MODELING GROWTH, DEVELOPMENT AND YIELD OF CHICKPEA AND ANALYSIS OF CLIMATE CHANGE IMPACT AND MANAGEMENT OPTIONS IN NORTHEASTERN ETHIOPIA

Abstract

Chickpea is one of the important cool season food legumes in northeastern Ethiopia but its productivity is adversely affected by various abiotic and biotic constraints among which climate variability is the major one. Research on impact of climate change and adaptation strategies for chickpea are very in the study region. Crop productivity must be increased to meet the rapidly growing food demands. New agricultural research system is needed to provide sufficient information. The present study was conducted 1) to calibrate and evaluate the CROPGRO-chickpea model in DSSAT (Decision Support System for Agrotechnology Transfer) for simulating growth, development, yield and water balance of chickpea 2) to determine variability and trend of observed and future (2030 and 2050) rainfall and temperature at selected stations in the study area 3) to asses impact of climate change on grain yield of chickpea 4)to identify crop management and genetic options that increase chickpea yield under present and future climate condition. The calibration of the crop model was performed using sowing date experiment conducted in 2014 at two locations. The model was evaluated using data sets of variety trial experiment obtained from Sirinka agricultural research center. The well-adapted chickpea cultivar (Kutaye) was used as a test crop. The efficiency of the model was tested using the d-stat (index of agreement), RMSE (root mean square error) and R2 (coefficient of determination) values. To achieve the second objective, variability, and trends of rainfall (1983-2013) and temperature (1981-2010) at annual, seasonal, and monthly time scales were analyzed for six weather stations. The non-parametric tests (Mann-Kendall’s and Sen’s slope) were used to detect trend and magnitude of change. To determine the magnitude of change in future climate by 2030s and 2050s, ensembles of model outputs from the 17 CMIP5 GCMs run under all the RCPs were downscaled to the study stations using MarkSimGCM. To achieve the third objective, the downscaled temperature and rainfall data for the 2030s and 2050s were input in to the crop model. Soils, crop management practices and crop genetic coefficients were assumed to be the same as the present period. To achieve the fourth objective, options that include changing in sowing dates, cultivars with different maturity durations and supplemental irrigation have been tested for their effectiveness in terms of increasing yield. The results showed that the model simulated well the effects of varying sowing dates and variety trial experimental data sets. This indicated that if properly xxiii calibrated, the model could be used for decision making to improve chickpea productivity in the region. The result of rainfall and temperature analysis showed that annual and Belg (short season) maximum temperature and Kiremit (long season) rainfall showed significant increasing trends. On the other hand, annual and Belg season rainfall totals showed decreasing trends. Regarding future climate changes, annual mean air temperature at Sirinka is projected to increase in the range of 1.2-1.6 oC by 2030s and in the range of 1.4-2.7 o C by 2050s across the RCPs whereas it is projected to increase at Chefa in the ranges of 1.3-1.7 oC by 2030s and 1.3 to 2.6 oC by 2050s. Mean annual rainfall is also projected to increase at Sirinka by about 14% both by 2030s and 2050s whereas it is projected to increase at Chefa by about 2% and 9% by 2030s and 2050s, respectively for all the RCPs. Simulation result without CO2 fertilization showed that grain yield will not significantly increase by 2030s and 2050s as compared to baseline yield. Although not significant, yield is predicted to increase in the ranges of 9 to 17% at Sirinka 4 to 6% at Chefa by 2030s and in the ranges of 8 to 17% at Sirinka and 5 to 8% at Chefa by 2050s. When CO2 fertilization was considered, grain yield is predicted to significantly increase by 2030s and 2050s. Yield is predicted to increase in the ranges of 17% -26% at Sirinka and 11% -15% at Chefa by 2030s. Similarly, it is predicted to increase in the ranges of 19%-50% at Sirinka and 14%-31% Chefa by 2050s. Using short duration cultivar at Sirinka is predicted to increase grain yield by about 11%, 10% and 11% in the baseline, 2030s and 2050s, respectively whereas long duration cultivar is predicted to decrease grain yield by about 8%, 12%, and 13% across the respective time periods under RCP4.5 and RCP8.5 scenarios. In contrast, short duration cultivar at Chefa is predicted to decrease grain yield by about 9%, 3% and 3% for the same time periods. On the other hand, chickpea grain yield at Sirinka is predicted to significantly increase under early sowing (SSD-20 days) by about 43%, 42% and 48% and by about 33%, 40% and 12% at Chefa in the baseline, 2030s and 2050s, respectively under the same scenarios. In the same manner, application of two times supplemental irrigation during the critical growth stages of chickpea is found to significantly increase grain yield at Sirinka by about 47%, 46% and 44% and by about 17%, 16% and 19% at Chefa across the same time periods and scenarios. The highest grain yield could be achieved through the combined application use of early sowing, suitable cultivars and supplemental irrigation.