Abstract
Systematic work on water quality aspects, particularly on the accumulation and fluctuation of plant nutrients and heavy metals, has not being carried out at the Mahakanumulla tank cascade in the dry zone of Sri Lanka. Therefore, the main objective of this research was to study the seasonal changes of the concentration of major plant nutrients viz., Nitrogen (NO 3- ), Phosphorus (PO4 3- ), Potassium (K + ), and heavy metal Cadmium (Cd +2 ) in water along the cascade system. The concentrations of NO 3- , PO4 3- , K + and Cd +2 in water samples showed significant spatial and temporal variations over the study period and showed a bimodal pattern. The highest concentrations of the measured parameters were observed in months of April and May in the Yala season. Low nutrient concentration observed in the Maha season could be due to dilution effect caused by the comparativelyhigh volume of tank water. Spatial distribution of NO 3 - , PO4 3- , K + and Cd +2 concentrations in the water of three sampling locations of each paddy tract showed a significant increasing trend from the first sampling point to third point of the paddy field. Tropical Agricultural Research Vol. 24 (3): 279 – 288 (2013)
Highlights
The dry zone of Sri Lanka is located in lowest part of island and consists large number of inland valleys
The results of the concentrations of major plant nutrients ; NO3, PO43, K+ heavy metal Cd+2 in water samples of the Mahakanumulla cascade from February 2011 to January 2012 are given in Tables 1, 2, 3 and 4
These high NO3- values observed during the months of April to May and October to November were coincided with the fertilizer application period in rice cultivation of the area
Summary
The dry zone of Sri Lanka is located in lowest part of island and consists large number of inland valleys. This type of topography, climatic condition, soil and surface hydrological conditions favour the establishment of cascade irrigation system with small tanks in dry zone of Sri Lanka (Pannabokke, 2002). Small tank systems are perceived as human adaptation to rain fall pattern, a water harvesting system that enables through irrigation, to change the uneven distribution of water. Mahakanumulla cascade system located in North Central Province is a branch type cascade and consists of 27 small tanks. The equilibrium state of tank in relation to the water quality could be disrupted by the intensive agriculture practices and human activities with growing population. Accumulation of nutrient elements in tank water due to the added fertilizers, dung and urine of the large cattle population could degrade water
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