Laurie E. Trenholm

INFLUENCE OF SILICA ON GROWTH, QUALITY, AND WEAR TOLERANCE OF SEASHORE PASPALUM

Wear is a predominant stress affecting growth of turfgrass. Silica, which is deposited in epidermal cells of leaf blades, may potentially increase rigidity of a turfgrass stand. This research was undertaken to determine if application of silicon (Si) would enhance turfgrass wear tolerance, growth, and quality. This research was conducted during two consecutive field trials in 1998 on two greens-quality ecotypes established on a native Applying (Typic Kanhapludult) soil at the University of Georgia Experiment Station in Griffin, GA. Silica was applied to two ecotypes of seashore paspalum (Paspalum vaginatum Swartz.) as potassium (K) silicate at two foliar rates (1.1 and 2.2 kg Si ha−1) and as a soil drench rate of 22.4 kg Si ha−1. Potassium chloride, which added K at the amount in the drench treatment (15.6 kg K ha−1), was also applied as a K check. Best turf quality responses on nonwear plots resulted from highest rates of Si application as well as from the K only treatment. A positive association was found between leaf tissue K concentration and turf quality scores, while increasing Si concentration reduced quality scores. Wear tolerance was enhanced either by K alone or by the high rate of Si and K. Turf growth was not affected by fertility treatments. Enhanced wear tolerance, due to application of either K alone or Si and K, reduced wear injury from 35% to 14% (K) or 20% (Si and K) averaged across both studies. This may be attributed to increased leaf turgor pressure or reduced total cell wall (TCW).

Tolerance of 'Salam' seashore paspalum (Paspalum vaginatum) to postemergence herbicides.

Field studies were conducted to assess the tolerance of seashore paspalum (‘Salam’) to postemergence (POST) herbicides in Florida in 2000 and 2001. POST applications of bentazon (2,200 g/ha), clopyralid (420 g/ha), dicamba (280 g/ha), halosulfuron (70 g/ha), imazaquin (420 g/ha), mecoprop + 2,4-D + dicamba (160 + 180 + 40 g/ha), metsulfuron (30 g/ha), and quinclorac (1,700 g/ha) resulted in ≤10% injury 7 and 15 d after treatment (DAT), indicating their safety for POST application. Clethodim (280 g/ha) and sethoxydim (310 g/ha) caused 67 and 46% injury, respectively, 15 DAT averaged across 2000 and 2001. Ethofumesate was inconsistent between years, causing 30 and 60% injury 7 and 15 DAT, respectively, in 2000, but only 5 and 13% 7 and 15 DAT, respectively, in 2001. Imazapic and trifloxysulfuron-sodium caused an average of 47% injury 7 DAT in 2000 and 45% injury 15 DAT in 2001. Clethodim, ethofumesate, imazapic, sethoxydim, and trifloxysulfuron-sodium can not be safely applied POST to Salam seashore paspalum; however, bentazon, clopyralid, dicamba, halosulfuron, imazaquin, mecoprop + 2,4-D + dicamba, metsulfuron, and quinclorac are safe. Nomenclature: Bentazon, clethodim, clopyralid, dicamba, ethofumesate, halosulfuron, imazapic, imazaquin, mecoprop + 2,4-D + dicamba, metsulfuron, quinclorac, sethoxydim, trifloxysulfuron-sodium; seashore paspalum, Paspalum vaginatum Swartz ‘Salam’ #3 PASVA. Additional index words: Turfgrass tolerance, turfgrass injury. Abbreviations: DAT, days after treatment; OCGC, Old Collier Golf Club; WFREC, West Florida Research and Education Center.

St. Augustinegrass Fertilizer Trials

ABSTRACT Research was conducted to verify the current fertilization recommendations for St. Augustinegrass (Stenotaphrum secundatum Walt. Kuntze) lawns. Currently, a range from 100 to 300 kg nitrogen (N) ha− 1 per growing season is suggested, based on factors such as location in the state, desired maintenance level, soil conditions, etc. Research was conducted at the G.C. Horn Turfgrass Field Laboratory in Gainesville, FL from 2000 to 2002, utilizing medium to high management levels and at a sod farm in Bradenton, FL from 2001 and 2002, under low management conditions. Nitrogen (N) and potassium (K) treatments were arranged in a randomized complete block design with three replications in both locations. In Gainesville, best visual quality was generally obtained with medium (MN) or high nitrogen rates (HN). In Bradenton, MN, and HN rates provided best visual quality responses in 2002 and 2003, but higher rates of N were required than in Gainesville to maintain acceptable quality. This higher N requirement could be due to the longer growing season in Bradenton or to poor turfgrass growth resulting from inadequate pest control. In the absence of biotic or abiotic stresses, the highest rates of N were not necessary to maintain an acceptable quality lawn.

Warm-Season Turfgrass Response to Fertilizer Rates and Sources

Abstract The objectives of this study were to evaluate effects of natural organic and inorganic fertilizers on various warm-season turfgrass species and to determine if lower rates of natural organic products would provide adequate turfgrass response. Studies were conducted in 2000 and 2001 in two locations in Florida on St. Augustinegrass (Stenotaphrum secundatumWalt. Kuntze) and bermudagrass (Cynodon dactylon × C. transvaalensisBurtt-Davy) cultivars. Each fertilizer product was applied at a low and a high rate throughout the growing season at rates consistent with current University of Florida recommendations for best turfgrass performance and response. In general, highest visual ratings for quality, color, and density were obtained with the higher rate of nitrogen (N), regardless of source, although the low rate of the 27N-1.3P-3.3K fertilizer produced ratings equal to the higher (N) rates from other sources in St. Augustinegrass. Trends were similar for spectral reflectance values, in that best results generally occurred in response to higher N rate, with the exception of the 27N-1.3P-3.3K fertilizer at the lower rate. From the results of this research, it appears that the higher N rate produces better turfgrass responses, regardless of fertilizer source.

NITRATE LEACHING AND TURF QUALITY IN NEWLY SODDED ST. AUGUSTINEGRASS

There are increasing concerns about the fate of fertilizers applied to lawn grasses. The objectives of this research were to evaluate nitrate leaching and turf response to nitrogen (N) treatment and irrigation in newly sodded St. Augustinegrass. The research was conducted in Citra, FL in 2006 and 2007. Nitrogen was applied at three rates day of sodding and again at 30 days after planting. Analysis of variance indicated there were no differences in nitrate-N (NO3–N) leached due to N treatment or timing. During the establishment period, NO3–N loading was greater than reported for established turf and could possibly present a source of nitrate contamination. Turf quality and color were above or just below an acceptable score at all N rates. Due to the potential for high amounts of NO3–N leaching in new sod, it is not recommended to apply N fertilizer to St. Augustinegrass in the first 30–60 days after planting.

Comparison of Soil P Test Procedures for St. Augustinegrass

St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze] is a home lawn grass widely used in the southern United States. At present, phosphorus (P) fertilization of St. Augustinegrass is based primarily on Mehlich 1 P test. One criticism of Mehlich 1 extractant is that it extracts some fraction of soil P pool that is not available to plants, whereas, iron (Fe) oxide P and water‐extractable P methods are reported to be better related to plant growth in some cases. Literature relative to the soil test procedure comparison for St. Augustinegrass was not found. The objective of this study was to evaluate Mehlich 1 P, Fe oxide P, and water‐extractable P to identify the most suitable soil test method for St. Augustinegrass growth. Established pots of ‘Floratam’ were subjected to P application of 0, 0.14, 0.27, 0.54, and 1.07 g m−2 every 4 wk for 12 wk. Measurements included tissue growth rates, tissue P concentration, soil Mehlich 1 P, Fe oxide P, and water‐extractable P concentrations. Phosphorus application increased soil test P concentrations. Soil Mehlich 1 P, Fe oxide P, and water‐extractable P concentrations were closely correlated to each other. Three soil test P levels and tissue P concentrations were highly correlated with Mehlich 1 P, which best predicted tissue P levels. Three soil test P levels were also closely correlated to the St. Augustinegrass top growth rate. Critical minimum Fe oxide P and water‐extractable P concentration was 3 mg kg−1. Overall, Mehlich 1 P was the best soil P test for St. Augustinegrass among the three extractants tested.

Nitrogen Required for Acceptable Centipedegrass Quality, Color, Growth Rate, and Nitrate Leaching

In northern Florida, nitrogen (N) application recommendations for centipedegrass [Eremochloa ophiuroides (Munro) Hack.] range from 49 to 98 kg ha−1 yr−1. The objective of this study was to determine the minimum amount of N necessary to produce acceptable quality centipedegrass while also measuring the influence of irrigation rate on color, growth rate, and NO3–N leaching. Nitrogen was applied at rates of 18, 36, 74, and 147 kg ha−1 yr−1 split evenly into three application cycles in 2006 and again in 2007 to common centipedegrass. Acceptable turf quality and color was produced by N applied at 18 kg ha−1 yr−1 during all cycles. Turf color and quality increased with increasing N rate (NR) for yearly average and many of the cycles. Nitrate N leaching was equivalent for NRs 18 and 147 kg ha−1 yr−1. However, when NRs increased from 18 to 36 and 74 kg ha−1 yr−1, annual NO3–N leaching was reduced by ~50%. Current recommended NRs may be more than is necessary to produce acceptable quality centipedegrass; however, the rates do not pose an increased risk to NO3–N leaching. T.W. Shaddox, UF/IFAS Fort Lauderdale Research and Education Center, Univ. of Florida, 3205 College Ave. Ft. Lauderdale, FL 33314; L.E. Trenholm, Dep. of Environmental Horticulture, Univ. of Florida, PO Box 110670, Gainesville, FL 32611; J.B. Unruh, West Florida Research and Education Center, Univ. of Florida, 4235 Experiment Dr. Jay, FL 32565. Received 18 Apr. 2016. Accepted 16 Sept. 2016. Assigned to Associate Editor Mark Carroll. *Corresponding author (shaddox@ufl.edu). Abbreviations: EFC, early-fall cycle; LSC, late-spring cycle; NR, nitrogen rate; SC, summer cycle. Published in Int. Turfgrass Soc. Res. J. 13:86–93 (2017). doi: 10.2134/itsrj2016.04.0241