Measurements of instantaneous hydraulic fluxes under bare soil and wheat in Canterbury : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Agricultural Science in the University of Canterbury

Abstract

Thermocouple psychrometric characteristics and behaviour were discussed during calibrations. The physical properties of a Templeton silt loam profile were determined by field and laboratory procedures. Combined pressure-water content relationships obtained in the laboratory and field with tensiometer, pressure plate and neutron probe were found to be valuable at pressure from near saturation to wilting and were considered more reliable. Hydraulic conductivity and soil water diffusivity in the field were determined from flux and hydraulic-head gradient data. Hydraulic-head gradients were obtained from tensiometric measurements of pressure at various depths. In the soil profile that was subject to both evaporation and drainage, the position of a downward moving "zero flux" boundary was determined. Flux across any depth was obtained by integrating the rate of change of water content with time between the "zero flux" boundary and the depth. The "zero flux" boundary techniques are useful for measuring hydraulic conductivity for higher suctions. Tensiometer readings with time and depth in the field were useful in measuring soil water diffusivity in a uniform profile. Mathematical techniques (cubic spline function) of differentiation and integration were used in the calculation of hydraulic conductivity and soil water diffusivity, and are useful tools for the study of soil moisture. Actual evaporation rate in the field was compared with potential evaporation on a graphical representation based on soil and meteorological condition with time and water depletion patterns on bare soil plot. Actual evapotranspiration and drainage losses were determined in the field under growing wheat and water depletion patterns were discussed with plant growth, soil condition and meteorological data.