| Frost damage to winter cereals in northern Iraq Tarik A. TABRAH State Board for Applied Agricultural Research, Abu Ghraib, Baghdad, Iraq. In Iraq about 6 million donums (1.5 million hectares) of wheat and 3 million donums (750,000 hectares) of barley are annually planted. The country, which lies between 29o5' and 37o22' north latitudes and 38o45' and 48o45' east longitudes, could be divided into two major winter cereal zones. The northern zone, between 35o and 37o latitudes, characterised by rain fed agriculture, predominantly pastoral and range management, and the central mesopotomian plains between the rivers Tigris and Euphrites, chracterised by irrigated agricultural production systems. The latter zone is characterised by saline soils and barley is the dominant winter cereal. Nearly 80% of the total production of cereals are from the northern zone. The national productivity levels of wheat and barley are rather low at 600 to 800 kg per hectare more due to low levels of management than to ravages by pests or diseases. In the north the productivity levels fluctuate because of its dependency on rainfall. Besides, rarely occuring frost damage could be a contributing cause. The present note describes one such incidence. During the crop season of 1979-80, frosty weather prevailed in the northern parts, in the Nineveh governorate (which accounts for 50% of the wheat and 25% of the barley area in the country), on the night of the 16 April, 1980, when the wheat and barley crops were in the late flowering to early dough stage. The damage was of the 'head frosting' type. Whole ears or sections of ears turned white and failed to develope further (Fig. 1). Developing grains were found shirivelled. Younger heads although with no apparent damage, had pronounced sterility. Glumes opened up with a translucent appearance with water soaked tissues. An average visual estimate of the damage could be placed at 50% of grain loss. Since the area affected was fairly large, this would imply a substantial reduction in wheat production this year. Although infrequent in occurance the potential nature of this threat to wheat production is obvious, and should be taken into account in the cereal production systems of northern Iraq, and assess feasible protection measures, if any. The meteorological conditions that favour frost are clear, cold, dry and calm atmosphere, into which there is an influx of dry cold air mass. When the temperature of the invading air mass is above the freezing point, there is a net loss of radiant energy from the plants and soil resulting in the rapid fall of temperatures of the plant body and soil. When the vapour pressure of the crop surface exceeds that of the surrounding air, there is a quick loss of heat by evaporation. The net result of these events is the formation of ice in the intercellular spaces, and this is lethal to the plant tissues. The affected parts take on a wilted appearance. Thus the climatological variables in the predisposition to frost are, (i) the temperature gradient between the plant and its environment, (ii) the corresponding vapour pressure gradient, and (iii) the wind speed over the plant surfaces. |
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