Water relations and photosynthesis as criteria for adequate irrigation management in 'Tahiti' lime trees

Irrigation scheduling based on soil moisture status is one of the most useful methods because of its practicality and low cost. The effects of available soil water depletion on evapotranspiration (ETc), transpiration (E), leaf water potential at predawn (psiP) and midday (psiM), stomatal conductance (gs) and net CO2 assimilation (A) in lime 'Tahiti' trees (Citrus latifolia) were evaluated to improve irrigation schedule and minimize water use without causing water stress. The trees were spaced 7 <FONT FACE=Symbol>&acute;</FONT> 4 m and drip-irrigated by four drippers with the available soil water content (AWC) depleted by suspension of irrigation (40 days). Leaf water potential was measured on a pressure chamber (psiP and psiM) and leaf gas exchange was measured by infrared gas analyzer (E, gs and A). Evapotranspiration was determined with the aid of weighing lysimeter. Water soil content and potential (psiS) were monitored with TDR probes and tensiometers, respectively, installed at 0.3, 0.6 and 0.9 m depths. Meteorological variables were monitored with an automatic weather station in the experimental area. The threshold AWC level for the onset of ETc decline was 43%, and 60% for gs, A, E and Y P. Also, psiP was more sensitive to AWC than psiM, and is therefore a better tool for irrigation. When AWC was around 60%, values of psiP and psis were -0.62 MPa and -48.8 kPa, respectively

Wetland vision: adapting freshwater wetlands to climate change - Task 3 Typology

The overall objective of this project is to develop a toolkit consisting of a tiered set of methods to assess the impact of climate change on wetlands and use this to provide a framework for assessing wetland adaptation strategies and assessing whether management options will be sensitive to future climate change. Task 3 of the project is to define a typology. This document describes the typology development

A controlled water-table depth system to study the influence of fine-scale differences in water regime for plant growth

A method was developed to maintain water-table depths at a constant level in outdoor mesocosms. The system included a water treatment reservoir, where tap water was microbially deoxygenated and denitrified; an adjustable-level control chamber that set desired water-table depths and plant growing mesocosms. The soil water status was evaluated by constant monitoring using tensiometers, pressure transducers and dipwells. The robustness of the system was tested by inducing sudden incidents of flooding and drainage. The system was able to revert to the original set water-table depths within 5 and 10 min, respectively. It also reliably sustained consistent water-table depths throughout the growing season without the need for maintenance. As an example, the method was used to grow plants at five set water-table depths: 50, 150, 250, 350, and 450 mm below ground surface. Two wet grassland species Festuca pratensis (meadow fescue), and Carex nigra (common sedge) were grown and dry biomass production recorded. Results showed differences in growth response between the two species to subjected water-table depths. In monoculture, F. pratensis production followed the order 50 = 150 = 350 > 250 = 450 mm (p 50 = 350 = 450 mm (p 250 > 350 = 450 mm (p < 0.001). The ease of the system to establish constant and/or dynamic water-table depths and its reliability outdoors renders it useful for a wide variety of studies involving plant growth