Introduction
Tomato and muskmelon production in the Willamette Valley is limited by cool springs, a short growing season, and relatively cool nights, even during mid-summer. Cultural techniques to increase the mean air and soil temperature around plants, such as black plastic ground mulch, floating row covers, and tunnels, have hastened development and increased yield of both these crops.
Melons have nearly always responded favorably to row covers at the North Willamette Station, although in 1983, fruit size was reduced. Tomatoes have responded favorably to covers in most instances, but tomato yields have been reduced by covers during unusually warm seasons. Other plant protection devices, such as hotcaps and water-insulated shields, have not been compared directly to row covers for melon and tomato production. The purpose of these trials was to compare the effectiveness of several plant protection devices in increasing early and total yield of tomato and muskmelon, for both very early and normal transplant dates.
Methods
'Pikred' tomato was seeded in 2-inch pots in a heated greenhouse on 16 February and 13 March, 1987, and on 31 March, 1988. 'Goldstar' muskmelon was seeded on 8 April and 23 April, 1987, 'SuperStar' muskmelon on 20 April, 1988. The plot area was prepared by rotary tillage in late March following a broadcast application of ION-8.7P-8.3K fertilizer at 1,000 pounds/acre. Black plastic mulch (0.04 mm x 1.2 m) was applied to the appropriate plots after laying drip irrigation tubing and the first transplanting of tomatoes was made on 2 April, 1987. The six plant protection treatments were applied immediately after planting with four replications in randomized block design. Each planting and crop was a separate experiment. Plot size was 3.7 m of row with five plants/plot. Between-row spacing was 2 meters.
Treatments for the early 1987 plantings consisted of a bare ground check, black plastic mulch, black plastic plus WallO'Water (water-filled tubes encircling the plant), black plastic plus Protecta-Cap (a self-venting hotcap installed in the vent-open position), black plastic plus Agryl P-17 (nonwoven polypropylene) floating cover, and black plastic plus Agryl P-17 supported by hoops at 1 meter intervals. Treatments for the other plantings were the same except that the row cover-tunnel material was Agronet M (coextruded polypropylene-polyamide). The second or "normal" planting date for tomato in 1987 was 28 April, still an early planting for the Willamette Valley. Tomatoes were transplanted on 10 May in 1988. Melons were transplanted on 4 May and on 14 May, 1987, and 17 May, 1988.
In 1987, air temperatures were sensed by thermocouples placed 2.5 cm above the soil surface and were recorded on a Speedomax multipoint recorder for three replications of each treatment of both tomato plantings and the first melon planting. The temperature record was maintained from 2 April until 26 May. Plant protectors, except black mulch, were removed from the first tomato planting on 14 May, the second tomato and first melon plantings on 26 May, and the late melon planting on 11 June, 1987. Plots were harvested at least weekly from first fruit ripening until 14 October. In 1988, air temperature was recorded from 25 May until 14 June, when the plant protectors were removed.
Results
Treatment effects on mean daily maximum and minimum air temperatures and heat unit accumulation are given in Table 1. All protectors increased maximum temperatures and heat units compared to bare ground in 1987. The floating cover always provided the warmest environment. Minimum temperatures were consistently increased by all protectors except the ground mulch. The WallO'Water had less effect on daytime temperatures for the later planting in 1987 and in 1988 than for the first planting of 1987. Algae growth in the tubes was greater late in the spring and produced some shading. Increased plant growth in the WallO-Water environment also produced shading. Minimum temperatures were always highest in the WallO'Water as the water-filled tubes released heat into the plant environment at night.
The WallO'Water and floating cover were particularly effective in reducing plant exposure to temperatures of less than 4°C (Table 1); the Protecta-Cap and tunnel also reduced exposure to low temperatures. The floating cover and tunnel treatments, whether Agryl P-17 or Agronet, resulted in the greatest number of days of temperatures considered excessively high (over 30°C) for tomatoes.
In 1987, the number of tomato flowers reaching anthesis at time of plant protector removal was greater than in the check for all treatments except the mulch (Table 2). Anthesis of perfect flowers of muskmelon tended to be earlier for all protectors, including the ground mulch (Table 4).
Time to first ripe tomato was reduced by most protectors in the first planting of 1987 but not for the other plantings (Table 2). Plant protectors tended to increase early yield for the first planting (Tables 2 and 3) of 1987 and in 1988. In the second planting of 1987, the Protecta-Cap did not increase yield and the percentage increase with the other protectors was smaller than for the first planting. For all plantings, early yields were higher with tunnels than with floating covers, perhaps because of excessive heat or abrasion under the floating covers. Early tomato yield did not correlate significantly with mean maximum or minimum temperatures or with heat unit accumulation in any planting.
Total yield for the season for the first planting of 1987 did not vary greatly among plant protectors, but was more than double the check plot yield. Black plastic mulch provided as great a total yield as any of the more expensive treatments (Tables 2 and 3). For the second planting, yield with plant protectors exceeded check yields and there were-significant differences among protectors. The Protecta-Cap and WallO'Water plots had greater yields than did the other treatments. Unlike the first planting, the tunnel treatment was relatively low yielding. In 1988, total yields were lower because of the shorter, cooler growing season. The tunnel and WallO'Water treatments were the highest yielding. For all plantings, mean fruit weight did not vary greatly with treatment.
Days to first melon harvest were reduced markedly by ground mulch for all plantings (Table 4). Except for the Protecta-Caps in 1988, addition of the other plant protectors provided further reductions in days to first harvest. Earliest harvest was with the floating or hoop-supported cover for all plantings. In 1987, no ripe fruit were obtained by mid-August on bare ground; in 1988, check plots did not produce ripe fruit until September. Mulching produced a significant early yield and floating row covers or tunnels further increased early yield for the first planting.
For the entire season, mulch greatly increased yield for all plantings (Table 5). In the first planting of 1987, the cover treatments tended to increase total yield over that with mulch alone. In the second planting, the Protecta-Cap also increased total yield. In 1988, only the tunnel and WallO'Water increased total yield over that with mulch alone. Greatest mean fruit weight occurred with the mulch treatment for both plantings in 1987, but with the WallO'Water treatment in 1988. In all plantings, all protectors tended to increase mean fruit weight, although the differences were not usually significant. This is in contrast to results in 1983, when floating covers reduced fruit size compared to mulch alone.
The response of muskmelon to plant protectors other than mulch was generally more favorable than was the tomato response. The floating and hoop-supported cover treatments were particularly effective in increasing early and total yield. For both muskmelon and tomato in the Willamette Valley, row covers, hot caps, and other relatively expensive methods of plant protection should be compared to black plastic mulch rather than to bare ground for an accurate determination of costs and benefits.
Table 1. Effect of plant protection systems on air temperatures and heat unit accumulation, 1987 and 1988 Treatment Mean air temp., Celsiusz Heat unitsy Days under Days over Daily max. Daily min. (degree days) 4 C 10 C 30 C 38 C First tomato, 1987 Bare ground 27.1 6.9 258 12 31 15 5 Mulch 29.7 6.8 327 12 32 23 6 WallO'Waterx 30.8 8.7 394 7 32 23 6 Protecta-Capx 32.7 7.8 404 9 29 33 13 Floating coverx 41.5 8.3 566 7 29 37 28 Tunnelx 36.9 8.1 474 9 30 36 17 LSD (0.05) 3.1 0.5 56 Second tomato, 1987 Bare ground 30.4 8.9 199 4 15 13 5 Mulch 32.7 8.8 295 4 15 14 5 WallO'Water 31.4 11.7 317 0 10 14 6 Protecta-Cap 34.2 10.2 348 0 13 23 9 Floating cover 41.7 10.7 449 0 11 27 22 Tunnel 39.6 10.5 411 0 13 26 17 LSD (0.05) 3.3 0.4 50 First melon, 1987 Bare ground 31.1 9.4 156 4 12 11 2 Mulch 34.2 8.8 244 4 12 16 5 WallO'Water 32.7 11.8 253 0 7 11 4 Protecta-Cap 36.0 10.3 284 0 10 22 7 Floating Cover 43.6 10.5 356 0 10 23 20 Tunnel 41.4 10.2 339 0 10 23 15 LSD (0.05) 3.2 0.6 43 <="" u=""> Bare ground 24.1 5.1 93 9 21 3 1 Mulch 27.3 5.1 130 9 21 6 1 WallO'Water 21.7 6.7 91 2 20 1 0 Protecta-Cap 24.1 5.8 107 6 21 1 0 Floating cover 37.4 6.0 244 6 21 18 9 Tunnel 32.2 6.6 199 5 20 13 3 LSD (0.05) 6.3 0.7 69 zRecorded 2.5 cm above the soil. ySummation of the difference between the daily mean temperature and 10°C for the measured period. xTreatment also included ground mulch. Table 2. Effect of plant protectors on plant development and yield by number of grade No. 1 'Pikred' tomato, 1987 and 1988 No. flowersz/ Days toy Early yieldx Total yield plant first harvest (No. fruit/plant) (No. fruit/plant) Planting Planting Planting Treatment 1st 2nd 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd Bare ground 2.6 6.0 110 86 77 0.7 1.0 1.0 26.3 23.7 16.4 Black mulch 2.6 7.2 110 87 86 1.2 1.5 1.2 50.5 47.5 35.2 WallO'Water 8.0 9.8 105 84 88 4.2 3.3 2.0 47.8 64.9 38.1 Protecta-Cap 6.6 8.4 109 93 81 2.1 0.2 1.3 52.5 57.6 43.2 Floating cover 4.2 7.8 103 90 90 2.5 1.5 1.9 56.7 53.1 38.0 Tunnel 6.6 10.6 101 84 86 7.1 2.9 3.3 60.3 40.9 51.9 LSD (0.05) 4.1 3.8 5 6 NS 3.2 1.4 0.9 18.3 16.2 6.7 zAt removal of plant protectors, 1987. yDays from transplanting to first ripe fruit harvest. xNo. of fruit harvested through 31 July, 1987; 17 August, 1988. NS: no significant differences (P = 0.05). Table 3. Effect of plant protectors on total yield by weight and mean fruit weight of 'Pikred' tomato Early yield (kg/plant)z Total yield (kg/plant) Mean fruit wt. (g) for season Planting Planting Planting Treatment 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd Bare ground 0.2 0.3 0.2 6.3 3.6 5.2 158 184 197 Black mulch 0.4 0.4 0.3 12.6 7.8 11.4 141 185 210 WallO'Water 1.0 0.8 0.4 12.2 9.7 13.7 138 169 225 Protecta-Cap 0.5 0.2 0.2 13.5 8.5 13.8 146 176 176 Floating cover 0.8 0.4 0.3 13.7 8.2 13.0 160 201 187 Tunnel 1.9 0.7 0.5 14.2 11.0 8.8 149 176 188 LSD (0.05) 0.8 0.3 0.2 3.7 1.6 2.8 NS NS 25 zThrough 31 July, 1987; 17 August, 1988. NS: no significant differences (P = 0.05). Table 4. Effect of plant protectors on development and early yield of muskmelon Treatment No.z Days to Early yield per planty flowers first harvest 1st planting 2nd planting 3rd planting per Planting No. Mean wt. No. Mean wt. No. Mean wt. plant 1st 2nd 3rd (g) (g) (g) Bare ground 0.2 142 130 112 0.0 - 0.0 - 0.0 - Black mulch 2.3 87 99 98 1.4 1016 0.0 - 0.9 1690 WallO'Water 1.6 84 95 92 1.2 1081 0.2 1350 1.1 1917 Protecta-Cap 1.3 84 93 104 1.3 966 0.1 1365 1.4 1768 Floating cover 3.0 82 86 95 2.1 901 0.5 1243 1.3 1876 Tunnel 5.9 82 87 89 2.5 1034 0.7 1232 1.9 1851 LSD (0.05) 1.7 4 5 7 1.1 NS 0.4 NS 0.8 NS ZPerfect flowers at anthesis by 26 May, 1987, early planting. yThrough 15 August, 1987; 31 August, 1988. NS: no significant differences (P = 0.05). Table 5. Effect of plant protectors on total yield of musk-melon Treatment Total yield per plant 1st planting 2nd planting 3rd planting No. Mean wt. No. Mean wt. No. Mean wt. (g) (g) (g) Bare ground 0.4 950 0.2 1040 0.9 968 Black mulch 3.9 1207 2.3 1278 2.8 1811 WallO'Water 3.9 1151 2.7 1207 3.5 2069 Protecta-Cap 3.5 1089 3.9 1336 2.6 1888 Floating cover 4.3 977 4.3 1257 2.7 1847 Tunnel 5.6 1061 3.7 1212 3.6 1817 LSD (0.05) 1.4 214 1.3 NS 1.1 365