Long-Term Effects of Liming and N Fertilization on Bahiagrass Pasture Martin B. Adjei and Jack E. Rechcigl Revenue loss from the decline in bahiagrass forage production and cost of pasture re- establishment combined is ~$50 million yr -1 in Florida. Damage first appears as yellow patches of grass that later die and turn brown. Feeding by “Tawny” mole crickets (Scapteriscus vicinus Scudder) is the principal terminal cause but other predisposing factors are suspected to play a role Objective This study determined the interactive effects of fertilizer and lime applications on bahiagrass yield, nutritive value and stand persistence under grazing conditions. Materials and Methods Design: Split plot experiments on 2 separate bahiagrass pastures. Main plots: 3 randomized complete blocks of limed (to maintain a soil pH >5) vs. no- lime treatments on each pasture. Dolomitic lime applied every 2-3 yr on limed plots. Sub plots: Four annual fertilizer treatments applied to the same 15.2 x 15.2 plots from 1998 through Soil: Pomona fine sand (sandy, silicious, hyperthermic, Ultic Alaquod). Fertilizer treatments: 1) 67 kg N ha -1 (N), 2) kg N-P-K ha -1 (NPK), 3) kg N-P-K ha-1 plus 22 kg ha-1 of micronutrient mix (NPKM), and 4) control (no fertilizer) with N from ammonium sulfate. Micronutrient analysis: 24 g B kg -1, 24 g Cu kg -1, 114 g Fe kg -1, 60 g Mn kg -1, 0.6 g Mo kg -1, and 66 g Zn kg -1. Plots fertilized once in March, yearly ( ) Pastures were grazed every 35 d following the initial fertilization Forage regrowth under cage harvested every 35 d after grazing and cage moved to a new cut (7.5 cm stubble) area in plot. Forage subsamples dried, ground and analyzed for CP, IVOMD, P, K, Ca. Mg, Fe, Zn Cu and Mn. Fertilization Grazing Botanical composition Forage yield Six, 1-m 2 quadrats evaluated per plot in May, yearly for % green, yellow or dead and invaded by weeds Good plotDamaged plot Soil Sampling Soil sampled from top to 15 cm depth (Ap horizon) and at the spodic (Bh) horizon before the experiment and at end of each season ( ) Results Effect of lime and fertilizer on mean annual DMY on pasture 87 a a a b a a a b 30% better response to N with lime Effect of fertilizer on mean annual DMY on pasture 71A a a a b Response to N but not lime Dry Matter Yield Nutritive Value Mean Tissue Minerals pH 4.2 pH 4.3 Cont NPKM NPK N a b b c NS N by Lime effect on Spring Vegetative Ground Cover Damage to No-lime plots except the control on pasture 87 in spring 2003 Yellowing of No-lime plots except the control on pasture 71A in spring 2005 Pasture 87, 5th yrPasture 71A, 7 th year Limed strip No-lime strip Pasture 71A, spring 2005 N NPK Cont NPKM Conclusions N was key to bahiagrass pasture production. DMY Increase due to P & K was not cost- effective under grazing conditions. Repeated N fertilization without lime dropped soil pH, increased spring grass yellowing and promoted stand deterioration. Is problem S or Fe deficiency or Al 3+ toxicity? Monitor soil pH every 2-4 years and lime to maintain pH of 5-6 for stand persistence. Nutrient Range P* ( g kg -1) K* (g kg -1) Ca*(mg kg -1 ) Mg*(mg kg -1 ) Zn (mg kg -1 ) Fe (mg kg -1 )50-70 Cu (mg kg -1 ) Mn (mg kg -1 ) * Affected (P < 0.01) by P, K or dolomite application 6-yr Mean Soil pH SiteFertilizerNo limeLimed 87 N NPK NPKM Cont A N NPK NPKM Cont Without repeated lime soil pH declined to the native state. Soil Depth ApBh Sitemg Al kg A yr Mehlich-1 Al Same across treatments c c b a Nitrification cause of acidity: 2NH O 2 = 2NO H 2 O + 4H + (Nitrosomonas) 2NO O 2 = 2NO 3 - (Nitrobacter)