Assessment of climate change and its impact on growth and yield of wheat under temperate and sub-tropical conditions*

due to double CO 2 and 17.1% and 8.6% due to increase in temperature respectively. To find the possibility of wheat cultivation in rice based system by manipulating agronomic practices specially dates of sowing and varieties and find the effect of climate change on crop growth and grain yield of wheat using dynamic crop growth simulation model CERES-wheat is useful. This model takes into account climate variables, soil variables and the ABSTRACT Field experiments were conducted at research farm of SKUAST-K, Shalimar campus, Srinagar for 2 years (2003-04 and 2004-05) on silt clay loam soil and at research farm of Integrated Farming System, SKUAST-J, Chatha, Jammu for 7 years (2003-04 to 2009-10) at sandy loam soil in order to find out the impact of climate change on wheat crop under temperate and sub tropical condition by using crop simulation model (DSSAT-v4.0). The results showed that under temperate condition the phenology of wheat is more affected compared to sub tropical condition if temperature increased and decreased. Simulated grain yield of wheat increased up to 18.31 per cent by elevated CO 2 to 350 ppm from the base value 330 ppm in temperate condition.

Climate of Jammu and Kashmir varies from sub tropical to temperate conditions. Wheat is grown in an area of about 2.66 lakh ha with annual production of 4983 thousand quintals with productivity of 19 q ha -1 (Anonymous, 2008-09). Temperature has profound effect on the yield mainly through phenological development processes. Increase in air temperature may be more important than the expected rise in atmospheric CO 2 concentrations as there are no evidences that elevated CO 2 concentrations may directly induce changes in development (Lawlor and Mitchell 1991). In temperate region, temperature drop below freezing point for couple of weeks. According to IPCC, 2007 the CO 2 level will rise to 605-755 ppm by 2070 and warming of 1.5 o C by 2015-2050 and 3 o C by 2050 to 2100. The data revealed that the day temperature in Jammu has decreased by 0.7° C from last two decades while night temperature has gone up by 0.6° C. On the other hand in Srinagar, both maximum and minimum temperatures have gone up by 1.0 and 0.4° C, respectively. Similarly the rainfall in these places has increasing trend of 2.0 mm year -1 in Jammu and decreasing trend of 8.0 mm year -1 in Srinagar. The rates of most biophysical processes are highly dependent on climate variables such as radiation, temperature in addition to moisture. For example, rates of plant photosynthesis depend on the amount of photosynthetically active radiation and levels CO 2 . Temperate crops may benefit more from increasing CO 2 than tropical. The C 3 pathway characteristic of nontropical plant (eg. wheat, soybean, cotton) will be affected adversely more with increasing CO 2 concentration and increase in temperature. Various studies showed that increase in temperature by 2.5°C to 4.9°C, the rice yield will decrease by 15 % to 49 % and wheat yield will decrease by 25 % to 42 % without carbon dioxide fertilization. Mall, (2008) reported that the yield of rice and wheat increased by 26.6% and 18.4% due to double CO 2 and 17.1% and 8.6% due to increase in temperature respectively. To find the possibility of wheat cultivation in rice based system by manipulating agronomic practices specially dates of sowing and varieties and find the effect of climate change on crop growth and grain yield of wheat using dynamic crop growth simulation model CERES-wheat is useful. This model takes into account climate variables, soil variables and the

MATERIALS AND METHODS
The crop, weather and soil data required for the present study were taken from research farms at SKUAST-

Sensitivity analysis
After validation of model the sensitivity analysis were carried out by changing in input weather parameters (Pathak et al., 2003). Detailed treatment combinations of different climate scenario are given

Effect on maturity of wheat crop
The simulation results showed that the wheat crop sown under normal temperature and carbon dioxide took 263 days to mature under temperate condition, while under subtropical condition wheat crop mature in about 164 days. The increase in maximum and minimum temperature by 2 o C and 4 o C without change in CO 2 concentration during the crop growing period the wheat maturity observed earlier by 17 and 30 days under temperate condition, while 10 and 18 days under subtropical condition, respectively. Hundal and Prabjyot Kour (2007) revealed that increase in temperature by 4 o C decreased days to maturity by 17 days for wheat in Punjab. However increase in carbon dioxide levels to 350, 450 and 750 ppm under normal temperature did not affect maturity of wheat crop under temperate condition of Jammu and Kashmir, but it enhances the wheat maturity by 3-5 day under sub tropical condition (Table 2). Wheat crop matured in advance by 6 to 18 days under sub tropical condition, while 17-30 days in temperate condition. But when the temperature decreased to 2 o C and 4 o C the ripeness of wheat crop was delayed by 20 to 38 days and 10 to 17 days under   temperate and sub tropical condition, respectively and the results confirmed with findings of Kalra et al., (2008).

Effect on growth parameters
Simulation study was carried out to describe the effects of climate change on leaf area index in wheat (Table  3). The leaf area index of normal sown wheat crop increased with advancement of the crop and it was found maximum at about 100 days after sowing, thereafter it declined up to the physiological maturity of crop, but with the increase in temperature by 4 o C, shorten the vegetative phase of wheat crop and the maximum leaf area index stage observed around 50 days after sowing in sub tropical areas. While leaf area index increased with increase in CO 2 concentration and observed maximum of 3.85 at 700 ppm CO 2 concentration at normal temperature. In temperate region, leaf area index increased with the increased in temperature in combination with increased concentration of CO 2 and vice versa. Increase in temperature by 2 o C enhanced leaf area index by 12 per cent in this region.
The leaf dry weight was found maximum (1230 kg ha -1 ) at CO 2 concentration of 700 ppm under temperate condition. But when temperature decreased by 2 and 4 o C coupled with normal CO 2 concentration, the leaf dry weight slowly increased up to 150 DAS and then abruptly increased at 200 and 220 DAS under temperate condition (Table 4). Under sub tropical condition the effect of climate change on leaf dry weight substantiate the analogous outline as in case of leaf area index, but it was found maximum at 100 days after sowing, when concentration of CO 2 increases up to 700 ppm with no change in temperature. Amir and Sinclair (1991) from Israel highlighted that the influence of cool conditions were clearly advantageous for increasing leaf area duration and accumulated biomass development of wheat crop in Asia. It was shown that the effect of climate change on total biomass production in Impact of climate change an wheat yield in J & K December 2013 wheat crop had been found more under subtropical condition compared to temperate condition.

Effect on grain yield of wheat
Simulated effect of increase in maximum and minimum temperature by 2 o C and 4 o C throughout the crop growing periods reduced the crop yield by 29.09 and 37.29 per cent, respectively under temperate condition and 17.52 and 32.18 percent, respectively under subtropical condition as compared to normal temperature (Fig. 1) and results confirmed by Rosenzweig (1991). Increase in maximum and minimum temperature by 2 o C under elevated CO 2 concentration 450 ppm abruptly decreased wheat yield by 16.82 per cent, while increase in temperature by 2 o C with CO 2 concentration of 700 ppm enhanced grain yield by 13.14 per cent in temperate condition and similar type of results reported by Tubiello et al., (1995). Decrease in maximum and minimum temperature by 2 and 4 o C with normal concentration of CO 2 decreased wheat yield by 7.07 and 26.96 per cent in temperate condition and such type of results reported by Miyata et al., (2004).

CONCLUSION
In temperate condition increase in temperature (4 o C) shortened the wheat crop duration about one month, which declined the wheat yield up to 37.29 percent, but in subtropical condition seed yield reduced by 32.18 per cent. The seed yield fluctuation was found more in temperate condition compared to sub tropical condition.