubled early yield in 1986, from 1.2 to 2.9 t·ha-1. This early yield advantage resulted from an advancement of flowering rather than an increase in fruit number or size. In Spring 1987, high temperature caused increased fruit abortion with all rowcovers, resulting in early yield reduction. Flower production on the first two clusters for either year was not reduced by high temperatures and was increased for `Heinz 1810'. Tomatoes under slitted, white covers, the best-yielding treatment in 1987, yielded only 72% of those without rowcovers. Sustained high temperature, ≈ 40C for 3 consecutive hours or more, occurred with all rowcovers and correlated with early yield loss.

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Karen Joslin*, Henry Taber, Sara Helland and Mark Gleason

Disease management in organic tomato production poses one of the greatest challenges for organic producers in humid climates. Both organic and conventional tomato growers have relied on copper (Cu) fungicides to control many diseases, including Septoria lycopersici common in tomato production. Concerns have been raised regarding the use of Cu fungicides, because of their potential to cause plant damage and toxicity to beneficial organisms. The objectives of this research were to: 1) investigate the efficacy of compost tea made from either windrow composted cattle manure (WCCM) or vermicomposted cattle manure (VCM), and 2) compare the efficacy of organic fungicides with conventional fungicides to control S. lycopersici in organic tomatoes. Treatments included 1) a control, 2) a conventional treatment in which fungicide applications of Bravo plus Cu and Quadris plus Cu were alternated, 3) copper fungicide (Champion), 4) Serenade™ Fungicide (Bacillus subtilis), 5) WCCM compost tea, and 6) VCM compost tea. Disease pressure was mostly from the bacteria speck/spot complex. Disease severity was significantly (P < 0.05) reduced and marketable yield was 60% higher with the two Cu treatments (No. 2 and 3), compared to other treatments. A follow-up greenhouse experiment is in progress and will be presented with the field data.

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Fredy R. Romero*, Richard J. Gladon and Henry G. Taber

Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the US, based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total nitrogen (N) concentration and the ratio of N sources. Our objective was to determine the N concentration and ratio of N sources that optimize bedding-plant impatiens growth and development. We used four N concentrations (3.5, 7, 10.5, and 14 mmol·L-1 of N) in factorial combination with four ratios of nitrate-N (NO3 --N) to ammonium-N (NH4 +-N) (4:0, 3:1, 1:1, and 1:3). Application of treatments began at day 30, and every-other-day applications were conducted until day 60. From day 60 to day 70 only deionized water was applied. N concentration and source displayed interation for most growth parameters. When N was supplied at a concentration ≤7 mmol·L-1, the NO3 --N to NH4 +-N ratio did not affect growth. When N was supplied at a concentration ≥10.5 mmol·L-1, a 1:3 NO3 --N to NH4 +-N ratio yielded the greatest shoot dry weight, shoot fresh weight, plant diameter, and number of flower buds per plant. With a NO3 --N to NH4 +-N ratio of 4:0, these growth parameters decreased. To produce high-quality, bedding-plant impatiens, N should be applied at NO3 --N to NH4 +-N ratios between 1:1 and 1:3 in combination with an N concentration of 10.5 mmol·L<-1 at each fertigation from day 30 to day 60 of the production cycle.