Monday, November 5, 2007

Trace Metals in Runoff Waters from Soil Amended with Granulated Poultry Litter.

Gurpal Toor, Soil & Water Science, Gulf Coast REC. University of Florida-IFAS, 14625 C.R. 625, Wimauma, FL 33598 and Brian Haggard, University of Arkansas, 203 Engineering Hall, Fayetteville, AR 72701.

Despite the fact that best management practices have been established to decrease non-point source pollution from agricultural land that regularly receive animal wastes, surface runoff from intensive animal production areas continues to present a major problem of water quality deterioration. Our objective in this study was to determine the effects of application of poultry litter on trace metals (As, Cu, Zn) in runoff waters, when raw and granulated litter with urea were applied at 3 kg Water Extractable P (WEP) ha-1 with WEP determined at three extraction ratios (1:10, 1:100, 1:200). At these WEP application rates, the addition of soluble trace elements with an one-time litter application was 9-53 g ha-1 for WE-As, 8-101 g ha-1 for WE-Zn, and 33-389 g ha-1 for WE-Cu. Rainfall simulations were conducted over a three-week period by packing wooden boxes (1-m long, 20-cm wide, 7.5-cm deep) with Captina silt loam (Fine-silty, siliceous, active, mesic Typic Fragiudult). A rainfall simulator was used to simulate a 7.0 cm h-1 rainfall for 10 min as this was enough to generate continuous runoff from the boxes. During first simulation event, concentrations of soluble As in runoff waters from litter amended soil ranged between 0.29 and 1.73 mg L-1, compared with 0.12 mg L-1 from control soil.  In the subsequent rainfall events, concentrations of As were <0.19 mg L-1 and by third event, As was below detection limit for all treatments. Concentrations of As were greater from raw litter than granulated litter except when litters were applied at 1:10 WEP basis. The observed As concentrations during first two rainfall events were much greater than USEPA limit of 0.01 mg L-1 for drinking water, therefore these concentrations can cause potential water quality problems if they reach drinking water supplies. Concentrations of soluble Cu in runoff water were 0.26-1.07 mg L-1 during first simulation event, which decreased to 0.02-0.19 mg L-1 (second event) and to 0.02-0.10 mg L-1 (third event). Generally, soluble Cu concentrations were lower from granulated litter than raw litter treatments. The USEPA suggested limit for Cu in drinking water is 1 mg L-1; all of our samples had concentrations <0.65 mg L-1 except for one sample from raw litter (1.07 mg L-1) during first event. Soluble Zn concentrations ranged from 0.08 to 0.34 mg L-1 for litter treatments and were higher than the control (0.04 mg L-1). These concentrations decreased in subsequent rainfall event, with concentrations more or less similar during second and third event. Zn concentrations were greater in runoff water from raw litter than granulated litter treatments. The Zn concentrations observed in the present study are well-below the USEPA limit of 5 mg L-1 for drinking water, suggesting no potential threat to water contamination. In summary, surface applied raw litter produced greater losses of trace elements (As, Cu, Zn) than granulated litter, suggesting that granulation of poultry litter is an environmentally sound management practice to reduce water quality contamination concerns.