Implications of shallow groundwater dynamics on water and salinity management at Kasinthula Sugarcane Scheme, Malawi

Abstract

A study to understand the implications of shallow groundwater dynamics was carried out at Kasinthula Irrigation Scheme in Chikwawa District, Malawi. Water table fluctuations, groundwater salinities and soil solute levels were monitored every week from August to December 2017. Soils in the area are clay to clay loam and there is a uniform aquifer with a low hydraulic conductivity of 0.06 m/day and very high soil salinity reaching up to 8.5 dS/m. Effect of water table fluctuations on historical sugarcane yields were assessed and was observed to have very little effect on yields, however, a comparison of actual yields against expected yields from the Maas Hoffmann salinity function revealed low correlation since some areas with highest soil salinity had higher yields as compared to the areas with low soil salinity that were expected to produce higher yields. The area with highest soil salinity happened to have average water table closer to 1 m which is known to help supplement irrigation water requirements. However, sugarcane yields were noted to be declining over time as some fields registered as low as 26 ton/ha from their previous highest yields of 120 ton/ha. These low yields can be attributed to poor water management and agronomic practices carried out at the scheme that lead to waterlogging and nutrient leaching. It is from this background that a shallow groundwater monitoring tool known as a floating flag is proposed so that farmers can easily observe water table fluctuations in their fields which can help them better manage water application through adjusted irrigation schedules through observing colour changes in the floating flags. This will help reduce waterlogging and salinization problems because the groundwater will be utilised to supplement irrigation and thus reduce operational costs to the farmers.