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Modelling phosphorus leaching to watercourses from extended autumn grazing by cattle
Author(s) -
McGechan M. B.
Publication year - 2003
Publication title -
grass and forage science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.716
H-Index - 56
eISSN - 1365-2494
pISSN - 0142-5242
DOI - 10.1046/j.1365-2494.2003.00364.x
Subject(s) - macropore , environmental science , grazing , leaching (pedology) , phosphorus , surface runoff , soil water , pollution , hydrology (agriculture) , agronomy , environmental chemistry , soil science , ecology , chemistry , biology , geology , mesoporous material , biochemistry , geotechnical engineering , organic chemistry , catalysis
A modelling approach was undertaken to investigate the effect of grazing animals on phosphorus pollution of water draining from grazed fields. Following a similar study in relation to slurry spreading in winter, the dual‐porosity hydrological and contaminant transport model, MACRO, was calibrated to represent transport of phosphorus from faeces through the soil to field drains. Rapid flows, through water‐filled macropores in wet soil, of phosphorus sorbed onto colloidal particles in the faeces of cattle appeared to be the dominant transport mechanism. The outputs of the model supported experimental evidence that levels of phosphorus pollution of water draining from grazed fields can rise substantially if grazing is extended into late autumn, particularly if grazing is extended until soil has wetted up to around the field capacity water content. The critical housing date, to avoid phosphorus losses rising to an unacceptable level, varied considerably between years. The outputs of the model suggest that phosphorus pollution does not occur during grazing under dry conditions where soil macropores do not contain water, so that losses would remain low if animals are housed before soil substantially wets up in the autumn.