Introduction
The purpose of this trial was to investigate the effect of Kimberly Farms row cover on the yield and earliness of broccoli, muskmelon, and tomato.
Methods
All crops were transplanted from seedlings grown in a heated glasshouse. 'Pikred' tomato was seeded on March 24, 1986, (first planting) and April 4 (second planting). 'Gem' broccoli was seeded on March 31 (first planting) and April 16 (second planting). 'Gold Star' muskmelon was seeded on April 8 (first planting) and April 21 (second planting). The Willamette silt loam soil was rototilled following application of 1,000 pounds 10-20-10 fertilizer/acre. Drip tubing and black plastic mulch were laid on six-foot centers on April 24.
The first planting was set out on May 6, hoop-supported covers installed, and max-min thermometers set out in each crop. Each crop was planted on a 40-foot section of bed. Within-row spacing was 24 inches for broccoli, 36 inches for tomato and melon. The second planting was set out on May 20.
Covers were removed from the appropriate rows in the first planting on May 20, May 30, and June 11. Covers were removed from the second planting on June 3, June 13, and June 23. Broccoli harvest started on June 13, melon and tomato harvests on July 31. Each crop was harvested at least weekly after the initial harvest. Temperatures were recorded from the first planting date through July 14.
Results
A light frost occurred at the six-foot level the morning of May 14, but the plants were not affected. A few melon plants in the first planting had weak root systems, probably from fungus gnat larvae, and were replaced on May 16. Weather from this point on through the end of June was unseasonably warm and sunny, with the heat unit summation for June (464 degree-days, 50°F base) hitting a new high for the 30 years that records have been kept for this site. Temperatures recorded by the max-min thermometers often exceeded 100°F for uncovered rows and occasionally exceeded 130° under the tunnels. These temperatures are considered excessive for broccoli and tomato, marginal for muskmelon.
Although subjected to high temperatures, early broccoli yield increased for plants under tunnels in the first planting (Table 1). Total yield did not seem to be affected by the tunnels. Early yield was lower for plants covered 5 weeks than for plants covered 2 weeks or 3.5 weeks, possibly indicating heat stress. Average grade was higher for the uncovered plants, again indicating excessive heat under the tunnels. Mean head weight did not vary much with covering interval.
For the second broccoli planting, early yield was highest with the longest covering interval. This is in contrast to the results for the first planting and makes it difficult to draw a general conclusion. Grade was again higher for uncovered plants, decreasing with increasing covering interval.
The effect of covers on early yield of grade No. 1 tomatoes was striking. Yield for both plantings decreased with increasing covering interval (Table 2).
There were no noticeable trends in early production of small (No. 2) and deformed (No. 3) fruit. Total yield of early fruit also decreased with increased covering interval. The major cause of decreased yields was a decrease in mean fruit weight with covers. For the second planting, a decrease in number of fruit harvested also contributed to the yield decrease.
The yield of tomatoes for the entire season did not vary as greatly with treatments (Table 3). Covers tended to reduce total yield and No. 1 yield for the first planting but increase yield up to the 3.5 week covering interval for the second planting. The yield of small fruit was very high and mean fruit weight was very low for the 5-week covering interval. for the second planting. This treatment was covered through most of the warm June weather and may have suffered excessive stress. However, the number of fruit harvested/plot was highest for this treatment, and greater competition for photosynthate may have caused the reduced fruit size.
For the first planting of muskmelon, row covers did not favor either early or total yield (Table 4). For the second planting, however, early yield was more than doubled by tunnels for the first two covering intervals. The 5-week covering interval produced a very low yield. Fruit set and size were good but the fruit simply did not ripen on this treatment. The foliage was also noticeably greener and thicker. These may be heat stress-related symptoms. Total yields for the season were not increased by covers for either planting date.
Discussion
The lack of favorable response of transplanted broccoli, a cool weather crop, to tunnel culture is not surprising, since the ambient temperatures during the growing period were already optimal for crop growth. The lower grade of covered plants was mainly from a rough, uneven pearl and premature flower opening, both symptoms of heat stress. Row covers would be more likely to aid in broccoli development during the stand establishment phase of a direct-seeded broccoli crop, particularly in very early spring plantings.
The decreased early yield of tomatoes under tunnels was surprising in view of the work of A. Abbes and N. S. Mansour in 1984, in which covering tomatoes with floating covers of highly perforated polyethylene or spunbonded polyester increased early yield of 'Pikred' tomato. However, this was for an early planting (April 20) in a very cool. year. Both of these materials also produced smaller temperature increases than did Kimberly Farms in measurements made by Hemphill in June 1986. The temperatures experienced in the tunnels in 1986, particularly in early June, may have caused blossom loss or poor fruit set.
Both spunbonded polyester and highly perforated polyethylene greatly increased earliness and yield of 'Gold Star' melon in 1983 and 1984 and 'Sweet Success' cucumber in 1985 and 1986. The response in 1986 was much smaller than in the cooler spring of 1985, however. Although the trend was not clear for the first planting, tunnel culture clearly promoted early melon yield in the second planting. The low yield at the longest covering interval indicates that this cover remained on too long. In 1983, another warm spring, a slitted polyethylene cover (Xiro) severely reduced melon fruit size, but increased earliness. It is encouraging that the KF tunnels did not reduce melon fruit size, at least in the second planting.
Table 1. Effect of Kimberly Farms covers on broccoli yield and grade, 1986 Planting Covering Yield No. of Mean Mean head interval EarlyZ Total heads gradeY wt. (g) (weeks) ----kg/plot---- Early 2 1.12 3.29 17 2.5 194 3.5 1.61 3.65 17 2.5 243 5 0.53 2.93 15 2.1 195 0 0.28 3.37 15 2.9 198 Late 2 0.49 3.23 21 2.7 154 3.5 0.66 2.67 17 2.6 157 5 1.48 3.02 18 2.4 168 0 0.93 2.13 16 2.9 133 ZFirst of three harvests. Y4-point scale with 3 = perfect, 0 = unacceptable. Table 2. Effect of Kimberly Farms covers on early tomato yield, 1986 Planting Covering YieldZ (kg/plot) No. of fruit/plot Mean interval No.lY No.2X No.3W Total No.1 No.2 No.3 Total fruit (weeks) wt. (g) Early 2 41.5 2.1 12.9 56.5 150 34 59 243 233 3.5 37.2 4.0 19.5 60.7 192 42 87 321 189 5 32.1 2.4 10.0 44.5 126 23 46 195 228 0 49.1 0.7 14.6 64.4 160 7 56 223 289 Late 2 11.6 2.5 3.3 17.4 47 31 17 95 183 3.5 8.6 0.5 2.7 11.8 36 8 15 59 200 5 5.6 2.3 5.4 13.3 27 38 27 92 145 0 32.5 2.0 3.6 38.1 129 20 20 169 115 ZHarvested by August 15. Yover 120 g, no defects. Xunder 120 g, no defects. Wdeformed fruit, usually catfacing. Table 3. Effect of Kimberly Farms covers on total tomato yield, 1986 Planting Covering Yield (kg/plot) No. of fruit/plot Mean interval No.1Z No.2Y No.3X Total No.1 No.2 No.3 Total fruit (weeks) wt. (g) Early 2 99.6 10.9 23.6 134.1 430 130 136 696 193 3.5 106.2 11.9 30.3 148.4 533 131 148 985 151 5 116.1 16.1 25.9 158.1 555 173 138 866 183 0 138.7 7.0 27.9 173.6 581 73 153 807 215 Late 2 128.4 21.7 33.7 183.8 578 246 179 823 223 3.5 144.7 25.9 35.3 205.9 715 287 166 1168 176 5 90.3 50.6 37.9 178.8 543 638 276 1277 140 0 114.6 30.4 36.1 181.1 560 401 239 1200 151 Zover 120 g, no defects. Yunder 120 g, no defects. Xdeformed fruit, usually catfacing. Table 4. Effect of Kimberly-Farms covers on muskmelon yield, 1986 Planting Covering Yield (kg/plot) No. of fruit/plot Mean fruit wt. (g) interval Early Total Early Total Early Total (weeks) Early 2 30.93 70.28 20 48 1547 1464 3.5 40.85 92.20 30 79 1362 1167 5 61.95 72.62 50 60 1239 1210 0 56.19 125.82 40 89 1405 1414 Late 2 24.95 118.75 23 114 1085 1042 3.5 25.12 132.47 19 134 1269 989 5 1.50 122.43 1 114 1500 1074 0 10.33 131.56 10 118 1033 1115