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-25 and -31% in grain yield with increase of 1, 2, 3, 4, 5°C temperatures, respectively. In the same region, and at the same temperatures but at 550 ppm, these yield changes were 12, 7, 1, -5 and -11%, respectively. Similar interaction could be noted for other regions as well. Thus, in eastern and northern regions, the beneficial effect of 450, 550 and 650 ppm CO2 was nullified by an increase of 1.2-1.7,3.2-3.5 and 4.8-5.0°C, respectively (Table 2.1). In southern and western regions, positive CO2 effects were nullified at temperatures lower than these. It can be concluded that in improved management conditions, the regions, such as southern and western parts of India, which currently have relatively lower temperatures, are likely to show less increase in rice yields under climate change compared to northern and eastern regions.

The effect of sowing at different dates on the yield of wheat was simulated for different locations. Areas having higher potential yields of wheat had greater reduction in yield per day delay in sowing from the optimal date. A few locations (north eastern parts) showed a small yield reduction with delayed sowing. With the temperature rise, the adjustments in the date of sowing to have the similar weather conditions can be ensured, but it can imbalance the cropping system schedule, which is also important for developing countries where intensive cultivation is practiced on small and marginal lands.

Aggarwal and Kalra (1994), by using WTGROWS, demonstrated the shift of iso-yield lines of wheat in India with 425 ppm of CO2 concentration and 2°C rise in temperature. The rise in carbon dioxide concentration of the atmosphere effectively influences the productivity of crop plants. For these studies, open top chamber facilities have been developed at various Institutes in India. In these chambers, the coupled weather and canopy environment also change along with CO2, and thus the differences in growth and yield of crops become complex function of these parameters. To work out the impact of carbon dioxide and temperature only, Free Air Carbon Dioxide Enrichment (FACE) facilities have been established at the Indian Agricultural Research Institute, New Delhi in collaboration with National Physical

Table 2.1 Temperature increases (°C) that will cancel out the positive effect of CO2 in different regions at two levels of management

Management

CO2 concentration

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