• Temperature and rainfall are key climatic factors influencing rice yield variation in Sri Lanka
•  Stronger focus needed on both below and above-ground conditions
•  Site-specific macro-micro nutrient mgt needed  

Improved crop management practices introduced in Sri Lanka over the past two decades have not led to significant increases in rice productivity in more than 90 per cent of the tested variety-location-season combinations, indicating a widespread stagnation in rice productivity despite advancements in the recommended management practices. Therefore, there is a clear need to identify and develop more effective crop management strategies to overcome this stagnation and enhance future rice productivity.

These findings and recommendations were made in a research article on the "Impact of improved crop management practices over the last 20 years on rice productivity in different climatic regions of Sri Lanka" which was authored by M N Sudusinghe, D Kumarawansha and L D B Suriyagoda, J Senanayake and T, and H K Kadupitiya and A Abesekara and published in the Ceylon Journal of Science in June 2026.

Rice is the staple diet of Sri Lankans and the single most important crop, accounting for 14% of the total land area. The average extent sown with rice is approximately 807,000 ha during the Maha season, while 481,000 ha are sown during the Yala season. Sri Lanka produces 4.69 million metric tonnes of rough rice per year, and the Nation is self-sufficient in rice.

Over the years, rice crop productivity in the country has increased, e.g. the yield of rice has risen. Despite this productivity increment, the harvested extent has not significantly changed. This implies that the increase in national rice production was mainly attributed to productivity related improvements. According to the predictions, the local demand for rice in Sri Lanka will increase at 1.1% per year, and to meet this demand, rice production needs to be increased at a rate of 2.9% per year. The demand for rice is increasing gradually due to the increase in the population, the shifting of food habits from wheat flour to rice, and the increasing demand for other rice-based products. With the increasing local demand for rice, elevating the productivity is crucial. To meet the future rice demand, it is recommended to focus on increasing land productivity rather than expanding the cultivated extent. However, since 2010, the productivity of rice has plateaued. Moreover, the actual productivity of rice is still far less than the potential productivity.

For any given crop, major factors affecting crop productivity are genetics, the natural environment conditions, and crop management practices. Apart from genetics and the natural environment, the implementation of improved management practices with time, such as access to quality seed paddy, the use of new technologies for land preparation, pest and disease management, and water management, and decision making based on precise weather predictions can increase rice crop productivity. Enhanced management practices have been implemented over the years; however, whether they have significantly influenced improving rice crop productivity is not known. One approach to isolating the effects of management and environmental changes, while minimising genetic variation, is to evaluate the performance of a single variety grown continuously in the same location over time. In order to test this, an analysis of the data collected from a single rice variety grown in one location over an extended period of time is required. The data and information available in the research managed as the National Coordinated Rice Varietal Testing (NCRVT) program of the RRDI meets and satisfies this requirement.

Materials and methodology

Sudusinghe et al.'s study was conducted using rice crop productivity data generated under the NCRVT program at 12 research stations belonging to the Department, representing the major rice-growing agro-climatic zones. According to the climate classification, the stations at Sammanthurai, Aralaganwila, Ambalantota, Mahailluppallama, Murunkan, Paranthan, and Vavuniya are situated in the Dry Zone, while the stations at Girandurukotte and Bathalagoda are located in the Intermediate Zone, and the stations at Bentota, Bombuwala, and Labuduwa are all within the Wet Zone. Only the rice varieties used as the standard checks in the NCRVT program representing different maturity durations were used, i.e., Bg300 and Bg352 were selected as the short-duration rice varieties, and Bg358 and At362 were selected as the medium-duration varieties.

Daily weather data, namely, maximum and minimum temperatures and the rainfall of all the locations, were obtained from 1998 to 2020 from the NRMC. The arithmetic average of the daily minimum and daily maximum temperatures was considered as the daily-mean temperature.

The average of the daily minimum, mean, and maximum temperatures over a season was considered as the average seasonal - minimum, mean, and maximum temperatures, respectively. The difference between the seasonal maximum and seasonal minimum temperatures was considered as the temperature difference of that season. The rainfall and temperature data from the date of crop establishment until harvest were considered as the season for each variety, location, season, and year.

Results

Changes in rice productivity over time

Regression analysis for a given variety in the same location in the same season across years revealed that productivity has not changed over the years for 90% of the situations, with only a few exceptions.

Mean productivity of different rice varieties in different seasons, locations, and climatic zones

The mean productivity of different varieties in different locations and seasons varied. When comparing climatic zones, crop productivity was lower in the Wet Zone than in the Intermediate and Dry Zones. When comparing locations, particularly during the Maha season, Murunkan recorded the highest productivity for all the varieties. When comparing varieties, Bg362 outperformed the other three varieties tested in both the seasons and the three climatic zones.

Relationships between rice productivity and the weather parameters

The average maximum temperature and the temperature difference had significant positive correlations with rice crop productivity. The average minimum temperature and rice crop productivity were negatively correlated for Bg358 and Bg362, while the other varieties were not responsive. However, the average seasonal temperature did not have a significant correlation with crop productivity.

Discussion

Among the 96 location-season-variety combinations tested, rice productivity has changed with time only in nine combinations while stagnating in 87 combinations. The observed variation in rice productivity change over time (increase, decrease or stagnation) may have several reasons.

Possible reasons for yield stagnation

Despite the advancements made in management practices over the last two decades, the productivity of popular rice varieties has stagnated over time in many locations representing the Dry, Intermediate, and Wet Zones, even under research-managed conditions. This productivity stagnation over time suggests that those recommended management practices are not technically sound enough to improve productivity in rice. Therefore, whether improved technologies are needed to sustain productivity is a question.

The key improved management practices introduced during the period considered were nutrient management strategies, water management decisions, and pest and disease control methods. Additionally, the accessibility to weather forecasts and the accuracy of those predictions have also been improved during this period. Considering the improvements needed to be made in rice crop productivity and fertiliser-use efficiency, the Department has introduced a comprehensive fertiliser recommendation in 2001, followed by a revised recommendation in 2013 based on the climatic zone, the age-class of the rice varieties grown, and access to irrigation water. This includes the application of Nitrogen, Phosphorus, Potassium, and Zinc-containing-fertilisers as well as the incorporation of organic matter into the soil. By aligning fertiliser application plans to specific soil and climatic conditions of different regions, it is expected to optimise nutrient management in rice fields. However, all these fertiliser recommendations may be related to enhancing fertiliser use efficiency, which is environmentally friendly while reducing the cost of fertiliser and sustaining the present productivity, but not to enhance productivity.

Irrigation water management is another critical factor for rice productivity, as it directly influences crop growth However, water is well managed in NCRVTs as they are conducted in research stations. Therefore, water management has minimal influence on the change in productivity over time in NCRVTs. Continuous efficient water management influences sustaining productivity, but not decreasing productivity over time.

There were numerous initiatives, such as Integrated Weed Management, Integrated Pest Management, and the continuous development of more effective agrochemicals during the past two decades. However, their influence on productivity enhancement over time appeared minimal, they have definitely sustained productivity without decreasing over time. Although local research and development efforts on these issues are ongoing, progress remains slow. Therefore, the prevalence of biotic stresses in the rice sector may have also contributed as a barrier to improving productivity.

Given these complexities, it is evident that further improvements in technically sound rice crop management practices are essential to overcome yield stagnation in Sri Lanka. A stronger focus on both below-ground and above-ground conditions is necessary. Climate-resilient management strategies such as innovative management practices, precision agricultural tools, and advanced weather forecasting could offer valuable solutions. Further improvement in site-specific nutrient management, considering both macro and micro nutrients, is also important.

Relationship between weather parameters and the yield

Temperature and rainfall are key climatic factors influencing rice yield variation in Sri Lanka. Both variables have complex, non-linear effects on rice crop production. Their effects are not only stage-specific but also highly interdependent, depending on the timing, duration, and intensity of the exposure.

Within the tested range of temperature, higher rice crop productivity was observed in locations with higher maximum temperatures and a higher difference in the daily maximum temperature and the minimum temperatures. Temperature affects all stages of rice crop growth, from emergence to ripening and grain maturity. An increase in the maximum temperature in the sub-optimal range at the vegetative stage increases the rate of photosynthesis, however shortening the rice crop life cycle. The correlation between the minimum temperatures and crop productivity was negative. An increase in the minimum temperatures leads to an overgrowth of rice plants, decreasing the amount of incoming solar radiation on the earth’s surface, ultimately leading to a negative rice crop growth. Temperatures above the optimal range may cause negative implications for Sri Lankan rice crop production, as the predicted climate change would cause more locations and/or seasons to be in the supra-optimal range of temperatures for rice. Therefore, rice crop productivity is determined by the maximum temperatures, the minimum temperatures, and the difference between the maximum temperatures and the minimum temperatures, irrespective of whether these temperatures are in the sub-optimal or supra-optimal range for rice, as well as the development stage of the rice crop.

Rainfall has an impact on all stages of rice crop growth. Among those, rainfall has a positive impact on rice crops during the heading and flowering stages of the reproductive phase. In addition, rainfall hurts rice crops at the milking and dough stages during the ripening phase, potentially leading to reduced grain quality and yield (a Thai study). It is also important to consider the interactive effects of temperature and rainfall. e.g., high temperatures combined with water scarcity can exacerbate heat stress, while excess rainfall during high-humidity periods can worsen disease outbreaks. Increasing temperature can directly enhance the hatching rates of pests (a European study) and, in the presence of moisture, increase the germination and proliferation of fungal spores. Additionally, elevated temperatures combined with sufficient rainfall would provide favourable conditions for weed growth. These interactions underscore the importance of integrated climate-smart agricultural practices to sustain rice yields under changing climatic conditions.