Model development for nutrient loading
from paddy rice fields
Sang-Ok Chung
a,*
, Hyeon-Soo Kim
b
, Jin Soo Kim
c
a
Department of Agricultural Engineering, Kyungpook National University, Taegu 702-701, South Korea
b
Rural Research Institute, KARICO, Ansan 425-170, South Korea
c
Department of Agricultural Engineering, Chungbuk National University, Cheongju 361-763, South Korea
Accepted 6 January 2003
Abstract
The objective of this study was to develop a model groundwater loading effects of agricultural
management systems in paddy fields (GLEAMS-PADDY) to predict nutrient loading to surface
waters from paddy rice fields. This model was developed by modifying the GLEAMS model that is
used for uplands. The GLEAMS-PADDY model is composed of hydrology and chemical sub-models.
In the hydrology sub-model of the GLEAMS-PADDY model, the ponded depth routing method was
used to handle ponded water condition of paddy fields. With the chemical sub-model, the soil was
assumed to be saturated, and the soil profile in the root zone was divided into oxidized and reduced
zones.
Field experiments were performed at the Soro region, Chungbuk Province of South Korea, from
May to September 1999 and 2000. Field data included rainfall amount, irrigation water input,
drainage water output, and percolation. Concentrations of total nitrogen (T-N) and total phosphorus
(T-P) in irrigation water, rain water, ponded water, surface drainage water, and percolated water were
analyzed.
The coefficient of determination (r
2
) and root mean square error (RMSE) between observed and
model predicted surface drainage volume relative to the 1:1 line were 0.66 and 66.6 mm, respectively.
The r
2
and RMSE between observed and predicted T-N concentrations in the ponded water were 0.74
and 1.43 mg l
À1
, respectively. The same statistics for T-P were 0.64 and 0.03 mg l
À1
, respectively.
The observed and predicted total T-N loadings from surface drainage were 72.4 and 72.6 kg ha
À1
,
respectively. The observed and predicted total T-P loadings were 1.70 and 1.69 kg ha
À1
, respectively.
The r
2
and RMSE between observed and predicted T-N concentrations in the surface drainage water
were 0.79 and 2.71 mg l
À1
, respectively. The same statistics for T-P were 0.73 and 0.04 mg l
À1
,
respectively.
Comparisons of observed and model predicted water balance components, nutrient concentrations,
and loading rates exhibited reasonably good agreement. Hence, the GREAMS-PADDY model can be
Agricultural Water Management 62 (2003) 1–17
*
Corresponding author. Tel.: þ82-53-950-5734; fax: þ82-53-950-6752.
E-mail address: sochung@knu.ac.kr (S.-O. Chung).
0378-3774/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0378-3774(03)00078-7