Physical and Cultural Weed Control Working Group of - European ...

9 th EWRS Workshop on Physical and Cultural Weed Control 68
Samsun, Turkey, 28 – 30 March 2011
Leaf RWC Determination. For each plant species and timing of flaming, one set of three pots
were kept aside only for leaf RWC determination. These plants did not receive any flaming
treatments. Leaf RWC was determined according to the standard method of Barrs and Weatherley
(1962). A composite sample of leaf discs from each plant was weighted immediately, providing a
measure of fresh weight (FW). After weighing, the disks were soaked in deionized water for 24 h
and then weighted again to obtain a fully turgid weight (TW). Finally, the leaf discs were ovendried
to a constant weight at about 85 C and weighted to get a dry weight (DW). The leaf RWC is
calculated as follows (Barrs and Weatherley 1962):
RWC = (FW – DW) / (TW – DW) [1]
Although originally defined as a percentage, leaf RWC is now commonly expressed in decimal
form (Smart and Bingham 1974) and this convention is followed in our studies (Table 2).
Flaming Procedure. Flaming was done at four times of day (0, 4, 8, and 12 HAS), which covered
four different leaf RWC. To obtain different leaf RWC, the soil in each pot was watered up to field
capacity at 6 P.M. of the previous day, thus flaming was done approximately at 12, 16, 20, and 24 h
after watering. Flaming treatment was conducted utilizing a handheld flamer with a single VT 2-
23C vapor phase burner 1 positioned 20 cm above soil surface and angled horizontally at 30˚. The
propane pressure was 120 kPa, which produced a flow rate of 95 g h –1 . The application speeds
(conducted by walking) were 1.6, 3.2, and 4.8 km h –1 , which corresponded to the propane doses of
87, 43, and 29 kg ha –1 , respectively.
Visual Plant Injury Estimation and Fresh Weight. Visual plant injury was assessed at 1, 3, and 7
d after treatment (DAT) using a scale from 0 to 100%, where 0 represented no plant injury based on
the nonflamed plants, and 100 represented plant death. At 7 DAT, each plant species was clipped at
the soil surface and shoot fresh weight was recorded.
Statistical Analyses. Analysis of variance (ANOVA) was performed by the PROC GLIMMIX
procedure in SAS (SAS Institute 2005) to test for the significance (P < 0.05) of experimental runs,
treatments, replications, and their interactions on the basis of the visual ratings of plant injury and
fresh weight data. There were no significant interaction effects of treatment and experimental run;
therefore, the data were pooled over two experimental runs. Data were subjected to a non-linear
regression analysis and were analyzed using the four-parameter log-logistic model (Seefeldt et al.
1995):
Y = C + (D − C) / {1 + exp[B(log X − log E)]} [2]
where Y is the response (e.g., percent injury), C is the lower limit, D is the upper limit, X is the
propane dose, E is the dose resulting in a 50% response between the upper and lower limit (also
known as inflection point, I50 or ED50), and B is the slope of the line at the inflection point (also
known as a rate of change). All statistical analysis and graphs were performed with the open-source
statistical software R 2.3.0 2 utilizing the dose–response curves (drc) statistical addition package
(Knezevic et al. 2007). For visual plant injury, the hours after sunrise when flaming resulted in a
90% of the maximum injury (HAS90) for crops and weed species were calculated from Figure 1b
and presented in Table 4. Time of day that corresponded to each HAS90 value in Table 4, was
calculated on the basis of an arbitrarily assigned day of June 15, 2009.
Results and Discussion
Plant Injury. Significant interaction (P = 0.02) between propane dose and time of day was
observed with the visual plant injury data at 7 DAT (Figures 1a–b). All plant species exhibited more
injury when flamed during the afternoon, particularly at 12 HAS (Figure 1a). There were no
differences in the injury levels among 0, 4, and 8 HAS treatments for most of the plant species