The Influences of Amounts and Distribution of Irrigation During the Hot and Dry Season on Emergence and Survival of Some Desert Winter Annual Plants in the Negev Desert

In a flat loess area in the Negev Desert of Israel, different amounts and distribution of irrigation were given to 48 squares of 0.25 m² on 1 and 30 August, 1977. At this time evaporation rates were high and the range of temperatures near the soil surface between irrigation and seedling emergence was 15–53 °C. Of the species appearing in winter in the Negev, only 22 emerged, and only 3 appeared in substantial numbers. Seedlings of species that emerge during winter after about 10 mm of rain did not emerge after the first irrigation in squares receiving 60 mm of water, a few emerged after 90 and 120 mm, and only 57 after 150 mm. After the second irrigation, when evaporation rates and temperatures were lower, in the same squares, 154, 334,534, and 763 seedlings emerged after receiving90, 120, 150, and 200 mm, respectively. The highest number of seedlings emerged, but the lowest percentage survived, when the water was divided into equal daily irrigations during the first 9 days. As the daily water amounts decreased, the number of emerging seedlings also decreased, but the % survival increased. As the daily number of irrigations of 30 or 10 mm increased, the number of emerged seedlings and the % survival increased. However, there were significant differences among the species that emerged. The amounts and distribution of water evaporation rates and temperatures were found to be the important germination regulators in those plants which also inhabit regions receiving summer rains.