Cool Season Seedling Growth Response to Soil Phosphorus Fertilization On a Calcareous Sub-Soil.

Adequate soil phosphorus (P) is vital for rapid seedling establishment because P-deficient seedlings lack vigor and can form low density turf areas. Two greenhouse studies were conducted on a Stark (Aeric Ochraqualfs) clay-loam, calcareous sub-soil with an inherent soil P-level of 12 and 4 mg P kg^-1 for the Olsen and Bray P-1 soil test, respectively, to quantify the effects of seven P-rates on seedling establishment and growth for two commonly cool-season lawn species; tall fescue [Schedonorus phoenix (Scop.) Holub.; TF)] and Kentucky bluegrass (Poa pratensis L.; KBG). Additionally, the influence of TF endophyte (E) stem infection (TFE+) on establishment and rooting was assessed. In the first greenhouse study, lasting 11 wks, seven soil P-rates (0, 3, 9, 15, 25, 45 and 75 mg P kg^-1) were applied to a sub-soil. Tall fescue was much quicker to establish reaching 50% turf cover 14 d quicker than KBG. Even at a rather low endophyte stem infection rate (24%), TFE+ had superior turf coverage on six of nine rating dates compared to TF without E (TFE-) during the first 8 wks of establishment. The addition of 45-75 mg P kg^-1 (98-161 kg P₂O₅ ha^-1) to the surface soil surface optimized establishment for both species in this study. Leaf tissue P concentrations (LTP) were generally low or critical (1.6-3.8 g kg^-1) for P rates ranging between 3-25 mg P kg^-1 for KBG.  Tall fescue produced more total dry matter yield (DMY) than KBG, while TFE+ (2,157 kg ha^-1) produced more DMY than TFE- (1,745 kg ha^-1).  In a follow-up greenhouse study, root dry weight for TFE+ was 2.28 g pot^-1 compared to TFE- that only had 2.08 g pot^-1.  This may partially explain why TFE+ outperformed TFE- throughout our study, perhaps contributing to greater soil nutrient acquisition.