Data from the first year of specialty crops agrivoltiacs research at RAREC in 2024

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In 2024, the first year of agrivoltaics (AV) specialty crops research was completed at RAREC near Bridgeton, New Jersey where fresh-market tomato ‘Red Deuce’, bell pepper ‘Turnpike’, and sicilian eggplant ‘Palermo’ were grown using standard production practices in either a no panel (control), single-panel, or double panel AV system. A timeline for the AV research done at RAREC during the 2024 production season can be found below by clicking on the links.

Bed formation and plastic mulch laying at RAREC in 2024

Transplanting specialty crops at RAREC in 2024

Staking and tying specialty crops at RAREC in 2024. First tie and second tie

Harvesting the specialty crops at RAREC in 2024. First harvest, mid-season harvest, and final harvest

Breaking down the specialty crop trial in 2024.

Experimental Design. The experiment’s error-control structure was a split-split-split-plot design, with the whole-plot factor arranged in randomized complete blocks (Figure 1). This blocking was implemented to mitigate the influence of field geographic variability, a recognized nuisance factor. In the 2024 growing season, the vegetable experiment was confined to a single block of the randomized complete block design. Future iterations of this experiment are planned to achieve replication at the block level. The initial year’s experimentation focused on within-block treatment effects.

The treatment structure comprised a 3 × 2 × 5 × 3 factorial arrangement of the factors: array type, East-West side, proximity to the central row, and crop species, respectively. The whole-plot factor, array type, had three levels: 1) control (no photovoltaic panels), 2) single panels in portrait orientation (ground coverage ratio [GCR] of 0.202), and 3) double panels in portrait orientation (GCR of 0.404)(Figure 1). All arrays were single-axis trackers with North-South row orientation and a pivot height of 2.44m (8 ft) above ground level. Each whole-plot experimental unit contained three rows of the same array type (or equivalent imaginary rows for the control). The split-plot factor was the cardinal direction relative to the central array row (East or West) within the whole-plot experimental unit. Proximity to the central array row constituted the split-split-plot factor. Within each split-plot experimental unit, five raised beds were established, oriented North-South and spaced 1.52 m (5 ft) on center, to investigate the effect of proximity. The split-split-split-plot factor was crop species, with levels: 1) eggplant (Solanum melongena cv. ‘Palermo’), 2) fresh-market tomato (Solanum lycopersicum cv. ‘Red Deuce’), and 3) bell pepper (Capsicum annuum cv. ‘Turnpike’) (Figure 1). Within each raised bed, crop species were randomly allocated to 4.6 m (15 ft) long sections. Figure 1 shows a detail of the design. To ensure isolation, each split-split-split-plot experimental unit was buffered by three guard plants at each end.

Crop Management. On May 20 2024, soil was prepared  by broadcasting and incorporating 85 lb/A of 14-4-14 prior to bed formation. On June 5, raised beds were formed and Devrinol herbicide applied for weed control. On June 6, white-on-black plastic mulch  was laid on 5 ft centers in each whole plot for a total of 10 beds. Seedlings were transplanted in single rows with 12” between transplants into beds on June 10 and 11. Standard management practices were performed according to local recommendations, and included staking (June 28), tying (July 3, 16, 22; and August 13) on fresh-market tomato and (July 3, 18; and 13 August) on eggplant, (July 3 and 26) on bell pepper. All whole plots were fertigated either once or twice per week from June 28^th through 11 Oct for a total of 21 times each using 1 lb actual N/acre of NPK (20-20-20). Additional drip irrigation was done as needed. A protectant fungicide + insecticide program was initiated and on July 15, 23, and 29; on August 5, 17, 23; September 5, 20, and 26 pesticides were applied using an air–blast sprayer for the control of important pests and diseases according to local standard recommendations. Additionally, on July 31, a miticide was applied to all plots for the control of broad mites.

Data Collection and Statistical Analysis. Data collection involved multiple hand harvests of commercially mature fruits at intervals of 5 to 10 days, depending on crop, weather conditions, and fruit maturation. Harvest began on August 2, 2024, and ended October 18, 2024, for a total of 13 eggplant, 7 pepper, and 10 tomato harvests. All harvested fruits were weighed and subsequently sorted into marketable and cull categories, with separate weights recorded. Season-long total yields and percent marketable fruit (on a weight/weight basis) were calculated for each sub-sub-sub-plot and used for subsequent statistical analysis. A mixed-effects analysis of variance model was fitted using the GLIMMIX Procedure of the SAS System (ver. 9.4, SAS Institute, Cary, NC 27513). Model adequacy was assessed through conditional studentized residual plots. The model evaluated main effects of cardinal direction, proximity to array, and crop species, along with all their two- and three-way interaction effects. Additionally, two- and three-way interaction effects involving array type with the aforementioned factors were examined. Significant (P<0.05) interaction effects, all of which included proximity, were further investigated by fitting linear and quadratic polynomials across proximities within each level of the interacting model effects. As quadratic terms were statistically significant, quadratic curves were fitted and used for interpretation and presentation.

Effects on Crop Yield. Results indicated a significant three-way interaction effect of Crop type x Array type x Proximity to the center array row on total yield (P=0.0107). All three crops exhibited reduced yields in those beds closest to the array row (Figure 2), where eggplant yield exhibited the greatest reduction, especially in the beds closest to the double-panel rows. There was no significant effect of E-W nor any interaction of E-W with the other effects. There was a clear numerical trend towards lowered yields in the single panel whole plot and even lower yields in the double-panel whole plot for all three crops compared to the control (no AV panels).

Percentage marketable fruit. Results indicated that fruit quality, expressed as the percentage of harvested fruit marketable, was unaffected on tomatoes and peppers, but it was higher closer to the module arrays for eggplant (Figure 3) (Three-way interaction effect of Array type x Crop species x Proximity, P=0.0200). There was no significant effect of E-W nor any interaction of E-W with the other effects.

This study will be repeated in 2025 and 2026 to test the main effect of array type.

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