Effect of Subsurface Drainage on Water Availability in the Red River Valley of the North

Abstract

Subsurface drainage (SSD) is an effective way to remove excessive water from soil and it can also be used to control the salinity level in the upper soil layer. To evaluate the effect of SSD on water availability (water quantity and water quality), a field experiment was conducted in the Red River Valley (RRV) of the North in North Dakota. Corn (Zea mays) was grown on a 44 ha field in 2008 and 2009. For this paper, data in 2009 growing season were used and analyzed. The experimental field has been divided into three sections: A) Undrained (UD) (22 ha), B) subsurface drained (11 ha), and C) subsurface drained and subsurface irrigated. Various instruments were installed in the field to quantify each component in the water balance. All subsurface drainage water was directed to a pump lift station. Drainage volume was determined by measuring the on and off cycles of the pumping. Automatic and manual rain gages were used to record rainfall amount. The UD area was considered to have a natural drainage toward a county ditch on the north side of the field. Eight piezometers were installed in each part of the field, and were equipped with pressure transducers to measure water level changes. Using the same piezometers, water sample were collected on a biweekly schedule during the growing season. Salinity and sodicity parameters, such as electrical conductivity (EC), total dissolved solids (TDS), and sodium adsorption ratio (SAR), were determined for these water samples in addition for the samples from the adjacent drainage ditch and the sump. Preliminary results from April to November 2009 indicated that the TDS and the EC values were the highest in the UD part of the field, but lower in the sump and the ditch. Average SAR was relatively high in the UD field, but was at acceptable range. EC, TDS, and SAR were lower in the subsurface drained field. The pumping volume was high after a rainfall, which showed an appreciable effect of the SSD system. Seasonal changes of daily average pumping volume of 190×103L/day were observed during the spring, and fall pumping periods, indicating that agricultural water management may change the soluble salts distribution in the field. These results indicate that soil and groundwater salinity may have been reliably controlled by the subsurface drainage system.