Assessing the impact of dry spell during monsoon season on rice productivity -Acase study over Patna district

Abstract

The monthly, seasonal and yearly rainfall characteristics, frequency of occurrence of 10 days or more consecutive dry spells during monsoon season and their influence on rice productivity were investigated using daily rainfall data for 49 years (1960-2008) recorded at Agricultural Research Institute, Patna, Bihar. The results revealed that monsoon season receives 84.4% (959.5 mm) of the annual rainfall (1136.8 mm) followed by 7.9% (89.6 mm) during post-monsoon season. The coefficient of variation of annual rainfall was recorded as 26% and the monthly values ranged from 43.2% (August) to 210.9% (December). The data on rice productivity was fitted into different models in curvefit program and it was observed that R value was higher for 10 degree polynomial fit. The scattering of data points from the trend line (10 degree polynomial curve) indicated higher year-to-year variability. During the study period, 10 days or more consecutive dry spells occurred in four years (1966, 1982, 2004 and 2005) during July. During all the years, the rice productivity was recorded below the technological trend productivity. Similarly, 10 days or more consecutive dry spells during August occurred in four years (1968, 1973, 2004 and 2006) affecting the productivity. This clearly showed that if any 10 days or more consecutive dry spells occur during the months of July and August, there is likelihood of low rice productivity. This study also showed occurrence of 10 days or more consecutive dry spells during September may not have impacted severely rice productivity because of the flooded paddy fields along with higher relative humidity reducing the water demand and thereby the rice crop never experienced severe water stress situations.