Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 31, 2011
Publication Date: June 15, 2011
Citation: Zhang, M., He, Z., Zhao, A., Zhang, H., Endale, D.M., Schomberg, H.H. 2011. Water extractable soil organic carbon and nitrogen affected by tillage and manure application. Soil Science. 176:307-312. Interpretive Summary: Water extractable organic matter (WEOM), or alternatively, dissolved organic matter (DOM), is generally regarded as the most labile form of soil organic matter fraction. Its importance in agriculture has been long recognized due to its crucial role in plant nutrient uptake and soil microbial activities (soil organic matter decomposition require water as medium). The objectives of this research were to ascertain 1) dynamics of WEOM affected by tillage and poultry litter application; 2) spectroscopic properties of UV-Vis and fluorescence of the WEOM from different tillage practices and year of poultry litter application; and 3) vertical distribution and properties of WEOM as affected by tillage and poultry litter application. Our results indicated that manure application increased WEOM in soil. However, different sources of nutrient addition and tillage did not affect fluorescence components of WEOM. This might be attributed to the fact that all water extractable organic matter in soil results directly or indirectly from soil biological activities. Less condensed, but ring structured N compounds were more mobile in soil and accumulated in the lower soil depths. Over all, quantity and spectral properties of WEOM responded to the types of nutrient application and tillage practices. Further study is needed to verify if this portion of WEOM is the major contributor of DOC and DON to fresh or seawater ecosystem.
Technical Abstract: 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 soil 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 experiment in Watkinsville Georgia at different times and soil depths. Soluble C and N, absorptivity at 254 nm, fluorescence excitation and emission matrix (EEM) in the water extracts of these soil samples were determined. Results showed that poultry litter application accumulated higher amounts of soluble C and N than NH4NO3 application. But no significant difference was found between tillage and no tillage for soluble C and N. Absorptivity at 254 nm decreased over cropping years for conventional tillage and NH4NO3 application, indicating accumulation of aliphatic organic compounds in WEOM, but the fluorescence measured humification index showed an opposite trend. For no-tillage and poultry litter application treatments, there was no difference in absorptivity over the sampling time. Parallel factor analysis of EEM data showed that WEOM consisted of three fluorophore components: humic-, fulvic-, and tyrosine-like “compounds”, and relative distribution of these components differed among treatments and changed over soil depths. The Tyrosine-like component tended to accumulate in the lower sampling depth (>15 cm). Over all, quantity and spectral properties of WEOM responded to the types of nutrient application and tillage practices.