Influence of Plot Size on Severity of Frost Damage to Canola in Experimental Fields R. Ward, E. Cebert, S. Sangireddy and K. Ward Department of Natural Resources and Environmental Sciences Alabama A&M University, P.O. Box 1208, Normal, AL 35762 ABSTRACT Several winter canola cultivars have been selected for agronomic performance and adaptability to environmental conditions in north Alabama. Canola cultivars vary in their ability to tolerate cold temperatures. Freeze injuries sustained by plants generally depend on several factors including phenological stage, water content of plant tissues and the duration of freezing temperatures. Canola is susceptible to frost damage at flowering and early pod stages, and when prolonged freezing temperatures occur. Winter canola planted in Fall 2006 at the Alabama A&M University Winfred Thomas Agricultural Research Station sustained frost damage in April 2007, when temperatures dropped below freezing for three consecutive days. Damage included whole plant freeze burn, flower and early pod drop, and seed abortion. Freeze damage on winter canola (Jetton) was measured and compared among different-sized canola plots (i.e., 30 x 15 m2 , 6 x 6 m2 and 6 x 1 m2). Our data showed that severity of frost damage on canola varied with size of experimental plots. Percent panicle loss was found significantly higher in small plots compared to those in large plots. Fig. 1 A. Small plots (6 x 1m2); note early maturing canola in bloom and late maturing ones (including Jetton) at pre-flowering stage. Fig. 1C. Early maturing canola (foreground) at senescence; late maturing lines including Jetton at seeding stage. Fig. 1 B. Small plots of early maturing winter (with arrows) canola at 100% seeding stage while late maturing lines are still in full bloom. RESULTS Table 1. Freeze damage (% panicle loss) on winter canola (Jetton). Mean separation by DMRT (P>0.05). Plot Size (m2) Number of Plants (N) % Panicle Loss Replications Average 1 2 3 4 30 x 15 120 88.9 79.4 88.2 79.5 84.0 a 6 x 6 200 89.5 90.8 89.3 84.9 88.7 b 6 x 1 90 98.0 87.5 97.9 - 94.5 c Fig. 2A. Jetton at early flowering stage (6 x 6 m2 plots). Fig. 3. Jetton planted in large plots (30 x 15 m2 ). Fig. 2B. Jetton plots (6 x 6 m2); note dark brown, freeze damaged plants. Fig. 2C. Jetton 6 x 6 m 2 plots; note naked primary panicles. CONCLUSIONS Jetton planted in smaller plots (1x 6 m2 and 6 x 6 m2 ) sustained significantly higher panicle loss compared to the those in large (30 x 15 m2) plots (Table 1). Percent panicle losses were determined only from the primary panicle; loss or damage was measured as the ratio of panicle length with aborted pods and flowers to the total length of the panicle. Plant yield per plant sample was expressed in terms of total number of pods and corresponding pod weights. There was no correlation (r= -0.008) detected between damage (% panicle loss due to freeze burn) and crop yield, which was determined at the end of the season. Weight and number of pods that were not affected by freezing temperatures were not measured separately from those that incurred freeze damage. Prolonged freezing temperatures killed young and terminal region of the plants (Figs. 4, 5A-C). However, plants were able to recover and compensate for lost pods. Early maturing lines were at the most vulnerable stage when freezing temperatures occurred. Nearly 100% of fruiting structures were decimated (see Fig. 1C) Canola is generally sensitive to elevated temperatures after vernalization requirements are met, particularly during seed set and seed fill. This study indicates that plot size is an important consideration when measuring impact of freeze damage on canola plants prior to seedpod maturity and senescence; early responses to spring freezes, however, are useful indicators when screening for cold hardiness. INTRODUCTION In April 2007, temperatures dropped below freezing for three consecutive days, resulting in severe crop losses in Alabama and across the region. Sustained freezing temperatures that reached -3.3 °C killed many plants and decimated early maturing canola lines, particularly those that had reached fruiting stage (Figs. 1A-C). Freeze injury varies with plant species and cultivar, stage of development, plant moisture content, duration of freezing temperatures, time interval between freezes and temperature hikes after freeze. Freezing temperatures over a very short period of time may not cause significant economic injury to plants as long as the meristematic tissues are not killed, allowing the plants to recover. The size of experimental plots used in agronomic studies varies extensively from a few square meters to several hectares. To assess and document freeze damage on winter canola in northern Alabama and to determine whether plot size played a role in the expressed severity of plant damage, data were collected from experimental plots designed for various research studies and established in proximal areas within Alabama A&M University’s Winfred Thomas Agricultural Research Station (WTARS), located near Meridianville, AL. Fig. 5C. Naked primary panicle of freeze-damaged canola plant. Fig. 4. A 0.5 m2 quadrat used during plant sampling. Fig. 5A. Freeze-damaged Jetton plants with dead, dark brown stems. Fig. 5B. Upper parts of canola plants severely burn along edge of 6 x 6m2 canola plots. MATERIALS AND METHODS Study Site Several experimental plots were established at WTARS during the 2006-07 cropping season. These plots were set up for separate and independent experiments that employed different sized plots (i.e., 30 x 15 m2, 6 x 6 m2 and 1 x 6 m2) of winter canola. Treatment plots for each experiment were replicated four times. The experimental plots were located in close proximity, in the same general area of the experiment station. Jetton cultivar, along with other commercial and experimental winter canola lines, has been included in all our field experiments. However, only plots planted to Jetton were used in our assessments of freezing damage, due to its widespread use and consistent performance over several years of variety trials and other experiments. REFERENCES Andrews, C. J. and M. J. Morrison. 1992. Freezing and ice tolerance for winter Brassica. Agron. J. 84:960-962. Otypkova, Z. and M. Chytry. 2006. Influence of sample plot size on the data analysis. In: Proceedings European Vegetation Survey. 15th Workshop. Vegetation in Agricultural Landscapes and NATURA 2000, pp. 13-42. ( http://cat.inist.fr/?aModele=afficheN&cpsidt=14808136) Raymer, P. L.,, D. L. Auld and K. A. Mahler. 1990. Agronomy of canola in the United States.pp-25-35. In F. Shahidi (ed). Canola and rapeseed: Production, chemistry, nutrition and processing technology. Van Nostrand Reinhold. NY. Rife, C. and H. Zeinali. 2003. Cold tolerance in oilseed rape over varying acclimation durations. Crop Science 43: 96-100. Teutonico, R. A., J. P. Palta and T. C. Osborn. 1993. In vitro freezing tolerance in relation to winter survival of rapeseed cultivars. Crop Science 33: 103-107. MATERIALS AND METHODS (Cont’d.) Damage and Yield Estimates To determine the influence of plot size on the amount of damage caused by freezing temperatures, 30 to 50 plants per replication per plot size were sampled. Freeze damage was gauged in terms of percent panicle loss. Panicle loss was measured as the ratio of panicle length of aborted pods to the total panicle length of the primary stem. To determine yield data for each plot size, pods from all plant samples were excised, counted and weighed. Plant samples for yield data were collected at the end of the growing season. Data analyses were done using Proc GLM, with means separation by Duncan Multiple Range Test (DMRT). Data were also analyzed for correlations between panicle loss and pod weight. MATERIALS AND METHODS (Cont’d.) General Procedure Conventional methods of land preparation were followed. All plots were prepared and received similar rates of herbicide and fertilizer applications. Preplant herbicide (Treflan) was incorporated in the soil at the rate of 4.7 l/ha (2 qts/acre). Seeding was done with 18 -cm row spacing at 1.11kg/ ha (6 lbs/acre) seeding rate. Split applications of 13-13-13 NPK were made; 54 kg/ha was applied in the fall (6 weeks after planting) and 112 kg/ha in the spring. The crop was rain-fed.