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Canopy interception and its evaporation into the atmosphere during irrigation or a rainfall event are important in irrigation scheduling, but are challenging to estimate using conventional methods. This study introduces a new approach to estimate the canopy interception from measurements of actual total evapotranspiration (ET) using eddy covariance and estimation of the transpiration from measurements of sap flow. The measurements were conducted over a small-scale sprinkler-irrigated cotton field before, during and after sprinkler irrigation. Evaporation and sap flow dynamics during irrigation show that the total ET during irrigation increased significantly because of the evaporation of free intercepted water while transpiration was suppressed almost completely. The difference between actual ET and transpiration (sap flow) during and immediately following irrigation (post irrigation) represents the total canopy evaporation while the canopy interception capacity was calculated as the difference between actual ET and transpiration (sap flow) during drying (post irrigation) following cessation of the irrigation. The canopy evaporation of cotton canopy was calculated as 0.8 mm, and the interception capacity was estimated to be 0.31 mm of water. The measurement uncertainty in both the non-dimensional ET and non-dimensional sap flow was shown to be very low. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Model-based adaptive control strategies can be used to determine site-specific irrigation volumes with the aim of maximising crop water use efficiencies and/or yield. These strategies require infield weather, soil and crop measurements to calibrate a crop model: the crop model is then used to determine the irrigation applications throughout the crop season which produce the desired simulated crop response or condition (eg. maximum yield). However, data collection spatially over a field and throughout the crop season will potentially lead to a large sensed data requirement which may be impractical in a field implementation. Not all the collected data may be required to sufficiently calibrate the crop model and determine irrigation applications for model-based adaptive control; rather, a smaller dataset consisting of only the most influential sensor variables may be sufficient for adaptive control purposes. This paper reports on a field study which examined the utility of five sensed variables - evaporative demand, soil moisture, plant height, square count and boll count - to calibrate the cotton model OZCOT within a model-based controller and evaluate the relative significance of each sensed variable (either individually or in combination) as a control input. For the field study conditions, OZCOT was most effectively calibrated (and therefore able to predict the soil and crop response to irrigation application) using full data input, while for situations where only two data inputs were available, the simulations suggested that either weather-and-plant or soil-and-plant inputs were preferable. [ABSTRACT FROM AUTHOR]

The potential utility of monomolecular layers ("monolayers") and other surface film materials for the reduction of open water evaporation has long been argued. However, outside the laboratory, trials to quantify the effectiveness of artificial surface films have produced highly variable results after application to water surfaces, whether natural water bodies or managed farm storages. This paper briefl y reviews the physical mechanisms involved in evaporation suppression and the biophysical literature on aquatic surface microlayers. The wide-ranging results from 16 months of outdoor trough-scale and (simultaneous) replicated bucket-scale evaporation reduction trials are interpreted using biophysical measurements made on microlayer and immediate subsurface water samples taken from the experimental troughs. When the prevailing environmental conditions and other ancillary measurements are taken into account, plausible hypotheses arise to account for at least some of the observed trial-to-trial differences in evaporation reduction and surface film performance. Results for the commercial monolayer product are inconclusive, as the concentration of the active ingredient in its formulation lacked the uniformity required for the accuracy at which these trials were conducted. Results for the temperature differential between open (unprotected) water and film-covered water, and the infl uence of windspeed on evaporative loss, indicate that the mechanism of evaporation suppression for mono-molecular (monolayer) organic films differs from that for thicker silicone oil films. These results have implications for both small-scale trialling of evaporation suppressants and the deployment and management of artificial surface film materials on agricultural water storages. In addition, it concluded that despite the attractiveness of simple side-by-side comparisons of performance, meaningful interpretation of results must consider prevailing meteorological conditions, and a timescale of hours rather than days. [ABSTRACT FROM AUTHOR]

Chemical monolayer films are potentially an economical low-impact means of reducing evaporative loss from farm water storages. However, their performance can be highly variable as they are affected by climatic and environmental factors: principally wind, wave action and bio-degradation. Some of this observed variability is associated with the monolayer materials themselves and their interaction with the water-surface physics and biology, but the fact that they are only a few nanometres thick means that a very small amount of material has to be distributed over a very large area. Therefore, appropriate and timely autonomous application of monolayer, with regard to prevailing (and changing) wind conditions on-site, is required. Although a number of autonomous application systems for monolayer already exist, none has proved overly successful. It is argued that while this is in part due to sub-optimal performance of monolayer materials, it is also due in large measure to inaccuracies and/or inappropriate design in both application systems and particularly application strategies, which are not adaptive to the prevailing environmental conditions. Therefore a control system is being developed to adaptively and spatially vary monolayer application rates according to changing conditions monitored on-site. This will form part of an autonomous electromechanical system for the optimal application and spreading of any given chemical monolayer. This paper reports progress towards this objective; firstly by evaluation of the design requirements for automated systems at a range of spatial scales; and secondly via the construction of a first pre-prototype to act as an evaluation platform and concept demonstrator. [ABSTRACT FROM AUTHOR]

An in-field vision system has been developed that automatically and non-destructively measures internode length (i.e., the distance between successive main stem branches) of plants in a growing cotton crop for the purpose of inferring plant growth performance and informing crop irrigation management. The system uses monocular video acquisition behind a plant-contacting transparent panel that moves through the crop. Line features are extracted from acquired imagery to estimate candidate nodes on the plant's main stem via a two-stage process that may be implemented in real-time. Firstly, candidate nodes are identified in each individual image; secondly, the comparison of sequential images permits the removal of erroneously identified nodes (false positives) and compensation for missed nodes (due to occlusion by a leaf, commonly). Ninety-five internode length measurements were automatically detected from 168 video sequences of 14 plants. Algorithm run-time calculations and the rate of internode measurement acquisition were shown to be adequate for real-time input to spatially varied irrigation control. For this data set, the median absolute error was 5.3 mm in comparison with physical plant measurements, and the standard error in measurement ranged from 1.1 to 5.7 mm, with an average of 3.0 mm. [ABSTRACT FROM AUTHOR]