Effect of partial soil wetting on transpiration, vegetative growth and root system of young orange trees

The wetted area fraction is a factor critical to the success of drip irrigation. This study aimed to evaluate the effect of partial soil wetting on transpiration, vegetative growth and root system of young orange trees. The experiment was carried out in a greenhouse where plants were grown in 0.5 m3boxes internally divided into compartments. The wetting of 12 % of soil area was tested on two types of soil cultivated with ‘Valencia’ orange trees grafted onto Rangpur lime and ‘Swingle’ citrumelo rootstocks. Transpiration was determined in 40 plants. Water extraction and root density were evaluated in the compartments. Transpiration is reduced by restriction in wetted soil area, and such reduction is influenced by the number of days after the beginning of partial irrigation, atmospheric evaporative demand and plant phenological stage. Mean transpiration of plants with partial irrigation was equivalent to 84 % of the mean transpiration of plants with 100 % of wetted soil area in the period studied. However, after 156 days of imposing partial irrigation there was no difference in transpiration between treatments. Plant acclimation was caused by an increase in root concentration in the irrigated area. After a period of acclimation, if the entire root system is wetted, soil water extraction becomes proportional to the percentage of wetted area after a short period of time. Despite the reduction in transpiration, there was no difference between treatments with 12 % and 100 % of wetted soil area in terms of vegetative growth

Measuring unsaturated sorptivity and hydraulic conductivity using multiple disc permeameters

A new field method of obtaining, with minimal disturbance, the unsaturated hydraulic conductivity (K0) and sorptivity (S0) from unconfined disc permeameter measurements is introduced. Conventionally, the sorptivity is obtained from the initial square‐root‐of‐time behaviour of discharge from the disc permeameter. In some cases this can be difficult to measure, in part because multi‐dimensional flows approach quasi‐steady state very rapidly. As an alternative we extend the ponded twin‐ring method to unsaturated discs of several radii. This method has the advantage that only long‐time, quasi‐steady discharges are needed to obtain K0 and S0. In the present study, the two methods are tested using data obtained for a fine sandy loam at a supply potential (Ψ0) of – 35 mm and agreement is good

Combining laboratory and field measurements to define the hydraulic properties of soil

In situ field measurements and laboratory determinations are presented of the saturated and unsaturated flow properties of two contrasting soils. Field measurements were obtained with ponded rings or disc permeameters of different radii. A pressure-transient outflow technique was used in the laboratory on undisturbed cores. The soil water diffusivity function from this, when integrated, provides a good rendition of the growth of the field-measured sorptivity as the surface potential, ψo, approaches zero. The undisturbed wetting hydraulic conductivity K(ψ) from the cores of both soils merged neatly with the near-saturated field results. One soil from within the herbicide strip of an apple orchard had a smoothly continuous K(ψ) befitting its texture. However, the K(ψ) of the other soil, from a dairy pasture, displayed a matrix-macropore dichotomy due to its high level of soil floral and faunal activity. Here, a mean pore size weighted for unsaturated flow, when ψo < −100 mm, was 17 ± 4 µm. For ponded infiltration, this changed abruptly to 2.2 ± 0.6 mm. Large and connected macropores caused K to change three orders of magnitude as ψo went from just −100 mm to zero

Sprinkler irrigation, roots and the uptake of water

Clearer perception and better modelling of soil water and chemical flow will be aided by improved measurement of the appropriate saturated and unsaturated flow characteristics of field soil. In situ measurements, at and near saturation are presented for two contrasting soils: the herbicided, coarse soil of an apple orchard, and a biologically-active, finer-textured soil growing pasture. These data are combined with more-unsaturated data from laboratory analysis on undisturbed cores. Soil water content measurements made after sprinkler irrigation of the orchard are interpreted in terms of simple notions of unsaturated flux-infiltration. Our water extraction observations stress the prime role of surface roots. These deep-rooted apple trees exhibited a depth-wise flexibility in root water uptake