Sorghum Water Loss in Relation to Irrigation Treatment

摘要

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 imgation- 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 coeffi- cient k_c values for sorghum. The model, although tending to underestimate actual evapotranspiration by 4-10,