Abstract
The growth-promoting effects of Gluconacetobacter diazotrophicus inoculation on the leaf lettuce (Lactuca sativa L.) cultivars “Black Seeded Simpson” and “Bibb/Limestone” were investigated. Plants of each cultivar were grown hydroponically in Kratky jars in a growth chamber-controlled environment in a completely randomized factorial design with three or four replications. Each experiment was repeated once. Factors were (1) with or without inoculant and (2) seven levels of nitrogen (N) fertilization ranging from deficient (37.5 mg L−1 N) to excessive (172.5 mg L−1 N). The shoot, root, and total biomass accumulation, nitrogen density, and carbon/nitrogen (C/N) ratios were measured for each variety. Black Seeded Simpson demonstrated a shifting of production towards aerial tissues, with significantly greater shoot production and reduced root production. The observed increase in shoot biomass was greatest at the slightly deficient N rate of 105 mg L−1 N where inoculated plants produced 14.8% more than uninoculated plants. Lower N density and higher C/N ratios in inoculated shoot tissues indicate greater N use efficiency. Bibb/Limestone responded to inoculation with an average increase of 10.9% in shoot production and with greater root biomass. Bibb/Limestone also exhibited lower N density in inoculated shoot tissues with a corresponding increase in the C/N ratio. For growers looking to maximize lettuce yields, G. diaz inoculation may present a beneficial additive to the growing system by increasing leaf yields while not increasing N fertilizer requirements.
Highlights
Lettuce (Lactuca sativa L.) is one of the most important vegetable crops sown in the United States, ranking third in total acreage (106,027 hectares) and first in economic value (USD 3.493 billion) in 2019 [1]
Several impediments to the intensification of field-grown lettuce production have arisen in recent years, including limited acreage of ideally suited farmland, high nitrogen (N) requirements for optimal production, risk of fecal bacterial contamination when manures are used as an N source for organic lettuce production, and significant irrigation demands
For growers looking to maximize lettuce yields on a static agricultural footprint, G. diaz inoculation may present a beneficial additive to the growing system
Summary
Lettuce (Lactuca sativa L.) is one of the most important vegetable crops sown in the United States, ranking third in total acreage (106,027 hectares) and first in economic value (USD 3.493 billion) in 2019 [1]. Several impediments to the intensification of field-grown lettuce production have arisen in recent years, including limited acreage of ideally suited farmland, high nitrogen (N) requirements for optimal production, risk of fecal bacterial contamination when manures are used as an N source for organic lettuce production, and significant irrigation demands These water demands are increasingly placing a burden on lettuce production, with chronic drought and increased salinity hindering yields [2,3]. Large-scale operations in these states have been impacted by food safety recalls over contaminated produce, leading to millions of dollars of losses and erosion of public trust [1] The sustainability of such geographically constrained production can be questioned, especially when coupled with the negative environmental impacts of cross-country transportation. Environmental conditions outside of these growing areas are unsuitable for year-round production
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