Acknowledgments

1. EFFECTS OF FERTILIZER MANAGEMENT STRATEGIES ON NITRATE LEACHING AND AESTHETIC QUALITY OF ST. AUGUSTINEGRASS. RajendraGautam*, George Hochmuth* and Laurie Trenholm** *Soil and Water Science Dept., UF; ** Environmental Horticulture, UF. • Turf color was monitored on a weekly basis by the use of NDVI (Normalized Difference Vegetation Index) turf color meter (Fig. 2 b). • Fig. 2. a) Leachate Sample collection assembly b) NDVI turf color meter • NO3-N loads (Fig. 3 and 4) of the leachate for any date were less than 0.12 kg ha-1 regardless of treatments and season. • The leaching load of NO3-N was significantly higher (0.0035 kg ha-1) in mid-April as compared to other times of the year (Fig.4). • Greater NO3-Nload was observed during early spring (slow growth rate of grass). • Higher rainfall amounts during June, July and August did not increase NO3-N leaching (faster growth rate of grass). • Fig. 3. Effects of season and treatments on NO3-N load • Fig.4. Seasonal effect on NO3-N leaching load (means with the same letter are not significantly different by LSD, P=0.05) • The NO3-N concentrations of the leachate was found to be always less than 0.3 mg/l (Fig.5) regardless of season and N rate • NO3-N concentrations with all the treatments during higher rainfall period (June, July and Aug.) were low (Fig.5) • Fig.5. Treatment effect on NO3-N concentration at different sampling dates • More than 75 % of turf in Florida is planted in urban residential venues (Hodges et al., 1994). • St Augustinegrass, is the most widely used lawngrass in Florida (Trenholm et al., 2000) and occupies about 36% of the total land under turf (Hodges et al., 1994). • Fertilization is important to maintain the health and quality of grass. • Landscape fertilization is cited by some as one of the common nonpoint sources of nitrate in groundwater (Puckett, 1995). • There is a need to develop N fertilizer management strategies that reduce nitrate leaching and maintain the health and quality of the grass. • To address this research need, this experiment was conducted at the Plant Science Research and Education Unit, Citra, Florida in 2011. • Determine a N management practice that maintains a healthy turf without significant nitrate (NO3-N) leaching loss. • Higher dose of N fertilizer (244 kg/ha) will not only result in enhanced color and aesthetics but also in greater NO3-N leaching. • Ten fertilizer treatments (Table.1.) were arranged in a randomized complete-block design with four replications. • Table.1. Treatment detail • *CRF=Controlled-Release Fertilizer • Drainage lysimeters(57 cm diameter and 80 cm deep) were installed (Fig. 1 a) with the top rim 10 cm below the surface of the soil. • Polythene tubing was connected at the bottom of the lysimeter and was conveyed to central sample collection box (Fig.2 a). • Lysimeters were filled with gravel in the bottom and then filled with the excavated soil. • ‘Floratam’St. Augustinegrass sod was planted in March 2010. • Leachate samples were collected every two weeks (Jan –Aug. , 2011) following EPA’s sample collection and handling procedure. • Leachate volume was measured for the calculation of NO3-N load • Samples were analyzed for NO3-N by Automated colorimetry, Method EPA 353.2 • Fig.1. a) Lysimeters with excavated pit b) Irrigation system • Application of 244 kg N/ha from CRF had similar effect on NO3-N load as the fertilizer dose of 195 kg N/ha as ammonium nitrate and no application of fertilizer (Fig.6). • However difference among treatments was observed (Fig.6). • The NO3-N load values with all the treatments were very low. • Fig.6. Treatment effect on NO3-N load (means with the same letter are not significantly different by LSD, P=0.05). • There were significant differences in NDVI values due to treatments. • Higher N rate resulted in greater values of NDVI (Fig. 7). • Fig. 7. Effect of fertilizer treatments on NDVI (means with the same letter are not significantly different at P=0.05) • The NO3-N leaching load (<0.02 kg ha-1) as well as the NO3-N concentration (<0.3 mg/L) of leachate were low throughout the study period. • However, NO3-N load during early spring was higher than for the summer(Fig. 4). • When the grass was growing faster (June, July and August) the load declined to near zero. • NO3-Nleaching from the high N rate (244 kg ha-1) with CRF was statistically equal to the N rate of 195 kg ha-1(ammonium nitrate) and control plots. • NO3-Nleaching was highest in the early spring and reduced in the summer • The leaching of NO3-N from St. Augustinegrass was very low (<0.15 % of fertilizer used) and hence does not have a significant role in NO3-N pollution of water bodies. • Higher values of NDVI for higher dose of fertilizer implies that the aesthetic quality of grass increased with the increase in fertilizer dose but did not increase the leaching loss. • Hodges, A.W., J.J. Haydu, P.J. van Blokland, and A.P. Bell. 1994. Contribution of the turfgrass industry to Florida's economy, 1991-92: A value-added approach. University of Florida Institute of Food and Agricultural Sciences Food & Resource Economics Department Published as Economics Reoprt ER 94-1. • Trenholm, L. E., J.L. Cisar, and J.B. Unruh. 2000. St. Augustinegrass for Florida lawns. Univ. of Fl. Coop.Ext. Serv., ENH 5. Univ. of Florida, Gainesville, FL. • Puckett, L. 1995. J. Environ. Sci. Technol.29: 408-414. • Funding for this project is being provided by Agrium Advanced Technologies and University of Florida. Special thanks goes to Dawn Lucas , Basil Wetheringtonand Stephen Thomas at University of Florida. BACKGROUND LSD=0.013 RESULTS AND DISCUSSION OBJECTIVES . HYPOTHESIS LSD=0.0089 MATERIALS AND METHODS CONCLUSIONS a ab bc bc bc bc bc bc Acknowledgments c c c c c Figure 3: Average NO3-N leaching load for 13 leachate collection events ( p=0.073) REFERENCES Fig 1. Lysimeter ACKNOWLEDGEMENT