Phosphorus Variations in Surface Runoff from Agricultural Lands as a Function of Land Use
1980
Wendt, R. C. | Corey, R. B.
Phosphorus (P) carried in surface runoff from agricultural lands can be a major source of algal-available P in surface waters. The available P may include both dissolved and some fraction of the sediment-bound forms. In this study the effects of land use, time of year, and application of animal manure on several forms of P in runoff from farmed and forested lands were investigated. Simulated rain was used to generate runoff. Losses of dissolved molybdate-reactive P (DMRP), the majority of which is dissolved orthophosphate, were greatest from established or newly seeded alfalfa fields (Medicago sativa L.) in the fall after the foliage had been killed by frost. The fraction of total P lost as DMRP was greater for alfalfa than for corn (Zea mays L.) or a conventionally prepared seedbed. Greatest total P losses were from corn and seedbed areas due to greater sediment losses. Phosphorus potentially available to algae was estimated by extraction with hydroxy-aluminum resin. Amounts extracted were equal to DMRP plus an average of 17 and 34% of the remaining total P for samples with and without apparent sediment, respectively. Greatest losses were associated with highest sediment loads. Surface-applied manure on corn and alfalfa increased P concentrations in runoff but, due to increased infiltration, did not significantly increase P losses. Loss of P from forest land was less than from crop land.
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