Run-off water harvesters and agro-wells for supplementary irrigation of rain-fed sugarcane at Sevanagala in Sri Lanka: A preliminary investigation

Abstract

Soil moisture deficit during dry spells has been a major cause for low productivity in rain-fed sugarcane in the Sevanagala sugar project of Sri Lanka. This has reduced average annual cane production in the rain-fed sector by about 21%. This study was conducted in 2009 and 2010 to investigate the possibility of run-off water harvesting and use of agro-wells for supplementary irrigation to mitigate this drought effect in rain-fed sugarcane.  Irrigation water was collected in to earthen runoff water harvesters constructed using sand bags. Depth to ground water table was recorded weekly in the wells constructed in close proximity to sugarcane fields. The recharge capacities of these agro-wells were recorded after each pumping operation.

The results revealed that there was a potential to harvest about 125 to 150 m3 of run-off water during the rainy period in the rain-fed sector of Sevanagala. The groundwater table in the low-lying areas of the sugarcane fields fluctuated between 50 - 350 cm below the ground surface during wet and the dry seasons. The wells constructed in these locations got recharged within 3 to 7 days after each irrigation.

This exhibits the availability of groundwater in shallow unconfined aquifers in the area. Thus, run-off water harvesters and agro wells could be used to irrigate rain-fed lands during dry spell. It was observed that the use of these two water sources together was more effective than their individual use. However, to get maximum benefit of the limited volume of water available in these two sources, deficit irrigation method has to be practised instead of furrow irrigation which over saturates the soil during irrigation. Detailed studies on irrigation methods need to be carried out to find out more efficient utilisation of this limited water for sugarcane crop.