| heal.abstract |
Aiming towards rational irrigation water management in a seasonally dry climate, sorghum water losses via evapotranspiration were studied during a two-year experiment in relation to irrigation treatments in Central Greece. Relative to high irrigation (I(H)), that provided the root depth with 458 mm of water in 1994 and 512 mm in 1995, 56 and 64% of the water was supplied by the medium (I(M)) and 34 and 46% by the low (I(L)) treatments, respectively, during the two years. A fourth treatment (I(HA)) was performed like (I(H)) until the end of anthesis, when irrigation stopped. Gravimetric soil moisture was measured, biometric measurements were taken and all meteorological parameters required to estimate evapotranspiration by the Penman-Monteith equation were logged. A model estimating sorghum actual water loss was first run with the 1994 data. During the model-establishment year, it was found that (a) surface resistance r(s), consisting of a canopy r(sc) and a soil (r(ss)) resistance acting in parallel, was almost exclusively dependent on soil water shortage, (b) under the I(M) and I(L) irrigation treatments, the lowest possible (immediately after water application) canopy resistance r'(sc), higher than the (I(H)) minimum canopy resistance r(sc) (min) = 40 sm-1, was irrigation-deficit dependent and (c) the r(ss) (min) was as high as 1200 sm-1, common to all treatments. The model established was then verified with the 1995 data and used to calculate the crop coefficient K(c) values for sorghum. The model, although tending to underestimate actual evapotranspiration by 4-10%, depending on the treatment, may be considered as reliable. The k(c) values calculated are considerably higher than the k(c) values suggested for sorghum by the Food and Agriculture Organization (FAO). Therefore, taking also into account that any additional mm of water supplied results in an increase of 0.052 t of dry biomass per hectare, higher irrigation water applications could be recommended, although the low irrigation treatment made slightly better use of water.Sorghum water losses via evapotranspiration in relation to irrigation treatment were studied during a two-year experiment in Central Greece. The gravimetric soil moisture was measured, biometric measurements were taken, and all meteorological parameters required to estimate evapotranspiration by the Penman-Monteith equation were logged. A model estimating sorghum actual water loss was first run with the 1994 data. The established model was then verified with the 1995 data and used to calculate the crop coefficient values of sorghum. The model, although tending to underestimate actual evapotranspiration by 4-10%, depending on the treatment, was considered reliable. |
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