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Effects of Phosphorus, Sulfur, Calcium Hydroxide, and pH on Growth of Annual Bluegrass¹

ABSTRACT

The degree of annual bluegrass (Poa annua L.) infestation of turfgrass areas has been observed to be dependent on applied elemental sulfur (S) and phosphorus (P). The purpose of these experiments was to elucidate the effects of P, S, Ca(OH)₂, and imbibitional solution pH and acid source on germination, establishment, and clipping yield of annual bluegrass in monoculture. Annual bluegrass was grown in 15- by 15-cm pots filled with Myakka fine sand (sandy siliceous, hyperthermic Typic Haplaquods) in two glasshouse experiments. Treatments for Experiment I were factorial combinations of the following: 0, 250, and 500 kg S ha^–1; 0, 40, and 120 kg P ha^–1; and 1.5 and 2.0 cmol(+) Ca(OH)₂ kg^–1. Establishment and average clipping yield responded positively to applied P and Ca(OH)₂, while the response to applied S was negative. The magnitude of the response to added P was dependent on S and Ca(OH)₂ rates. Conversely, the magnitude of the negative response to S was dependent on P and Ca(OH)₂ levels. An optimum tissue P concentration was predicted at 0.52 dag P kg^–1 indicating a high requirement for P. In Experiment II, annual bluegrass emergence, establishment, and clipping yield responded in a negative linear fashion to S mixed with the 0- to 2.5-cm soil depth at 0, 50, 100, and 150 kg ha^–1. At this soil depth a pH range of 5.6 to 4.3 resulted from these S treatments. These results suggest that annual bluegrass stands can be reduced by acidifying the zone of seed germination using S. Under growth chamber conditions annual bluegrass seed was subjected to acid imbibitional solutions derived from either HCl, H₂SO₄, or H₃PO₄ at various pH levels. The first phase was performed at pH levels of 3.0, 4.0, 5.0, and 7.0. Nongermination of annual bluegrass seed was greatest at pH 3.0, but declined rapidly with increasing pH. Abnormal germination or emergence of the plumule only was greatest at pH 4.0 and still evident at pH 5.0. The second phase involved germination of annual bluegrass seed at pH levels of 4.3, 4.8, 5.3, and 7.0. Non-germination of seed was minimized for this pH range so the decrease in normal germination with increasing acidity was reflected in abnormal germination levels. The decrease in radicle development under high H⁺ ion concentrations may be due to a loss of membrane integrity and thus, inhibition of cell division in the root tip. Annual bluegrass infestation of turfgrasses may be reduced by limiting P applications and maintaining the soil pH near 5.0, but the infested turfgrass must be tolerant of these conditions.

¹ Contribution from the Institute of Food and Agricultural Sciences, Univ. of Florida, Gainesville, FL. 32611, J. Series 4940.

² Former Graduate Assistant (now Graduate Assistant, Agronomy Dep., Univ. of Kentucky; Lexington), and Associate Professor of Soil Fertility, Dep. of Soil Science, respectively.

Received for publication September 17, 1984. Accepted for publication July 23, 1985.