Water use by Irrigated cotton in Sudan. 1. Reflection of short-wave radiation.
As the crop developed and the sun's declination changed, mean values per day of the reflection coefficient increased from 0.15-0.23. After rain or irrigation the values were relatively small and rose during the intervals between irrigations; this effect became smaller as the leaf-area index of the crop increased. Smaller coefficients were recorded over wilting plants than over turgid plants probably due to the increased proportion of bare soil, rather than to increased "trapping" or difference in reflection between turgid and wilted leaves. For bare soil, mean values of the reflection coefficient at local noon In Sept. (solar altitude 70°) over wet and dry soil were 0.110 and 0.167 respectively. The soil was a deep, dark brown, strongly alkaline, heavy cracking clay of low permeability.