การเปลี่ยนแปลงความเข้มรังสีแสงอาทิตย์ต่อปริมาณแสงที่ใช้ในการสังเคราะห์แสงของข้าวนาปีในจังหวัดเชียงใหม่

Abstract

This research examined the variation of solar radiation affecting photosynthetically active radiation of in-season rice in Chiang Mai province. The objectives of this study were 1) to study the changes in solar radiation intensity in spatial and time dimensions of Chiang Mai province and 2) to study the photosynthetically active radiation of in-season rice according to the growth period in Chiang Mai province. The study was used statistical methods and geospatial techniques and TERRA/AQUA MODIS satellite toanalyze spatial solar radiation intensity. The results showed that changes in surface solar radiation in time dimension were characterized by both positive and negative changes. The downward trend was detected in areas ofhigh human activity. In natural areas or low human activity areas, surface solar radiation tends to increase. For changes in the spatial surface solar radiation, the amount of aerosols in the atmosphere and land use are influence factors. It was found that the results of the analysis of the relationship between surface solar radiation and aerosol optical thickness showed an inverse relationship. In addition, the relationship between the aerosol optical thickness and land use characteristics also helps to understand the relationship of land use that affects the increase or decrease of aerosols, which influences the change of surface solar radiation. The aerosol optical thickness was directly relation to agricultural areas and building-up areas, whereas, it is an inverse relationship with the forest area. The empirical evidence of the first objective was applied to study the influence of positive and negative surface solar radiation on photosynthesis of the in-season rice. The result showed that the amount of light for the highest photosynthesis efficiency in the photosynthesis of in-season rice is lower during the June period (Representative of foliar and stem growth stage), in August period (Representative of reproductive stage of growth) and October period (Representative of the seed growth stage) in the entire rice cultivation field in Chiang Mai province. This is partly due to the terrain of Thailand and the changing environment in the present. Therefore, the approach to mitigate the effects of changes in solar radiation intensity can be laid out in two measures. Firstly, preventive measure is increasing forest areas in both urban and rural areas. Secondly corrective measures are enhancing the efficiency of rice growth by adjusting the rice planting calendar, improving rice varieties suitable for the environment and providing climate knowledge to agencies as well as adapting to climate change for the future.