Year: 1995
Type: dissertation
Abstract: Well water monitoring programs have detected significant levels of nitrate-nitrogen (NO3-N) in groundwaters of Montana within geographical regions where crop-fallow rotation is the primary agricultural production practice.It is hypothesized that the mineralization of nitrogen (N) along with the slow but continual leaching of unused soil profile water in fallow cycles is responsible for the accumulation of NO3-N below the root zone.This study was designed to (i) determine changes in organic N and C status resulting from long-term crop-fallow management, (ii) determine differences in mineralization rates of N and C between crop-fallow and native range soils, and ( iii) evaluate the potential for N mineralization to account for high NO3-N levels in groundwaters associated with long-term crop-fallow management practices.Thirty-two soils consisting of 12 adjacent (same soil series) crop-fallow/native range pairs and eight additional soils were collected from different geographical regions in Montana.Soil characterization included pH, EC, total organic C (TOC), total Kjeldahl N (TKN), and texture.Soluble C and N characterization included dissolved organic C (DOC), anthrone reactive C (ARC), and dissolved organic N (DON) and was performed on a selected subset of 16 soils involved in an incubation study.Native range soils were observed to have significantly higher concentrations of TOC, TKN, DOC, ARC, and DON than adjacent crop-fallow soils.Mineralization rates of N and C were measured under laboratory conditions using column reaction vessels for 14 weeks at 22.5° C. Accumulation of N and C was linear with time over the 14 week incubation.Mineralization rates of N ranged from 0.11 to 1.41 mg N kg-1 soil d-1 while mineralization rates of C ranged from 1.7 to 14.0 mg C kg-1 soil d-1.Both N and C mineralization rates were observed to be significantly higher in native range soils than in paired crop-fallow soils.Annual N production based on mineralization rates observed in this study suggest that production of inorganic N via mineralization may often exceed crop N uptake.This establishes conditions which may lead to leaching of NO3-N beyond the root zone.
Author: Karnes E. Neill
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDGs: Zero hunger, Life on land
Open Access status: green
OpenAlex ID: W338091811