(ASABE) has recently defined mixed-species landscape water use normalized to reference evapotranspiration as plant factors, rather than crop coefficients ( ASABE, 2012 ; Beeson et al., 2014 ; Sun et al., 2012a ). The new S623 Standard attempts to define
Peter C. Andersen, Brent V. Brodbeck and R. F. Mizell III.
Homalodisca coagulata (Say), a xylem-fluid feeding leafhopper, vectors diseases induced by the bacterium Xylella fastidiosa such as phony peach disease and Pierce's disease. The purpose of this study was to investigate plant factors that influence feeding. H. coagulata were confined to stems of peach [Prunus persica (L.) Batsch] and crape myrtle (Lagerstroemia indica L.). Osmolarity, amino acid and organic acid concentrations of xylem fluid were maximum during the morning for peach and declined thereafter; xylem fluid chemistry of crape myrtle followed a less distinct trend. Irrigated plants had higher concentrations of organic constituents and feeding rates were higher on these plants. Feeding rates and xylem fluid tensions, were maximum during midday; feeding did not occur at night. In separate experiments feeding rates were greatly reduced at xylem tensions >1.5 MPa.
Janet S. Hartin, David W. Fujino, Lorence R. Oki, S. Karrie Reid, Charles A. Ingels and Darren Haver
measure and record temperature, solar radiation, wind speed, and relative humidity hourly with free online access to real-time and historical records. An ETAF further adjusts the ET o based on a plant factor (PF) and IE as follows: Plant factors
Mike Caron and Roger Kjelgren
We investigated growth, water relations, and water use of bare root (BR) and balled-burlapped (BB) Patmore green ash following transplanting into an irrigated landscape setting in a high desert climate. Treatments were green ash harvested as larger (40 mm caliper) BB and BR trees, and smaller BR stock (25 mm caliper). During establishment, we measured canopy growth for 3 years, and for 2 years plant water relations [predawn water potential and midday stomatal conductance (g S)] and water depletion within the root zone. All treatments expressed varying degrees of isohydric responses to root loss by reducing g S that maintained water potential nearly constant, but least so for the smaller BR trees. g S was greater than that of all larger trees, meaning that for the same cost in water potential as the larger trees, BR-Small benefitted from more open stomates and presumably greater carbon gain. Greater initial conductance apparently translated into more growth. Year 1, BR-Small trees had the least total leaf area, but by Year 3 total leaf area was not different among all treatments. Also during Year 1, the ratio of water use to local reference evapotranspiration [plant factor (PF)] was 0.36 for large BR trees vs. 0.56 for BB trees, similar to the recommended PF of 0.5 for trees in dry climates. These results suggest smaller BR trees are a cheaper alternative for high desert landscapes while reaching nearly equivalent growth to BB trees after 3 years. Achieving high growth of BR trees would need careful scheduling of irrigation amount and frequency based on leaf area, root zone size, and local reference evapotranspiration.
Hongyan Sun, Kelly Kopp and Roger Kjelgren
when plants are water-limited or stressed. Consequently, a plant factor, K p ( Eching and Snyder 2005 ; EPA WaterSense, 2009 ), rather than a coefficient K c , more candidly represents the attenuated relationship between heterogenous urban landscape
Zongyu Li, R. Karina Gallardo, Wendy Hoashi-Erhardt, Vicki A. McCracken, Chengyan Yue and Lisa Wasko DeVetter
plant factors), each of which included a number of traits that had been identified in consultation with PNW strawberry breeders, extension educators, industry representatives, and growers. Specific clusters and associated traits are presented and
Dennis R. Pittenger, David A. Shaw and William E. Richie
We conducted an evaluation of three commercial weather-sensing irrigation controllers to determine the climatic data they use, how easy they are to set up and operate, and how closely their irrigation regimes match landscape irrigation needs established by previous field research. The devices virtually controlled an existing reference irrigation system and used its system performance data as required in their initial setup. Reference standard treatments for cool-season turfgrass, trees/shrubs and annual flowers were calculated using onsite, real-time reference evapotranspiration (ETo) data and plant factors developed primarily from previous research. The reference irrigation system applied the correct amount of water to an actual tall fescue turfgrass planting whose water needs served as the reference standard treatment comparison for the cool-season turfgrass treatment. Virtual applied water was recorded for other plant materials and it was compared to the corresponding calculated reference standard amount. Results show each controller adjusted its irrigation schedules through the year roughly in concert with weather and ETo changes, but the magnitudes of adjustments were not consistently in proportion to changes in ETo. No product produced highly accurate irrigation schedules consistently for every landscape setting when compared to research-based reference comparison treatments. Greater complexity and technicality of required setup information did not always result in more accurate, water-conserving irrigation schedules. Use of a weather-sensing controller does not assure landscape water conservation or acceptable landscape plant performance, and it does not eliminate human interaction in landscape irrigation management.
development. Pannkuk (p. 322) used local ET o data and actual plant water use to calculate plant factors (PFs) for three model landscapes comprised of mixtures of turfgrass and shrubs. Turfgrass/shrub vegetative cover ratios were 80:20, 50:50, and 20
Yingqian Lin, Alexa R. Wilson and Pascal Nzokou
fertilization. Several soil and plant factors are known to determine green manure decomposition. Soil factors include texture, acidity, microbial activity, and soil fertility ( Fageria, 2007 ; Thonnissen et al., 2000 ). Main plant factors are the carbon/N and
Wenjing Guan, Xin Zhao and Donald J. Huber
accelerated fruit development might be associated with higher temperature as the season progressed. However, the fluctuation of air temperatures during April to May ( Fig. 2 ) implied that internal plant factors rather than external environmental conditions