Phytase supplementation and reduced-phosphorus turkey diets reduce phosphorus loss in runoff following litter application

Concerns about regional surpluses of manure phosphorus (P) leading to increased P losses in runoff have led to interest in diet modification to reduce P concentrations in diets. The objectives of this study were to investigate how dietary P amendment affected P concentrations in litters and P losses in runoff following land application. We grew two flocks of turkeys on the same bed of litter using diets with two levels of non-phytate phosphorus (NPP), with and without phytase. The litters were incorporated into three soils in runoff boxes at a plant-available nitrogen (PAN) rate of 168 kg PAN/ha, with runoff generated on Days 1 and 7 under simulated rainfall and analyzed for dissolved reactive phosphorus (DRP) and total P. Litters were analyzed for water-soluble phosphorus (WSP) and total P, while soils in the runoff boxes were analyzed for WSP and Mehlich-3 phosphorus (M3-P). Formulating diets with lower NPP and phytase both decreased litter total P. Phytase had no significant effect on litter WSP at a 1:200 litter to water extraction ratio, but decreased WSP at a 1:10 extraction ratio. Using a combination of reducing NPP fed and phytase decreased the total P application rate by up to 38% and the P in surplus of crop removal by approximately 48%. Reducing the NPP fed reduced DRP in runoff from litter-amended soils at Day 1, while phytase had no effect on DRP concentrations. Increase in soil M3-P was dependent on total P applied, irrespective of diet. Reducing overfeeding of NPP and utilizing phytase in diets for turkeys should decrease the buildup of P in soils in areas of intensive poultry production, without increasing short-term concerns about dissolved P losses.