Assessing water and nitrate‐N losses from subsurface‐drained paddy lands by DRAINMOD‐N II

Abstract

In this study, the effects of various drainage systems on water and nitrate-N losses were investigated using DRAINMOD-N II. Required field data were obtained during three growing seasons of canola in a subsurface drainage pilot in Mazandaran Province, northern Iran. The calibrated model was used to assess the effects of different drain depths (D = 0.10-0.90 m with 0.10 m intervals) and spacing (L = 10-90 m with 10 m intervals) on seasonal drainage water and NO 3 −-N concentration in drainage effluents. DRAINMOD-N II performance was assessed using different criteria including absolute deviation (AD), root mean square error (RMSE) and determination coefficient (R 2). The simulated and observed drainage discharges (0.97 vs 0.96 mm day −1) and NO 3-N concentrations (9.1 vs 14.1 mg l −1) were in good agreement in the calibration process. The model performance was also acceptable in the validation process (AD = 0.59-0.79 mm day −1 ; RMSE = 1.01-1.28 mm day −1 ; R 2 = 0.59-0.79 for drainage discharge and AD = 8.3-16.3 mg l −1 ; RMSE = 12.4-27.6 mg l −1 ; R 2 = 0.4 for NO 3-N). Based on the scenario analyses, the D0.40L50 drainage system was the best one, resulting in fewer environmental effects from the nitrate-N and water loss viewpoints.

DRAINMOD simulation of drain spacing impact on canola yield in heavy clay soils in the Canadian prairies

“…Based on Figure 7, to achieve at least 80% of potential yield regardless of the precipitation amount, drains should be closely spaced, at most 15 m apart, for the heavy clay soil in Arborg, Manitoba. The results of this study agree with some field and simulation studies (Acharya et al, 2019; Hashemi et al, 2020; Singh & Nelson, 2021). Scherer et al (2015) recommended close spacing for finer soils such as clay.…”

“…Recent canola species have a shorter growing period as they are due for harvest between 90 and 100 days after planting (DAP). Although the maximum rooting depth for the canola crop can reach 1 m (Cutforth et al, 2013), the effective rooting depth is where more than 70% of water uptake occurs (Hashemi et al, 2020). Therefore, the effective rooting depth ranged from 3 to 30 cm, as shown in Table 3.…”

“… where is measured values, is the predicted values, is the mean of observed values , and n is the total number of observed data points. An optimal model is obtained when R 2 is equal to 1, and RMSE, MAE and MBE are equal to 0 (Hashemi et al, 2020; Mkhabela & Bullock, 2012).…”

“…In a field study in North Dakota, Acharya et al (2019) reported that narrow spacing resulted in the highest crop yield and residual soil nitrate in silty clay loam soil. Hashemi et al (2020) reported that drain spacing greater than 40 m with heavy clay soil resulted in reduced drainage, increased surface runoff and potential for runoff. However, close drain spacing has economic and environmental concerns (Askar et al, 2020;Cordeiro & Sri Ranjan, 2015).…”

“…Models can accommodate climatic variability using historical weather data. Models run with long-term weather data have been used to evaluate drainage design (Cordeiro & Sri Ranjan, 2015;Sands et al, 2015), operation strategies of water table management systems (Ale et al, 2009) and fertilizer rates and application (Hashemi et al, 2020;Wilson et al, 2020) in order to suggest better alternatives. With increased climatic variability and uncertainty, there is a need to identify a cost-effective drainage system that maximizes crop yield and reduces nutrient loss.…”