Crop Productivity

Increase in atmospheric carbon dioxide has a fertilization effect on crops with C3 photosynthetic pathway and thus, promotes their growth and productivity. On the other hand, an increase in temperature, depending upon the current ambient temperature, can reduce crop duration, increase crop respiration, alter photosynthate partitioning to economic products, effect the survival and distributions of pest populations thus developing new equilibrium between crops and pests, hasten nutrient mineralisation in soils, decrease fertilizer use efficiency, and increase evapotranspiration. Indirectly, there may be considerable effects on land use pattern due to availability of irrigation water, frequency and intensity of inter- and intra-seasonal droughts and floods, and availability of energy. All of these can have tremendous impact on agricultural production and hence, food security of any region.

Wheat growth simulator (WTGROWS), developed at IARI, New Delhi, has been extensively tested for different agro-environments (Aggarwal and Kalra 1994). In past, it has been successfully used for the resource management, forecasting of wheat yields and climate variability related studies. Using WTGROWS, a strong linear decline in wheat yield was noticed with the increase in January temperature. For every degree increase in mean temperature, grain yield decreased by 428 kg/ha. Inter-seasonal climatic variability analysis carried out through yield response of wheat indicated that impact of the variability was lowest for Kota and highest for Solapur. Inter-seasonal climatic variability has been characterized through growth and yield response under different production environments, which clearly indicate the use of crop model as an indicator of climatic variability/change.

The change in rice yields at improved level of management with change in temperature and CO2 is plotted in Fig. 2.1. Increase of 1°C temperature without any increase in CO2 resulted in 5, 8, 5 and 7% decrease in grain yield in north, west, east and southern regions, respectively. Increase of 2°C temperature resulted in 10-16% reduction in yield in different regions, while a 4°C rise led to 21-30% reduction. Sinha and Swaminathan (1991) reported that a 2°C increase in mean air

Fig. 2.1 Points that must be considered while doing the study of impacts of climatic changes on agriculture

Fig. 2.1 Points that must be considered while doing the study of impacts of climatic changes on agriculture

temperature could decrease rice yield by about 0.75 t/ha in the high yield areas and by about 0.06 t/ha in the low yield coastal regions. Further, a 0.5°C increase in winter temperature would reduce wheat crop duration by seven days and reduce yield by 0.45 t/ha. An increase in winter temperature of 0.5°C would thereby translate into a 10% reduction in wheat production in the high yield states of Punjab, Haryana and Uttar Pradesh. The reduction was lower in eastern India compared to all other regions (Fig. 2.1). Mean grain yields of control crops in eastern region were 7.9 t/ha as compared to 8.7-9.9 t/ha in other regions. This was because of relatively higher temperatures in east (32.2/25.3°C) both during grain formation and filling phase, accompanied by lower radiation. As a result, these crops had fewer grains and shorter grain filling duration. Although temperatures were high in northern India as well (33.8/25.0°C), the region also had more radiation, which resulted in higher grain yields.

The impact of interactions between carbon dioxide and temperature can also be seen in Fig. 2.2. At 350ppm in north India, there was a change of -5, -12, -21,

North

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