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Furrow irrigation and fertigation systems should be designed and managed to optimize the availability of water and fertilizer to plants and minimize their losses through evaporation, deep drainage and leaching. We developed a furrow irrigation submodule for HYDRUS (2D/3D) and used it to evaluate the effects of different furrow soil surface treatments and different timings of fertigation on root water and solute uptake, deep drainage and solute leaching in a loamy soil. Numerical simulations showed that more water was available for transpiration in the treatments with plastic placed at the furrow bottom compared to the control treatments. However, more water was lost due to evaporation and less water was drained from the soil profile for these treatments. The highest and lowest root solute uptake was achieved when fertigation was applied in the middle and at the beginning of the irrigation cycle, respectively. The least amount of solute was leached from the soil profile for treatments with the plastic bottom and when fertigation was applied at the end of the irrigation cycle. The scenarios with plastic and irrigation in alternate furrows showed a reduction in transpiration and yield, more water loss due to deep drainage, and less water lost due to evaporation. However, similar crop yields were obtained for this alternate furrow strategy as for the control furrow surface treatments. When only half the water was used for irrigation in this scenario, the reduction in yield was less than 20 % compared to the control treatments, producing higher water-use efficiency.

This glasshouse pot experiment demonstrated that a new sprayable and degradable polymer reduced soil water evaporation and promoted cotton seedling emergence and establishment. The polymer was tested on two contrasting soils (sandy loam and clay), representative of those used to grow cotton in Australia. Changes in soil water content in nontreated and polymer-treated pots were monitored over 80 days, after surface or subsurface watering. Plant biomass, soil water content and soil chemical properties were determined at harvest. The polymer reduced soil water evaporation by up to 35% in sandy loam and up to 20% in clay, did not compromise seedling emergence and improved plant growth per unit water applied by up to 26.2%. The polymer underwent extensive degradation after 80 days to produce low molecularweight polymers or oligomers and water-extractable silicon species that may have implications for plant nutrition. Additional keywords: clay, mulch, sandy loam, sprayable polymer, water use efficiency. Received 23 October 2019, accepted 11 January 2020, published online 18 February 2020, Introduction As access to water will become more variable in Australia's cotton growing regions due to climate change (Roth et al. 2013), the economic viability of Australia's cotton industry will [...]

Global climate change is projected to continue and result in prolonged and more intense droughts, which can increase soil water repellency (SWR). To be able to estimate the consequences of SWR on vadose zone hydrology, it is important to determine soil hydraulic properties (SHP). Sequential modeling using HYDRUS (2D/3D) was performed on an experimental field site with artificially imposed drought scenarios (moderately M and severely S stressed) and a control plot. First, inverse modeling was performed for SHP estimation based on water and ethanol infiltration experimental data, followed by model validation on one selected irrigation event. Finally, hillslope modeling was performed to assess water balance for 2014. Results suggest that prolonged dry periods can increase soil water repellency. Inverse modeling was successfully performed for infiltrating liquids, water and ethanol, with R2 and model efficiency (E) values both > 0.9. SHP derived from the ethanol measurements showed large differences in van Genuchten-Mualem (VGM) parameters for the M and S plots compared to water infiltration experiments. SWR resulted in large saturated hydraulic conductivity (Ks) decrease on the M and S scenarios. After validation of SHP on water content measurements during a selected irrigation event, one year simulations (2014) showed that water repellency increases surface runoff in non-structured soils at hillslopes.

Application of a new theory for the radial conduction of a short-duration heat pulse away from an infinite line source and the use of a dual-probe instrument help determine various soil thermal properties including thermal diffusivity, heat capacity and conductivity. Experimental results from air-dry sand and clay materials using this heat-pulse theory agree with the results of independent methods. This heat pulse theory is compared with the theory for an instantaneously heated line source.

A simple heat-pulse instrument is used to establish the volumetric heat capacity, and therefore, the water content of porous media. When actual heater-to-sensor probe spacings were employed in the computations, precise variations in soil water content were obtained from the estimates made at three depths during the drying of a laboratory soil column. The instrument has three needle probes. The sensor and reference probes have thermocouples, and the heater probe has a heating element.

Preemergent maize growth was found to be sensitive to small differences in soil drying. The rate at which soil strength increased was critical to the success of maize emergence. Shoot growth was impeded at a cone index of 1.1 megapascals (MPa) and ceased at 2 MPa. The effect of drying rate was not only because of soil water loss but also due to the altered distribution of near-surface soil moisture. The elongation rates of internodes were decreased by high soil strength. Buckling and twisting of the coleoptile were more prevalent at high soil strengths.

ABSTRACT Preformed plastic films produced from nondegradable materials such as poly(ethylene) are widely used in agriculture to enhance crop production by modifying soil temperature, conserving soil water, and supressing weeds, but are generally removed and disposed of after each growing season. We aim to circumvent the need to retrieve and dispose of plastic films by using water-borne, degradable polymers that can be sprayed directly onto the soil surface to form a barrier to reduce soil water evaporation. We report the synthesis and characterization of a series of nonchain extended poly(urethane)s (PUs) for this purpose, that were prepared from poly(dimethylsiloxane) (928.3 g mol−1) and poly(ethylene glycol) (1020 g mol−1). These new materials undergo hydrophobic-hydrophilic switching of their surface properties when in contact with water, which we exploit as a means of minimizing water evaporation from soil when the polymer layer is dry (e.g., in sunny conditions), but permitting the infiltration of liquid water through the treatment into soil during rainfall or sprinkler irrigation. The surface wettability and restructuring phenomena leading to these fascinating properties are intensively investigated using water contact angle measurements, surface-free energy estimates and depth profiling X-ray photoelectron spectroscopy (XPS). Laboratory pot trials demonstrate that soil water evaporation reduced by more than 70% when soil was treated with a low loading of the polymer. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44756. [ABSTRACT FROM AUTHOR]

Water footprint (WF) accounting as proposed by the Water Footprint Network (WFN) can potentially provide important information for water resource management, especially in water scarce countries relying on irrigation to help meet their food requirements. However, calculating accurate WFs of short-season vegetable crops such as carrots, cabbage, beetroot, broccoli and lettuce presented some challenges. Planting dates and inter-annual weather conditions impact WF results. Joining weather datasets of just rainfall, minimum and maximum temperature with ones that include solar radiation and wind-speed affected crop model estimates and WF results. The functional unit selected can also have a major impact on results. For example, WFs according to the WFN approach do not account for crop residues used for other purposes, like composting and animal feed. Using yields in dry matter rather than fresh mass also impacts WF metrics, making comparisons difficult. To overcome this, using the nutritional value of crops as a functional unit can connect water use more directly to potential benefits derived from different crops and allow more straightforward comparisons. Grey WFs based on nitrogen only disregards water pollution caused by phosphates, pesticides and salinization. Poor understanding of the fate of nitrogen complicates estimation of nitrogen loads into the aquifer. [ABSTRACT FROM AUTHOR]

Elevated dissolved organic carbon (DOC) has been detected in groundwater beneath irrigated sugarcane on the Burdekin coastal plain of tropical northeast Australia. The maximum value of 82 mg/L is to our knowledge the highest DOC reported for groundwater beneath irrigated cropping systems. More than half of the groundwater sampled in January 2004 (n=46) exhibited DOC concentrations greater than 30 mg/L. DOC was progressively lower in October 2004 and January 2005, with a total decrease greater than 90% indicating varying load(s) to the aquifer. It was hypothesized that the elevated DOC found in this groundwater system is sourced at or near the soil surface and supplied to the aquifer via vertical recharge following above average rainfall. Possible sources of DOC include organic-rich sugar mill by-products applied as fertilizer and/or sugarcane sap released during harvest. CFC-12 vertical flow rates supported the hypothesis that elevated DOC (>40 mg/L) in the groundwater results from recharge events in which annual precipitation exceeds 1500 mm/year (average=960 mm/year). Occurrence of elevated DOC concentrations, absence of electron acceptors (O2 and NO3- ) and both Fe2+ and Mn2+ greater than 1 mg/L in shallow groundwater suggest that the DOC compounds are chemically labile. The consequence of high concentrations of labile DOC may be positive (e.g., denitrification) or negative (e.g., enhanced metal mobility and biofouling), and highlights the need to account for a wider range of water quality parameters when considering the impacts of land use on the ecology of receiving waters and/or suitability of groundwater for irrigated agriculture. [ABSTRACT FROM AUTHOR]