Janendra De Costa

• PhD
• Professor (Full) at University of Peradeniya

The change of soil carbon (C) mineralization of tropical montane forests (TMFs) across elevation remains unclear. The objective of the present study was to determine the variation of soil C mineralization along an elevation gradient in TMFs in Sri Lanka. Soil samples were collected from four permanent sampling plots (PSPs): 1042 (Sinharaja-Enasalwa...

Tropical lowland rainforests (TLRFs) of Sri Lanka are considered as diverse ecosystems which play a vital role in climate change mitigation. In recent years, increasing deforestation leads to diminishing their potential ecosystem roles. For efficient forest conservation, knowledge of both above-and below-ground characteristics of TLRFs is required....

A significant portion of crop production in the tropics occurs at subsistence level with high vulnerability to climate change. Process-based crop simulation models are effective tools to predict environmental impacts, including climate change effects, and make management decisions on crop production. The principal objective of this work was to deve...

Soils in untouched forest regions are considered less-polluted from anthropogenic activities. Hence, they can be considered as a soil environment that represents natural background element levels. Exploring the distribution and abundance of rare earth elements (REEs) in soil is essential to understand their role in nature. This study aimed to compa...

Tropical Montane Forests (TMFs) and Tropical Sub Montane Forests (TSMFs) play an important role in watershed function, climate change mitigation and conservation of biodiversity. In the past few decades, increased deforestation has reduced their potential ecosystem roles and services. Although to-date, above-ground information on these forests is s...

in the periodic table are well-known as rare-earth elements (REEs). They are useful in assessing the soil formation processes under tropical weathering and are considered highly immobile and mostly retained in the soil profile. In this study, we investigated two undisturbed soil formations in order to understand the mechanisms that are responsible...

Increasing deforestation leads to reduce climate change mitigation capacity of tropical lowland rainforests (TLRFs) in Sri Lanka. For efficient forest conservation, knowledge of both above-and below-ground characteristics of TLRFS is required. Up to date, above-ground information sufficiently available but below-ground details are scarce. Therefore...

Lanthanide series that consists of 14 elements (from La to Lu) is the major portion of the rare earth elements (REE). There is an increasing interest to study lanthanides in pedology as their role in nature is still poorly understood. The objective was to present the role of REEs in nature by determining REE content within the soil in montane fores...

Tropical rainforests (TRFs) play a vital role in the global carbon (C) cycle. Understanding spatial variation in soil C mineralization in TRFs is crucial to determining the net C balance. The objective of the present study was to determine variation in soil C mineralization rate along an elevation gradient in Kanneliya and Pitadeniya TRFs in Sri La...

The leaf area index (LAI) of a forest is a key determinant of its primary productivity. Estimation of LAI via remote sensing of forest canopies offers an alternative to direct measurement, which is difficult in tropical rainforests (TRFs). Our objectives were to determine the variation of LAI and Normalized Difference Vegetation Index (NDVI) of a r...

Understanding taxon level responses of key plant traits to environmental variation across tropical rainforests (TRFs) is important to determine their response to climate change. We used an altitudinal gradient (from 150 to 2100 m above sea level, asl) across TRFs in Sri Lanka to answer the following questions: (a) Does the response to altitude by s...

Global warming cause due by increasing atmospheric CO2 concentration, and the resulting increase in air temperature is a considerable challenge in crop production. Hence, the objectives of this study were to determine the: (a) responses of biomass and sucrose accumulation of sugarcane to elevated CO2 (ECO2) and elevated temperature (ETa), both indi...

BACKGROUND In this study, we surveyed through a structured and pilot‐tested questionnaire, the practices of pesticide usage by small‐scale (< 1.25 ha) chilli and tomato farmers from four districts of Sri Lanka and their perceptions on the effectiveness of pesticides and willingness to adopt integrated pest management (IPM). RESULTS We found signif...

Tropical rain forests (TRFs) are a major carbon sink and play an important role in regulating the global climate. Floristic composition, structure and carbon storage in biomass of TRFs could vary substantially with climatic and edaphic factors. Altitudinal transects represent an excellent setting for investigating the responses of TRFs to environme...

Sustainable food production for the future should incorporate crop management practices to reduce the environmental cost by lowering the use of synthetic pesticides and inorganic fertilizers. Such practices also need to be successful in a future environment of higher temperatures and more variable rainfall. Crucially, crop management packages desig...

Rapid advances in molecular biology and functional genomics during the last two decades have created considerable optimism about their potential to increase global food production by raising the yields of major agricultural crops via breeding of new crop varieties. However, yield increases achieved so far have come largely through conventional plan...

Increasing air temperatures due to long-term global climate change are predicted to exert substantial negative impacts on a majority of agricultural crops in the tropics, where most smallholder farms have a mixture of crops. Modification of the composition of cropping systems by incorporating crop species with greater growth and yield performance a...

Long-term temperature increases pose a major threat to tropical crops. Furthermore, high doses of synthetic pesticides for crop protection and inorganic fertilizer to achieve higher yields on degraded soils have caused considerable environmental and health hazards. Therefore, cropping systems which are more resilient to increasing temperatures and...

Climate change is one of the most-discussed issues in current global fora. The objective of this paper is to seek evidence for climate change in Sri Lanka by analyzing longterm (i.e. from 1869 to 2007) monthly data of air temperature and rainfall from seven selected locations (i.e. Anuradhapura, Kurunegala, Kandy, Ratnapura, Badulla, Nuwara Eliya a...

Background and AimsManagement options to reduce the negative impacts of iron (Fe2+) toxicity in lowland rice (Oryza sativa L.) are limited. Improving productivity and ensuring sustainability of such systems requires a sound ecophysiological understanding of this widespread problem. Methods The effectiveness of dolomite [CaMg (CO3)2] application to...

Inorganic fertilisers need to be applied only when the inherent soil fertility alone cannot supply the plant nutrient demand for rice. When managing such systems, identification of the most sensitive morphological and/or physiological characteristics of a rice plant and the growth stage at which those responses appear when soil phosphorus (P) and p...

Scarcity and high cost of labour has become an alarming problem in the Sri Lankan tea cultivations. Although mechanical tea harvesting is an alternative, it has reported high yield reductions in Sri Lanka. In order to identify the physiological basis of yield decline under mechanical harvesting the present study compared manual harvesting with thre...

Stomatal functioning regulates the fluxes of CO2 and water vapour between vegetation and atmosphere and thereby influences plant adaptation to their habitats. Stomatal traits are controlled by external environmental and internal cellular signalling. The objective of this work was to quantify the effects of CO2 enrichment (CE) on stomatal density-re...

Growth of rice when soil phosphorus (P), potassium (K), and moisture are co-limiting is poorly known. An experiment was conducted using two rice varieties (long (LD) and short (SD) duration), two moisture conditions (continuous flooding and top-soil drained after flowering), and five fertiliser treatments (with and without the applications of P and...

Potato is one of the key annual upland cash crops cultivated in the Jaffna District of Sri Lanka. However, potato farmers are challenged by climate extremes, increasing pest/disease loads and excessive use of agro-chemicals all of which are expected to increase in the future. To address these critical issues, a package of climate change-adaptive an...

Drought causes a substantial reduction in national yield of coconut and also a loss of coconut palms in severe droughts thus resulting in serious economic consequences to the coconut industry in Sri Lanka. Therefore, it is of prime importance to identify some putative drought tolerant forms to use in drought-prone areas. As the long generation and...

Among upland cereals, Maize (Zea mays L.) is considered as the most important cereal crop in Sri Lanka. Successful expansion of maize cultivation requires knowledge on its yield potential. Conventional agronomic research may require considerable time and physical resources to generate the relevant knowledge whereas simulation modelling would enable...

Carbon sequestration is a concept which has gained attention in the context of climate change. Therefore the objective of this study was to estimate the carbon sequestration potential of tea plantations in Low-country, Mid-country,Up-countryandUvaregionsofSri Lanka. Thecarbonsequestrationofteaplantswereestimated using the stock difference method th...

Maize (Zea mays L.) yields in Sri Lanka have been below its potential yield mainly due to biotic and abiotic stresses. This situation is likely to be aggravated in a changing climate in the future. This study was conducted under field conditions to determine the response of maize to temperature and different soil management practices during Maha se...

Adapting cropping systems to the potential negative impacts of climate change by enhancing their resilience has become important especially for the farming communities in vulnerable regions like Northern Province of Sri Lanka. Increased ambient temperatures, altered rainfall patterns, declining soil fertility and changed pest/ disease dynamics are...

Background and aims: Knowledge on periodic uptake, accumulation and allocation of nitrogen (N), phosphorus (P) and potassium (K) in different tissues of a rice plant under different soil moisture management conditions is important when implementing efficient and effective water management practices ensuring sustainable rice production. Methods: Ric...

Increasing temperatures pose a significant threat to crop production in the tropics. A field experiment was conducted with mung bean at three locations in Sri Lanka representing an increasing temperature gradient (24.4–30.1 °C) during two consecutive seasons to (i) determine the response of mung bean to increasing temperature and (ii) test a select...

Methods: Using large pots a three-factor factorial experiment was conducted with two moisture treatments (i.e. continuous flooding, and draining of top soil after flowering while subsoil was kept moist through capillary action), three fertilisation treatments; with (P1) and without (P0) applications of inorganic P fertilisers, and 25 % of inorganic...

This study was conducted to generate the baseline data on carbon sequestration potential of the community of tea plantations with different types of medium and high shade trees in different tea-growing regions in Sri Lanka. The carbon sequestration potentials were estimated based on the rates of average net carbon storage in biomass for tea and sha...

The national average potato yield of Sri Lanka is lower than its global average with the absence of an optimum temperature regime for tuber bulking being a major contributory factor. Increasing air temperatures due to the enhanced greenhouse effect have the potential to further reduce potato yields in Sri Lanka. Therefore, the primary objective of...

The devastating effects of anthropogenic climate change on crop production systems and thereby its threats on food security are well documented by a large volume of literature at global scale. These negative effects including increasing air temperatures and changes in rainfall have clearly been noticed in Sri Lanka through long term climatic data a...

Mung bean (Vigna radiata (L.) Wilczek) is a versatile crop which is used in maize-legume crop rotations in uplands and in the rice-legume crop rotation in lowlands in the dry and intermediate zones of Sri Lanka. Climate change and intensive use of synthetic agro-chemicals are problems in the production of any crop including mung bean. Adaptation me...

Mung bean (Vigna radiata (L.) Wilczek) is a versatile crop which is used in maize-legume crop rotations in uplands and in the rice-legume crop rotation in lowlands in the dry and intermediate zones of Sri Lanka. Climate change and intensive use of synthetic agro-chemicals are problems in the production of any crop including mung bean. Adaptation me...

No: 563 Climate and Environment Farmers have failed to realize the potential yield of mung bean under rainfed farming due to many biotic and abiotic stresses. These stresses may be aggravated in a changing climate in the future. Thus, understanding the magnitudes of impact and development of adaptive measures are important. A field experiment was c...

Increasing temperature of the growing season is important in view of the expected increases in air temperature as part of greenhouse gas-induced long-term climate change. The demand for tomato mainly depends on fruit quality attributes including sugar content, acidity and flavor. Therefore, a field experiment was conducted during yala 2013 at Rahan...

Carbon Sequestration Potential of Tea Plantations in Sri Lanka T.L. Wijeratne1*, W.A.J.M. De Costa2 and M.A. Wijeratne3 1Agronomy & Plant Physiology Division, Tea Research Institute, Talawakelle 2Department of Crop Science, Faculty of Agriculture, University of Peradeniya 3Tea Research Institute, Low country Regional Centre, Ratnapura, Sri Lanka Ca...

Abstract: Rice is highly sensitive to salt stress, an expanding abiotic stress factor that limits rice yield improvement. Development of salt tolerant rice varieties based on molecular breeding methods requires identification of genes responsible for various mechanisms and responses that contribute to salt tolerance. The objective of the present w...

Increasing water use efficiency (WUE), which is defined as the biomass increase per unit of water transpired, is a promising avenue for crop yield improvement, especially in drought-prone environments. The present study tested whether significant inter-varietal variation exists for WUE in common bean (Phaseolus vulgaris L.) under weil-watered and w...

Tea is a rain-fed plantation crop which is highly vulnerable to long-term climate change. Simulation modelling is a powerful technique to predict the impacts of climate change on crop processes and productivity. Therefore, the objective of the present study was to adjust and adapt the Sheffield Dynamic Global Vegetation Model (SDGVM) and predict th...

Salt tolerance of plants during the first phase of salt stress requires a combination of physiological traits conferring tolerance to both osmotic stress and ionic stress. Accordingly, the objectives of the present study were: (a) to screen a substantial number of varieties (102) from the Sri Lankan rice (Oryza sativa) germplasm and thereby identif...

The stomatal responses of tea plants to elevated carbon dioxide was investigated. The abstract is attached.

Abstract A field experiment was conducted to evaluate sugarcane varieties based on their radiation use efficiencies (RUE) at the Sugarcane Research Institute, Uda Walawe, Sri Lanka. Sugarcane was grown under irrigated (soil water potential[-0.05 MPa) and rain-fed conditions in a split plot design. Biomass accumulation, canopy development, leaf angl...

Forest plantations have the ability to sequester carbon in their biomass and reduce the rate of increase of atmospheric carbon dioxide. Therefore, plantation forestry forms an important option for mitigating global warming and consequent climate change. The objective of the present study was to estimate the biomass and carbon stocks of the existing...

Significant variations in the time series patterns of key climatic variables of a particular region over a prolonged time period provide proof of climate change. The objective of this study was to demonstrate the long-term variation patterns of air temperature and rainfall and to show their magnitude of variation between different locations of Sri...

Increased anthropogenic emissions of greenhouse gases (GHGs) have led to gradual warming of the earth's atmosphere. It is predicted that by the year 2100, the average annual global air temperature will increase by 1.1 - 6.4 oC. This has triggered a series of long-term changes in the atmospheric and soil environments. As forests form a key component...

The objective of this study was to investigate the effects of soil moisture deficits on the growth of root system and its effect on soil moisture utilization in sugarcane to identify relationship of root growth with drought tolerance of sugarcane varieties. An experiment with eight sugarcane varieties under rain-fed and irrigated conditions in a sp...

A field experiment was conducted during both rainy (kharif) and winter (rabi) seasons of 2007-08 to determine the physiological basis of yield variation comprising six sweetpotato (Ipomoea batatas) genotypes. The improved whitefleshed sweetpotato genotype 'CIP-SWA 3' out yielded all the other genotypes in both the seasons. However, among the orange...

Water is an essential resource for agriculture and forestry. It is highly likely that decreasing rainfalls and increasing evapotranspiration (ET) rates resulting from global-warming induced climate change would decrease the water availability for agriculture. The water balance of a given location during a defined period provides a measurement of it...

Climate change is a crucial factor that is altering the water resources and availability of water spatially and temporally through global warming process. The objective of this study was to investigate the long-term (i.e. 1869 to 2009) variation of water balance in a set of fifteen selected locations (i.e. representing different Agro-Ecological Reg...

An introduced and naturalized plant species which increases its population excessively at the expense of other species in a given community is defined as a n invasive species. The objective of this study was to determine whether some selected physiological characteristics were responsible for the invasive behaviour of eight plant species in the Uda...

Agriculture is one of the key sectors of the Sri Lankan economy, which contributes a significant percentage to its gross domestic product (GDP) and provides direct or indirect employment to a sizeable proportion of its population. Climate change involves long-term slow changes in climate, short-term year-to-year climatic variability and unpredictab...

The consequences of this are alarming and are already visible if one cares to take a closer look at many of the public-sector S & T institutions and universities where severe restrictions in capital investment have resulted in degraded infrastructure for meaningful research. As a result, in almost all disciplines of scientific research, the local s...

Effect of electromagnetic potential gradients on the uneven growth of shoot apex of Phaseolus vulgaris was investigated. Phaseolus vulgaris plants were fixed to a 3 - D clinostat with microelectrodes which applied an electromagnetic potential gradient (E.M.P.G.). The effect of gravity on the plant fixed to the 3-D clinostat was eliminated by rotati...

Tea [Camellia sinensis (L.) O. Kuntze] is one of the most important beverage crops in the world. The major tea-growing regions of the world are South-East Asia and Eastern Africa where it is grown across a wide range of altitudes up to 2200 m a.s.l. This chapter reviews the key physiological processes responsible for yield determination of tea and...

The objective of this Study was to elucidate the physiological basis of the significant yield decline that occurs during the fourth year of the pruning cycle of tea. Biomass partitioning, which was hypothesized to be a major factor in causing this yield decline, was measured by destructive harvests of entire tea bushes, in two contrasting, mature,...

ABSTRACT The study was conducted to evaluate some physiological characters of commercial sugarcane varieties under different growing conditions in Sri Lanka. A field experiment was conducted at the Sugarcane Research Institute, Uda Walawe (6o21’N latitude, 80o48’E longitude and 76 m altitude) using eight sug-arcane (Saccharum hybrid L.) varieties g...

Tea [Camellia sinensis (L.) O. Kuntze] is one of the most important beverage crops in the world. The major tea-growing regions of the world are South-East Asia and Eastern Africa where it is grown across a wide range of altitudes up to 2200 m a.s.l.. This paper reviews the key physiological processes responsible for yield determination of tea and d...

This study investigated the mechanisms of salt resistance of four maize (Zea mays L.) hybrids [cultivar (cv.) Pioneer 3906 and newly developed hybrids SR03, SR12 and SR13] during the first phase of salt stress. Plants were grown in aerated nutrient solutions at 1 mM Na+ (control) and 100 mM Na+ (salt stress). Stress was imposed in 25 mM steps and p...

Increasing atmospheric carbon dioxide concentration (Ca) is one aspect of global change that will have a significant impact on the productivity of agricultural crops. Crop yields have been shown to increase with increasing Ca. The magnitude of yield response to increased Ca could vary depending on genotypic and environmental factors. The objective...

Managed food production systems started with the early civilizations that saw humankind change its lifestyle from hunting and gathering of food to agriculture. This transformation was accompanied by a reduction in the number of plant species on which man depended for essential nutrition. Although the hunting and gathering stage was characterized by...

Anatomical and physiological characters of the leaf surface and its physico-chemical environment substantially influence the density and diversity of phyllosphere-inhabiting microorganisms, which may include natural antagonists of important pathogens. The objective of this investigation was to quantify the phyllosphere (i.e. leaf surface) microbial...

A substantial portion of rice in South Asia is grown in tropical and sub-tropical climates under relatively high temperatures (i.e. >30 °C). Increases in atmospheric carbon dioxide (Ca) concentration have been shown to increase total biomass and grain yield of C3 crops including rice. However, doubts have been expressed whether the expected yield i...

Smallholder cropping systems are a vital component in the agricultural sectors of tropical Asia, especially in the developing nations. These systems are important for producing food and providing a livelihood to a major proportion of the populations of Asia. While the rice systems, usually cultivated under puddled conditions are considered stable,...

Deep-rooted trees that dominate the multilayered homegardens (MHG) in Central Sri Lanka might adversely impact the catchment water yield because of their high transpiration rates. Our objectives were to quantify the water use of three representative tree species in an MHG and to identify the major determinants of transpiration. The species were Art...

The primary objective of the present study was to determine the capacity for soil fertility improvement in hedgerow intercropping systems (HIs) involving six different hedgerow species (Calliandra calothyrsus Meissner, Senna [Cassia] spectabilis (DC.) H. Irwin and Barneby, Euphatorium innulifolium (R.M. King and H. Rob.) H.B.K., Flemingia congesta...

Incorporation of tree hedges along contours has been proposed as a means of reducing soil erosion and increasing soil fertility of tea (Camellia sinensis (L.) O. Kuntz) plantations on sloping terrain in high-rainfall zones of Sri Lanka. Tea yields in these hedgerow intercrops are determined by the balance between the positive (i.e., increased soil...

Increasing air temperature (T) negates the positive effects of increasing atmospheric CO2 concentration ([CO2]) on rice in the tropics. We studied the impact of both increased T and [CO2] on spikelet sterility and grain yield of different medium duration varieties of indica rice (Oryza sativa L) under lowland field conditions using open top chamber...

The objective of the present paper is to determine the response of the physiological parameters related to biomass production and plant water relations in a standard Sri Lankan rice (Oryza sativa) variety (BG-300) to elevated CO2 (i.e. 570 µmol/mol). During two seasons, rice crops were grown under three different experimental treatments; namely, at...

Increasing atmospheric CO2 is recognized as a major aspect of global climate change that would have a significant impact on the productivity of major agricultural crops. Two field experiments were done, with the objective of quantifying the response of a short-duration rice (Oryza sativa) variety (BG-300) to elevated atmospheric carbon dioxide, in...