EFFECTS OF MOISTURE, ADDED NO3−, AND MACERATED ROOTS ON NO3− TRANSFORMATION AND REDOX POTENTIAL IN SURFACE AND SUBSURFACE SOILS

Abstract

Samples of the Ap, BA, and Bt horizons of a Huron soil were used to study in the laboratory the effects of three moisture levels, added KNO3, and macerated corn roots on NO3− transformation and redox potential (Eh). The soil systems were incubated at 30 C in an atmosphere of 21% O2 and 79% He. Without the addition of NO3− and soil moisture level equivalent to one-half field capacity [Formula: see text] and field capacity (FC), NO3− accumulation occurred. Adding KNO3 alone or KNO3 and macerated roots, and increasing the moisture to twice field capacity (2FC) resulted in NO3− reduction. The relationship between Eh and NO3− reduction and accumulation was similar for the three soil samples. The rate of NO3− reduction or accumulation was stimulated by the addition of macerated roots and was in the order Ap > BA > Bt. NO3− accumulation was accompanied by an increase in Eh from 400 to 430 mV. [Formula: see text] and FC only a portion of the added NO3− was reduced, and the Eh decreased from 400 to 350 mV and was poised thereafter. In saturated soil (2FC) the Eh decreased from positive values to negative values. However in the BA and Bt soils treated with NO3−, macerated roots, or both, the Eh was temporarily poised at 200 mV until all NO3− was reduced.