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 this study was to determine the response of phenology, growth and yield of potato to increasing temperature in the upcountry of Sri Lanka, which is the principal potato-growing region of the country. Furthermore, effectiveness of an integrated pest management (IPM) package and a modified soil management regime aimed at soil moisture conservation and reducing excessive use of synthetic pesticides and fertilizers were also tested. A field experiment was conducted during Maha 2012/2013 at Sita-Eliya (SE) and Rahangala (RG) of Sri Lanka, which represented a temperature increase of 5.2 o C from 15.1 o C to 20.3 o C. Potato (Solanum tuberosum L.) variety Arnova was grown with four treatments: T 1-Recommended crop management; T 2-Mulching with recommended crop protection (non-IPM) and fertilization (100 % inorganic fertilizer); T 3-Mulching with IPM and recommended fertilization and T 4-Mulching with IPM plus 25% of N provided as organic amendments. Crops matured a month earlier at the higher temperature site RG, i.e. in 81 days as compared to 111 days at SE. However, the thermal duration from planting to maturity was approximately similar at both sites (i.e. 1689 o Cd and 1662 o Cd at SE and RG, respectively). Crop growth rates were higher at RG, thus compensating for the lower crop duration so that total dry weights at harvest and tuber yields of T 1 did not differ significantly between the two sites. At both sites, the tuber yield of T 2 did not differ significantly from T 1. The growth and yield response to mulching was greater at RG due to the lower rainfall and low soil fertility as compared to SE. The IPM treatments (i.e. T 3 and T 4) resulted in an effective control of the incidence and severity of late blight at SE but not at RG, where the prevailing temperature regime was optimum for spore formation of the late blight pathogen. Consequently, while the tuber yields did not show significant inter-treatment variation at SE, at RG the IPM treatments (i.e. T 3 and T 4) showed significantly lower yields than the non-IPM (T 1 and T 2) treatments. Analysis of the interrelationships between tuber yield, yield components and growth data showed that potato yields of the present study were primarily source-limited.

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 season 2012/2013 at five locations (Rahangala, Peradeniya, Kundasale, Mahailluppallama and Kilinochchi) in Sri Lanka representing an environmental gradient together with three soil management systems (SMS) in a Randomized Complete Block Design (T1-standard management; T2-standard management plus mulching; T3-mulching + 75% of N supplied by inorganic fertilizer + 25% N from organic manure). The rate of progress to maturity showed a significant positive linear relationship with the mean location temperature (MLT), thus shortening the crop duration with increasing temperature. Leaf area index (LAI) and total dry weight (TDW) at 50% flowering in all SMSs showed significant second-order polynomial relationships with MLT. The optimum temperatures for the maximum LAI and TDW were 23.0 and 22.8 o C, respectively. Total dry weight of T3 and T2 were 22% and 9% greater than T1 thus, showing the beneficial effects of mulching and adding organic manure. The grain yield of maize also showed a significant second-order polynomial relationship with MLT with an optimum temperature of 22.5 o C. It is notable that all major maize growing regions of Sri Lanka (i.e. dry and intermediate zones) have temperatures, which are above the respective optima for growth and yield of maize. Furthermore, the fitted polynomial relationships showed that the rates of decline in maize yield (i.e. 489 kg ha-1 o C-1), LAI (0.98 o C-1) and TDW (1390 kg ha-1 o C-1) with each 1 o C increase in the supra-optimal range of temperatures were greater than the corresponding rates of increase in the suboptimal range (15 kg ha-1 o C-1 , 0.33 o C-1 and 330 kg ha-1 o C-1 for yield, TDW and LAI, respectively). Therefore, increased temperature due to future climate change will have significant negative impacts on maize yields in Sri Lanka, unless more heat-tolerant varieties are bred and introduced.

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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 develop crop-specific simulation models to predict phenology, canopy growth, and yield performance of maize, mungbean, and tomato crops grown in the tropics, with special relevance to locally adapted inbred germplasm. The developed models consisted of sub-models to simulate canopy growth, radiation interception and conversion, and dry matter partitioning. All sub-models were parameterized by detailed measurements of leaf growth, dry matter accumulation, and partitioning on locally adapted varieties of the three crops over two cropping seasons. The same crop varieties were established in a multilocational field experiment spanning a sufficiently wide temperature gradient over four cropping seasons for model validation. Models were validated by comparing model predictions of phenological development and yield against field observations and additional secondary data from the literature. Overall, simulated phenological development (R 2 >0.5, RMSE<5 days for all three crops) and yield (R 2 >0.5, RMSE<68, 48 and 476 g/m 2 for maize, mungbean, and tomato, respectively) of the three crops were in agreement with the observed data under a wide range of environmental conditions. These modelling approaches can be successfully applied to open-pollinated (maize) and inbred varieties (mungbean and tomato) growing under the farmer fields in tropical South Asia.