Assessing the impacts of seasonal dry spells and mean temperature variations on Nerica rice yield production in Central Uganda
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The determination of seasonal rain fall amount received and distribution are tremendously crucial in rain fed Nerica upland rice. The objective of this study was to analyze the seasonal and annual trend of dry spells and there effects on seasonal Nerica yield and also identify the dependence of Nerica on seasonal rain fall variability in central Uganda. Excel and INSTAT v3.36+ software were used in data analysis. Meteorological data for 13 years were used from Namulonge Agrometeorological station and also Nerica rice yield data for MAM and SOND seasons for 7 years were used obtained from the same place. Nerica yield data were found to have a negative trend. The amount of seasonal and annual rain received is crucial and should be well distributed in all phonological stages. The onset, cessation, length of the growing season were determined and found to be variable in different growing season in entire study period with early onset dates from 2003-2007 and a delay in start of rain of 7days after initial stated date from 2008-2016. The average water balance in the soil was found to be low during the first 50 days of the year which cannot sustain the growth of any crop. Since Nerica rice is a C3 crop, it cannot withstand such a long dry spell and sowing of Nerica rice should be done after 60 DOY. The length of growing season in MAM are determined by the start of rainy dates than the cessation. More water is required in germination and grain formulation stage and if a dry spell of 5-7 consecutive days with < 1mm occurred, it will have adverse impact on Nerica yield. The rain fall was found to have a positive correlation with Nerica upland rice and it determines 35% of the rice yields. A negative correlation was found between minimum temperature and Nerica which means that the increase in minimum temperature leads to decrease in Nerica yields by 4%. From computation, dry spells was found to have adverse impact on Nerica and any increase in dry spells length of over 7 days will affect Nerica rice by 6.6%. In conclusion, the area experiences a long dry spell length of 5,7,10 days with higher average probability chance of 0.75 in SOND season. The maximum dry spell was in 2008 SOND season with 15 dry days and yield of 2 ton/ha were obtained. These low yields were accountable by delays in rain fall start and many dry day which led to insufficient soil moisture content and resulted into low Nerica rice yields.