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Alfalfa Yield and Water Use When Forced into Dormancy by Withholding Water During the Summer¹

Under the hot (air temperature reaching 40 C) and dry conditions of the inland areas of Cyprus, alfalfa (Medicago sativa L.) yields decline markedly in July to August. Water-use efficiency (kg DM/m³ of water taken up) decreases from 2.25 to 2.85 in March through May to 0.50 to 0.65 kg/m³ in July through August. This study evaluated several alternatives for increasing wateruse efficiency for alfalfa production.

Not irrigating the alfalfa for one growth period in July reduced yield during that period by 68%. However, not irrigating for a second or a third growth period resulted in no forage yield during these periods. When irrigation was resumed, plots not irrigated for one or two growth periods yielded as much as plots irrigated at all growth periods, but plots not irrigated for three growth periods produced 20% less yield during the first period following resumption of irrigation. In the following growth periods, however, these yielded as much as plots irrigated at all growth periods. Discontinuing irrigation for the three growth periods of July to August reduced annual dry matter yield to 17,700 kg/ha compared to 21,500 kg/ha when adequate water was applied throughout, but saved 610 mm of irrigation water out of a normal annual irrigation requirement of 1,400 mm. As a result, water-use efficiency in 1978–1979 increased from 1.32 kg DM/m³ of water taken up when adequate irrigation was applied throughout the growing season to 1.60 when irrigation was withheld for the three growth periods of July to August. The corresponding figures for 1979–1980 were 1.41 and 1.81, respectively.

Key Words: Medicago sativa L. • Pan evaporation • Water-use efficiency

² Assistant agricultural research officer and head, Soils and Water Use Section, respectively.

Received for publication July 21, 1980.