Assessing the Effects of Management Practices and Climate Change on Lowland Rice Production using the Dssat Crop Model in The Gambia and Mali

Abstract

Agricultural production particularly rice production is one of the priority areas for vision 2020 agricultural and natural resources policy document for the Gambia. An agronomic trial was conducted in 2017 and 2018 at the National Agricultural Research Institute experimental stations of Sapu and Kuntaur in The Gambia. The main objective of this study was to assess the actual and perceived impacts of Climate change under different fertilizer levels and transplanting dates for the yield of Sahel 134, IET 3137 and Gambiaka rice varieties, through experiments, simulation modelling and participatory methods for effective coping mechanism among small scale farmers in The Gambia and Mali. Data were collected on plant height, panicle length, number of fertile tillers per plant, grain yield, days to 50% flowering and days to physiological maturity at different transplanting dates on the selected rice varieties. The results showed significant difference at both varietal levels and nitrogen fertilizer rates on the crop parameters at (p<0.05.The experimental data set of 2017 and 2018 were used to adapt the Ceres- rice crop model of Decision Support System for Agrotechnology Transfer (DSSAT version 4.7). Outputs of the model indicated that the measured and simulated rice grain yields, anthesis dates have very close relationship. The relative difference for all the transplanting dates, at different fertilizer levels, and across varieties ranges from -0.5 to +14.6% for the grain yield. The historical daily climate data alongside with the projected near term (1980 to 2039) and midcentury (2040 to 2069) climate data with emission scenario of RCP 4.5 and RCP 8.5 for Segou, Mali and Kuntaur, The Gambia. The results indicate a yield decline for all the transplanting dates for both emissions scenarios when CO2 fertilization was not considered, but CO2 fertilization did compensate for yield declines caused by increasing temperatures when projected CO2 values were incorporated into the DSSAT. A yield gain of 1 to 50% was noticed with cool GCM (GFDL-ESM2G) and 1 to 35% was observed with hot GCM (HadGEM2-ES) for both RCP 4.5 and 8.5 time periods, across varieties and at different fertilizer level and transplanting dates. More gains on the yield was noticed at Kuntaur location especially on the improved varieties (Sahel 134 and IET 3137) and at July transplanting. Focus group discussion was held with twenty rice growing farmers at Sapu and Kuntaur, they divided into five groups. Personal interview and key informant involves the heads of the two village, two youth development chairpersons (VDC) and the extension worker overseeing both village. This was done to gain in-depth knowledge on the subject matter. The analysis results indicated that farmers rely heavily on their own perception or knowledge that were mainly obtained from families or extension service.