Agriculture, Ecosystems and Environment 79 2000 187–197
Influence of water table and nitrogen management on residual soil NO
3 −
and denitrification rate under corn production in sandy loam soil in Quebec
Abdirashid A. Elmi
∗
, C. Madramootoo, C. Hamel
Department of Natural Resource Science, Macdonald Campus of McGill University, 21 111 Lakeshore Road, Ste-Anne-de-Bellevue, Que., Canada, H9X 3V9
Received 9 February 1999; received in revised form 23 September 1999; accepted 3 December 1999
Abstract
Nitrate-N NO
3 −
effluents from agricultural ecosystems contributing to the degradation of water quality has become a serious environmental problem. A field experiment was conducted in 1996 and 1997 at St. Emmanuel, Que., Canada, to
investigate the combined effects of water table management WTM and N fertilization on soil NO
3 −
level and denitrification rates in the top soil layer 0–0.15 m. The field was planted to corn Zea mays L. in both years. Treatments consisted of a
factorial combination of two water table treatments, free drainage FD at about 1.0 m and subirrigation SI at 0.6 m below the soil surface, and two N fertilizer rates, 200 kg ha
− 1
N
200
and 120 kg ha
− 1
N
120
. SI reduced NO
3 −
concentration in the top soil layer by 42 and 16 in 1996 and 1997, respectively. Nitrate levels in soil were 50 lower in N
120
plots in 1996, and 20 in 1997 compared to the N
200
plots. Denitrification was higher in SI compared to FD, but not influenced by N rate. As a consequence, WTM practices have implications for both water quality and greenhouse gas emissions. Climatic conditions
played a large role in regulating N dynamics in the soil. Due to drier and cooler conditions in 1997, denitrification rates were lower than in 1996, leaving higher residual NO
3 −
in the soil profile following corn harvest. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Denitrification rate; Emissions; Nitrate; Subirrigation; Water quality
1. Introduction
Nitrogen N is a key element in plant nutrition. High yielding crops, such as corn Zea mays L., re-
quire large amounts of N fertilizer to ensure optimum yield. Corn has become a major crop in the province
of Quebec because of its high potential productivity.
∗
Corresponding author. Tel.: +1-514-398-7759; fax: +1-514-398-7990.
E-mail address: aelmipo-box.mcgill.ca A.A. Elmi
Liang et al. 1992 reported a maximum grain corn yield of 15.2 Mg ha
− 1
resulting from the best com- binations of hybrid, population density, fertilizer rate
and irrigation. In an attempt to reach such an optimal yield, high rates of N fertilizer are often applied. Con-
sequently, significant quantities of nitrate NO
3 −
may be lost via leaching and eventually reach groundwater
Prunty and Montgomery, 1991. In many agricultural areas in the US, NO
3 −
levels have already exceeded USEPA safety limit for drinking water, 10 mg l
− 1
Hubbard and Sheridan, 1989. Similarly, in the
0167-880900 – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 9 9 0 0 1 5 7 - 7
188 A.A. Elmi et al. Agriculture, Ecosystems and Environment 79 2000 187–197
province of Quebec Madramootoo et al. 1992 docu- mented NO
3 −
concentrations as high as 40 mg l
− 1
in subsurface drain flow from a sandy loam field cropped
to potato Solanum tuberosum L., a value far exceed- ing the present Canadian health standard of 10 mg l
− 1
. Nitrate levels higher than 10 mg l
− 1
are linked to cases of methemoglobinemia also known as blue baby
syndrome which can ultimately result in the death of infants of up to 6 months Gelberg et al., 1999.
The amount of leachable NO
3 −
in the soil pro- file generally increases with fertilizer application rate
Angle et al., 1993; Errebhi et al., 1998. For exam- ple, Angle et al. 1993 measured 2.5 mg NO
3 −
kg
− 1
in plots which had never been amended with ma- nure or fertilizer, while plots fertilized with 260 kg
N ha
− 1
contained 8.7 mg NO
3 −
kg
− 1
. A significantly higher NO
3 −
concentration 25 mg NO
3 −
kg
− 1
was observed when corn was fertilized with excessive N
Angle et al., 1993. Thus, a major challenge, now, for agricultural scientists is to develop management
strategies which will minimize the adverse impacts of N fertilizers on the environment and water resources,
without concomitant reductions in crop yield.
Water table management WTM systems, includ- ing controlled drainage and subirrigation SI, have
been identified as beneficial practices for reducing NO
3 −
content in groundwater by enhancing denitri- fication in the water saturated zone Gilliam and Sk-
aggs, 1986; Wright et al., 1992. Kalita and Kanwar 1993 and Madramootoo et al. 1993 found NO
3 −
concentrations in the unsaturated zone to be higher than in the saturated zone. Gilliam and Skaggs 1986
predicted a 32 decrease in NO
3 −
leaching losses due to controlled drainage. While reduction for the poten-
tial NO
3 −
contamination of surface and ground waters is a positive aspect of denitrification Gilliam, 1994,
emission of N
2
O is a serious environmental concern. It contributes to the greenhouse effect and participates
in the depletion of ozone Mooney et al., 1987. In order to properly assess ecological impacts associated
with N
2
O, knowledge of the proportion of denitrifi- cation gases entering the atmosphere as N
2
O relative to N
2
is paramount. In laboratory experiments, Weier et al. 1993 and Maag and Vinther 1996 indicated
that under wet soil conditions N
2
rather than N
2
O is the dominant end-product of denitrification.
The integration of WTM into a N fertilization strat- egy could further reduce environmental degradation in
crop production systems. Knowledge of interactions between WTM and N fertilizer is essential for the de-
velopment of best management practices. The objec- tives of this study were to investigate the combined
impacts of water table depths and N fertilization rate on 1 the quantity of potentially leachable nitrates in
the upper soil layer, and 2 the relationship between denitrification rate and the reduction of NO
3 −
concen- trations in the soil profile of a corn field.
2. Materials and methods
