The present study was aimed at stimulating the growth and yield of Sri Lankan tea cultivar TRI 2025 grown in different climatic regions in the country. The model was developed and calibrated using weather, crop and soil data collected from different climatic zones. The model is designed to simulate shoot replacement cycle, leaf area of a shoot, shoot growth, dry matter partitioning and tea shoot yield. The model was validated using shoot development and growth data not used for model calibration. These validation data were collected from low, mid and high elevations representing temperature and rainfall gradients in the country. Model calibration showed that thermal time required to initiate the fish leaf, 1st, 2nd and 3rd normal leaf in a tea shoot from the time of natural senescence of the scale leaves were 129, 188, 235, 296 °C days, respectively, and a tea shoot reached the harvestable stage after 393 °C days. The model simulated leaf area (cm2) and fresh weight (g/m2) of tea shoots at different developmental stages and locations which were in good agreement with the measured values at the validation stage (R2 > 0.92 and 0.98, respectively). Similarly, simulated shoot yields (g/m2/month) at the validation stage were strongly correlated with the measured values (n = 12, R2 > 0.58, RMSE = 5–17 g/m2/month). Thus, the model can be used to estimate the shoot yield of tea cultivar TRI 2025 grown in different climatic conditions in Sri Lanka. Areas requiring further improvements to the model are also discussed.

Three field experiments were conducted to study the leaf and shoot expansion in tea [Camellia sinensis (L.) Kuntze] and their relationships with thermal time. The study site was Glen Alpine estate, Badulla, Sri Lanka located at an altitude of 1120 m above mean sea level (AMSL). The first experiment was carried out to develop a mathematical model to predict the area of an individual leaf and total leaf area of a harvestable shoot of widely grown tea cultivars namely, TRI 2025, TRI 2023, TRI 2043 in the Uva region. In the second experiment, the number of days required to initiate different leaves of a tea shoot of TRI 2025 was investigated. In the third experiment, the degree-days (thermal time) accumulated for producing different leaves and a harvestable tea shoot with three leaves of tea cultivar TRI 2025 were estimated. Stepwise regression resulted in a model with the product of leaf length and width to estimate the leaf area of a single tea leaf for all the evaluated cultivars with a high precision (R 2 =0.99). From the bud break, 128.5, 187.5, 234.5, 295.5 ºC days were required to initiate the fish leaf, first normal leaf, second normal leaf and third normal leaf, respectively, of the tea cultivar TRI 2025. A harvestable tea shoot was produced after accumulating 392.5 ºC days by the cultivar TRI 2025.

The introduction of synthetic fertilizers has brought various types of detrimental impacts and people attempt to find out eco-friendly alternatives to chemical compounds for minimizing the dependency on synthetic chemicals. In this context, the exploitation of alternative growth substrates is of great interest like compost-like substrates. Therefore, the study was made to study the effect of compost and different levels of NPK fertilizer on growth and yield performance of three different recommended tomato varieties under different field conditions at Walimada, Sri Lanka. Treatment consisted of three tomato varieties (Roma, Thilina, and T 245) and five different fertilizer levels including compost & NPK fertilizers. Treatments were considered as control (without compost and NPK fertilizer), 100 % of compost, 100 % of recommended dosage of NPK fertilizers, 50% of compost with 50% of recommended dosage of NPK fertilizers, and 75 % of compost with 25 % of recommended dosage of NPK fertilizers. Field management practices were practiced according to the recommendations given by Department of Agriculture of Sri Lanka. Effect of different fertilizers on vegetative growth, reproductive growth and yield of three tomato varieties was evaluated. According to results, there was a significant different among control treatment and treatment consisted with 50% of compost with 50% of NPK fertilizer treated Roma and Thilina on days to attained 50% of flowering. There were no significant differences between treatments consisted with 100% of NPK fertilizer with 50% of compost and 50% of NPK fertilizer on days to attained 50% of flowering, number of fruit per plant and yield of varieties except the yield of Roma variety (P<0.05). Results showed that all treatments except chemical fertilizer application improved the soil organic C, total N, P and K status. Increase in microbial biomass C and N was observed in soils receiving organic manures only or with the combined application of organic and chemical fertilizers.

This study was conducted to investigate the allopathic effects of Cyperus rotundus and Cynodan dactylon (L.) extracts on seed germination and seedling growth characters of lettuce (Lactuca sativa). Four concentrations (5, 10, 15 and 20 %) of whole plant aqueous extracts of both weeds were tested for assessing their allelopathic effect on seed germination and seedling growth of Rapido 344 lettuce variety. This study was conducted at Biology Laboratory of Uva Wellassa University, Sri Lanka in 2014 and experimental units were petri dishes in depths and diameters of 2 and 5 cm, respectively. The shoot and root length, dry weight, germination percentage were measured. The experimental results revealed that all the concentrations of both the weed extracts had inhibition effect on germination percentage, shoot & root length and dry weight of lettuce. The inhibitory effect of the extracts was concentration dependent. However, at 5% of C. dactylon extract did not significantly affect on seed germination and growth of seedlings. The highest degree of growth inhibition was observed in 20 % of both weed extracts.

Pineapple is the third largest agricultural product after tea and coconut, which has a demand in export market. Although the nature has blessed with an ideal climate for growing wide range of delicious fruits including pineapple, Sri Lanka is not in a position to meet the growing demand. Therefore, that is very important to study about the export performance of fresh pineapple in Sri Lankan context. The general objective of this study was to identify the determinants of contribution of pineapple growers for export volume in Gampaha district. A structured questionnaire based survey was carried out to collect the data from random sample of 130 pineapple growers in Dompe and Diulapitiya DS divisions in Gampaha district. The result of Tobit model revealed that the contribution of pineapple growers for exports of pineapple was significantly determined by the age of grower, experience of grower, pineapple cultivated land extent, amount supply for local market, domestic price and export price. In the study of specific objectives, there was an upward trend from 1990 to 2004 and trend was declined from 2004 to 2012 with some fluctuations. The reason was that the export of preserved pineapple has shown a significant improvement within last few years and in developing the forecasting model for future forecast and the generalized model for current situation analysis for fresh pineapple exports in Sri Lanka. Vector Autoregressive Model (VAR) was used to develop the forecast model and the generalized model was developed without considering the time factor. The result revealed that the export of fresh pineapple was significantly determined by the average exchange rate and the domestic price.

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