Research & reports

Leigh Whittinghill, Major Ballard, Anju Chaudhary, Smriti Kandel, Caitlin Mullins, Pradip Poudel · HortScience · United States

This study analyzed runoff water quality from four different nutrient management treatments (conventional fertilizer, organic fertilizer, low-compost + organic fertilizer, and high compost) in raised beds and small plastic pool container plots in the United States. Water samples, collected monthly, were analyzed for pH, conductivity, color, turbidity, nitrate-nitrogen, ammonia-nitrogen, total phosphorus, and potassium. While significant differences existed between raised beds and container plots, these did not translate to meaningful water quality differences for most variables, except for nitrate-nitrogen. The conventional fertilizer treatment showed greater or more variable nutrient leaching than other treatments.

Jennifer Engels, Sheree J. Watson, Henrietta Dulai, Kimberly Burnett, Christopher A. Wada, ‘Ano‘ilani Aga, Nathan DeMaagd, J. J. McHugh, Barbara Sumida, Leah L. Bremer · PLoS ONE · United States (O‘ahu)

A researcher-farmer collaboration on O‘ahu's Sumida watercress farm conducted a 25-year trend analysis and a year of intensive spring water sampling. Negative correlations were found between historical crop yields and increases in the Oceanic Niño Index, temperature thresholds, and pest outbreaks. Despite urbanization, on-farm water quality was very high, and microbial analyses suggested the farm provides nutrient retention services to downstream systems. The study demonstrates that challenges facing urban agricultural systems shift over time.

Gaston E. Small, Paliza Shrestha, Geneviève S. Metson, Katherine Polsky, Ivan Jimenez, Adam D. Kay · Environmental Research Communications · United States

Survey data from 142 gardeners and urban farmers in the Twin Cities Metropolitan Area, USA, characterized phosphorus (P) and nitrogen (N) inputs and harvest, and measured soil P concentrations at a subset of sites. Median application rates were 300 kg P/ha and 1400 kg N/ha, with low nutrient use efficiencies (2.5% for P, 5.0% for N). Garden soils had a median Bray P value of 80 ppm, far exceeding recommended levels, indicating a buildup and potential loss of P and N. Urban gardens, though only 0.1% of land area, constitute one of the largest inputs of P to the watershed.

Monika Egerer, Alessandro Ossola, Brenda B. Lin · BioScience · United States (California central coast)

This study conceptualizes community garden soils within the novel ecosystem framework, arguing that gardeners cultivate novel agroecosystems from their garden beds' soil. On the California central coast, community garden soils may not be influenced by land-use legacies associated with geographic location. Instead, intensive soil reworking by gardeners can wash out legacy signals and decadal chronological trends, leading to soil homogenization that reduces biophysical ties to the underlying earth.

John Taylor, Sarah Taylor Lovell, Sam E. Wortman, M.K. Chan · Renewable Agriculture and Food Systems · United States (Chicago)

In Chicago, semi-structured interviews and plant inventories were conducted with 59 African American, Chinese-origin, and Mexican-origin households regarding ecosystem services and tradeoffs in their home food gardens. A total of 387 plant species were identified; gardens of African American households were rich in ornamental species, while those of Chinese-origin households had a depauperate flora. Shade trees and a developed shrub layer were absent from most gardens, suggesting a tradeoff in ecosystem services favoring food production. Only 9.6% of the inventoried species were native to the Chicago area.

Shane R. de Solla, Pamela A. Martin · Environmental Toxicology and Chemistry · United States

Because many reptiles oviposit in soil within agricultural landscapes, this study evaluated the toxicity of two commonly used nitrogenous fertilizers — urea and ammonium nitrate — to snapping turtle (Chelydra serpentina) egg survivorship. Eggs were incubated, unmanipulated and under ambient conditions, in a community garden plot treated with urea at realistic rates up to 200 kg/ha in 2004 and ammonium nitrate up to 2,000 kg/ha in 2005, and separately in covered laboratory bins designed to minimize nitrogen loss through volatilization or leaching. In the field, neither urea nor ammonium nitrate affected hatching success or development, despite ammonium nitrate showing overt toxicity to native plants. In the laboratory, however, both fertilizer exposures reduced hatching success, lowered body mass at hatching, and reduced post-hatching survival compared with controls. The authors attribute the field's lack of toxicity to leaching and atmospheric loss of nitrogen in soil, and conclude that nitrogenous fertilizers likely have little direct impact on turtle eggs deposited in agricultural landscapes.