Analysis of Length of Growing Season in Some Agro-ecological Zones Using Non-parametric Trend Test
The ever increasing population and consequently increase in demand for food and the increasing exploitation of the land justifies the need for adequate studies on rainfall as an important factor affecting agricultural production. The date of the onset of rains is an important factor in planning agricultural operations such as land preparation and sowing. The study conducted agro-statistical analysis of rainfall characteristics over three different zones of Nigeria. Daily rainfall data were collected for the period between 1971 and 2005 for 6 stations and were subjected to standard analysis to determine trends and variations in the onset dates, cessation dates, length of rainy season, number of wet days, drought episodes. The results showed that the inter-annual variability of the onset dates is higher than that of cessation dates with a progressive shift in both onset and cessation dates. The length of rainy season varied from 77-291 days in Guinea zone, 77-243 days for Savannah and 73-155 days for the Sahel. Changes in the length of growing season ranged between -9 and -10 for Guinea zone, -21 and 11 days for Savannah zone and -28 and 20 days for the Sahel. Similarly, the numbers of wet days have declined over Nigeria. The information presented in this study are to serve as input for proper land and water resources management for productive agricultural enterprise across the three major agro-ecological zones of Nigeria.
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