Crop yield response to water - Cra

ox 9 Examples of soil water monitoring in different situationsShallowDeepDeficitDeepExcessShallowDeepShallowCorrectThe three soil water status trends were obtained with sensors installed in shallow (dottedlines) and deep (solid lines) soil layers. The top example indicates insufficient water application(deficit irrigation), based on the decline of soil water in the lower depth (solid line). Thecenter graph shows an increase with time in soil water deep in the profile which indicatesexcessive applications. The soil water fluctuations in the shallow depth (dotted line) show thetypical responses to irrigation applications followed by fast extraction at shallow depths. Thethird graph at the bottom represents a pattern indicative of adequate irrigation applications.Note that even if the water content in the deep layer does not change deep percolation mayoccur even without apparent water content changes.overlaid with aluminum foil or any opaque, sealed bag) for a period of time (around 20 min)prior to excision. The practical elimination of transpiration by enclosing the leaf equilibratesits water status with that of the adjacent stem and presumably, the trunk. The SWP is lessaffected by evaporative demand (and by leaf-to-leaf variations in stomatal opening) and ismore representative of the water status of the whole tree than the water potential of anexposed leaf. In some species, measurements of the water potential of uncovered, shadedleaves inside the canopy have proven to be closely correlated with SWP. Thus, taking themeasurement on shaded leaves may be a viable, faster alternative to having to bag the leaves.Plant water status varies in response to atmospheric demand and soil water levels. Even whenthe soil water level is high, the SWP varies, declining from predawn hours until about solarnoon when a plateau is reached through the midday hours, at least on clear days. The SWPmeasurements are normally taken during this plateau period; from solar noon to 1400, andrepresent the minimum for the day. The maximum value taken at predawn is used in somecases to represent a SWP close to equilibrium with the soil water. It is not practical to measurepredawn water potential for commercial scheduling given the time of day and the limitedtime to make the measurements.Yield Response to Water of Fruit Trees and Vines 273