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This study was conducted to identify the dendrometric variables highly correlating with above-ground (AGB), below-ground (BGB) and total (TB) biomass of tea grown in Uva and Up Country Sri Lanka, develop allometric models to estimate AGB, BGB and TB of tea plants, and to investigate the applicability of already developed allometric models in other countries to Sri Lanka. Twelve experimental plots from TRIORCON field experiment at Tea Research Institute of Sri Lanka, and 18 farmer fields in Uva region, Sri Lanka were selected as the study sites. Representative tea plants were uprooted from the selected sites and seven dendrometric variables were measured. Fresh and dry AGB and BGB of the tea plants were determined. The best allometric models to predict AGB, BGB and TB using dendrometric variables were developed using multiple linear and non-linear regression analyses. Non-linear allometric models fitted best when predicting AGB and TB. Over 64% of total variability of AGB and TB was explained by these models using collar diameter at the soil level. Linear allometric fitted best when predicting BGB. Over 92% of total variability of BGB was explained by linear regression models using collar circumference, mainstem circumference, mean length and circumference at end of the primary branches. Leave-one-out cross validation showed strong positive (AGB and TB) and moderate positive (BGB) correlations between observed and predicted biomass values. Developed linear allometric models in comparison to those in literature showed better fit to data collected under Sri Lankan conditions and precisely estimated AGB, BGB and TB. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa L.) is the staple food in Sri Lanka and phosphorus (P) and potassium (K) are major nutrients for the rice plant. However, the variation of P and K contents (mg kg-1) in rice soils and rice grains as affected by agro-climatic zones (ACZs), water source used (i.e., major irrigation, minor irrigation and rain-fed) and cropping systems adopted (i.e., fallow, vegetable, perennials, other field crops) by Sri Lankan farmers are not well elucidated, and are thus investigated in the present study. A total of 200 rice soil and 230 rice grain samples across the country were collected from farmer fields, representing different ACZs, water sources used, and cropping systems adopted using a stratified random sampling approach. The total and available P and K contents in rice soil, and the P and K contents in rice grains were determined. The plant-available P contents in soil were similar among ACZs, water sources, and rice-based cropping systems. Exchangeable K content was higher in rice fields where vegetables were cultivated in the previous season. Grain P and K contents were similar among the water sources used and rice-based cropping systems. Grain P contents was the lowest in the Low country Wet zone. Soil available-P and total-P contents (r = 0.29, p < 0.0001), and grain P and K contents were positively correlated (r = 0.51, p < 0.0001). The knowledge generated in the present study is important in P and K nutrient management in rice cultivation in the country. [ABSTRACT FROM AUTHOR]

Vegetables are widely cultivated in high rainfall and mountainous regions in Sri Lanka with poor soil conservation practices. Accumulation of essential mineral and toxic trace elements in the soils and widely cultivated vegetables of this region are poorly understood. One hundred soil and vegetable (i.e. cabbage, carrot and potato) samples were collected at the time of harvest and analysed for element concentrations. Soils contained high concentrations of essential mineral (N, P, K, Cu, Zn and Mn) and toxic trace elements (As, Cd and Pb). When comparing edible parts, cabbage contained the highest concentrations of mineral and toxic trace elements, and potato contained the lowest. Irrespective of the crop, edible parts contained high concentrations of N, P, K (14–35, 2–6, 15–24 g/kg, respectively), and Cu, Zn, Mn (2.5–6.7, 11–30, 8–147 mg/kg, respectively). Vegetables also contained As, Cd and Pb (0.04–1, 0.02–0.15, 0.02–0.26 mg/kg, respectively), but did not exceed the maximum permissible limits. Irrespective of the crop, 36–64 kg N, 6–11 kg P and 35–45 kg K per ha were removed with the harvest. According to the current rate of vegetable consumption by Sri Lankans (i.e. 240 g fresh weight (FW) per day), per capita consumption of 0.05–0.2 mg Cu, 0.45–0.65 mg Zn and 0.5–2 mg Mn per day through these vegetables was observed, i.e. 5–23% Cu, 7.5–11% Zn and 22–87% Mn of the recommended daily intake. Vegetables grown in the region served as a key source of essential mineral elements. However, agronomic mitigation strategies are needed to improve soil health and sustainability of these cropping systems. [ABSTRACT FROM AUTHOR]

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 individually and together, and (b) genotypic variation of these responses. A three-factor factorial experiment considering the combination of CO2 concentrations and temperatures as the main-plot factor and eight sugarcane varieties as the sub-plot factor arranged in a split-plot design in open-top chambers. Plots in open field conditions were the negative control. The main plot factor had four levels, combinations of ambient/elevated CO2 concentrations (344-351/777-779 ppm) and ambient/elevated temperatures (34.9-35.6/36.6-38.4 °C). Significant treatment × variety interaction effects observed on the number of shoots per hill, sucrose% (Pol), and pure obtainable cane sugar (POCS) in cane juice. Genotypic variations were significant in all variables measured. Elevated Ta increased the number of shoots per hill in 4 out of 8 varieties. Biomass accumulation of sugarcane on the dry weight basis did not respond clearly to the simulated future climatic conditions. The response of Pol and POCS to ECO2 and the combination of ECO2 and ETa varied depending on varieties with decreased, increased, or no response. Notably, Pol and POCS in the variety SL88116, which had higher respective values at ambient and simulated future climatic conditions, were not affected by either ECO2 or ETa individually or in combination. The responses and the significant genotypic variation observed in sucrose accumulation to ECO2 and ETa, both individually and together, demonstrate considerable scope in sugarcane to breed varieties to maintain the stability of sugar recovery in CO2-rich warm climates. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 fertilizer treatments (with and without the applications of P and/or K). Phosphorus uptake rate, translocation of P and K from roots, and retranslocation of P and K from senescing leaves were reduced in drained soil compared with flooded condition. LD had greater- root length, root dry weight, specific root length (m g−1), and increased availability of P in soil than SD. Even though LD was better adapted to co-limitations of P, K, and moisture in soil than SD, those adaptive responses were not sufficient to increase the arrested growth, P and K nutrition when P, K and moisture supply was co-limited than their optimal supply. [ABSTRACT FROM AUTHOR]

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 selected set of crop management practices aimed at decreasing essential inputs such as water, synthetic pesticides and inorganic nitrogen fertilizer. The control treatment (T1) consisted of standard crop management including irrigation, chemical crop protection and inorganic fertilizer application. Adaptation system 1 (T2) included mulching with rice straw at 8 t ha-1 with 30 % less irrigation and crop protection and nutrient management as in T1. Adaptation system 2 (T3) included crop protection using a pretested integrated pest management package with water and nutrient management as in T2. In adaptation system 3 (T4), 25 % of the crop's nitrogen requirement was given as organic manure (compost) at 0.8 t ha-1 while 75 % was given as inorganic fertilizer with water management and crop protection as in T3. Durations of both pre- and post-flowering phases were reduced with increasing temperature. In the warmer (25.4-30.1 °C) yala season, seed yield (Y) of T1 decreased with increasing temperature at 366 kg ha-1 °C-1. However, in maha season, Y did not show a significant relationship across the narrower temperature gradient from 24.4 to 25.8 °C. Pooling the data from both seasons showed a second-order polynomial response with an optimum temperature of 26.5 °C. In addition to shortened durations, reduced crop growth rates and reduced pod numbers per plant were responsible for yield reductions at higher temperatures. In yala, yields of all adaptation systems at all locations were on par with yields of the respective controls. Furthermore, yala yields of T2 and T3 were less sensitive than T1 to increasing temperatures (265 and 288 kg ha-1 °C-1). In maha, T3 and T4 had greater yields than the control at the relatively cooler site while having lower yields than the control at the warmer site. Maha yields of T2 were on par with the control at both temperature regimes. While demonstrating the significant temperature sensitivity of mung bean yields, results of the present work showed that components of the tested adaptation systems could be promoted among smallholder farmers in Asia, especially in view of their long-term environmental benefits and contributions to sustainable agriculture in a warmer and drier future climate. [ABSTRACT FROM AUTHOR]

The present paper compares standard and novel methods for analysing aggregated patterns of plant death in designed field experiments; these methods include binomial (BN), beta-binomial (BBN), logistic-normal-binomial (LNB), BN models with random blocks, BN models with smooth-scale spatial components and principal coordinates of neighbour matrices (PCNM). PCNM is a relatively new technique used in ecology to determine how much observed variability can be explained by spatial and environmental variables, and has not yet been applied to agricultural studies. The survival data of two pasture species, collected from a designed field experiment that was replicated at multiple locations, were used. First, the occurrence of overdispersion was tested using the BN and BBN distributions. Goodness-of-fit tests proved that the BBN model provided a better description (better fit) of the observed data in some cases than did the BN distribution, indicating overdispersion was present. When overdispersion was not present, the BN distribution was adequate to describe the data, and the use of the BBN distribution was superfluous. It is then shown that the PCNM approach, the BN model with smooth-scale spatial components and the LNB model were able to account for some of the variation as spatial variability, thus reducing the species effect compared with that explained under the standard BN model. The amount of variation among species according to the BN model and the BN model with random blocks was similar. Therefore, it is argued that the novel PCNM approach warrants further testing when exploring the spatial variability in designed experiments in agriculture and using LNB, PCNM and BN with smooth-scale spatial components may provide better predictions of species effects than do other, more conventional, approaches. [ABSTRACT FROM PUBLISHER]