1. Root Extension of Bahiagrass as Observed in Acrylic Columns Carlos Acuna 1, Cheryl Mackowiak 2, Thomas Sinclair 1, Ann Blount 2, and Kenneth Quesenberry 1 1 University Of Florida, PO Box 110500, Gainesville, FL 32611-0500, 2 University of Florida - NFREC, 3925 Hwy 71, Marianna, FL 32446 Introduction Bahiagrass, Paspalum notatum Flügge, is one of the most important forage and utility turf of the southern USA. Bahiagrass germplasm differs markedly in seasonal forage production. This might be partially related to genotypic variability for developing deep roots. Deeper roots can recover additional soil water and nutrients, particularly nitrogen. The present study examined genotypic differences in root depth development rates (RDDR) and the effect defoliation had on RDDR. Materials and Methods Plant Material Two highly apomictic genotypes were used: the cultivar Argentine, and the experimental clone Tifton 7. Root Depth Development Rates (RDDR) Plants were grown in 1-m long clear acrylic columns (3.5-cm or 10-cm diameter), containing a sandy soil (Typic Quartzsamment) or potting mix (Figure 1). Two trials in 2006 (16 May to 17 July, and 7 August to 7 October) were located outdoors in Gainesville, FL. The depth of the deepest visible root was recorded three times per week. Above- and below-ground plant dry mass were determined at the end of each trial. Effect of Defoliation on RDDR Plants in the second trial were defoliated every one or two weeks, beginning on 9 September 2006. Results Greater RDDR was observed for Tifton 7 (2.6 cm d -1 ) as compared with Argentine (2.2 cm d -1 ) between 16 May and 12 June (Figures 2 and 3). Tifton 7 also produced greater above- and below-ground mass during the first trial as well as greater above-ground mass during the second trial. There was no RDDR difference between soil media but greater rates were recorded from the larger columns. Even so, growth patterns were similar between the two column sizes. Weekly defoliation slowed RDDR and decreased above and below ground plant mass similarly and independent of the genotype (Figure 4). Conclusions The greater RDDR observed for Tifton 7 at the beginning of the growing season appears to be associated with its ability to produce higher forage yields. Although more evidence is needed, rapid access to water and nutrients present in deep soil layers could result in higher yields. The negative effect of defoliation on RDDR should be considered when management practices are defined. Defoliation during or before water stress periods will reduce the velocity at which a plant can extend its roots into deep soil layers to reach stored water. Figure 1. Bahiagrass plants growing in acrylic columns: picture on the left shows plants growing in columns (10-cm diameter) filled with sandy soil; picture on the right shows a plant growing in a column (3.5-cm diameter) filled with potting mix. Figure 4. Defoliation effect on root depth development. The shoot clipping treatment was begun on day 26. Figure 2. Root depth development for Argentine and Tifton 7 growing in columns (10-cm diameter) filled with potting mix. Figure 2. Root depth development for Argentine and Tifton 7 growing in columns (3.5-cm diameter) filled with sandy soil.