Salinity dynamics and the potential for improvement of waterlogged and saline land in a Mediterranean climate using permanent raised beds

Abstract

Waterlogging and salinity in the Mediterranean climate of Western Australia (WA) have long been recognized as major constraints to the production of agricultural crops and pastures. While raised beds (RB) prevent waterlogging, the impact of RB on salinity is not known. Their impact on salinity was studied at 3 sites in the Wheatbelt of WA. The salinity dynamics was captured through frequent soil sampling. Two small trials with different mulches were also conducted to investigate possibilities to alter salinity dynamics in other ways. Each of the sites responded differently to the RB. At Cunderdin, being the driest site, little impact of the precipitation on the movement of salt was found, and no difference between the RB and Control. The deeper salinity was found to be more associated with the presence of the shallow saline groundwater. At Woodanilling, a high-rainfall site, salinity changes were governed by precipitation, and the RB greatly reduced waterlogging in the top 10 cm of the soil surface and improved productivity. Little differences were found between RB and Control with respect to salinity due to the incorporation of clayey subsoil. At North Stirlings with medium rainfall, the RB were very effective in reducing waterlogging, improving productivity as well as reducing salinity, following the disruption of the gravelly subsoil layer. Applying a sand mulch made a bare salt scald reasonably productive again. The dry-soil mulch process is also thought to be responsible for the low salt concentrations near the soil surface at Cunderdin. Maintaining the physical properties of this topsoil is crucial for sustaining a productive system. It is also proposed that the salinity–waterlogging interactions are not relevant to the dry-land salinity conditions in WA as the soil surface was either waterlogged or saline but not both at the same time. Our findings have narrowed down the benefits of permanent RB to the waterlogged medium-to-high-rainfall area of WA in regards to waterlogging and loamy gravelly duplex soils in regards to waterlogging and salinity control. As growers in a changing climate (physical and economical) become interested in cropping the waterlogged and saline areas of the valley floors in WA, RB will make that a realistic option. This would equally apply to other parts of the world where waterlogging and salinity are major constraints provided due consideration is given to soil properties of the top soil, particularly the soil texture.