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Using time domain reflectometry for monitoring mineralization of nitrogen from soil organic matter
Author(s) -
De Neve S.,
Van de Steene J.,
Hartmann R.,
Hofman G.
Publication year - 2000
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1046/j.1365-2389.2000.00306.x
Subject(s) - mineralization (soil science) , reflectometry , organic matter , soil science , nitrogen , environmental chemistry , nitrogen cycle , environmental science , time domain , geology , chemistry , soil water , computer science , organic chemistry , computer vision
Summary The mineralization of nitrogen from soil organic matter is important when one tries to optimize nitrogen fertilization and assess risks of N losses to the environment, but its measurement is laborious and expensive. We have explored the possibilities for monitoring N mineralization directly using time domain reflectometry (TDR). Net N and S mineralization were monitored over a 101‐day period in two layers (0–30 and 30–60 cm) of a loamy sand soil during aerobic incubation in a laboratory experiment. At the same time electrical conductivity of the bulk soil, σ a , was measured by TDR. A series of calibration measurements with different amounts of KNO 3 at different soil moisture contents was made with the topsoil to calculate the electrical conductivity, σ w , of the soil solution from σ a and θ . The actual σ w was determined from the conductivity of 1:2 soil:water extracts ( σ 1:2 ) with a mass balance approach using measured NO 3 – concentrations, after correction for ions present prior to the addition of KNO 3 . The average N mineralization rate in the topsoil was small (0.12 mg N kg −1 day −1 ), and, as expected, very small in the subsoil (0.023 mg N kg −1 day −1 ). In the top layer NO 3 – concentrations calculated from σ a determined by TDR slightly underestimated measured concentrations in the first 4 weeks, and in the second half of the incubation there was a significant overestimation of measured NO 3 – . Using the sum of both measured NO 3 – and SO 4 2– reduced the overestimation. In the subsoil calculated NO 3 – concentrations strongly and consistently overestimated measured concentrations, although both followed the same trend. As S mineralization in the subsoil was very small, and initial SO 4 2– concentrations were largely taken into account in the calibration relations, SO 4 2– concentrations could not explain the overestimation. The very small NO 3 – and SO 4 2– concentrations in the B layer, at the lower limit of the concentrations used in the calibrations, are a possible explanation for the discrepancies. A separate calibration for the subsoil could also be required to improve estimates of NO 3 – concentrations.