Vegetables and Ornamental Horticulture : Reflective Mulch in Trellised Tomatoes

REFLECTIVE WHITE-ON-BLACK MULCH INCREASES FRUIT YIELD OF 'MOUNTAIN FRESH' TRELLISED TOMATO AT HIGH PLANT DENSITY

Amy B. Ouellette and J. Brent Loy

Department of Plant Biology
University of New Hampshire
Durham, NH 03824

Fresh-market tomato production systems in the northeast that utilize polyethylene mulch- covered raised beds, trickle irrigation and trellising can produce high yields of quality fruit. These intensive growing systems are particularly important to growers located in urban areas, where land prices are high. Over the past few decades, several products including reflective mulches have been evaluated for their effects on the growth and yield of tomato.

The first work with reflective mulch and field grown tomato was done in South Carolina in the 1980's. These studies found that red mulch increased the early yield of tomato over black mulch. Since then, several experiments comparing colored mulches have been conducted, with inconsistent results. The current study was prompted by two years of intriguing results at the University of New Hampshire. Early in the 1997 growing season, reflective red-mulched tomato plants had greater total dry biomass than plants grown on black mulch. Almost twice as much light was reflected from the surface of red mulch than black mulch. It appears that the additional light reflected from red mulch must have increased photosynthate production in the red-mulched plants. By the end of the season, there was no difference in biomass between red and black-mulched plants. This red effect was most likely lost by late season due to the plant canopy covering the surface of the mulch. In 1998, a preliminary experiment was conducted with reflective white-on-black mulch. This mulch was applied to the ground between raised beds, which we call the "interrow" area. Fruit yield from plots with the interrow white much were significantly higher than yields from plots with bare soil interrows.

Materials and Methods

Four mulch treatments were evaluated for their effects on the growth and yield of trellised field-grown 'Mountain Fresh' tomato. In 1999, treatments included: standard black-mulched raised beds with bare soil interrows (B), black-mulched raised beds with white-on-black mulched-interrows (BW), Sonoco reflective red-mulched raised beds with bare soil interrows ®, and red-mulched raised beds with white-on-black interrows (RW). Only the B and BW mulches were tested in 2000. The white mulch was secured to the ground by 9 gauge wire bent into 4 inch square U-shaped clips.

We reasoned that photosynthetically active radiation (PAR) would be more limiting and reflective light mulches more beneficial with closely spaced plants. The following three plant densities were compared in 1999 and 2000: 7,260 plants per acre (12" within row spacing), 4,840 plants per acre (18" spacing), and 3,630 plants per acre (24 inch in-row spacing). Rows were spaced on 6 foot centers. Water and fertilizer was provided by trickle irrigation. Basket weave trellising between hardwood stakes supported the tomato vines.

Yield data were collected from eight plants in each plot twice weekly for a period of six weeks each summer. Biomass studies were conducted three times during the season to determine if the mulch treatments or plant density have an effect on plant growth. Three plants per plot were harvested and dissected into leaves, stem, flowers, and fruits, and roots during each study. Fresh and dry weights were recorded. Soil temperatures and light reflectivity were monitored in 2000.

1999 Results

At the 18 and 24 inch plant spacings, there were no significant differences in either early or total yield among any of the mulch treatments; however, at the 12" spacing, the black mulch/white-mulched interrow treatment yielded 25 to 27% higher per acre than the other three treatments. Fruit yield per plant increased as plant density decreased. Fruit weight increased with decreasing plant density, with averages of 8.2 oz from the 12" spacing, 8.8 oz from the 18" spacing, and 9.0 oz from the 24" spacing.

Partitioning of photosynthate among plant organ groups was not affected by mulch treatments. These analyses did reveal that plant density (spacing) affects biomass accumulation of fruit. As with the yield study, plants grown with wider plant spacing had greater fruit weight than those grown more closely together.

2000 Results

In 2000, only black-mulched raised beds with bare interrows and black-mulched raised beds with white-mulched interrows were compared. There were no differences in yield between the two mulch treatments at the 18" and 24" spacings. At the 12" spacing, per acre fruit yield from plants grown on black mulched raised beds with white-mulched interrows was 39% higher than plants grown without the white-mulched interrows. Average fruit weights were 10.3 oz in the 12 in spacing, 10.9 oz in the 18" spacing, and 11.4 oz in the 24" spacing.

The August and September biomass accumulation revealed that plants grown on black-mulched raised beds with white-mulched interrows had greater reproductive and total plant biomass than those grown without white-mulched interrows. Plant density (spacing) also affected field reproductive and total plant biomass accumulation.

Soil temperatures were similar between the two mulch treatments. Three times as much light was reflected toward the plant canopy from the white-mulched interrows than from bare interrows, representing about 14% of full sun.

Summary

Most growers in the northeast use a fresh-market production system that includes basket-weave trellising, black mulched raised beds with trickle irrigation, and 18" plant spacing. In our study, this system yielded an average of 87,000 lbs per acre in 1999 and 102,000 lbs per acre in 2000 of marketable "Mountain Fresh" tomato. In contrast, plants grown with 12" spacing on black-mulched raised beds with white-mulched interrows yielded 134,000 and 144,000 lbs per acre respectively, in 1999 and 2000. This corresponds to yield increases of 54% in 1999 and 41% in 2000. Only a small reduction in fruit size was compromised by the closer spacing together with the reflective mulch.

Results from the1999 and 2000 studies suggest that in high plant densities, white-mulched interrows enhance fruit yield of tomato by increasing the amount of light reflected into the lower plant canopy. Because plant density affects light interception into the canopy, a more densely populated plant stand is more limited by light than a less-dense stand, provided nutrition and watering are maintained.