ASHS 2025 Conference

With populations rising and cities expanding, it is necessary to consider new ways to supplement current energy and food systems. Urban agriculture has the potential to enhance food systems, energy production and stormwater management within urban areas. This can be achieved by implementing rooftop agrivoltaics (RAV), a combination of rooftops, agriculture, and photovoltaics. This study evaluates the growth and yield of leafy greens in RAV by examining how shade from photovoltaic arrays influences leafy green production. An RAV system was built at the CSU Spur Campus in Denver, Colorado, featuring a 45 cm deep substrate and three treatments: full sun, opaque silicon PV modules, and bifacial silicon PV modules. Leafy greens—arugula, kale, lettuce, spinach, and Swiss chard—were germinated and transplanted in randomized rows, with environmental conditions monitored continuously using HOBO sensors. Fresh weight, dry weight, stomatal conductance, and plant size at harvest were collected, and statistical analysis was conducted using two-way ANOVA to assess the effects of the treatments on each crop type. Leafy greens grown under the PV treatments had reduced stomatal conductance compared to the full sun treatment. The plant size at harvest was also higher in lettuce and spinach grown under the PV module treatments compared to the full sun. Fresh and dry weight of plants grown under the opaque and bifacial PV module treatments, however, were reduced compared to the full sun treatment. By understanding these interactions, the research aims to determine the feasibility of RAV systems for urban agriculture.

Extensive green roof mediums are shallow with low nutrient content and oftentimes susceptible to rapid drainage, which results in the use of concentrated synthetic fertilizers that can have a negative affect on runoff water quality. Therefore, a study was conducted on ‘Sweet Hungarian’ pepper (Capsicum annuum) over three growing seasons to compare organic and conventional synthetic fertilizers at manufacturer recommended rates for their impacts on fruit yield, leaf chlorophyll content (SPAD), and plant vigor on a green roof having an expanded clay medium. The fast release synthetic fertilizer utilized produced the highest yield per unit fertilizer cost while the controlled release synthetic fertilizer had the highest overall yield but at much higher cost compared to other treatments. Bloodmeal had the highest yield among organic treatments and was similar to the fast release synthetic. Although SPAD was correlated with yield differences among treatments, plant vigor rating better explained these variations in yield. Pre and post growing season medium analyses revealed several interesting trends over the three-years of the study regarding pH, soil organic matter and nutrient contents that will be reviewed in detail. Additionally, an analysis of yield tradeoffs with fertilizer product costs among several popular organic and synthetic fertilizers for a nutrient-demanding crop grown in an extensive green roof environment will also be discussed. Green roof agriculture is a promising solution to enhance sustainability, especially where growing space is limited, but nutrient management is an important part of this system that needs to be sufficiently considered.

Urban agriculture is important to provide sources of local food for urban residents. Extensive green roofs can be used to provide spaces for local agriculture in these urban environments, although extreme conditions in these environments can be challenging for edible crop production. Moisture in these environments are often the most limiting factor influencing growth and often create problems for urban agriculture activities. Therefore, two culinary herb experiments were conducted on the Southern Illinois University – Carbondale extensive green roof located on top of the agriculture building to evaluate the influences of various water management strategies on resulting plant growth and overwintering. Results indicated weekly irrigation was critical to increase both annual (basil) and perennial (sage and thyme) plant vigor compared to biweekly watering. Although the use of pine bark mulch improved basil growth, sage and thyme growth was not affected by its use. The addition of hydrogels in the medium for water retention did not influence resulting plant growth for either the annual or perennial herbs evaluated. Our results highlight the importance of consistent water supply for growth and overwintering success for both annual and perennial culinary herbs grown in an extensive green roof environment. Although many culinary herbs thrive in dry, well-drained conditions, mimicking their native Mediterranean climate, water management strategies are still important considerations for sustaining culinary herb production on extensive green roofs.

Fresh local produce is often limiting in densely populated cities, resulting in unhealthy food option for urban residents. Roof tops are underutilized spaces that can be used to help supplement production of fresh edibles for urban consumers. Peppers are used in a variety of cuisines and desired by many consumers in urban areas. Therefore, three pepper (Capisum annuum) varieties (San Joaquin, Red Impact, and Pot-a-Peno) having different growth habits and fruit types were compared with the application of a pine bark mulch or no mulch for resulting growth and yields in the extensive green roof environment located atop the Southern Illinois University-Carbondale Agriculture Building. Growth characters were collected during early-, mid-, and late-season, while fruit were harvested at 4-week intervals six times through the growing season. Pepper variety and mulch use did not generally influence (P > 0.05) leaf chlorophyll content or plant vigor at any timing. Marketable fruit yields differed (P < 0.05) among varieties, with ‘San Joaquin’ having higher fruit numbers than ‘Red Impact’ and weights greater than ‘Red Impact’, and ‘Pot-a-Peno’. Pepper plant vigor, leaf chlorophyll content and yield results indicate that this crop can be effectively grown in an extensive green roof environment with proper variety selection although mulch use was not beneficial. These results will be further discussed regarding the use of pepper as an edible crop in extensive greenroof environments.

Urban farmers across Indiana are facing the effects of rising fertilizer, chemical, and energy prices. In this climate, soil health has emerged as a top priority. In a 2023 statewide survey of Indiana urban farmers, 91.6% expressed interest in learning more about improving soil health (n=81), underscoring a strong desire for practical, sustainable strategies that reduce costs and boost productivity. Cover crops and compost application represent two fundamental approaches to improving soil health and fertility. Implementing cover crops and incorporating compost are essential practices for regenerating and maintaining healthy soil ecosystems. Farmers seeking to enhance soil vitality often rely on two primary methods: planting cover crops and applying compost. Soil health can be significantly improved through the integration of cover cropping systems and regular compost applications. hairy vetch, sunn hemp, rye, and mustard, are gaining traction as an alternative or complement to compost. These crops can trap nitrogen, build organic matter, and improve water retention, which are relevant benefits in compacted, nutrient-depleted, and low-organic-matter soils common in urban spaces. However, barriers like limited space, short-term leases, and concerns about short-term yield reduction can make adoption difficult for small-scale growers. When managed properly, composting transforms organic waste like food scraps, straw, and manure into a slow-release soil amendment that boosts organic matter, microbial life, and nutrient retention. However, not all compost is created equal. Overapplication, especially of manure-based compost, can lead to nutrient imbalances, phosphorus buildup, nitrate leaching, and elevated pH, which may reduce yields. Urban farmers are encouraged to test compost for nutrient content and monitor soil health regularly to guide application timing and rates. The Soil to Market project, an ongoing Purdue-led study launched in 2021, is evaluating cover crop and compost combinations at multiple Indiana locations. At the Meigs Purdue Agriculture Center in Lafayette, IN, cover crops alone, particularly sorghum and sunn hemp, did not significantly increase total available phosphorus (P). In contrast, compost treatments, especially high volume (2 yd³), manure-based applications, resulted in statistically significant increases in soil P, with mean values ranging from 280 to 365 mg/kg. These treatments highlight potential effectiveness in improving P availability in nutrient-depleted, urban soils. However, high phosphorus levels in compost treatments highlight the need for careful, adaptive management in sensitive environments, such as near waterways due to the increased risk of P runoff or leaching. Management of application timing, placement, and rates is crucial to maximize benefits while minimizing environmental impacts on urban farms.