Introduction
Muskmelon production in the Willamette Valley is usually limited by cool springs, a short growing season, and relatively cool nights, even during mid-summer. Cultural techniques to increase air and soil temperature around plants, such as black plastic mulch and row covers, have hastened development and increased yield of muskmelon in the valley.
A new development in mulch technology is the wavelength-selective film. It provides much of the weed control benefit of black plastic mulch, but warms the soil more than does black mulch. Thermic films, such as the IR-303 Thermofilm, were originally developed as greenhouse covers. They are reputed to reduce maximum and increase minimum temperatures slightly more than standard polyethylene films. These thermic films may have a role as hoop-supported row covers (tunnels). In a preliminary trial in 1990, the combination of black mulch and tunnels of either Lutrasil or IR-303 Thermofilm produced greater early yield than either black film or wavelength-selective mulch films alone. Thermofilm appeared promising for promoting greater total yield. Trials in 1991 and 1992 compared combinations of four mulch films with two different covering materials in enhancing earliness and yield of muskmelon.
Methods
In 1991, Superstar muskmelon was seeded in 5-cm pots in an unheated greenhouse on 15 April. The plot area of Willamette silt loam was prepared by rotary tillage, following a broadcast application of 10N-8.7P-16.6K fertilizer at 400 pounds/acre. Mulches and drip irrigation tubing were applied on 22 May. Melons were transplanted and hoop-supported covers (tunnels) were applied on 23 May. Treatments consisted of a factorial combination of four mulches and three hoop-supported tunnels, with mulches as main plots and tunnels as subplots. Main plots were replicated four times in randomized complete block design. Subplot size was 4 meters with five plants per subplot. The mulches were a standard 1.25-mil black polyethylene, a 0.8-mil brown wavelength-selective poly (AL-OR) from Polyon-Barkai, a 1.25-mil green wavelength-selective poly (IRT-76) from AEP Industries, and a standard 1.25-mil clear polyethylene. The tunnel treatments included a non-covered check, a spunbonded polypropylene (Typar, 60 grams per square meter), and a 2-mil perforated IR-303 Thermofilm (Polyon-Barkai).
Replicated soil temperature measurements were made at 5-cm depth from 23 May until 3 June with copper-constantan thermocouples and a Speedomax 150 recorder. Replicated air temperature measurements were made at 5 cm above ground from 3 June until 11 June. Covers were removed on 19 June. Plots were harvested at least weekly from first fruit ripening in mid-August until the end of September. Early yield was defined as that obtained during the first 10 days of harvest. Only marketable fruit were included in the yield.
In 1992, methods were the same except as follows. Superstar and Passport muskmelon were seeded on 13 April. Mulches were applied on 11 May. Melons were transplanted on 12 May and tunnels were applied on 13 May. Treatments consisted of a factorial combination of two cultivars, four mulches, and three tunnels with cultivars as main plots, mulches as subplots, and tunnels as sub/subplots. Mulches were as in 1991 except that a 0.6-mil clear (Polydak, Polyon-Barkai) replaced the 1.25-mil clear mulch. Among tunnel treatments, the polypropylene material was replaced with a 1.1-mil perforated polyethylene (Ken-Bar, Inc.).
Replicated soil temperature measurements were made 19 May until 26 May. Covers were removed on 2 June. Harvest was from mid-July until early September.
Results and Discussion
1991
Transplants that did not survive were replaced on 29 May or 6 June. Treatment affected plant survival (Table 1). Type of mulch had no effect, but among tunnel treatments, the IR-Thermofilm tunnel resulted in greater mortality than did the non-covered checks or the Typar. The soil was colder than normal at transplanting and saturated with moisture. The plants under the Thermofilm wilted rapidly and did not recover. Mean maximum air temperatures were greater under Thermofilm than under Typar or over mulch alone (Table 2). This could explain the observed differences in wilting and survival, as the root system could not deliver enough water to satisfy the transpiration demands of the shoots in the Thermofilm tunnel environment. The greatest mean minimum air temperature also occurred in the Thermofilm tunnel. The greatest mean maximum soil temperature occurred with the combination of IRT-76 mulch and the Thermofilm tunnel (Table 2). Averaged over all mulches, the IR-Thermolfilm also produced the highest mean maximum soil temperatures. Among mulches, the clear mulch produced the greatest mean minimum soil temperature. Soil maximum temperatures tended to be greatest with the IRT-76 mulch, but the differences were not statistically significant. Air minimum temperature was not affected by mulch type, but mean maximum air temperature was highest above the black mulch. Tunnels hastened flower development but mulch type had no significant effect on the number of flowers that reached anthesis within five weeks after transplanting (Table 1).
Early yield was affected by tunnels but not by type of mulch (Table 1). Early yield with either Typar or Thermofilm was nearly tripled compared to plots without tunnels. The greatest early yield of 1.5 marketable melons per plant was on plots with the combination of clear mulch and Thermofilm tunnel.
For the entire growing season, melon yield was affected by both mulch and tunnel (Table 1). Plants on clear mulch and the two wavelength-selective mulches produced significantly greater numbers of marketable fruit than did those on black mulch. Tunnel-covered plants outyielded those without a cover. Type of cover did not significantly affect yield. The greatest number of fruit per plant (4.5) was produced with the combination of clear mulch and the Thermofilm tunnel. Both mulch type and tunnels affected mean fruit weight (Table 3). Fruit weight was slightly lower with clear mulch as compared to the other mulches, and lower with tunnels as compared to non-covered plants. In each case, this may be due to competition for carbohydrates or nutrients since the treatments producing smaller mean fruit size were also those producing the greatest number of marketable fruit per plant.
These results are consistent with those obtained in 1990 and indicate that during a typical spring and summer, wavelength-selective mulches are best for melon production in the Willamette Valley. However, the best mulch is still inferior to the combination of a mulch and a tunnel. Weed growth was not a problem under the black or the wavelength-selective mulches. Weeds grew readily under the clear mulch but did not impair muskmelon growth and the number of fruit produced. However, the decrease in mean fruit weight with clear mulch might have been caused by weed competition.
1992
A substantial number of transplants did not survive and were replaced on 2 June. In contrast to 1991, the type of mulch affected survival, with greater mortality on black plastic than with the other materials. Among tunnel treatments, the two tunnels resulted in greater mortality than did the non-covered checks (Table 3). Although soil temperature was greater than normal in the two weeks after planting, the greater soil temperature under the wavelength-selective and clear mulches may have favored root development and plant survival. Air temperatures could not be measured while tunnels were in place. However, excessively high air temperatures under the tunnels may have contributed to plant wilting and death. This is consistent with results obtained in 1991. The greatest mean maximum soil temperature occurred with the combination of AL-OR mulch and the IR-Thermofilm (Table 4).
Early yield was not affected by tunnels or type of mulch (Table 3). Mean temperatures in May and June set new 40-year records for NWREC. This may have prevented any response to treatment. In contrast, in 1991, both mulch and tunnels greatly increased early yield during a cold, wet season. In agreement with 1991, neither mulch nor tunnel affected mean fruit weight of the early fruit. However, the trend was for greater mean fruit weight on the clear and wavelength-selective mulches and in the presence of tunnels.
For the entire growing season, melon yield was significantly affected by tunnel but not by mulch (Table 3). Tunnel-covered plants outyielded those without a cover, and the plants covered with the Ken-Bar tunnel outyielded those covered with the Thermofilm tunnel. The greatest number of Passport fruit per plant (4.8) was produced with the combination of clear mulch and the Ken-Bar tunnel; the greatest number of Superstar fruit (3.6 per plant) was produced with the combination of IRT-76 mulch and the Ken-Bar tunnel. In contrast to 1991, neither mulch type nor tunnels affected mean fruit weight. However, as in 1991, the trend was for tunnels to reduce mean fruit weight for the entire growing season.
Weed growth was, again, not a problem under the black or the wavelength-selective mulches. Some weeds grew under the clear mulch, but not to the degree in 1991. The weed growth was not sufficient to impair muskmelon growth and the number of fruit produced.
In conclusion, even in an unusually warm year, row tunnels are a desirable addition to wavelength-selective mulches for muskmelon production in the Willamette Valley.
Table 1. Main effects of mulch and tunnel on transplant survivalz, floweringy, early and total yield, and fruit weight of muskmelon, NWREC, 1991 Early season Total season Transplant Open blossoms/ Fruit/ Fruit wt. Fruit/ Fruit wt. survival (%) plant plant (g) plant (g) Mulch Black 78 0.8 0.8 1565 2.2 1466 AL-OR 90 1.3 0.9 1631 2.9 1405 IRT-76 85 1.2 1.0 1546 3.0 1464 Clear 93 1.3 1.0 1374 3.3 1290 LSD (0.05) NSx NS NS NS 0.6 150 Cover None 99 0.5 0.4 1648 1.9 1537 Typar 93 1.7 1.1 1526 3.2 1364 Thermofilm 69 1.3 1.2 1413 3.5 1318 LSD (0.05) 12 0.5 0.5 NS 0.5 131 zSurvival five days after transplanting. yTotal number of flowers reaching anthesis before 26 June. xNS: No significant differences, p=0.05. Table 2. Interaction of mulch and tunnel on mean maximum and mean minimum air and soil temperatures (degrees F), NWREC, 1991 Mulch Cover Soil min. Soil max. Air min. Air max. None None 50.0 74.0 47.7 83.7 Black None 54.9 72.6 47.6 90.1 Typar 53.8 89.1 49.2 103.1 Thermofilm 59.3 90.1 52.4 119.3 AL-OR None 54.0 77.8 47.6 93.2 Typar 57.8 81.4 49.8 97.3 Thermofilm 61.0 95.6 51.8 117.0 IRT-76 None 56.3 84.2 47.8 90.4 Typar 60.0 82.5 50.6 105.1 Thermofilm 59.8 101.5 51.4 112.3 Clear None 58.1 81.0 48.2 86.1 Typar 60.9 79.8 51.3 99.5 Thermofilm 62.4 98.2 52.5 112.6 LSD (0.05) 1.7 11.7 1.6 4.4 Main effects: Black 56.6 83.9 49.7 104.2 AL-OR 59.4 84.9 49.7 102.5 IRT-76 59.9 89.4 49.9 102.6 Clear 61.7 86.3 50.7 99.4 LSD (0.05) 1.0 NSz NS 2.5 None 55.8 78.9 47.8 90.0 Typar 58.1 83.2 50.2 101.3 Thermofilm 60.6 96.4 52.0 115.3 LSD (0.05) 0.8 5.8 0.8 2.1 zNS: No significant differences, p=0.05. Table 3. Main effects of mulch and tunnel on transplant survival and on early and total yield and mean fruit weight of muskmelon, NWREC, 1992 Early season Total season Transplant Fruit/ Fruit wt. Fruit/ Fruit wt. survival (%) plant (g) plant (g) Cultivar Passport 94 1.9 869 3.8 889 Superstar 91 0.4 1270 2.3 1021 Significance NSz * * * * Mulch Black 80 1.1 883 2.9 923 AL-OR 95 1.1 1114 3.1 993 IRT-76 95 1.2 1276 2.8 948 Clear 100 1.4 1004 3.2 955 LSD (0.05) 10 NS NS NS NS Cover None 100 1.4 1004 2.6 1019 Ken-Bar 89 1.0 1090 3.4 891 Thermofilm 89 1.2 1114 3.1 955 LSD (0.05) 9 NS NS 0.3 NS zNS,*: No significant differences and significant differences between means, p=0.05, respectively. Table 4. Interaction of mulch and tunnel on soil temperature (F), NWREC, 1992 Mulch Cover Soil min. Soil max. None None 57.3 90.6 Black None 61.4 86.8 Ken-Bar 67.4 101.3 Thermofilm 67.5 103.4 AL-OR None 61.0 105.6 Ken-Bar 67.0 109.3 Thermofilm 68.9 114.6 IRT-76 None 61.0 98.4 Ken-Bar 68.4 106.0 Thermofilm 65.8 109.1 Clear None 63.0 104.3 Ken-Bar 67.3 112.0 Thermofilm 68.6 110.8 LSD (0.05) 2.1 13.7 Main effects: Black 65.5 97.2 AL-OR 65.6 109.8 IRT-76 65.1 104.5 Clear 66.3 109.0 LSD (0.05) 1.1 9.2 None 61.6 98.8 Ken-Bar 67.3 107.2 Thermofilm 67.7 109.5 LSD (0.05) 1.3 8.5