Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 4, 2004
Publication Date: November 4, 2004
Citation: Legorreta, F., Walters, D.T., Olk, D.C., Madhavan, S., Cassman, K.G. 2004. Long-term management effects on the mobile humic acid fraction [CD-ROM]. ASA-CSSA-SSSA Annual Meeting Abstracts. Madison, WI.
The mobile humic acid (MHA) fraction is a young pool of soil organic matter (SOM). It is less recalcitrant than other humic acids due to a lack of complexation with cations and it has higher nitrogen (N) and lower carbon (C) contents than more humified material. Temporal changes in MHA quantity and quality as well as carbon isotopic compositions (d13C) signature in archived soil from three long-term sites, all under continuous corn (CC) and corn soybean (CB) rotation with variable tillage, N rate or intensification characteristics were measured. The timeline of samples spanned 18, 7, and 4 years for each of the 3 sites. Changes in the d13C signature, C:N ratio, and yield (mg/kg soil) were very sensitive to management practices in the short term and some measured parameters showed more sensitivity in this fraction compared to whole soils. The N fertilizer inputs and crop rotation had a signficant impact on MHA formation and persistence in soil and the effect of crop rotation reflected differences in residue quality and C inputs. The N content in MHA (g N/kg soil) declined with soybean in the rotation reflecting the labile nature of MHA and was more pronounced under N-limiting conditions. Non-limiting N rates under CC or CB systems increased the mass of MHA due to higher residue inputs and quality as substrates for humification. More intensive tillage practices reduced the mass of MHA over time.