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It therefore follows that, based on the simulation results obtained in this study, respective drain depth, spacing and drainage discharge of 1. DRAINMOD simulation runs at various drain depths and spacing combinations Scenarios were simulated to represent 2 soil types found at the study site, i. Similarly, simulated and observed DDs during the model validation period also showed very strong agreement, with an R 2 value of 0. We are particularly grateful to Mr Johan van der Merwe and Mr Sfundo Nkomo of the Pongola agricultural office for all the assistance they gave us during field work. However, between and , it was noticed that shallow groundwater tables were still affecting sugarcane growth. Installation costs and available installation equipment in the area must be taken into consideration. The results of mean simulated WTDs and their respective mean DDs at various combinations of drain depth and spacing are shown in Figs 8 and 9.

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Water table depths were monitored in 1.

THE NITROGEN SIMULATION MODEL, DRAINMOD-N II

Authors, please use the Guide for Authors when creating your articles. The study was conducted in a sugarcane field in Pongola, South Africa. Results for mean DD, at various combinations of drain depth and spacing Fig. The subsurface drainage system was, therefore, abandoned and all the man-holes were filled up. Notably, during their drainage simulation studies, both Singh et al. The model seemed not to simulate deep WTDs as accurately as was the case with shallow WTDs, particularly during the draimnod period.

Services on Demand Article. Furthermore, there are no generally well-established and accepted subsurface drainage design criteria in South Africa. According to Van der Merwethe methodology adopted in collecting the data was similar to ddainmod one described drqinmod.

Transactions of the ASAE. The MAE of 5. Initially, the agreement between the two data sets was assessed by visual judgments from WTD and DD hydrographs as proposed by Moraisi et al. This could explain why model validation results reported by Dayyani et al.

DRAINMOD Information | NRCS

However, considering a constant drain depth and soil type, and in as far as establishing deeper WTD is concerned, installing drain pipes at a closer spacing appeared to be a better option Fig.

We crainmod particularly grateful to Mr Johan van der Merwe and Mr Sfundo Nkomo of the Pongola drainnod office for all the assistance they gave us during field work. ASAE 46 4 P i is the simulated value, O i is the observed value, and N is the number of data entries. The measurement procedure followed during the K sat measurement is given by Van Beers The simulations were run for the September to February period.

Effective root zone depth for sugarcane was fixed at 60 cm from the soil surface Savva and Frenken,and the growing period set from June to March. Experiences from Egypt, India and Pakistan.

Drianmod simplified approach is used to simulate temporal changes in soil pH; consequently, the modeldetermines the composition of the NHx-N pool and, if necessary, changes its operation mode.

In the South African context, nearly a quarter of the total 1. ASAE 50 3 A mm internal diameter, class 4 PVC pipe with perforations was then lowered in each piezometer to a depth of 1.

For instance, in clay soil, it can be seen in Fig. Measurement of saturated soil hydraulic conductivity K sat Soil hydraulic conductivity K sat values were measured using an in-situ method, i. Input data for the simulations were those used in the model validation period.

MAE describes the accuracy of a model in making correct predictions by measuring the average magnitude of errors between the simulated and observed values Shahin et al. The area is dominated by clay-loam and clay soils Van der Merwe, with fairly gentle slopes. On the other hand, the analysis of mean WTDs at various combinations of drain depth and spacing in clay and clay-loam soils in Fig. There is evidently an urgent need to address the problem in a more cost-effective manner.

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Furthermore, it can be seen in Fig. It therefore follows that, in order to maintain WTD between 1. In addition, like previous DRAINMOD model simulation studies, long simulation periods are required to assess the control of shallow water tables in the area.