Browsing by Author "Gamage, NPD"

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item: Thesis-Abstract
A Study of irrigation water use for paddy cultivation in the dry zone of Sri Lanka
Wickramaarachchi, TN; Wijesekera, NTS; Gamage, NPD; Senarath, DCH
Water is a scarce resource in the Dry Zone of Sri Lanka and it is a major problem faced by the cultivators in the area. Since their cultivations totally depend on irrigation water, every possible effort should be put in order to optimize the water usage to achieve increased crop production. Recent reports on water management activities of several irrigation schemes in the Dry Zone indicates that the water distribution is not meeting the demands of farmers in terms of adequacy, reliability & timeliness. Further it was said that there is considerable potential to increase paddy yield in this system through improved irrigation water management, especially by efficient irrigation scheduling. Following four study areas in the Dry & Intermediate Zones were selected from different irrigation schemes authorized by the different organizations. i) Block 404 & 406 of Mahaweli system H ii) Track 1 of Rajangana Irrigation scheme iii) Ridi Bendi Ela irrigation scheme The strengths and weaknesses of the presently adopted water allocations by the above schemes were identified. Further, the cultivation practices and present water usage in three irrigation schemes were compared. The irrigation requirements according to the Irrigation Department guideline recommendations were computed for each scheme using a spread sheet model and compared with present water usage in three schemes to find out optimum solutions for irrigation water use for paddy cultivation. The comparative analysis revealed that the practices adopted in issuing water in each scheme differ resulting disparity in water usage, farmers' satisfaction on water issues and paddy yield. Considering the above comparisons, the recommendations for water issues during both land preparation & crop growth in paddy cultivation were presented pertaining to the most appropriate date of commencement and duration of the land preparation, the variation of depth of water application and frequency of irrigation during different growth stages of paddy with possible water saving techniques incorporating farmer needs. The optimum quantity of water requirement for the land preparation with maximum utilization of rainfall, most favorable quantity of water to meet the crop water requirement at different growth stages of paddy and the selection of best canal grouping to optimize the water distribution were also presented in the study.
item: SRC-Report
Analysis of probability distribution of annual maximum, mean, and minimum stream flows in Sri Lanka
Gamage, NPD
Selection of a probability distribution for discharge series is very important in estimating floods accurately. Since the introduction of L-moments (Hosking 1990), numerous investigations have been carried out to assess the goodness of fit of various probability distributions to regional samples. L-moment diagrams were constructed for annual maximum flood flows, annual average daily stream flows, and annual minimum low flows at 46 catchments in Sri Lanka. The data were screened to eliminate gross errors and inconsistencies. For this purpose the Discordancy measure Di introduced by Hosking and Wallis in 1993 was used. The Discordancy measure allows for an objective determination of which sites, i, in a region, are grossly discordant with the group as a whole. For each flow series, sites were dropped with discordancy measures Di,> 3. Suitable distributions for each site were selected by comparing the observed and theoretical relations between L-cv and L-skewness of the flood flows. The goodness-of-fit test was then applied in order to examine the descriptive performance of screened distributions.
item: Article-Full-text
Decomposition and mineralization of Eichhornia crassipes litter under aerobic conditions with and without bacteria
Gamage, NPD; Asaeda, T
The water hyacinth (Eichhornia crassipes (Mart.) Solms.) plants in lakes and reservoirs have gained considerable attention in tropical and sub-tropical parts of the world due to its rapid growth. The amount of nutrients released from the dead plant materials is of particular interest. Thus, decomposition of water hyacinth plant parts under aerobic conditions was studied in the laboratory. Roots, petioles, and leaves of water hyacinth were enclosed separately in one litre polypropylene bottles which contained 500 ml of lake water. To study the influence of bacteria on the decomposition, antibiotics were added to half of the bottles. We observed that decomposition of leaves and petioles without antibiotics were relatively rapid through day 61, with almost 92.7 and 97.3% of the dry mass removed, respectively. Weight loss due to bacterial activities during 94 days decomposition was 22.6, 3.9, and 30.5% from leaf, petiole, and root litter. Decomposition of litter in lake water indicated that after 94 days 0.6, 0, and 0.6 g m)2 of leaf, petiole, and root N was dissolved in leachate, while 23.1, 14.4, and 6.0 g m)2 of leaf, petiole, and root N was either volatilized or remained as particulate organic N. Moreover, 0.2, 0, and 0.1 g m)2 of leaf, petiole, and root P remained dissolved in the leachate, while 3.1, 3.4, and 1.1 g m)2 of leaf, petiole, and root P was either precipitated or remained as particulate organic P. The carbon dynamics during the decomposition indicated that 7.4, 28.8, and 3.7 g m)2 of leaf, petiole, and root C remained dissolved in the leachate after 94 days while 228.0, 197.6, and 107.4 g m)2 of leaf, petiole, and root C was either diffused or remained as particulate organic C. These findings are useful for quantifying the nutrient cycles of very shallow lakes with water hyacinth under aerobic water environment. Further examination of the fate of the plant litter as it moves down in deep anaerobic water environment, is necessary to understand the leaching process better.
item: Thesis-Abstract
Development of a comprehensive ground water model to analyse the management options for Vavuniya region
Shanmuhananthan, S; Gamage, NPD
Due to low porosity and permeability, the recharge and yield are relatively low in the areas that comprise shallow weathered and rarely fractured hard rocks with thin soil mantle. Therefore the problems in sustainable groundwater management are of major and vital importance in these areas. Prevailing Groundwater condition in Vavuniya district is a typical example of this situation. The records reveal that the groundwater table in Vavuniya did not reach its previous year maximum level during the past 4 years. This may be due to the excessive exploitation of ground water or due to the reduction in recharge of aquifer or the combination of both. The prime intention of this research is to find out an appropriate strategy to ensure sustainability in groundwater management for this region. The objective of this study is to understand the groundwater systems of Vavuniya region aquifer and hence to improve the evaluation, development, and management of groundwater resources, and the controlof groundwater problems in that aquifer. Thespecific objectives are, (1) to achieve an understanding of the basic mechanisms that govern the flow in the aquifer through numerical modeling. (2) to examine the behavior of the aquifer under various operating conditions. (3) to prepare a water balance for the territory. MODFLOW,the three - dimensional, finite difference groundwater flow Computer Model, developed by Waterloo Hydrogeologic Inc was selected forthis study. As no processed reliable data were found for this study area, all basic physical and hydrological data required for this study were collected as raw material and processed to fit the Modflow model. Since, it is very difficult to attain more reliable results from calibration of a model if large numbers of variables are to be optimized; some of the important variables were optimized separately. The surface runoff and the recharge due to irrigation storage losses were optimized against reservoir water balance and rainfall recharge was optimized using Penmen - Grindly model. These optimized data were used for the groundwater model simulation to optimize the other variables such as hydraulic conductivity, specific yield, recharge due to riverand recharge due to irrigation. The degrees of influence of river and subsurface dam conditions in groundwater system were examined separately by removing river boundary condition and by introducing Wall boundary condition to the calibrated model. The overall water balance of the territory was prepared using the cumulative mass balance resulting from the model simulations, available data and the observed hydraulic head data. The results reveal that the groundwater usage has already reached its Optimum level in this region and immediate action is required not only to control further expansion of groundwater exploitation but also to regulate groundwater withdrawal, especially during low rainfall years. .Further, the analysis shows that the non - perennial river a tributary of Parankiaru has less influence in the groundwater system and the subsurface dam conditions certainly have an impact on groundwater system, but this has to be studied further in detail in order to minimize the negative impact and utilize the merits of this condition.
item: Conference-Full-text
Field data collection in soil erosion assessment using GIS
(2001) Karunatilaka, GRN; Wijesekera, NTS; Gamage, NPD
The erosion of soil by wind and water has been a problem ever since land was first cultivated, because erosion results in loss of productivity of soils thereby necessitating the use of fertilizer to maintain yields. Another problem of soil erosion is the increase of sediments in rivers, watercourses and reservoirs creating water quality problems. Due to the critical nature of soil erosion, it is of great importance to identify the critical zones of soil erosion and provide prevention or management measures. The mostly used equation for soil erosion estimates is the Universal Soil Loss Equation. However the coefficients in this equation requires field validation prior to application of same for particular regions. Therefore the coefficients of analytical equation should be based on field assessments. Field data collection for soil erosion assessment needs to carry out systematic surveys. However such studies are very limited and no clear case studies are available. The present study used a systematic field survey to identify the erosion, soil texture slope and land-use, highlighting the key issues that need to be considered for meaningful data collection.
item: Conference-Full-text
Field data collection in soil erosion assessment using GIS
(2001) Karunatilaka, GRN; Wijesekera, NTS; Gamage, NPD
The erosion of soil by wind and water has been a problem ever since land was first cultivated, because erosion results in loss of productivity of soils thereby necessitating the use of fertilizer to maintain yields. Another problem of soil erosion is the increase of sediments in rivers, watercourses and reservoirs creating water quality problems. Due to the critical nature of soil erosion, it is of great importance to identify the critical zones of soil erosion and provide prevention or management measures. The mostly used equation for soil erosion estimates is the Universal Soil Loss Equation. However the coefficients in this equation requires field validation prior to application of same for particular regions. Therefore the coefficients of analytical equation should be based on field assessments. Field data collection for soil erosion assessment needs to carry out systematic surveys. However such studies are very limited and no clear case studies are available. The present study used a systematic field survey to identify the erosion, soil texture slope and land-use, highlighting the key issues that need to be considered for meaningful data collection.
item: Thesis-Abstract
Field validation of erosion hazard zones for effective management of watersheds
Karunatilaka, GRN; Gamage, NPD
Land and water resources are primarily important for all developing countries, particularly in countries like Sri Lanka where the majority of the people are either directly or indirectly dependent on agriculture for their livelihood. Hence soil erosion is one of the most serious environmental problems of agricultural based developing countries since it removes soils rich in nutrients, increase natural level of sedimentation in rivers and other water bodies and causes flood and water quality problems. The final results are the reduction of the productivity of land, which can lead to increase in expenditure in fertilizers to maintain yields and reduction in capacity of rivers increasing the risk of flooding, blocking of irrigation canals and shortening the design life of reservoirs. Due to this critical nature of soil erosion, prevention of soil erosion is important. This means reducing the rate of soil loss to approximately to the loss that would occur under natural conditions, which relies on selecting appropriate strategies for soil conservation. Although all the areas under the threat of erosion cannot be developed due to financial constrains, it is necessary to priorities the vulnerable areas. This requires an understanding of the processes of soil erosion. The factors, which influence the rate of soil erosion is rainfall, soil type, slope length and steepness, plant cover and presence or absence of conservation measures. Considering these factors, most common method of estimation of soil erosion is the Universal Soil Loss Equation (USLE). A=RKLSCP where R is the rainfall erosivity, K is the soil erodibility, L & S are slope length and slope steepness factors, C is the cover management factor and P is the conservation practice factor. It predicts the long-term average annual rate of erosion. The USLE was developed by W.H. Wischmeier, D.D. Smith and others with the U.S. Department of Agriculture (USDA), Agricultural Research service CARS), Soil Conservation Service (SCS) and Purdue University in the 1950s. However the factors in this equation requires field validation prior to their application for a particular region. This study was carried out for a relatively small area. University of Moratuwa premises which covers the 25 ha was selected as the research area since the area has different land cover, topography, etc. and most importantly detailed field data can be collected easily. Geographical Information System (GIS) is the best option in comparing different scenarios and finding out the optimum solution for such situations. The soil erosion model was prepared using GIS Arc/Info and Arc/view software, considering the factors effecting soil erosion. The data related to rainfall erosivity, soil erodibility, slope length and steepness, cover management and conservation practice factors were obtained out from various departments, literature and field surveys. Final model was developed by taking weighted average of RKCP in the polygons within each similar LS polygon since slope class is polygon specific A field survey identified some spatial units with four erosion classes and these data were used for model calibration and verification. Out of 200 polygons, a randomly selected 100 were used for model calibration and the rest were used for verification. Parameter optimization shows a very good match with the results ranging from 0 to 47.9 tons/ha/yr. Mean Ratio of Absolute Error (MRAE) which is MRAE=(l/n) [(Eo-Ec)lEo]where E, 0, c, n are for erosion level, observed, calculated and for number of samples respectively, was used as the objective function for calibration and verification of the model. Based on the calculated erosion values and trial and error matching process a weighting scheme was selected during optimization process.
item: Conference-Extended-Abstract
Growth characteristics of water hyacinth: an application to bolgoda lake
(2002) Fernando, PUD; Gamage, NPD; Jayaweera, MW
Water hyacinth (Eichhornia crassipes (Mart). Solms) is considered as a serious pest in many lakes, irrigation canals, stagnant ponds, waterways and semi-wet areas in Sri Lanka. Bolgoda Lake has been severely affected by excessive growth of water hyacinth, which resulted in clogging of major waterways, adversely affecting navigation. This study was carried out to determine the growth characteristics of water hyacinth under influence of the physical and chemical factors in Bolgoda Lake. The parameters such as biomass, biomass production per day, phosphorus and nitrogen content in plant tissues and pH, temperature, salinity, phosphorus and nitrogen content in the water body were measured.
item: Article-Full-text
Guidance on use of rainwater tanks for the Jaffna Peninsula
(2014-02-19) Gamage, NPD
The Jaffna peninsula is characterized by erratic rainfall and high evaporation rates leading to unreliable water supply. The people of the Jaffna Peninsula have long recognised this need, and have developed water supply facilities well suited to these conditions. Numerous shallow, lowyielding wells distributed over large areas did not have the capacity to cause an imbalance of the dynamic conditions maintaining the fresh water lens. In more recent years the increased demand for water has led to pumping rates that have, in places, caused problems. An additional problem with the widely distributed shallow well system is that the groundwater is vulnerable to pollution without appropriate waste disposal arrangements. Therefore rainwater harvesting (RWH) and management offers an opportunity to mitigate present and future water demand in the Jaffna Peninsula. Rainfall data of the Jaffna Peninsula from 1941 to 1990 was analysed to prepare guidance on use of rainwater tanks. This paper presents rainwater harvesting guidelines for the Jaffna Peninsula.
item: Conference-Extended-Abstract
Optimization of biogas production using water hyacinth (eichhornia crassipes)
(2003) Jayaweera, MW; Gamage, NPD; Wijekoon, SLK; Dilhanil, JAT
The water hyacinth (Eichhornia crassipes) has been classified as an obnoxious freshwater weed in the tropical and subtropical regions of the world due to its rapid growth rate and asexual reproduction. In Sri Lanka widespread infestations occurred since its introduction to the Botanical Gardens in 1904. However it is reported that the aerial tissues (i.c. stems and leaves) of water hyacinth could be effectively utilized for biogas production under anaerobic conditions.
item: Thesis-Abstract
Optimization of biogas production with water hyacinth
Dilhani, JAT; Jayaweera, MW; Gamage, NPD; Wijeyakoon, SLJ
The water hyacinth (Eichhornia crassipes [Mart.] Solms) due to its high growth rate and vegetative reproduction has been classified as an obnoxious freshwater weed especially in the tropics and subtropics. It has been reported that the presence of water hyacinths in waterways results in the displacement of native freshwater plants due to intense competition for light, space and essential resources such as nutrients, restricts navigation, fishing activities, cultural and social usage by affecting water quality, harbors diseasing causing vectors, etc. However the use of water hyacinth in the production of biogas has been an appealing solution to control the ever expanding infestation of this nuisance plant. This study therefore aimed at optimizing the biogas production from water hyacinth by enhancing the hydrolysis process. This study also attempted to investigate the optimum nutritional state (i.e. C/N and C/P ratios) required for effective biomethanation and to evaluate the kinetics of anaerobic digestion. This study was conducted using six numbers of batch bed barreled digesters each having a capacity of 451. For this study aerial parts (stems and leaves) of water hyacinth were used as the substrate with fresh cow dung mixed in the ratio of 2:3 by wet weight (w/w). Several parameters such as TS and VS were measured once a week while TOC, TN and TP were measured every 2 weeks. Biogas production rate, p H and temperature were measured on a daily basis. The study was conducted at ambient mesophillic temperature for a period of 4 months. Both C/N and C/P ratios decreased after mixing with cow dung having a very low C /N and C/P ratio o f 8 and 165, respectively. The C /N ratios did not approach to the optimum range of 20-30. Nevertheless the C/P ratios exceeded the optimum ratio of 167 required to enhance biogas production. However gas production commenced from all digesters within 3 days of the study (i.e. a production rate of 0.73-1.35 1/kg/day was recorded). This study showed that substrates having TS and VS contents in the range of 63-77 g/1 and 45-50 g/1, respectively produced biogas more efficiently. Higher gas production rates were obtained from the substrates in the f-1 digester (i.e. digester containing the hyacinths grown in a nutrient solution containing 28 TN mg/1 and 7.7 TP mg/1) particularly during the period of 14th - 27th day. f-1 digester had the highest C/N ratio of 16, with an optimum initial pH of 7.28 and temperature of 30.3°C to account for optimum biogas production. This study concluded that cow dung and water hyacinth mixtures produced biogas even though the C/N ratios were not with in the optimum range of 20-30. Nevertheless higher biogas productions were reported from substrates having higher C/N ratios of 16. Chen and Hashimoto model fitted well with the experimental data except for a few initial values since the correction for the temperature, pH and mass transfer were not accounted. Kinetic constants pm and K for the substrates were in the range of 0.0074-0.0332 day"1 and 0.0360-0.0386 day"1 , respectively.
item: SRC-Report
Preparation of guidelines on use of rainwater tanks for potable use
Gamage, NPD
The Jaffna peninsula is characterized by Abstract: erratic rainfall and high evaporation rates leading to unreliable water supply. The people of the Jaffna Peninsula have long recognised this need, and have developed water supply facilities well suited to these conditions. Numerous shallow, low-yielding wells distributed over large areas did not have the capacity to cause an imbalance of the dynamic conditions maintaining the fresh water lens. In more recent years the increased demand for water has led to pumping rates that have, in places, caused problems. An additional problem with the widely distributed shallow well system is that the groundwater is vulnerable to pollution without appropriate waste disposal arrangements. Therefore rainwater harvesting (RWH) and management offers an opportunity to mitigate present and future water demand in the Jaffna Peninsula. Rainfall data of the Jaffna Peninsula from 1941 to 1990 was analysed to prepare guidance on use of rainwater tanks. This paper presents rainwater harvesting guidelines for the Jaffna Peninsula.
item: SRC-Report
Regional flood estimation by canonical correlation
Gamage, NPD
Canonical Correlation is an additional procedure for assessing the relationship between variables. Canonical Correlation permits one to establish the interrelations that may exist between two groups of variables, by identifying the linear combinations of the variables of the first group that are most correlated to some linear combinations of the variables of the second group. In regional flood frequency analysis, canonical correlation can be used to investigate the correlation structure between the two sets of variables represented by watershed characteristics and flood peaks. Regional frequency analysis is commonly used for the estimation of extreme hydrological or meteorological events, such as floods, at sites where little or no records exist. A homogeneous region is defined as a group of drainage basins whose standardized flood frequency curves are similar, to within a certain margin of sampling error. The Canonical Correlation method also helps to determine the degree of similarity between the groupings of basins in the spaces of the respective canonical variables of the basin and the flood characteristics. It also provides a basis for the determination of homogeneous regions in the space of basin characteristics which takes into account their relationships with the flood characteristics. A data set of 46 stations from Sri Lanka is used to demonstrate the advantage of this method.
item: Conference-Full-text
Regionalization of catchments in Sri Lanka for regional flood frequency analysis
(2001) Gamage, NPD
In flood frequency analysis the objective is to estimate flood quantile magnitudes for different return periods at a station or at a number of stations in a river system. An understanding of the hydrologic characteristics of a catchment is essential in order to obtain a reliable estimate of the relationship between extreme flood quantiles and the associated return periods. An approach to catchment regionalization is presented, in which an agglomerative hierarchical clustering algorithm is used to define homogeneous regions that can be used for regional flood frequency analysis. Catchment similarity is expressed using seasonality measures derived from the mean date of occurrence of the annual maximum flood and its associated dispersion. Regions that are largely geographically contiguous are obtained by incorporating gauge latitude and gauge longitude to the clustering algorithm. The initial regions formed using the clustering algorithm are subsequently modified in an attempt to enhance the overall regional homogeneity. The approach is demonstrated through an application to a set of catchments in Sri Lanka.
item: Conference-Extended-Abstract
The role of the mottled water hyacinth weevil (neochetina eichhorniaes on biological control of water hyacinth in Sri Lanka
(2003) Gamage, NPD; Jayaweera, MW; De Silva, SD; Kasige, AP
Water hyacinth (Eichhornia crassipesi has become one of the most obnoxious freshwater weeds \~ith numerous widespread infestations occurring in the North Western. Central and Southern provinces in Sri Lanka. Water hyacinth competes with native plants and phytoplankton in aquatic system for essential nutrients and space due to its rapid grow tho Further it clogs waterways thereby restricting recreational activities including fishing and navigation. lowers dissolved oxygen in water and limits light penetration due to the formation of an extensive network of mats.
item: Thesis-Abstract
Sustainable water resources management for optimum utilization of Walawe river basin
Abeysekara, SSM; Gamage, NPD; Gunarathna, PP
The basin is undergoing extensive changes due to agro-ecological, socioeconomic and institutional developments. Livelihoods vary from area to area depending on the physiographic conditions and availability of land and water. Irrigation development has been the major strategy- for livelihood enhancement of the people in the basin// However, tea plantations have replaced the natural vegetation that covered the mountains in the past and abandoned tea lands have been degraded by severe soil erosion. Newly introduced trees like pine and eucalyptus were planted under reforestation programs in the 1950s in this area . They have had a negative impact on the hydrology of the basin, causing some small streams to dry up.// The increasing trend of agro-chemicals usage for irrigated agriculture by the basin farmers is likely to have adverse impacts on the biodiversity of the lagoons. Irrigation development has had negative impacts on the aquatic environment also Specially, large scale deforestation, removal of vegetation cover and encroachment of reservations and other conservative areas with in the basin have drastically reduced watershed performance and environmental friendly behaviors which have severely affected the maximum efficiency of the catchments. An increasing competitive usage of water resources by several sectors can also be seen within this basin An accurate topographical maps to scale 1:50,GOO have been used to digitized the basin and it's sub catchments using geographic Information System(GIS1. Divisional Secretariat Divisions |DSD) falling into the Walawa basinand different types of land usages in the basin were identified using Multi Layer Analysis in GIS - Geoprocessing.// To obtain an average rainfall value over the catch men and sub catchments of Walawa basin, the Thiessen polygon method was used The runoff coefficients for the sub catchments Samanalawewa and Udawaiawaof the basin were calculated from the daily reservoir water balance computations under some assumptions for the period. Irrigation recharge contribution to ground water were also calculated. But, in this study, river recharges were not calculated due to the non-availability of required data. Ground water withdrawal for each seasons were also calculated separately for each zone.// Human, livestock, agio and industrial water consumptions were also calculated under some assumptions from year 2000 lo 2005.Collected the necessary data and information required for the identification of mitigatory measures towards watershed protection to promote soil and water resources conservation within the basin Therefore, the output objectives are directly related to draw our attention lo identify the suitable strategics for the equitable, efficient and effective water resources management and watershed management practices preserving soil, water and other natural resources, reducing waste to a minimum and meeting the water requirement of a given demand site. This will be very useful for the sustainable development of the basin.
item: Thesis-Abstract
The Role of Neochetina Eichhorniae and Neochetina Bruchi on biological control of water hyacinth in Sri Lanka
Kasige, AP; Gamage, NPD; Jayaweera, M
One of the major scourges accompanying water resource development in Sri Lanka is the explosive proliferation of water hyacinths (Eichhornia crassipes). A better sustainable solution to manage the infestations seems to be biological control and the main biological control agent used in many parts of the world including Sri Lanka is reported to be the weevil [(Neochetina eichhorniae Warner) (Coleoptera; Curculionidae)]. Fernando and Room used the weevil N eichhorniae for the first time in Sri Lanka in 1988. Although some 15 years have elapsed since the first release, infestation in the areas in which the weevil was released is as high as in the areas in which Neichhorniae was not released. The present study therefore focuses on the evaluation of the role of N eichhorniae and Nbruchi on controlling water hyacinth and is designed to evaluate the optimum weevil densities required to cause significant damage to the plants. Healthy plants of height 21 ern ±l were cultured in 6 and 4 fiberglass tanks respectively for a period of 8 weeks to complete one life cycle of weevil. Different weevil densities were used, varied from 1,3, 6,10 and 15 weevils per plant, and the control with no weevils. In case of Nbruchi the first 3 treatment levels were tested with the control. Field monitoring carried out in eight locations within the Western province and showed the average maximum weevil density in natural conditions as 2 per plant. The success of biological control using Neichhorniae will ultimately rely on host plant quality and the habitat conditions to establish a healthy population of weevil densities. Results showed that the treatments with weevil numbers less than 3 of Neichhorniae per plant did not significantly change (p>O.Ol) the water hyacinth stands, but 3 weevils per plant of Nbruchi was the best option in sustainable management. Densities of 10 of Nieichhorniae and 6 of Nbruchi were subjected to complete eradication of the plant.
item: Conference-Full-text
Water scheduling for better yield in paddy cultivation - a study from Mahaweli system h of Sri Lanka
(2001) Wickramaarachchi, TN; Wijesekera, NTS; Gamage, NPD
Agricultural production has given the highest priority in the Dry Zone of Sri Lanka and has become the main livelihood of people living in the area. It has been found that almost all the cultivation in the area totally depends on the irrigation water and hence proper management of irrigation water is needed in order to achieve increased crop production. The aim of this study is to analyze the present water management issues of the Distributory canal Dl at Block 406 in Mahaweli system H and come out with possible improvements to the existing system in order to optimize the water usage in achieving better paddy yield. A questionnaire survey was carried out among the farmers in the Block in order to collect information about the present water issue system. Hence the strengths and weaknesses of the existing water management system were identified. By the survey it was found that the present rotational water issue system does not concern very much on sensitivity of paddy to water stress, resulting low yield. Since paddy has some sensitivity to water stress, all the possible efforts should be put in order to avoid a water deficit during the entire season. Considering the varieties of paddy grown and their sensitivity to water shortage at different plant growth stages, an improved water management for paddy cultivation is presented in this study for the Block 406.
item: Article-Abstract
Water scheduling for better yield in paddy cultivation : A study from Mahaweli system 'H' of Sri Lanka
Wickramaarachchi, TN; Wijesekera, NTS; Gamage, NPD
Agricultural production has given the highest priority in the Dry Zone of Sri Lanka and has become the main livelihood of people living in the area. It has been found that almost all the cultivation in the area totally depends on the irrigation water and hence proper management of irrigation water is needed in order to achieve increased crop production. The aim of this study is to analyze the present water management issues of the Distributory canal D1 at Block 406 in Mahaweli system H and come out with possible improvements to the existing system in order to optimize the water usage in achieving better paddy yield. A questionnaire survey was carried out among the farmers in the Block in order to collect information about the present water issue system. Hence the strengths and weaknesses of the existing water management system were identified. By the survey it was found that the present rotational water issue system does not concern very much on sensitivity of paddy to water stress, resulting low yield. Since paddy has some sensitivity to water stress, all the possible efforts should be put in order to avoid a water deficit during the entire season. Considering the varieties of paddy grown and their sensitivity to water shortage at different plant growth stages, an improved water management for paddy cultivation is presented in this study for the Block 406.