Exploitation of differential temperature-sensitivities of crops for improved resilience of tropical smallholder cropping systems to climate change: A case study with temperature responses of tomato and chilli

Abstract

Increasing air temperatures due to long-term global climate change are predicted to exert substantial negative impacts on a majority of agricultural crops in the tropics, where most smallholder farms have a mixture of crops. Modification of the composition of cropping systems by incorporating crop species with greater growth and yield performance at higher temperatures is an important adaptation option. Accordingly, the principal objective of the present work was to demonstrate the feasibility of utilizing the differential temperature sensitivities of tropical crops to increase resilience of smallholder farming systems in the tropics to climate change, taking tomato and chilli in a case study. Tomato (cv. Thilina) and chilli (cv. MI-Green) crops were grown with adequate water, nutrients and recommended crop protection in a multi-locational field experiment traversing an altitudinal gradient (15–1200 m), which represented a gradient in seasonal mean temperature (Ta) ranging from 18.7 to 30 °C, over four consecutive seasons (Dec. 2012–Oct. 2014) in the humid- and sub-humid zones of Sri Lanka. Temperature response functions were estimated by linear regression of growth and yield parameters against Ta. Across the tested range of Ta, fruit yield of tomato showed a significant negative linear trend with increasing Ta (@ 2.83 Mg ha−1 °C−1) while the pod yield of chilli showed a significant positive linear trend (@ 0.51 Mg ha−1 °C−1). While the total biomass accumulation followed the same trend as fruit/pod yield, the harvest index of both crops showed significant negative trends, thus indicating the sensitivity of reproductive processes to increasing temperature. In tomato, fruit yield was significantly positively correlated to individual fruit weight, which decreased significantly with increasing temperature. In contrast, in chilli, pod yield was significantly positively correlated to number of pods per plant, which increased significantly with increasing temperature. These findings demonstrate the possibility of increasing the resilience of annual cropping systems in the tropical zone to future climate change by modifying their species composition via replacement of crops that are sensitive to higher temperatures (e.g. tomato) with those that are tolerant (e.g. chilli). The corresponding response functions to seasonal temperature extremes showed that biomass production, its partitioning to yield and yield of both crops were more sensitive to increases in seasonal mean daytime maximum temperature than to increases in night-time minimum temperature. However, yield responses to the diurnal temperature difference showed that differential sensitivity of the two crops to night-time minimum temperatures also played a significant role in determining their yield responses. These findings are useful in designing future cropping systems with greater resilience to climate change.