Influence of Current and Previous Crop On Soil Basal and Potential Denitrification Rates.

Soil and crop management including crop rotation and fertilization influences soil water content, available C and soil nitrate levels, which may in turn affect denitrification losses from soils. The objective of this paper was to determine how the current and previous crop affect denitrification by comparing the basal denitrification rate (BDR), denitrification rate with added nitrate (DAN) and potential denitrification rate (PDR) (amended with glucose and nitrate) of a clay loam soil under monoculture corn (C), soybean (S), and winter wheat (WW) with or without underseeded red clover (RC), and under each phase of a 2-year crop rotation (C-S), and two 3-year crop rotations (C-S-WW, C-S-WW+RC). The BDRs were greater in the 3-year C-S-WW rotation treatments than in the 2-year C-S rotation and monoculture C, S and WW treatments. The WW+RC phase of the C-S-WW+RC treatment was found to have a greater BDR and DAN than the corn phase of the rotation. Available organic C was found to limit denitrification in the BDR and DAN incubations as evidenced by the 2 to 21 fold increase in denitrification when glucose was added in the PDR assay. Further, the significant relationship between soil respiration and BDR suggests that available C was is a limiting factor. This study found that both the current crop and  previous crops in a rotation affected soil denitrification rates substantially; and that denitrification was increased when a mixture of crop residues were added to soil (i.e. from growing crops in rotation) relative to when only  a single residue was added (i.e. monoculture cropping).