ARS | Publication request: Manure and Soil Test Phosphorus Effects on Runoff P from Simulated Rain

Submitted to: Agronomy Abstracts
Publication Type: Abstract
Publication Acceptance Date: June 3, 2008
Publication Date: N/A

Technical Abstract: Manure application to cropland can contribute to runoff losses of nutrients and eutrophication of surface waters. We conducted a rainfall simulation study to assess the effects of dairy heifer diet P, soil test P, and manure incorporation on runoff P losses from two successive rains. We collected bedded manure (21% DM) from dairy heifers offered diets with or without supplemental P, resulting in manures with different P content (3.1 and 3.9 g/kg TP; 626 and 995 mg/kg WEP). A Withee silt loam soil with either low (21 mg/kg) or high (58 mg/kg) soil test P (Bray P1) was packed into 1 x 0.2 m sheet metal pans to a depth of 5 cm. Manure was either surface-applied (SURF) or incorporated (INC) at equal application rates, supplying the equivalent of either 43 or 51 kg P/ha for the low and high P manures. Control treatments (NO-MAN) received no manure. Runoff was collected for 30 min after runoff initiation from two simulated rain events (70 mm/h), one day and three days after manure application. We measured runoff volume, total (TP) and dissolved reactive P (DRP), and total (TS) and volatile (VS) solids in runoff. Manure incorporation reduced TP and DRP concentration and load by 85-90% (compared to SURF), resulting in a level that was no different from NO-MAN for DRP but still greater for TP. Incorporation also decreased DRP/TP. The concentration of TS was greatest from INC in Rain 1, but equal to NO-MAN in Rain 2. The VS (manure-derived) portion was greater from SURF (0.73) than from INC or NO-MAN (0.12-0.18). Manure P level had minimal effect on TP and DRP concentration because of counteracting effects on TS load; but the TP concentration of solids in runoff from SURF manure was greater from high than low P manure. Soil P level had little or no effect on P concentrations in runoff from Rain 1, however, TP concentration in solids was more than 50% higher from high P than low P soil in both INC and NO-MAN treatments. Soil P effects were more pronounced in the runoff from Rain 2, with twice the TP and DRP concentration from high P soil in the NO-MAN treatments and higher DRP in INC treatments. Runoff volumes from the second rain were similar to those from the first rain, but concentrations of TS, TP, and DRP were 25-75% lower for most treatments, and DRP/TP was higher from Rain 2 for manured treatments. These results show the large reduction in P runoff losses possible from incorporation of manure, and the additional benefits from reducing diet P and avoiding soils with excessive P.