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Purpose: Large diameter agro-wells are the most valuable water resources for farmers in Mahaweli system H in Sri Lanka to sustain crop production during the dry spells. Deterioration of water quality is harmful to the crop growth. Present study evaluated the variation of irrigation water quality and water levels of agro-wells in Thalawa irrigation block of Mahaweli system H.Research Method: Water samples from 10 agro-wells were collected during October 2016 to July 2017 once in a month and tested samples for irrigation water quality parameters using standard methods. Water levels were recorded for each sampling date.Findings: Most of the water quality parameters tested in almost all wells are within the acceptable range for irrigation except for Residual Sodium Carbonate (RSC). 50 % of the wells are safe and rest 50 % of the wells are within marginal range in terms of RSC. Irrigation water quality index (IWQI) was assessed and it varied from 32.6 to 87.7. Considering the mean IWQI (48.2), water of Thalawa block can be characterized as good. The study also revealed that there was suffi cient water in wells even during the dry spells and it varied with both the variation of rainfall and canal water availability.Research Limitations: Sampling was limited to 10 agro-wells for a period of 10 months. This was avoided by selecting representative wells and months covering both dry and wet spells.Originality/ Value: Overall, results envisaged that there is higher potential to use this water for any crop and soil without detrimental to crops grown.

The present study was conducted to evaluate the water quality of the inlet, irrigation outlet, and edges linked to Nuwarawewa reservoir, Mahakanadarawa reservoir, Hurulu wewa reservoir, Sangilikandarawa reservoir, and Nachchaduwa perennial reservoir in Anuradhapura, Sri Lanka. Water samples were taken from a designated position of each inlet, irrigation output, and edges in the second inter-monsoon, northeast monsoon, and first inter-monsoon seasons. Water quality indicators such as pH, electrical conductivity (EC), total dissolved solids (TDS), Na, K, Ca, Mg, Sodium Adsorption Ratio (SAR), NO3- -N, NH4+-N, dissolved reactive phosphorus (DRP), and heavy metals (Cd, As, Pb, and Hg) concentrations were measured in each water sample. Data was analyzed using SPSS statistica software. Considerable temporal fluctuations in water quality indicators were detected in inlets, irrigation outflows, and edges over the research period. The findings revealed that NO3- -N, NH4+-N, and DRP in Sangilikandarawa reservoir during the northeast monsoon were close but not above the FAO (1985) maximum levels guidelines for irrigation water. pH, EC, TDS, and heavy metals (Cd, As, Pb, and Hg) in all the other tanks were within permitted values according to WHO drinking water quality standards and FAO (1985) guidelines for irrigation water. This finding further demonstrated that the consequences of surrounding land use on water pollution in inlet water canals linked to Sangilikandarawa and Nuwarawewa are greater. It could be concluded that a pollution management plan needs to be implemented in order to stop further pollution.

Interpolation methods are extensively used to map the spatial distribution of water quality parameters. However, the selection of the most appropriate method is a critical issue in environmental studies. The relative performances of deterministic and geostatistical methods in explaining the spatiotemporal variation of water quality parameters/indices in a tank cascade landscape were assessed. Inverse distance weighted (IDW), global polynomial interpolation (GPI), local polynomial interpolation (LPI), radial basis function (RBF), kriging (KR), and empirical Bayesian kriging (EBK) methods were evaluated using root mean square error (RMSE) in a leave-one-out cross-validation. Coefficient of variance, normality, level of autocorrelation, and extreme values near boundaries of the dataset showed a clear relationship with the relative performances of the different interpolation methods. Therefore, a clear understanding of the quality of the dataset is required in order to select the appropriate method to interpolate water quality parameters. EBK performed well for most parameters throughout the study period and is recommended as the best method to interpolate water quality parameters/indices in the Ulagalla cascade and other tank cascade landscapes in Sri Lanka and similar environments.

Today's agricultural system relies heavily on synthetic inputs for higher yields. Prolonged use of chemical inputs pollutes and degrades the farming lands and it should go through a transition period to achieve soil fertility. Sri Lanka needs research to identify the potential and challenges of organic or integrated plant nutrient management strategies, particularly during the transition phase. More information is lacking on the soil fertility dynamics and yield performance among these diverse input systems for rice (Oryza sativa L.) hybrids as they were bred under conventional management. Main objective of this study was to compare the final grain yield between conventional (100% Department of Agriculture, DOA recommendation) reduced (50% DOA + 50% organic manure) and organic systems with great attention to soil fertility dynamics within its first transition year. The experiment was carried out in Puliyankulama, Anuradhapura during Yala season 2019. Soil samples were analysed for different fertility parameters. The final grain yield and yield parameters were also determined. Data were subjected to analysis of varience (ANOVA) using SAS software to distinguish treatment effects. With time stages, ammonium nitrogen (N), nitrate N, available phosphorous (P), and microbial biomass carbon (MBC) fluctuation among different input systems were significant (P<0.05). Nitrate N and available P revealed a significant increment within the organic system from the first transition year. Initial 77.27 mg kg-1 nitrate N of organic system reached up to 144.16 mg kg-1 at the end of the first transition year while available P surged from 2.25 to 15.1 mg kg-1. Conventional and reduced systems produced similar final yields for rice as 4.9 and 4.7 t ha-1, correspondingly while 2.7 t ha-1 final yield produced by organic input system. The results suggest a potential to replace inorganic chemical fertilizers by 50% with organic manure without much impact on the yield while reducing the cost of production applied for commercial fertilizers. Overall, long-term investigations are needed to confirm soil fertility dynamics and final grain yield of rice within its transition period.