Effect of watertable depth and salinity on growth dynamics of Rhodes grass (Chloris gayana)

Abstract

Depending on their depth, watertables can have a positive effect on plants by supplying water, a negative effect by creating waterlogged and/or saline conditions or a neutral effect. Rhodes grass (Chloris gayana), a tropical perennial forage adapted to saline soils, floods and droughts, is a viable choice for the lowlands in the Pampas region of Argentina. The effects of the depth and salt concentration of the watertable on the growth dynamics and biomass accumulation of Rhodes grass were quantified in a greenhouse experiment. The experiment consisted of 10 treatments, resulting from the factorial combination of five watertable depths (25, 75, 125, 175 and 225cm) and two salt treatments (EC 1.4 and 20.5dSm-1). The presence of non-saline watertable at a depth of 25cm produced a 5-fold greater biomass and showed an increase in water consumption of equal magnitude compared with deeper watertables. The increase in shoot biomass was explained primarily by higher tiller and stolon density, which increased 3.3- and 7.7-fold respectively, at watertables that were 25cm deep compared with deeper treatments. Furthermore, groundwater use efficiency was 30% higher in non-saline watertables at 25cm depth. Similarly, at this depth, the leaf blades were 50% longer compared with the deepest watertables evaluated. In contrast, the presence of saline watertables at 25cm depth had a detrimental effect on the production of biomass and its components, whereas the effect at 125cm and greater depths was neutral. Therefore, Rhodes grass is a species that can take advantage of the widespread shallow watertable environments of the Pampas region as long as the salinity levels are low.