Monday, November 5, 2007

Nitrogen Species 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.

Nitrogen (N), like phosphorus, may be transported in surface runoff, predominantly as adsorbed to clay mineral/organic colloids as NH4-N, or dissolved in solution as NO3 or dissolved organic N. We evaluated the effect of poultry litter granulation on nitrogen species in surface runoff using runoff boxes in rainfall simulations. Two poultry litters i.e. raw litter 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). The addition of total N at 1:10 WEP basis was slightly higher from granulated litter (98 kg ha-1) than raw (72 kg ha-1). Whereas, a greater amount of total N was applied from granulated litter (86-90 kg ha-1) than raw litter (14-22 kg ha-1) at 1:100 and 1:200 WEP basis application. 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. In the first simulation event, total N concentrations ranged between 333-363 mg L-1 for granulated litter treatments compared with 28-145 mg L-1 for raw litter treatments. This is because a greater amount of total N was added with granulated litter than raw litter. The concentrations of total N decreased from raw litter treatment as the litter was applied at increasing WEP extraction ratios (1:10 to 1:200) because the amount of total N applied decreased from 1:10 (72 kg ha-1) to 1:200 (14 kg ha-1). Conversely, total N concentrations in granulated litter treatment were not affected by the WEP extraction ratio differences because at all extraction ratios (1:10. 1:100. 1:200), the amount of total N added with granulated litter was similar (86-98 kg ha-1). The greater concentrations of total N in runoff from all the treatments than NO3 and NH4 could be attributed to the presence of greater amounts of organic N in the litter. The NO3-N losses in runoff waters increased from first to third simulation event. On the other hand, NH4-N concentrations in runoff decreased by several orders of magnitude from first to second event and then only slightly from second to third event. The observed total N concentrations in runoff from all litter treatments at the first simulation event were significantly greater than the USEPA limits for over enrichment of surface water. It should be noted that our granulated litter with urea contained greater amount of N, which culminated in higher total N losses but lower NH4-N than raw litter. Importantly, the observed edge-of-box N concentrations in runoff waters from all litter treatments were above the environmental limits suggested by USEPA. However, the interaction of litter with soil may remove a part of these nutrients by adsorption reactions or dilution of concentrations with less polluted water are evident in watersheds, which may reduce true concentrations and subsequently loadings to receiving waters.