Water Extractable Carbon and Nitrogen From Manure Application Under Different Tillage.

Water extractable organic matter (WEOM) contains labile organic carbon (C) and nitrogen (N) and is sensitive to soil management. The objective of this study was to determine quantity and spectral properties of WEOM responding to types of nutrient addition and tillage managements. Soil samples were taken from treatments (conventional tillage, no tillage, poultry litter, and NH4NO3 application) of a 10 –year tillage experiment in Watkinsville Georgia at different times and soil depths. Air-dried soil samples were extracted by Millipore H2O followed by filtration (<0.45 um), and soluble C, N, absorptivity of solution samples at 254 nm, solution fluorescence excitation and emission matrix (EEM) were determined. Results showed that water extractable C and N increased over the cropping years. Poultry litter application accumulated high amount of water extractable organic C and N as compared to NH4NO3 application. But no significant difference was found between tillage and no tillage for both water extractable C and N. Absorptivity at 254 nm decreased over cropping years for conventional tillage and NH4NO3 application indicating accumulation of easily degradable compounds in WEOM, but the fluorescence measured humification index showed opposite trend. For no-tillage and poultry litter application treatments, there was no difference in absorptivity over the sampling time. Parallel factor analysis (PARAFAC) of EEM data showed that the WEOM consisted of three fluorophore components: humic-, fulvic-, and tyrosine-like “compounds”, and relative distribution of these three components differed among treatments and changed over cropping times and depths. In all quantity and spectral properties of WEOM responded to types of nutrient application and tillage practices.