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  • Author or Editor: Katrine A. Stewart x
  • Journal of the American Society for Horticultural Science x
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Temperature modification is the most investigated environmental factor considered to affect muskmelon (Cucumis melo L. Reticulatus Group) growth in a mulched minitunnel production system. Until now, effects on CO2 concentrations within the tunnel have been ignored. Experiments on production of `Earligold' netted muskmelon were conducted in 1997, 1998, and 1999 to determine daily CO2 concentrations for 10 mulched minitunnel and thermal water tube combinations. Carbon dioxide concentrations under nonperforated (clear or infrared-blocking polyethylene) tunnels were significantly higher (three to four times) than that of ambient air. Soil respiration under the plastic mulch was primarily responsible for increased CO2 levels in the tunnel. Daily CO2 concentrations in the tunnels varied little during early muskmelon growth, but fluctuated widely as the plants developed. Ventilation significantly decreased CO2 concentrations in the tunnels but levels remained significantly above the control and perforated tunnel treatments. When using mulched minitunnels for muskmelon production, daily CO2 concentrations should be recognized as a significant factor influencing growth.

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Field experiments were conducted during 1997, 1998, and 1999 to determine effects of 10 combinations of mulched minitunnel and thermal water tube on air, soil, and water-tube temperatures and on vegetative growth of `Earligold' netted muskmelon (Cucumis melo L. Reticulatus Group) within the tunnels. Use of mulched minitunnels significantly increased air, soil and water temperatures during the preanthesis phase in all years compared with control treatments. Inclusion of water tubes and venting the tunnels decreased air temperature fluctuations in the tunnels. During the first 10 to 15 days after transplanting, plants grown in nonperforated tunnels had higher relative growth rates (RGRs), net assimilation rates (NARs), and dry weights (DWs) than those grown under perforated tunnels and control plots. Plants in tunnels containing thermal water tubes generally had higher RGRs, NARs, and DWs than those without tubes. During the later part of the experiment, from 11 to 16 days after transplanting until anthesis, however, there were no consistent effects of mulched minitunnels on RGR, NAR, and plant DW. Tunneled muskmelons had significantly higher RGRs, but generally lower NARs than those grown without tunnel. Use of mulched minitunnels significantly increased plant DW at anthesis in 1997, but not in 1998 and 1999. Plants grown in the minitunnels containing a thermal water tube generally had higher RGRs, NARs, and DWs than those without water tubes. Ventilating nonperforated tunnels generally increased RGR, NAR, and plant DW. Plants grown in the tunnels reached anthesis 10 days earlier than those without tunnels.

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A seaweed extract (Cytex) was incorporated at 0%, 1%, 2%, and 3% (v/v) into four carrier gels used for fluid drilling. The gels were: magnesium silicate (Laponite), starch acrylate polymer (Liquagel), potassium copolymer (Viterra Agrigel), and a starch (Water lock B-100). When moisture was not lost, the pH values were significantly different among diluted gels (1 gel : 1 water, v/v) and ranged from 6.8 to 9.2. Incorporation of the seaweed extract significantly decreased the pH of the gels. Osmotic potential values of all the gels were close to 0 MPa, with potassium copolymer having a significantly lower osmotic potential (−0.03 MPa) than that of starch acrylate polymer (−0.007 MPa). Incorporation of the seaweed extract signficantly decreased the osmotic potential of the gels between −0.12 and −0.16 MPa. When gels were dehydrated to simulate water stress conditions (0% to 50% water evaporation), pH values were decreased further (ranging from 4.6 to 6.8). Osmotic potential decreased in all the gels to a range between −0.22 and −0.36 MPa with increasing moisture loss.

Open Access

A simple method to predict time from anthesis of perfect flowers to fruit maturity (full slip) and yield is presented here for muskmelon (Cucumis melo L.) grown in a northern climate. Developmental time for individual muskmelons from anthesis to full slip could be predicted from several heat unit formulas, depending on the temperature data set used. When temperature at 7.5 cm above soil level was used, the heat unit formula resulting in the lowest coefficient of variation (cv=6.9%) accumulated daily average temperatures with a base temperature of 11 °C and an upper threshold of 25 °C. With temperatures recorded at a meteorological station located 2 km from the experimental field, the method showing the lowest cv (8.9%) accumulated daily maximum temperatures with a base temperature of 15 °C. This latter method was improved by including a 60-degree-day lag for second cycle fruit. The proportion of fruit volume at full slip of 22 fruit from the first cycle could be described by a common Richards function (R 2=0.99). Although 65% of the plants produced two fruit cycles, fruit from the first cycle represented 72% of total yield in terms of number and mass. The blooming period of productive flowers lasted 34 days, each cycle overlapping and covering an equal period of 19 days. Counting the number of developing fruit >4 cm after 225 degree days from the start of anthesis (when 90% of the plants have at least one blooming perfect flower) could rapidly estimate the number of fruit that will reach maturity.

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Growth of `Earligold' muskmelon (Cucumis melo L.), expressed as plant dry weight from transplanting to anthesis, could be predicted using a multiple linear regression based on air and soil temperatures for 11 mulch and rowcover combinations. The two independent variables of the regression model consisted of a heat unit formula for air temperatures, with a base temperature of 14C and a maximum reduced threshold of 40C, and a standard growing-degree day formula for soil temperatures with a base temperature of 12C. Based on 2 years of data, 86.5% of the variation in the dry weight (on a log scale) could be predicted with this model. The base temperature for predicting developmental time to anthesis of perfect flowers was established at 6.8C and the thermal time ranged between 335 and 391 degree days in the 2 years of the experiment.

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