CALCIUM AND PHOSPHORUS INFLUENCE CREEPING BENTGRASS AND ANNUAL BLUEGRASS GROWTH IN ACIDIC SOILS

Acidifying soil to prevent annual bluegrass (Poa annua L.) from infest ing creeping bentgrass (Agrostis palustris Hud.) reduces soil P and Ca availability. This study examined Ca and P effects on the growth of t hese two grasses in four moderately acidic soils using CaSO4 as a Ca s ource. Each soil received four P rates (0, 10, 40, or 80 mg.kg) and th ree Ca (as CaSO4) rates (0, 400, or 800 mg.kg-1). Neither Ca nor P tre atments substantially changed pH or exchangeable soil Al. Clipping yie lds, tissue P concentration, and P uptake of both grasses were affecte d by soil NaHCO3-P levels. Compared to bentgrass, annual bluegrass had higher clipping yields and P uptake at high P rates or high NaHCO3-P levels; this result indicates that annual bluegrass was as acid-tolera nt as the bentgrass, provided that available P in the soil is adequate . Adding CaSO4 to the Papac soil, which contained the least amount of exchangeable Ca among the four soils, markedly enhanced the clipping t issue P concentration and P uptake of creeping bentgrass but not those of annual bluegrass; this result indicates that a differential respon se to Ca existed between the two grasses. Maintaining an adequate soil Ca availability was necessary to improve bentgrass growth, particular ly for the acid soil containing low available Ca initially.