Date of this Version
Phosphorous Runoff Risk During Years following Manure Application
Manure application may result in increased water infiltration and reduced runoff but it can also lead to excessive soil P levels and increased P concentration in runoff. Research was conducted to determine the residual effects of composted manure on runoff loss of water, sediment and phosphorus, and to evaluate soil P tests in prediction of P concentration in runoff. The residual effects of previously applied composted feedlot manure were studied from 2001 to the spring of 2004 at a runoff facility established in 1998 at the UNL Agricultural Research and Development Center. The runoff facility consisted of 21 plots of 36 ft length with a median slope of 5.5%. Low P and high P compost had been applied annually three times in 1998 to 2001 resulting in total phosphate applications of 1500 and 2300 lb/A. Irrigated corn and soybeans were grown in rotation. Bray-1 P in the surface 2” of soil was increased from 16 ppm with no compost applied to 780 ppm with application of high P compost. Runoff loss was more with the no-compost treatment than with compost applied (Table 1). P concentration in runoff, especially bioavailable P, increased as the amount of P applied in compost increased. Bio-available P loss in runoff (lb/Ac) was generally more where compost was applied but the effect of higher concentration with the compost treatments was partly offset by the reduced runoff with the compost treatments. The effect of reduced runoff was even more pronounced for total P loss. In fact, total P loss for 2002-4 where no compost was applied was as much as with the high compost treatment. In interpreting these results, we need to remember that plot length was just 36’; given that runoff and erosion potential are dependent on slope length, the actual losses measured are likely to be considerably less than would occur at a typical field scale with 5.5% slope.