Rice Production in Tonle Sap Floodplains in Response to Anthropogenic Changes in Hydrology, Climate, and Agronomic Practices

Abstract

Rice is the most important agricultural commodity in Cambodia as food and source of livelihood. Majority of rice production happens around the Tonle Sap floodplains sustained by the sediment-rich flood from the Mekong River. With the increased construction of hydropower dams upstream, the natural flow of water, organic materials, and fish species delivered to the Tonle Sap Lake is altered. While these changes open up more areas for rice cultivation especially during the dry season, the quality of the sediments is expected to decline. Moreover, drought is becoming a frequent occurrence and temperature is increasing. This study examined how the rice cultivation in the Tonle Sap floodplains is impacted by the hydrological changes, climate, and agronomic practices. Specifically, we 1) assessed the impacts of the increasing presence of dams on the timing and location of rice cropping, and 2) tested and applied an ecophysiological crop model to simulate the effect of changes in hydrology, agronomic practices, and increasing temperature on rice production in Tonle Sap floodplains. Spatio-temporal effect of dams in rice production was identified following the PhenoRice algorithm, focusing on two rice-growing provinces, Kampong Thom and Battambang, using time-series satellite images from 2001 to 2019. Yield simulations to determine the effect of hydrology, agronomic practices, and increasing temperatures were executed in ORYZA (v3) Rice Model, validated by actual field measurements and personal interviews with farmers. The model estimated the total production per planting time and yield responses to varying soil organic carbon content, N application, and temperature. PhenoRice results showed that the rice cultivation increased with lake extent during dry season. In addition, location and the timing of crop establishment were adjusted depending on the availability of floodwater. The identified rice areas from PhenorRice were used to estimate the total production in ORYZA (v3), as influenced by changing climate and hydrology. The rice model predicted that the yield penalty with decreasing soil organic carbon was greater than the yield gained from increasing it. We determined the optimum N required and efficient timing of applications to get the maximum attainable yield. The model also showed that increasing temperature decreases yield but drastic loss occurred when temperature was increased by more than 2 °C. This study provides information on how hydrology, climate, and agronomic practices impact rice production in Cambodia that are vital for making important decisions related to water management and food security in the Lower Mekong Region.