Transport of Residual Nutrients Through Intact Soil Cores Amended With Fresh or Composted Beef Cattle Manure for Nine Years

Abstract

Although fresh beef cattle (Bos Taurus) manure has traditionally been applied to cropland in Western Canada, application of composted manure has recently increased, and the environmental impact of increasing application of composted manure is unknown. Our main objective was to compare the effect of fresh versus composted feedlot manure on transport of residual nitrate-nitrogen (NO3-N), chloride (Cl), and total reactive P (TRP) to subsurface soil. Fresh and composted feedlot manure was annually applied at 0 and 77 Mg ha−1 dry wt. for nine years to a clay loam soil in a replicated field experiment. Intact soil cores (0-30 cm depth) were taken from the field in the spring of 2007, and the residual soil chemicals were eluted from the soil cores by applying deionized water to obtain breakthrough curves. Although mean values for peak and flow-weighted mean concentrations, and mass loss of NO3-N, Cl, and TRP were, in general, significantly (P ≤ 0.05) higher for the amended cores compared to the unamended control, there were no significant differences between fresh and composted manure. Asymmetrical breakthrough curves and peak concentrations prior to one volume for NO3-N and Cl indicated preferential transport in macropores, whereas a gradual increase in concentration for TRP indicated transport by matrix flow. The cumulative mass of NO3-N and Cl were described using an exponential equation with asymptote and negative rate constants, and reflected a rapid initial release of these chemicals followed by a steady-state condition. In contrast, TRP loss from amended cores was best fit with an exponential growth equation and positive rate constant, and reflected a gradual slow release of this chemical. Mean peak concentrations exceeded the Canadian drinking water guideline of 10 mg NO3-N L−1 by 44 fold for composted manure (438 mg L−1), 34 fold for fresh manure (339 mg L−1), and 15 fold for the unamended control (153 mg L−1). The P sorption index was similar for fresh and composted manure, but mean values were significantly lower for the amended compared to unamended soil cores. Our findings suggested no statistical evidence for more transport of these nutrients for composted compared to fresh manure but there was a greater risk of transport for amended compared to unamended soils, particularly for macropore transport of NO3-N and Cl.