Dairy diet phosphorus and rainfall timing effects on runoff phosphorus from land-applied manure.
Surface-applied dairy manure can increase P concentrations in runoff, which may contribute to eutrophication of lakes and streams. The amount of dietary P fed to dairy cows (Bos taurus) and the timing of a rain event after manure application may further affect runoff P losses. The objective of this study was to examine dietary P supplementation effects on manure and runoff P concentrations from rain events occurring at different time intervals after manure application. Manure from dairy cows fed an unsupplemented low P diet (LP; 3.6 g P kg(-1)) or a diet supplemented with either an inorganic (HIP; 4.4 g P kg(-1)) or an organic (HOP; 4.6 g P kg(-1)) source was hand-applied onto soil-packed pans at 56 wet Mg ha(-1). Thirty min of runoff was collected from simulated rain events (30 mm h(-1)) 2, 5, or 9 d after manure application. Total P (TP) concentrations in runoff from HIP and HOP diet manure from the 2-d rain were 46 and 31% greater than that of the LP diet. Runoff P concentrations from high P diets were numerically higher than that of the LP diet at 5 and 9 d after application, but differences were significant only for dissolved reactive P (DRP) at 5 d. Large decreases in runoff TP (89%) and DRP (65%) concentrations occurred with delay of rainfall from 2 d until 5 d. The proportion of TP as DRP increased as the time between manure application and runoff increased. Results showed that reducing dietary P and extending the time between manure application and a rain event can significantly reduce concentrations of TP and DRP in runoff.
Hanrahan
Laura P
LP
Vermont Agency of Agriculture, Food, and Markets, Montpelier, VT, USA.
Jokela
William E
WE
Knapp
Joanne R
JR
D000821:Animal Feed; D000818:Animals; D002417:Cattle; D004032:Diet; D008372:Manure / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D011891:Rain; D013997:Time Factors; D014877:Water Pollution, Chemical / Q000032:analysis*
D008372:Manure; D010758:Phosphorus