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.

Low cost, high N content, and favorable handling characteristics of urea fertilizer (46-0-0) make its use common in turfgrass management. While many investigations conirm incomplete recovery of foliarly applied urea-N by turfgrass putting greens, the eicacy of urease-inhibiting additives, calcium-maleicitaconic polymer or N-(n-butyl) thiophosphoric triamide (NBPT), in preventing NH 3 volatilization is currently undocumented. Furthermore, NH 3 emissions reduce air and water quality. From 2014 to 2015, NH 3 volatilization was measured 0 to 24 h following foliar application of conventional or stabilized urea fertilizers to 'Penn G2' creeping bentgrass (Agrostis stolonifera L.) putting greens at a 20 kg ha-1 N rate in four separate trials. Using a 63% trapping-eiciency lux chamber system under the duration and conditions described, 11.1% of conventional or calcium-maleic-itaconic polymer-amended urea-N was lost as NH 3. Alternatively, combined amendment by NBPT and dicyandiamide (DCD) prevented 1.3 to 1.4 kg ha-1 NH 3-N emissions, reducing volatilization loss to only 3.8 to 4.6% of the foliarly applied urea-N.

Easy handling and low unit N cost make prilled urea (46-0-0) a popular fertilizer. While incomplete recovery of granular urea applications by turfgrass is documented, field evaluations of NH 3 volatilization mitigation by coatings or bioinhibitor efficiency enhancements are limited. Meanwhile, NH 3 emissions reduce air quality and contribute to nutrient loading of water resources. Our objectives were to quantify 3-and 6-d ammonia emission and 9-week turfgrass recovery of unincorporated granular fertilizer application to turfgrass. In 2014 and 2015, commercial urea-N fertilizers were broadcast over a mature Kentucky bluegrass (Poa pratensis L. 'Midnight') lawn at 43 kg ha −1 . Treatments included conventional urea and three enhanced-efficiency fertilizers; a blended fertilizer with 25% of its urea-N supplanted by polymer-and polymer-/sulfur-coated prills, or two stabilized urea fertilizers both amended by N-(n-butyl) thiophosphoric triamide (NBPT) and dicyandiamide (DCD) inhibitors. Using a 51% 'trapping-efficiency' flux chamber system under the field conditions described, 23.1 or 33.5% of the conventional urea-N was lost as NH 3 over the respective 3-or 6-d period following application. Alternatively, dual amendment by NBPT and DCD resulted in approximately 10.3 or 19.6% NH 3 -N loss over the respective 3-or 6-d periods, and greater fertilizer-N recovery by the turfgrass over the 9-week experiments. concentration gradient [18]. Over a 48-hour period following a foliar urea-N application of 50 kg ha -1 , assimilation by perennial ryegrass (Lolium perenne L.) was observed to exceed 17 kg ha -1 [19].Alternatively, urea is hydrolyzed into ammonia and carbon dioxide by urease [20], an enzyme ubiquitous to soil, thatch, and turfgrass leaf and shoot surfaces [21]. The position of urea at hydrolysis significantly influences the fate of its products [10]. Prompt incorporation of granular urea into soil, either mechanically [22][23][24] or via precipitation/irrigation-facilitated dissolution and infiltration [13,[25][26][27], has been shown to reduce subsequent ammonia volatilization rate. Accordingly, best management practice (BMP) includes prompt but judicious 'watering-in' of urea fertilizer applications to turfgrass [9,28,29].Yet given the perennial nature of turfgrass, limited availability and/or opportunity often preclude(s) mechanical incorporation and/or irrigation/rainfall concomitance when scheduling granular urea-N fertilization events. To that end, N-(n-butyl) thiophosphoric triamide (NBPT, C 4 H 14 N 3 PS) is one of a few compounds so dependably inhibitive of biological N transformation that it has been commercially adopted [30]. Under aerobic conditions, this soluble alkane decomposes to N-(n-butyl) phosphorotriamide [31] and inhibits urease activity by forming a tridentate bond that binds its active site [32]. Subsequent meta-analyses indicate NBPT amendment of urea supports a near 50% relative-reduction in NH 3 loss following broadcast application of urea to agricultural and horticultural production systems...