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 water‐use 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.

Presently in Cyprus, tobacco (Nicotiana tabacumL.) is grown under supplementary irrigation with water high in CI. The present study sought to investigate the irrigation/yield relationship and the attendant concentration of CI and other constituents in the leaves. In three experiments in which one to six irrigations were tested, maximum evapotranspiration (ET) determined by the soil water balance method was reached 40 to 50 days after planting, and equaled evaporation from a screened Class A pan. The ET started declining just before the first leaf harvest, even though soil water was adequate. However, since soil water became limiting soon afterwards, the course of potential ET could not be followed. From the second leaf harvest until the end of the season, ET was very low (< 1 mm/day). Fresh yield increased from 12 Mg/ha with 60 mm irrigation to 28 Mg/ha with 360 mm irrigation, the highest amount tested. In contrast, dry matter yield only increased from 2.3 to 4.2 Mg/ha, respectively. Moreover, midrib material increased from 20% with 60 mm irrigation to 30% of the total leaf dry matter with 300 mm irrigation. Concentration of CI for the whole leaf increased from about 2% with 60 mm irrigation to 3% with 300 mm irrigation (disregarding the last sampling). Concentration of K decreased from 4 to 2% between the first and the third harvest and in one experiment it tended to increase with irrigation. Leaf P increased from about 0.1 with 60 mm irrigation to 0.2% with 180 mm irrigation. The burn rate of laminae, determined in one experiment, increased with irrigation, even though CI also increased.

No abstract

No abstract

Grain barley was grown either continually or in rotation with fallow in a 12-year experiment. Annual rainfall ranged from 120 to 297 mm. As the water requirement of the crop is 240 mm, growth in most seasons occurred under water stress. The amount of water conserved under fallow was only significant (75-100 mm) in three of the 12 years and only once did the water conserved increase barley yield in the following year. The total grain yield over the experimental period was twice as high in the barley-barley sequence as in the barley-fallow sequence. Cultivo continuo de cebada o despues de barbecho RESUMENEn un experimento de 12 afios de duracion se cultivo grano de cebada en forma continua o en rotacion con barbecho. La cantidad de precipitaciones anuales fue de 120 a 297 mm. Dado que la necesidad de agua de este cultivo es de 240 mm, en la mayoria de las estaciones el desarrollo se produjo bajo condiciones de escasez de agua. La cantidad de agua conservada con barbecho solo fue significativa (75-100 mm) en tres de los doce arios, y en una sola oportunidad el agua conservada incremento el rendimiento de cebada al afio siguiente. El rendimiento total de grano durante todo el pen'odo experimental en la secuencia cebada-cebada fue dos veces el de la secuencia cebada-barbecho.