The Effect of Colored Polyethylene Mulch on the Yield of Squash, Tomato and Cauliflower

Final Report to the Pennsylvania Vegetable Marketing and Research Commodity Board

M. D. Orzolek, J. Murphy and J. Ciardi
The Pennsylvania State University
University Park, PA 16802

The use of polyethylene mulch has increased dramatically in the last 10 years not only in Pennsylvania, but throughout the United States. In Pennsylvania, use of plastic mulch in vegetable crop production has gone from 7,000 acres in 1983 to about 25,000 acres in 1993. The increase in use of polyethylene mulch is due to its benefits when applied in the field: increase in soil temperatures especially in early spring, reduced weed problems, moisture conservation, reduction of certain insect pests, higher crop yields and more efficient use of soil nutrients. However, in the last ten years, there has been the introduction of degradable plastic mulch, selective wavelength films (IRT), and colored mulch. Degradable mulch was developed to help with disposal problems which have not been totally resolved through research. IRT or selective wavelength films were developed to increase soil temperatures while suppressing weed growth under the mulch. New colors were developed from work initiated at the ARS Vegetable Research Lab in Charleston, SC which demonstrated that tomato production was higher from plants grown on red mulch compared to black mulch. Color selection to that point had been limited to black, brown, clear or white. Introduction of colored mulch has challenged vegetable producers to new heights; which crops respond to different colored mulch? Unfortunately, there is very little research work published which might help growers resolve this problem.

Red, blue, yellow, gray, and black polyethylene mulch was received from Rochelle Plastic Films, Inc., Rochelle, IL on May 28, 1993. On the same day, the plastic mulches were laid in the field in a Randomized Complete Block Design with 3 replications. Plot size was 5' x 35' for each treatment and replication. Tomato transplants (variety 'Sunbeam') and zucchini transplants (variety 'Gold Rush') were also planted on March 28. Chapin drip irrigation tubing was installed at the same time the colored mulch was being laid and prior to transplanting the tomato and zucchini plants. The drip irrigation was immediately turned on for 5 hours after transplanting because of the extremely dry soil and climatic conditions during plant establishment, 78 to 82°F temperature and winds gusting up to speeds of 20 mph. Cauliflower transplants (variety 'Majestic') were planted on June 28, 1993. Weeds were controlled with a broadcast application of Dual at 0.2 lbs ai/A and Goal at 0.1 lb ai/A prior to laying the plastic mulch. In addition, weeds between rows were periodically hand hoed during the growing season. Soil temperatures were recorded in all treatments with the use of an Omnidata data logger and thermisters for a 6 week period.

The highest yield of tomato fruit, although not significantly different than the other colored mulch treatments, was produced on the blue colored mulch (Table 1). All mulch color treatments produced significantly more tomato fruit than the bare ground treatment. There was no difference in fruit number between the blue, gray and red mulch treatments, but there was a difference in average fruit weight. The largest fruit was produced on the blue mulch which was significantly larger than fruit from either the yellow and red mulch or bare ground check. Previous research has demonstrated that higher fruit yields were obtained from tomatoes grown on red mulch. The percentage of cull fruit was least on the bare ground check and highest on the yellow mulch treatment.

There was no difference in the yield of zucchini squash among colored mulch treatments, but they all produced significantly more fruit than the bare ground check (Table 2). In contrast to 1992, the blue mulch treatment produced less fruit than either the red, yellow or black treatments. There was no difference in the average fruit weight among the colored mulch treatments. The blue mulch treatment produced less fruit per plant than the yellow, red or black mulch treatments. In 1992, the yellow mulch treatment produced less fruit than either the blue or red mulch treatments.

There was no difference in the yield of cauliflower among colored mulch treatments and bare ground check (Table 3). The yellow colored treatment however did significantly produce larger cauliflower heads based on head diameter and average head weight (although non-significant) than the bare ground check. Because of the time of year, one would not expect a response in yield from cauliflower grown on plastic mulch. It was surprising that the cauliflower produced heads at all in such a stressful environment as high soil temperatures, high air temperatures, and minimum rainfall during the growing period.

As shown in the accompaning figure, blue mulch produced the highest soil temperatures followed by yellow, red and black. Surprisingly, the gray mulch had the coolest soil temperatures of all the mulches evaluated during the growing season. The differences in zuchinni squash response to colored mulch between 1992 and 1993 is partially based on the extreme high soil temperatures (maximum reaching 101°F in late July in the blue mulch treatments) and the drought conditions experienced for 6 weeks in 1993 compared to 1992. In addition to the increased temperature response of plants to polyethylene mulch, there is also a light response that occurs in relation to the color of the mulch. Blue reflects in the 510 to 720 nanometer range ( partial green, yellow, orange and red), red in the 380 to 570 nanometer range (violet, blue, partial green), and yellow in the 380 to 510 nanometer range (violet, blue). The difference in light reflectance by the various colors appears to influenec plant growth. It is apparent that some crops such as cauliflower may not respond to the increased soil temperature/ light reflectance produced with the use of colored mulches.

Summary

1. Soil temperatures under the various colored mulches in 1993 were at least 5°C warmer compared to 1992. The warmer soil temperatures appeared to have influence crop yields in 1993.
2. Tomatoes did not respond to red mulch as previously reported but highest yields in 1993 were harvested from the blue and gray mulch treatments; possibly due to the light reflectance from the mulch.
3. Zucchini squash did not appear to respond to the blue colored mulch in 1993 compared to 1992; highest yieldof squash was harvested from the red, yellow, or black mulch treatments. The high soil temperatures recorded under the blue mulch may have affected plant development.
4. There was no significant yield response observed in cauliflower production on colored mulch under summer growing conditions. Yield or earlier maturity response may be possible in either spring or fall production of cauliflower in Pennsylvania. While there was no yield response with cauliflower, significantly larger heads were obtained from cauliflower grown on mulch, regardless of color, compared to the bare ground check.
5. The numerous combinations of mulch color and vegetable crop have yet to be explored, additional research in this area is both fruitful and needed.

*Table 1. The effect of colored polyethylene mulch on the yield of 'Sunbeam' tomato grown at the Horticulture Research Farm, Rock Springs, PA - 1993.
_____________________________________________________________________________

Table 2. The effect of colored polyethylene mulch on the yield of 'Gold Rush' zuchinni squash grown at the Horticulture Research Farm, Rock Springs, PA - 1993.

Table 3. The effect of colored polyethylene mulch on the yield of 'Majestic' cauliflower grown at the Horticulture Research Farm, Rock Springs, PA - 1993.