Point-injected phosphorus effects on established cool-season grass yield and phosphorus content

Phosphorus applied to established grass has been shown to increase forage yield. However, broadcast P applications could result in more P runoff to surface waters compared with subsurface P application. A field study was conducted to evaluate if subsurface point-injected P is more effective than surface-applied P at increasing forage yield and tissue P concentration for established grass. Nine site-years with very low P soil tests and long-term (>10 yr) established cool-season grass stands were utilized. Fertilizer treatments were no fertilizer P and 29 kg P ha -1 [66 kg ha -1 phosphoric oxide (P 2 O 5 )] applied on the surface or point-injected beneath the surface. Fertilizer P significantly increased dry matter yields at four site-years. Placement of P did not influence forage yields at the P responsive sites, except for one site-year. Forage P concentration was increased by added P at seven of nine site-years. Forage P concentrations from point-injected P treatments were lower compared with broadcast P at five of the seven P responsive site-years. Results of this study suggest that point-injected P offers no advantage over surface-applied P for increasing forage yield or P concentration of established cool-season grass stands.