Spatial and temporal variation of soil, climate, plants and irrigation requirements are challenges for modern agriculture and complex turfgrass sites. Precision agriculture (PA) evolved to improve site-specific management based on obtaining site-specific information. The focus of this concept paper is on the emerging area of precision turfgrass management (PTM) with attention given to: (a) comparing the concepts of PTM and PA in terms of driving forces and challenges that must be addressed for PTM to progress in science and practice and (b) discussion of specific field mapping applications (purposes) for different turfgrass situations such as golf courses, sod production fields and sports fields. The field applications relate to site-specific management of irrigation, salinity, fertilizer application and cultivation. To illustrate the potential for PTM, different approaches that may be necessary for PTM compared to PA are discussed. The initial factor that hindered the adoption of PTM has been the lack of mobile sensor platforms that can determine both key soil and plant properties for turfgrass situations. This paper concentrates on PTM field applications that involve mapping of both soil and plant attributes, in contrast to only optical sensing mapping.

This paper presents the first micrometeorological-based measurements of methane (CH4) emissions from Asian rice paddies of which we are aware. The research features the tunable diode laser trace gas analyzer system (TGAS) recently developed at the University of Guelph. CH 4 fluxes were measured between March 9 and 24, 1992, from an irrigated rice paddy field at the International Rice Research Institute (IRRI), the Philippines. The daytime CH 4 flux averaged 6.0/xg m -2 s -1 . The CH 4 fluxes displayed a diurnal trend similar to daily soil temperature curves, with peak emissions of about 8/xg m -2 s -1 in the early afternoon. A tenfold increase in CH 4 emissions (to about 70/xg m -2 s -1) during a brief weeding experiment resulted from soil disturbance. Up to 25/xg m -2 s -1 of CH 4 were released during a drying of the field, after which unsuitable soil redox potentials apparently suppressed methanogenesis. The CH 4 flux was also arrested when the field was flooded with oxygen-rich water during a heavy rainstorm. where Fme flux of CH 4 (/xg m -2 s-l); K eddy diffusivity (m2 s -•); ACme change in CH 4 concentration (/xg m-3); Az (m) vertical height difference. TGAS measurements were used to determine a finite CH 4 concentration difference ACme. Three estimates of the eddy diffusivity K were inferred using micrometeorological tech-SIMPSON ET AL.' TUNABLE DIODE LASER MEASUREMENT OF METHANE FLUXES 7285 OF METHANE FLUXES 7289

Environmental pests may serve as reservoirs and vectors of zoonotic pathogens to leafy greens; however, it is unknown whether insect pests feeding on plant tissues could redistribute these pathogens present on the surface of leaves to internal sites. This study sought to differentiate the degree of tissue internalization of Escherichia coli O157:H7 when applied at different populations on the surface of lettuce and spinach leaves, and to ascertain whether lettuce-infesting insects or physical injury could influence the fate of either surface or internalized populations of this enteric pathogen. No internalization of E. coli O157:H7 occurred when lettuce leaves were inoculated with 4.4 log CFU per leaf, but it did occur when inoculated with 6.4 log CFU per leaf. Internalization was statistically greater when spinach leaves were inoculated on the abaxial (underside) than when inoculated on the adaxial (topside) side, and when the enteric pathogen was spread after surface inoculation. Brief exposure (∼18 h) of lettuce leaves to insects (5 cabbage loopers, 10 thrips, or 10 aphids) prior to inoculation with E. coli O157:H7 resulted in significantly reduced internalized populations of the pathogen within these leaves after approximately 2 weeks, as compared with leaves not exposed to insects. Surface-contaminated leaves physically injured through file abrasions also had significantly reduced populations of both total and internalized E. coli O157:H7 as compared with nonabraded leaves 2 weeks after pathogen exposure.

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In the past decade, leafy greens have been implicated in several outbreaks of foodborne illness, and research has focused on contamination during preharvest operations. Concerns have been raised that internalization of pathogens into the edible tissue occurs where postharvest chemical interventions would be ineffective. This study was initiated to measure the degree and fate of Escherichia coli O157:H7 internalized in the phyllosphere tissue of leafy greens when spray conditions, inoculum level, and type of leafy green were varied. Two spraying treatments were applied: (i) spraying individual spinach or lettuce leaves on plants once with a high dose (7 to 8 log CFU/ml) of E. coli O157:H7 and (ii) spraying spinach, lettuce, or parsley plants repeatedly (once per minute) with a low dose (2.7 to 4.2 log CFU/ml) of E. coli O157:H7 over a 10- to 20-min period. With the high-dose spray protocol, no significant differences in the prevalence of internalization occurred between Shiga toxin-negative E. coli O157:H7 isolates and virulent isolates (P > 0.05), implying that the Shiga toxin virulence factors did not influence internalization or the subsequent fate of those populations under these test conditions. Significantly greater internalization of E. coli O157:H7 occurred in spinach leaves compared with lettuce leaves when leaves were sprayed once with the high-dose inoculum (P < 0.05), whereas internalization was not observed in lettuce leaves but continued to be observed in spinach and parsley leaves following repeated spraying of the low-dose inoculum. Based on these results, it is surmised that a moisture film was generated when spraying was repeated and this film assisted in the mobilization of pathogen cells to plant apertures, such as stomata. E. coli O157:H7 cells that were internalized into spinach tissue using a low-dose repeat-spray protocol were temporary residents because they were not detected 2 days later, suggesting that plant-microbe interactions may be responsible.

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