Extractable DOC and DON from a dry-land long-term rotation and cropping system in Texas, USA

Soil solution chemistry may be responsible for the solubility and subsequent losses of DOC and DON from terrestrial ecosystems. The objective of this research was to determine whether there was a significant difference in recoverable soil dissolved organic carbon (DOC), organic nitrogen (DON), and dissolved inorganic nitrogen (DIN) extracted with cold and hot water, 10 mM CaCl2, 2 M KCl and 0.5 M K2SO4 in four long-term agricultural tillage and cropping management systems and whether the type of extractant, tillage or cropping regime was responsible for decoupling the relationship between DOC and DON. The recovery of DOC and DON from soils was highly dependent upon the method of extraction. 10 mM CaCl2 recovered the least DOC, which ranged from 49 to 139 mu g g(-1), while 0.5 M K2SO4 recovered the most DOC and ranged from 176 to 290 mu g g(-1). Hot water extracted significantly greater DON than any of the other extractants among all cropping and tillage systems. The relationship between DON and DOC was strong and significant in hot and cold water extracts (R-2=0.94 and 0.55 respectively), but their relationship was decoupled with chemical extractants and a continuous cropping. (c) 2013 Elsevier B.V. All rights reserved.