Stargrass Response to Lime and Phosphogypsum

Stargrass (Cynodon spp.) is an important forage in tropical Florida and other tropical regions of the world. Lime is believed to be a major input needed for stargrass production. A field study was conducted on a Pomona fine sand (sandy, siliceous, hyperthermic, Ultic Haplaquod) to determine the response of stargrass to lime and phosphogypsum and to determine if lime application levels can be reduced below the current agronomic recommendations for commercial growers (pH = 6.0). Treatments consisted of a check (0 tons lime or phosphogypsum/acre) and five rates of dolomitic limestone (0.5, 1.0, 1.5, 2.0, and 3.0 tons/acre) and two rates of phosphogypsum (1.0 and 2.0 tons/acre) in a randomized complete block design with four replications. Dolomitic lime increased stargrass dry matter (DM) yields quadratically in all 3 yr with yield maximizing when 2 ton/acre of dolomitic lime was applied. Application of dolomitic lime increased soil pH, soil Ca, and soil Mg linearly in the Ap soil horizon. Soil pH ranged from 4.6 to 6.0 and exchangeable Al ranged from 10.4 to 18.1 ppm for the Ap horizon for the 3.0 and 0 ton lime/acre treatments, respectively. Application of phosphogypsum resulted in increased yields in spite of the increase in soil acidity. Stargrass roots penetrated the spodic horizon regardless of phosphogypsum or lime rates. This study demonstrates the importance of dolomitic lime or phosphogypsum for stargrass production in low pH soils and that the recommended rate of lime application may be reduced without affecting forage production. Research QuestionStargrass, a warm season perennial forage, is becoming one of the most popular grasses throughout the tropics. It produces high quality forage that, when properly managed for grazing, results in good animal performance. With the exception of N, soil acidity may be the major factor limiting stargrass growth and production. The purpose of this study was to evaluate the Florida lime recommendations for stargrass production and to determine whether the recommended levels of lime could be reduced without harmful effects on stargrass production. Literature SummaryStargrass is demonstrating excellent potential as a high quality forage in tropical USA and many other tropical regions of the world. Because this grass has high yield potential, insect and disease resistance, persistence, and high forage quality, both dairy and beef cattle producers are increasing their acreage planted to stargrass. Stargrass has the unique ability to produce forage during saturated soil conditions in the warm season (70 to 95°F) and in the cool-dry season (50 to 70°F). Dairy farmers find stargrass grown under high fertility and harvested frequently will persist for many years, yielding high quality forage when harvested for hay or haylage on a 4-wk schedule. Since many soils in the tropical regions of the world are strongly acid, studies have to be conducted on defining the lime requirement needs for optimum stargrass production. Study DescriptionA 3-yr field study was conducted on a strongly acid, infertile spodosol at Ona, FL, to determine the response of six rates of incorporated dolomitic lime (0, 0.5, 1.0, 1.5, 2.0, and 3.0 tons/acre) and three rates of phosphogypsum (0, 1.0, and 2.0 tons /acre) on stargrass production and soil chemical characteristics Applied QuestionsWhat are the minimum calcium and pH requirements for stargrass production? Stargrass yields increased quadratically with increasing rates of dolomitic lime. Incorporated dolomite of 2.0 tons /acre increased soil pH from 4.6 to 5.5 in the Ap horizon and increased stargrass yields by 100%. Addition of lime above 2.0 tons/acre did not significantly affect yields (Fig. 1). Addition of 2.0 tons/acre of phosphogypsum resulted in a 50% increase in stargrass production (Fig. 1). Results of this study demonstrate the importance of dolomitic lime or phosphogypsum for stargrass production. Based on this study it would appear that dolomitic lime is essential for stargrass production and that the lime recommendations for stargrass could be reduced in Florida spodosols without seriously affecting the crop yield. Fig. 1Influence of dolomitic lime and phosphogypsum on stargrass production.