Simulating the impact of climate change on chickpea yield under rainfed and irrigated conditions in Madhya Pradesh

CROPGRO-chickpea model calibrated and validated with data collected from the experiments conducted with two cultivars (JG 315 and JG 11) of chickpea at Jabalpur (irrigated) and Tikamgarh (rainfed) during 2009-10 and 2010-11, was used to study the impact of climate change on phenology, growth and yield of chickpea. It was found that model closely simulated the phenological event as well as biomass. The model underestimated seed yield of both the cultivars but more error was involved in simulation of JG 11. Under rainfed conditions there was large differences between observed and simulated. Under climate change scenarios (increasing maximum temperature by +1 to +3 °C, minimum temperature by+0.5 to 2.5°C and CO2 from 400 to 600ppm); the seed yield of the chickpea cultivars would increased by 102.8 and 187.7 per cent under irrigated conditions at Jabalpur. The large variability in yield was noted under rainfed as compared to irrigated conditions.

Chickpea occupy a very significant place in farming all over India and have the growing area of 9.91 million hectares with an annual production of 8.22 million tones and average productivity is 895 kg ha -1 (Anonymous 2012). Madhya Pradesh share 33 per cent of total chickpea area and 38 per cent of total production (Anonymous, 2014).
To estimate the impact of climate change on predominate chickpea cultivars of Madhya Pradesh, five climate change scenario (taking business as usual scenario approach) was simulated and their impact on yield were analyzed.

MATERIALS AND METHODS
The input data required for running the crop simulation model(CROPGRO-Chickpea) of DSSAT V4.5 includes crop data, daily weather data, soil data and crop specific genetic coefficients.

Crop data
To evaluate the model, field experiments were conducted at Jabalpur (Lat. 23 0 09'N and Long.79 0 58'E. and altitude of 411m m.s.l.) with six dates of sowing (D 1 : October 11, D 2 :October 26, D 3 :November11, D 4 :November26, D 5 :December11, D 6 : December 26) and two varieties (JG 315 and JG 11) during rabi seasons of 2009-10 and 2010-11. Two irrigation (40mm); one at branching and one at pod filling stages in addition to the pre-sowing irrigation were applied. The same cultivars under rainfed conditions were grown at Tikamgarh(Lat. 24 o 40'N., Long. 77 o 80'E. and altitude 324m m.s.l.). during rabi 2009-10 and 2010-11. Sowing of the above two varieties of chickpea was done on 10 th , 17 th November in 2009, 30 th October and 4 th November in 2010. A recommended dose of fertilizer 20-60-20 kg ha -1 NPK was applied uniformly at the time of sowing. One pre-sowing irrigation was applied in the crop at Tikamgarh.

Weather data
The daily weather data of the year from 2009 to 2011 were collected from Agromet Observatory situated nearby (within 100 meter) the experimental plots.

Soil data
Physical and chemical parameters of soil are required. The soil albedo, soil water drainage constant, filed capacity, wilting point, layer wise information on initial soil moisture, organic carbon, pH and sand, silt and clay information were collected from Jabalpur and Tikamgarh.

Climate change Scenarios
The climate change scenario were selected as per fifth assessment report of IPCC (2013), in which increase in maximum surface air temperature by 3.0 0 C and minimum air temperature by 2.5 0 C with combination of CO 2 increase upto 600 ppm have been projected. These are given in Table  1. The climate change was incorporated in the model input files through modified weather and then yield were simulated under five climate change scenarios under irrigated and rainfed conditions. Test summary statistics like mean and standard deviation were also calculated. RMSE tests the accuracy of the model (Loague and Green, 1991) and set of RMSE values were calculated. A smaller RMSE indicated less deviation of the simulated from the observed values. The Coefficient of    (Xevi et al., 1996).

Calibration and Validation of CROPGRO mode
The genetic coefficients for chickpea cultivars JG 315 and JG 11 were adopted from Silawat et al.( 2016) and are given in Table 2. The model performance was assessed by running the model with independent crop data set for all six sowing days and two varieties at both the places Tikamgarh (rainfed) and Jabalpur (irrigated). The corresponding mean values of simulation results are reported in Table 2 and compared with experimental data and agreement has been checked by RMSE and CRM values. Table 3 shows that the model overestimated the anthesis days by 1 to 8 days across the variety and locations. The model underestimated the physiological maturity by 1 to 20 days across the different dates of sowing. The maximum difference was found for D1 sowing date. Except the early sown crop, the model showed the robustness in simulation of major phenological events.

Rainfed conditions (Tikamgarh) :
At Tikamgarh, under irrigated conditions, the model underestimated the anthesis days with CRM ranging between 8 and 10 per cent and also the physiological maturity with CRM of 5 to 6 per cent ( Table 3). The deviations between the simulated and observed biomass values were high for rainfed conditions. The model performance for yield simulation for both the cultivars under rainfed condition was not within the acceptable limit (±20%). The model overestimated both the biomass and yield under irrigated conditions and under estimated the biomass and yield under rainfed conditions. These results indicated that modification may be incorporated in the model for acceptable yield simulation results. The crop models were generally calibrated for nonlimiting water conditions. In addition, other changes could also be made to accurately predict the observed water stress.

Impact of climate change on seed yield
The per cent change in seed yields of chickpea cultivars simulated under all the five climate change scenarios are presented in Table 4. It may be seen that the seed yield of chickpea was found to increase under all climate change scenarios. The yield increased with increase in CO 2 concentration as well as with temperature.

Irrigated condition :
Under irrigated conditions at Jabalpur the impact on seed yield of two cultivars varied between 102 and 187 per cent. Between the cultivars JG-11 was found to have more beneficial effect (138 to 187%) than that of cultivar JG-315(102 to 137%). The increase in CO 2 concentration and maximum and minimum temperature had a profound influence on yield at different date of sowing and variety. In general the increase in CO 2 concentration and maximum and minimum temperature has increased the seed yield. Srivastava (2003), also reported a high impact (40-50 per cent increase in yield) with doubling of CO 2 concentration on the productivity of chickpea at Raipur. Vanaja et al. (2011) reported that seed yield of pigeonpea improved from 22.8 g -1 plant at ambient to 42.4 g -1 plant at 700ppm, thereby showing an increment of 85.9 per cent with enhanced CO 2 .
Under irrigation conditions among the different dates of sowings, the impact was found to be beneficial in all except in extremely late sown condition (Dec.26). The highest seed yield increase (+200 to 256%) was obtained under D1. With delay in sowing the impact of climate change was found to decrease. Under very late sown condition( D6) , the impact of climate change under S1, S2 and S3 scenarios was positive while under S4 and S5 scenarios it was negative. Thus under irrigated conditions the beneficial effect of climate change was observed (Table 4). This result indicated that for maximization of chickpea yield the early sowing date is recommended under climate change conditions also.

Rainfed condition :
The chickpea yield simulated under projected climate change scenarios (Table 4) showed beneficial effect in most of the cases under rainfed condition also. In this case variety, JG-11 was found to have more (87 to 108 %) beneficial effect than variety JG-315(61 to 97%).
Under different dates of sowing the impact on seed yield was similar to that observed under irrigated conditions. However, quantitatively, it was slightly lower. The maximum beneficial effect was observed under early sown (D1-Oct-11) crop. Under very late condition (D6) the impact on seed yield was negative.
Seed yield variability was found to be large increased in case of climate change and large variability was noted under rainfed condition as compared to irrigated condition. Hajarpoor et al. (2014) simulated the impact of changing climate on chickpea at four major producing dry areas of Iran with different sowing dates. They reported that chickpea yield would increase between 37-89 per cent in rainfed conditions under the future climate in all sites.

CONCLUSION
The impact of climate change on chickpea yield was found to be favourable. The cultivar JG-11 would be more benefited than JG-315. The early sown (Oct.) crop would be maximum benefited. With delay in sowing, the beneficial effect will decrease. Under irrigated conditions the yield increase would be more that that under rainfed conditions. However, such results need to be used cautiously as the model has its inherent error in simulation.