Monday, November 13, 2006 - 2:45 PM

Triticale Phosphorus Concentrations and P Removal Based Manuring.

Bradford Brown1, Joe Dalton2, Mireille Chahine1, Scott Jensen1, William Hazen1, Stephanie Etter1, and Dale Westermann3. (1) Univ of ID, 29603 U of I Lane, Parma, ID 83660, (2) Univ of Idaho, Caldwell, ID 83607, (3) USDA-ARS, Kimberly, ID 83341

National Research Council (NRC) mean values of 3.4 g kg-1 for triticale forage P concentrations are frequently used in Idaho nutrient management planning to estimate harvested P for P removal regulated manuring. Triticale boot stage forage P concentrations are poorly documented for southern Idaho manured fields. Early to late boot stage triticale from 44 southern Idaho manured fields over two years averaged 3.3 g kg-1, about the same as the NRC value, but ranged almost threefold from 1.8 to 5.3 g  P kg-1.  Two thirds of the samples differed by more than 10 percent from the average.  Forage biomass ranged from 3.6 to 13.4 Mg ha-1 and harvested P ranged from 7.8 to 40.3 kg ha-1.  The range in forage P concentration and uptake suggest more luxury consumption of P than previously considered.  Boot stage triticale P concentrations were positively correlated with forage K (r=0.50), more weakly correlated with Ca (r=0.17) and Mg (r=0.22) and exponentially associated (r2=0.88) with 0.5 M NaHCO3 extractable P that ranged from 8 to 432 mg kg-1.  Harvest was dictated less by triticale growth stage than by the need to timely plant subsequent corn. In a two year related study, triticale P concentration increased from 9 to 35% from mid stem extension to the boot stage and then decreased to flowering. Critical P concentrations necessary for boot stage forage may exceed those required for grain yield.  Given the range in soil P in manured fields and widely fluctuating P concentrations at harvest growth stages, using NRC P default values will provide misleading P removal estimates in most manured fields.