Sustainability of Biodrainage Systems Considering Declining of Evapotranspiration Rate of Trees Due to Soil Salinization

Abstract

Biodrainage is a natural system in which tree plantation strips absorb deep percolation losses of irrigation water applied to neighbouring crops. Loss of excess water through evapotranspiration maintains water table at a desired level. It is doubtful, however, if biodrainage can maintain soil salinity to an extent that crops could be grown economically (Heuperman et al. 2002). According to Kapoor and Denecke (2001) biodrainage could be used in various regions ranging from humid to semi arid areas, except when the ground water EC is greater than 12 dS m-1. The main constraints of biodrainage are salt accumulation in plantation strips, the need for salt removal and extra land for tree plantation. The sustainability of the system, however, is questionable except where the irrigation water is quite suitable and/or in humid regions with high annual precipitation. In saline environments, hybrid system that combines biodrainage and conventional drainage technology will be needed to achieve sustainability. The purpose of this research is to determine the sustainability of biodrainage systems in low hydraulic conductivity soils with moderate water salinity and different barrier depths. SAHYSMOD, a known drainage and ground water mathematical model was used to simulate ground water level and the soil salinity simultaneously at the end of each year. Plant evapotranspiration decreases annually due to salt accumulation in the root zone and increasing osmotic pressure. The results showed that the system life could not be more than 5 to 6 years, while it is around 10 years when the depth to the barrier increases to 10 meters. The main conclusion of the study is that biodrainage could not be considered as a sustainable technique in arid and semi arid regions without availability of good quality irrigation water and/or used in conjunction with conventional drains.