EFFECT OF PRECIPITATION EFFECTIVENESS INDICES ON THE YIELD OF SOME SELECTED CEREAL CROPS
Agriculture in Nigeria is mainly dependent on rainfall which is variable in nature. Therefore, the need to have a full knowledge of its pattern and trend is pertinent in order to achieve food sufficiency. This study examined the effect of precipitation effectiveness indices: Onset date, cessation date, length of rainy season and occurrence of pentad dry spells (5, 10 and ≤15) days on the yield of millet, sorghum, rice and maize in Sokoto State, between 1993 and 2008. Walter‟s 1967 method was used to derive the selected precipitation effectiveness indices while dry spell parameters, was derived in pentads. Crop yield data in (ton/ha) and the selected precipitation effectiveness indices wereharmonised using log10 method. Trendline and linear trendline equations where fitted to show the direction of change. While simple correlation was used to analyse the relationship between crop yield and the selected precipitation indices. Furthermore, regression analysis was used to determine to what extent the selected precipitation effectiveness indices influence the yield of the selected crops. The findings revealed that the trend of these precipitation effectiveness indices are characterized by marked “noises” and variability.
Additionally, onset dates of rainfall are arriving earlier while cessation dates are arriving latter. Consequently the length of rainy season is increasing. Dry spells of 5 days is common while dry spell incidents of 10 days and ≤15 consecutive days is decreasing. Similarly rice and maize yield are increasing, due to early onset date of rains. The regression summary shows that the selected precipitation effectiveness indices account for only 52.1%, 50.4%, 52.1% and 68% of yield variation in maize, millet, rice and sorghum respectively. The study therefore, recommends government support for farmers to increase the cultivation of rice and maize in the study area, and the introduction of more crop varieties that are tolerant to dry spells of 5 consecutive days.
1.1 BACKGROUND TO THE STUDY
The limit to the productive capacity of land resources are set by climate, as climatic variability constitutes a major constraint to agricultural production especially in developing countries. However, adequate knowledge of climatic parameters minimizes climatic constraint to food production (Farajzedah et.al., 2012).
The world population is projected to continue increasing well into the present century. The primary question is whether and how global food production may be increased to provide for the population expansion. It will be necessary to increase current level of food production more than proportional to the population growth so as to meet human demand in food production. The major source of water available either for agriculture or for human consumption is the rain that falls on the Earth Surface. Subsequently, the primary source for agricultural production for most of the world is rainfall. Hence, a detailed knowledge of the rainfall at a place is an important prerequisite for agricultural planning and management. More so, for rain-fed agriculture, rainfall is the single most important Argo-meteorological variable influencing crop production in the tropics (Ravindran, 2010).
The most important characteristics of rainfall are, Onset Date (OD), Cessation Date (CD), Length of Rainy Season (LRS), Mean Annual Precipitation (MAR), Hydrological Ratio (HR), number of Rainy Days (RD), Rainfall Intensity (RI), Specific Water Consumption (SWC), rainfall in months of the growing season (May, June, July, August and September), Seasonality Index (SI), Index of Replicability, and Pentad Dry Spells.