Annual bluegrass and creeping bentgrass tiller response to phosphate fertilizer and soil pH

Creeping bentgrass (CB; Agrostis stolonifera L.) grows well in low phosphorus (P) soils in monoculture, however, the soil P concentration range that provides CB an advantage over annual bluegrass (AB; Poa annua L.) in mixed swards is unknown. The objective of this research was to determine how P and soil pH influence species composition when AB and CB are established from tillers in polyculture. Replicate greenhouse experiments evaluated five P rates (0, 3, 6, 9, and 12 kg ha(-1) P via triple superphosphate) and two soil pH levels (5.6 and 7.1). The highest P rate in the high pH soil resulted in the most AB cover (61%). Phosphate applied at 3 kg ha(-1) P in the low pH soil provided the greatest CB cover (72%), which was fivefold greater than AB cover. All P-receiving treatments in the low pH soil had similar green cover, but a species advantage for CB was only observed in the 3 kg ha(-1) P treatment. Turfgrass quality was greatest when >= 6 kg ha(-1) P was applied to low pH soil but was only slightly reduced at 3 kg ha(-1) P. Regardless of pH, withholding P resulted in the lowest AB cover (<4%); however, these treatments resulted in poor turfgrass quality and low green cover (<30%). Aboveground shoot biomass increased linearly with P rate and was greater at the lower pH. In moderately acidic sand, AB was less competitive than CB when Mehlich-3 P ranged from 4 to 6 mg kg(-1).