Modelling the impact of pulsing of drip irrigation on the water and salinity dynamics in soil in relation to water uptake by an almond tree

Pulsing is the application of daily irrigation in a phased manner involving one hour irrigation and one hour off. A field experiment was conducted involving pulsed and continuous irrigation to almonds through surface drip during 2009– 10, and water applications and moisture distribution in the soil were monitored throughout the season. A finite element numerical model (HYDRUS 2D) was used to evaluate the impact of pulsed application of irrigation on water balance and salinity distribution in the soil. The modelled values of moisture content matched well with the weekly measured neutron probe values at all soil depths (10 cm to 160 cm) with RMSE of mean values varying from 0.01 to 0.08 and 0.01 to 0.05 in pulsing (Ip) and continuous (Ic) treatments respectively. The simulated seasonal water uptake was slightly higher (25 mm) in pulsing than continuous irrigation, whereas the soil storage was slightly higher (20 mm) under continuous irrigation. The leaching fraction amounts to 0.25 in both treatments and was higher during August and March-April because the water requirement of almond early in the growing season and after harvest remained relatively low. The salinity distribution was similar in both treatments and simulated average salinity of soil solution varied from 0.47 to 3.38 dS/m and 0.49 to 3.67 dS/m in Ip and Ic treatments respectively. Hence the modelling simulations revealed that pulsed irrigation at higher discharge rate (3.87 l/h) produced similar water and salinity distribution in the soil as obtained in low discharge (2 l/h).V. Phogat, M. A. Skewes, J. W. Cox & M. Mahadeva

Soil water and salinity dynamics under sprinkler irrigated almond exposed to a varied salinity stress at different growth stages

Water use and salinity dynamics in the soils are the crucial management factors influencing the productivity and long-term sustainability of almond and associated environment. In this study, HYDRUS-2D was calibrated and validated on measured spatial and temporal water contents and soil salinities (ECe) distributions under almond irrigated with different water qualities (ECiw) at different physiological stages. During two irrigation seasons (2014–15 and 2015–16), less saline irrigation water (average ECiw 0.78 dS/m) was substituted for recycled irrigation water (average ECiw 1.9 dS/m) in three phenologically different growth stages; pre-pit hardening, kernel growth, and post-harvest, along with no and full substitution during the entire season. Graphical and statistical comparisons (RMSE, MAE, ME, the Nash and Sutcliffe model efficiency, and the coefficient of determination) between measured and simulated values of water contents and ECe in the soil showed a close agreement in all treatments. The water balance data revealed that the seasonal crop evapotranspiration of almond (ETc) varied from 850 to 955 mm in different treatments over the two seasons which represented 68–79% of the water application. Trees irrigated with only less saline water through the two seasons (average ECiw 0.78 dS/m) showed 10% higher plant water uptake as compared to those irrigated with recycled water only (average ECiw 1.9 dS/m). Substituting less saline irrigation during the kernel growth phase, between pit-hardening and harvest, showed greater water uptake by almond and lower salinity buildup in the soil as compared to treatments that substituted less saline irrigation early or late in the season. For all treatments, the average daily root zone ECe (2.4–3.7 dS/m) remained above the level of the almond salinity tolerance threshold (ECe = 1.5 dS/m) throughout the period of investigation. Water use efficiency of almonds varied in a narrow range (0.21–0.25 kg m⁻³) for different treatments. Deep drainage below the root zone (2 m) varied from 22.4–31.1% of the total water application (Rainfall + Irrigation), which was episodic and insufficient to contain the salinity below the almond threshold. This study provided a greater understanding of soil water and salinity dynamics under almond irrigated with waters of varying qualities.V. Phogata, T. Pitt, J.W. Cox, J. Šimůnek, M.A. Skewe

Evaluation of water movement and nitrate dynamics in a lysimeter planted with an orange tree

Adoption of high input irrigation management systems for South Australian horticultural crops seeks to provide greater control over timing of irrigation and fertilizer applications. The HYDRUS 2D/3D model was used to simulate water movement in the soil under an orange tree planted in a field lysimeter supplied with 68.6mm of irrigation water over 29 days. Simulated volumetric water contents statistically matched those measured using a capacitance soil water probe. Statistical measures (MAE, RMSE, tcal) indicating the correspondence between measured and simulated moisture content were within the acceptable range. The modelling efficiency (E) and the relative efficiency (RE) were in the satisfactory range, except RE at day 19. Simulated daily and cumulative drainage fluxes also matched measured values well. Cumulative drainage flux was 48.9% of applied water, indicating large water losses even under controlled water applications. High drainage losses were due to light texture of the soil and high rainfall (70mm) during the experimental period. Simulated root water uptake was 40% of applied water.V. Phogat, M.A. Skewes, J.W. Cox, J. Alam, G. Grigson, J. Šimůne

Orthomagmatic quartz and post-magmatic carbonate veins in a reported porphyry copper deposit, Andean Intrusive Suite, Livingston Island, South Shetland Islands

A previously reported porphyry Cu + Mo deposit in an Eocene pluton within the South Shetland Island magmatic arc has been re-interpreted as three distinct hydrothermal assemblages. The oldest assemblage (1) exsolved under confinement from the deep (∼6 km?) cooling magma whereas assemblages (2) and (3) formed during tectonic ± magmatic episodes at depths of < 1.5 km in the late Cenozoic. The three assemblages occur over the 5 × 11 km mapped in Barnard Point tonalite pluton. Assemblage (1) comprises shallowly dipping sheets of aplite, biotite + tourmaline pegmatite, massive ‘grey’ quartz, and quartz + tourmaline + bornite + chalcopyrite + molybdenite veins. Magnetite + tourmaline + chalcopyrite breccias have associated biotite, K-feldspar and muscovite alteration. Fluid inclusions indicate formation from hot (∼600°C), saline (40 equivalent weight % NaCl + CaCl2) aqueous-carbonic fluids that exsolved from the partly consolidated magma. The primary control on solution chemistry and nature of fracturing was the depth of pluton emplacement. Assemblage (2) consists of steep, vuggy veins and country-rock breccias, with thick propylitic alteration selvages, cemented by microcrystalline quartz, complex inter-growths of FeMg carbonate, bladed barite and trace amounts of bornite and chalcopyrite. These rocks, previously described as breccia (sensu ‘pebble’) dykes in the porphyry complex, are reinterpreted as an influx of moderately hot (175–330°C), weak to moderately saline (2–21 EWP NaCl), aqueous-carbonic fluids that underwent isobaric boiling at 0.8 to 1.3 km depth. Assemblage (3) consists of thin, hematitic fault infillings formed during a second episode of brittle faultin