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Evaluating Colloidal Phosphorus Delivery to Surface Waters from Diffuse Agricultural Sources
Author(s) -
Heathwaite Louise,
Haygarth Phil,
Matthews Rachel,
Preedy Neil,
Butler Patricia
Publication year - 2005
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2005.0287a
Subject(s) - soil water , phosphorus , surface runoff , chemistry , turbidity , colloid , environmental chemistry , particle size , zoology , mineralogy , soil science , environmental science , ecology , biology , organic chemistry
Colloid‐facilitated phosphorus (P) delivery from agricultural soils in different hydrological pathways was investigated using a series of laboratory and field experiments. A soil colloidal P test was developed that yields information on the propensity of different soils to release P attached to soil colloids. The relationship between turbidity of soil extracts and total phosphorus (TP) was significant ( r 2 = 0.996, p < 0.001) across a range of agricultural soils, and a strong positive relationship ( r 2 = 0.86, p < 0.001) was found between “colloidal P” (H 2 O–CaCl 2 extracts) and turbidity. Linear regression of the proportion of fine clay (<2 μm) for each soil type evaluated against the (H 2 O–CaCl 2 ) colloidal P fraction gave a weak but positive relationship ( r 2 = 0.38, p = 0.082). The relative contribution of different particle‐size fractions in transporting P in agricultural runoff from grassland soils was evaluated using a randomized plot experiment. A significant difference ( p = 0.05) in both TP and reactive phosphorus (RP) in subsurface flow was recorded for different particle‐size fractions, with most TP transferred either in association with the 2‐μm fraction or with the 0.001‐μm or smaller fractions. Total P concentrations in runoff were higher from plots receiving P amendments compared with the zero‐P plots; however, these differences were only significant for the >0.45‐μm particle‐size fractions ( p = 0.05), and may be evidence of surface applications of organic and inorganic fertilizers being transferred through the soil either as intact organic colloids or attached to mineral particles. Our results highlight the potential for drainage water to mobilize colloids and associated P during rainfall events.