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Near‐Surface Soils as a Source of Phosphorus in Snowmelt Runoff from Cropland
Author(s) -
Wilson Henry,
Elliott Jane,
Macrae Merrin,
Glenn Aaron
Publication year - 2019
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/jeq2019.04.0155
Subject(s) - snowmelt , surface runoff , soil water , environmental science , loam , hydrology (agriculture) , tillage , fertilizer , phosphorus , leaching (pedology) , water content , soil science , agronomy , chemistry , geology , ecology , geotechnical engineering , biology , organic chemistry
In northern regions, a high proportion of annual runoff and phosphorus (P) export from cropland occurs with snowmelt. In this study, we analyze 57 site‐years of field‐scale snowmelt runoff data from 16 small watersheds draining fine‐textured soils (clay or clay loam) in Manitoba, Canada. These fields were selected across gradients of soil P (2.4 to 26.7 mg kg −1 , 0‐ to 15‐cm Olsen P), tillage intensity (high frequency to long‐term no‐till), and fertilizer input. The strongest predictor of flow‐weighted mean concentrations of total dissolved P (TDP) in snowmelt runoff was Olsen P in the top 5 cm of soil ( r 2 = 0.45, p < 0.01). Residual variation in this relationship related positively to volumetric soil moisture and negatively to water yield. Although Olsen P levels were relatively consistent from year to year, suggesting control by long‐term fertilization and tillage history, Olsen P stratification (ratio of 0–5/0–15 cm) increased with rates of fertilizer application. Particulate P (PP) comprised <34% of total P on average, and concentrations were not well predicted by soil or management characteristics. Loads of PP and TDP exported during snowmelt were primarily a function of water yield and size of accumulated snowpack; however, residual variation in the TDP relationship correlated positively with both soil moisture and Olsen P. Retention of runoff water on the landscape could reduce loads, but careful management of near‐surface soil P is required to prevent snowmelt runoff losses of P at the source and to reduce the potential for the eutrophication of downstream aquatic ecosystems. Core Ideas Snowmelt dissolved P concentrations increase linearly with surface Olsen P (0–5 cm). Concentrations of snowmelt dissolved P also increase with soil moisture. Total P export with snowmelt is primarily controlled by volume of snowmelt. Olsen P at 0 to 5 cm increases with rate of seed placed fertilizer P application. Surface soil P (0–5 cm) should be measured routinely to prevent excess accumulation.