A middle path for Sri Lankan agriculture: Sustainable intensification – II

By Professor W.A.J.M. De Costa
Senior Professor and Chair of Crop Science, Faculty of Agriculture, University of Peradeniya

Strategies to address the challenges posed by climate change on Sustainable Intensification

Cropping systems in all climatic zones of Sri Lanka at the lower (< 600 m above sea level) elevations are highly vulnerable to increasing temperatures and rainfall variability, which are two of the key features of climate change. Even those at higher elevations are not immune to these persistent trends in the climate because the crops and cropping systems at these elevations have evolved to be adapted to a lower temperature regime, which has been shown to be increasing at a faster rate than the temperatures at the lower elevations. Accordingly, incorporation of heat tolerance to all crops grown in Sri Lanka via a focused and sustained plant breeding effort is an essential medium-to long-term need.

It is important to note that unlike many new technologies that can be readily imported from overseas, new crop varieties have to be developed within Sri Lanka for them to be productive under the specific agro-environmental conditions (e.g. temperature, day length, rainfall regime, potential pests and diseases, soil conditions such as pH etc.). Accordingly, development of new crop varieties has to be based on the crop germplasm available in Sri Lanka. Even though foreign varieties with the required genes for heat tolerance may be incorporated via reproductive crossing or genetic engineering, such hybrid plants need to be genetically ‘purified’ and extensively tested under Sri Lankan agro-environmental conditions before being released to farmers. Therefore, given the challenging nature of the genetic and plant physiological modifications that need to be engineered in crops, new heat tolerant varieties of major food crops are unlikely to be released to Sri Lankan farmers in the near future.

Agronomic interventions to reduce the energy load on crops and soils should be introduced concurrently with the plant breeding efforts. In this regard, incorporation of shade into agricultural fields via suitable tree and shrub species, preferably leguminous trees, will be a win-win situation where several requirements for SI can also be fulfilled. The reduced radiation energy on the crop surface will reduce canopy temperature and thereby reduce the incidence of heat stress. Concurrent reduction of evapotranspiration rates will contribute to conservation of water and thereby increase the crops’ capacity to avoid possible drought periods. In addition to the amelioration of the crop’s microclimate, when properly managed through lopping and pruning, the shade trees can provide a supply of organic material to the soil and thereby ensure nutrient recycling.

A mulch of organic material will not only provide protection to the soil against building up excessive soil temperatures, but also help in conserving soil moisture while preventing erosion. Furthermore, the input of organic materials and their decomposition will bring about significant changes in the soil microbial population and thereby set in motion many of the soil biological, physico-chemical and ecological processes which are required for sustained regeneration of soil fertility. Incorporation of leguminous tree/shrub species will enable the harnessing of their ability to fix atmospheric nitrogen and thereby potentially reduce the requirement of inorganic nitrogen fertilizer.

Climate change is likely to accelerate crop developmental processes via increasing temperatures. While increasing temperatures have the possibility to increase crop growth rates in the currently cooler climates via increased photosynthetic rates, they are most likely to decrease growth rates in crops in the currently warmer climates via decreased photosynthetic rates and increased respiration rates. Similarly, all soil biological processes including decomposition of added organic material and release of nutrients through mineralization will be accelerated by the increased temperatures. Increased frequency of intermittent and terminal droughts will exert further limitations on crop growth and yields. These impacts of climate change will require careful fine tuning of the cropping systems and their management to increase resilience.

Many of the SI strategies have synergy with increasing crop resilience to climate change. For example, increasing water use efficiency of crops increase their drought tolerance. Strategies for increasing nutrient use efficiency can be synergised with strategies to reduce the emission greenhouse gases such as nitrous oxides and methane. Alternative water management strategies such as Alternate Wetting and Drying (AWD) and aerobic rice, which are primarily designed to reduce the total water use in rice cultivation, concurrently reduce methane emissions from rice fields. On the other hand, increased additions of organic material to crop lands could increase emissions of carbon dioxide, which is the major greenhouse gas that contributes to global warming and climate change. Therefore, careful management of different SI strategies is needed to maximize their benefits while minimising their adverse impacts.

Water management will have to play a key role in increasing climate resilience of Sri Lankan Agriculture. Climate models predict that the currently ‘wet’ areas (e.g. wet zone of Sri Lanka) could experience increased rainfall in a future climate, whereas the currently ‘dry’ areas (e.g. dry and intermediate zones of Sri Lanka) could experience decreased rainfall (termed as ‘wet getting wetter and dry getting drier’). Furthermore, climate models predict increased rainfall variability leading to a greater frequency of high rainfall events which are spaced apart over time. This means that there will be more extreme rainfall events leading to floods as well as more droughts in a future climate. In this regard, it is important to have a broad strategy to manage the river basins and the network of tank cascade systems in Sri Lanka to maximise the capture of excess water during high rainfall events and seasons, and ensure a controlled release to crop production and other purposes (e.g. hydropower generation) during dry periods. Rehabilitation of the networks of minor tanks in the cascade systems of major river basins such as the Mahaweli and Walawe, which had been abandoned or neglected with the implementation of the major irrigation schemes in these basins, could be a key initiative to ensure maximum use of rainwater that Sri Lanka receives in a future climate and thereby increase climate resilience in the cropping systems.

Concluding remarks

Sri Lankan Agriculture is at a critical juncture at present with a huge cloud hanging over its sustainability and capacity to ensure national food security in the face of biophysical challenges such as climate change, decreasing soil fertility and stagnating yields and socio-economic challenges such as increasing costs of production and decreasing farmer profits. Meeting these challenges require paradigm shifts in the way all stakeholders (i.e. farmers, researchers, extensionists, policy makers and all others in the entire value chain) approach the task of producing sufficient and safe food to the Sri Lankan people in an economically and environmentally sustainable manner. This situation presents an opportunity to have a new perspective and seek innovative and ‘out-of-the box’ solutions, especially while the Sri Lankan Agriculture is struggling to recover from the upheavals of recent policy decisions. In this regard, Sustainable Intensification offers a strategy and a set of practices among many others to all stakeholders, especially the farmers, researchers, extensionists and policy makers, to serious consider implementing. It is significant to note that Sustainable Intensification is increasingly adopted by a wide range of countries in all continents. Hence, it is appropriate that Sri Lanka is not left behind, but explores the potential of Sustainable Intensification for resolving the critical issues that its food production system and its associated value chain faces.

This article is adapted from a keynote address delivered by the author at the 3rd International Symposium on Agriculture organized by the Faculty of Agriculture of the Eastern University of Sri Lanka on the theme ‘Self-Sustaining Agriculture: Way forward for food security and safety’ on the 9th of March 2023. It has incorporated valuable comments on a first draft from Raj Gonsalkorale, Suchira Peiris, Vijith Gunawardena and Parakrama Jayasinghe.