6. Climatic analyses and cropping systems in the semiarid tropics.
In: Weather and Rice; Proc. of an Int. Workshop on the Impact of Weather Parameters on Growth and Yield of Rice; Publ. of IRRI, Los Baños, Philippines, 1987, pp. 215-220
Climate and agriculture are intimately related. Both long-term meteorological factors (climate) and short-term meteorological events (weather) affect crop growth, development, and production.
Studies of climate help understand crop production and other land use patterns that have evolved over a long period of time and assist in introducing new and more productive farming systems. At ICRISAT the relevance of climatic environment to the development of improved cropping systems for semiarid tropical areas are studied.
Semiarid tropical (SAT) areas are defined as those regions that have a mean annual temperature exceeding 18 C and mean monthly rainfall exceeding mean monthly potential evapotranspiration for 2-4.5 consecutive months in the dry SAT and 4.5-7 month in the wet/dry SAT.
Precipitation is characterized by annual and seasonal variability. the coefficient of variation for annual rainfall is 20-30%. Even within the rainy season, droughts of varying durations are common.
The major climatic constraint to crops in the tropics is lack of adequate water. Against a continuing evaporative demand, the supply is discontinuous and variable, particularly in the drylands.
To cope with the variable climate, farmers tend to grow a mixture of crops. They usually include long-duration crops in their cropping systems.
Traditionally, the SAT areas have had agropastoral, silvipastoral, and agroforestry production patterns. Cultivation had been mainly restricted to dryland crops, with a crop or two of rice in the lowlands or where irrigation water is available. With large population increases in recent years, most of the land is now sown to crops; the area under forests and grasslands is rapidly decreasing. Soil erosion has increased tremendously and surface waterstorage systems have lost much of their effective storage capacity. Crop production is much more variable in both drylands and irrigated areas. Average crop production from the drylands does not exceed 0.7 t/ha a year in most of the SAT.
Agroclimatic analysis helps define the recommendation domain for transferring technology from the research center to farmers' fields.
An efficient cropping system is determined largely by climatic, and management factors. A more complete quantification of the temporal and spatial distributions of natural resources is a key factor in assessing the agricultural production potential of a region. Mapping the agroclimate of an area in relation to its resources could give the recommendation parameters for improved cropping systems or farming systems technology.
A map of semiarid India showing the suitability of areas for the adoption of improved technology has been prepared.
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Africa, tropics, review, book, field crops production, agronomic practices, climatic factors, soil fertility, irrigation, drainage, cereals, roots, tubers, grain legumes, oilseed crops, fibre crops, beverages, CTA
ONWUEME, I.C. and T.D. SINHA
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