Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 17, 2004
Publication Date: December 1, 2004
Citation: Novak, J.M., Watts, D.W., Stone, K.C. 2004. Copper and zinc accumulation, profile distribution, ane crop removal in coastal plain soils receiving long-term, intensive applications of swine manure. Transactions of the American Society of Agricultural Engineers. 47(5):1513-1522. Interpretive Summary: Metals like copper and zinc are included in swine feed to maintain a healthy diet. Swine do not utilize all of the copper and zinc contained within the feed, therefore, a portion of these metals is excreted in the manure. When manure decomposes, metals will re-enter the soil nutrient cycle and contribute to its fertility. Plants will utilize metals in soils as a source of nutrients. Because some fields have received high swine manure application rates, there is a concern that these fields may contain soil metal concentrations that are much higher than crops nutrient needs. If nutrient concentrations accumulate to high enough levels, serious crop yield declines can occur. Because copper and zinc accumulations in swine-manure-treated soils have not received much attention, we measured copper and zinc concentrations in top soil from a North Carolina pasture field that had received 10 years of intensive manure applications. Soil samples were collected at several depths from across the pasture field. Soils were also collected from forest-covered sites (controls) as a comparison for metal concentrations in soils that have not received manure. Control soils had very low copper and zinc concentrations. Copper concentrations in the pasture soils were similar to the controls. Zinc concentrations, however, in some regions of the pasture field were higher than control soils. We concluded that soils in this pasture field did not have very much copper accumulation after 10 years of swine manure applications. Zinc has accumulated in this pasture field, but the soil zinc concentrations were far below levels considered harmful to sensitive crops.
Technical Abstract: Livestock production facilities in eastern regions of the USA are frequently concentrated in geographic areas that contain limited land area available for manure application. This constraint has resulted in some fields receiving repeated manure applications, which has resulted in the accumulation of excess plant nutrients. While the buildup of excess nitrogen (N) and phosphorus (P) has been well documented in these regions, copper (Cu) and zinc (Zn) accumulations from swine manure have not been well documented. In cases where soil Cu and Zn concentrations accumulate to phytotoxic levels, yields may decline for sensitive crops. We investigated soil Cu and Zn accumulations, profile distributions, and removal by Coastal Bermuda grass (Cynodon dactylon L.) in a Coastal Plain spray field that had received 10 yr of intensive swine manure application. Soil samples (0 to 15 and 15 to 45 cm deep) were collected across the spray field and at nearby control sites that received no swine manure. Additionally, deep soil cores (to 183 cm) were collected across the spray field in 1991 and 1997 and at the control sites in 1997. All soil samples were extracted using Mehlich 3 reagent, and Cu and Zn concentrations were measured using atomic absorbance spectrometry. Control soils had profile mean Cu and Zn concentrations that were <0.5 and 1.8 mg/kg, respectively. After 10 years of swine manure application, top soil (0 to 15 and 15 to 45 cm) had metal concentrations that ranged between 0.86 to 3.59 for Cu and 1.33 to 7.87 mg/kg for Zn. Only the mean Zn concentration in spray field top soils (0 to 15 cm deep) was significantly different (P <0.05) from the controls. Projected times modeled for Coastal Bermuda grass to reduce metal concentrations to background levels ranged between 21 to 152 for Zn and 73 to 2462 years for Cu. Results from this study show that after 10 years of intensive swine manure application, mean top soil Cu and Zn concentrations were far below concentrations considered phytotoxic to sensitive crops.