Monday, November 13, 2006 - 2:45 PM
116-4
Triticale Phosphorus Concentrations and P Removal Based Manuring.
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.
Recorded presentation