Rate of soil recovery following termination of long-term cattle manure applications

Livestock manure application increases soil nutrient levels, enhancing their bioavailability, but potentially increasing environmental concerns. This study investigates the residual effects of long-term cattle feedlot manure applications to continuously cropped fields under semi-arid conditions on soil properties, crop yields and rate of soil recovery after manure application ceases. Solid cattle feedlot manure was applied to a Dark Brown Chernozemic clay loam at 0, 30, 60 and 90 Mg ha− 1 yr− 1 under rain-fed and 0, 60, 120 and 180 Mg ha− 1 yr− 1 under irrigated conditions annually for 14 years (1973–1986) followed by 16 years with no further manure application (1987–2003). Soil samples to 1.5 m were taken and analyzed. Soil organic matter (OM), total nitrogen (TN), NO3−, total P (TP), soil test P (STP), and electrical conductivity (EC) levels remained significantly higher in previously manured treatments than in the Control 16 years after manure application ceased. The average grain yields were similar to the Control while straw yields in irrigated treatments were higher than values for the Control over the 16 years following the last manure application. Based on a three-parameter exponential decay (y = ys + a ⁎ e− bx) model, the estimated recovery time for soil to return to the pre-manure treatment state increased with the previous manure application rate and was shorter under irrigation. For soil TN, TP and STP, estimated recovery time ranged from 17 to 99 years for surface soil and 0 to 157 years for the 15 to 30 cm depth, while soil NO3− and EC in the soil profile (0 to 150 cm) requires 182 to 297 years under rain-fed and 24 to 52 years under irrigated conditions. Thus, long lasting N and P enrichment, from excessive long-term cattle manure applications could pose environmental threats long after application ceases.