Gunawardena T.A.,1 Boggo Road |
McGarry D.,1 Boggo Road
Soil Research | Year: 2011
Rising groundwater and salinity are potential risks across irrigated agricultural landscapes. Water is scarce in many areas that will benefit from efficient water use. Excessive deep drainage (DD, mm) beneath irrigated crops is undesirable because it may cause salinity and decrease water-use efficiency. Nine irrigated, commercial cotton fields (eight furrow-irrigated and one spray, lateral-move irrigated) were selected in the upper MurrayDarling Basin, on Vertosols with a wide range of clay contents (3875%). The lysimeters used, described as 'confined, undisturbed, constant tension, non-weighing', were installed to capture water passing 1.5m depth at three in-field positions: (i) near the head ditch, (ii) mid-way between head and tail ditches, and (iii) close to the tail ditch. At two sites, infiltration along the length of the field was monitored in two seasons using furrow advance-SIRMOD methods. Seasonal DD values of up to 235mm (2.4ML/ha.season) were measured (range 1235mm), equivalent to 27% of the irrigation applied at that location in that season. Individual DD events 90>mm accounted for 15 of 66 measured values from 26 furrow irrigations. DD varied strongly along the length of each field, with DD commonly reducing from the head ditch to the tail ditch. SIRMOD simulation mirrored this trend, with large decreases in infiltration amounts from head to tail. Greater DD at head locations was attributed to long periods of inundation, especially early in the season when siphons (in-flows) were allowed to run for up to 24h. Most of the DD occurred during pre-irrigation and the first two or three in-crop irrigations. Inter-season variation in DD was large; limited water supply in drought years led to fewer irrigations with smaller volumes, resulting in little or no DD. The DD under lateral-move, spray irrigation was almost zero; only one irrigation event in 4 years resulted in DD. Control of DD under furrow irrigation can be achieved by changing irrigation management to lateral-move, spray irrigation, which minimises DD and greatly increases water-use efficiency with no yield (cotton) penalty. Across all of the lysimetry sites, high salinities of the DD leachate indicated that large amounts of salt were being mobilised. The fate and impacts of this mobilised and leached salt are uncertain. © 2011 CSIRO.
Stork P.R.,Australian Department of Primary Industries and Fisheries |
Lyons D.J.,1 Boggo Road
Soil Research | Year: 2012
Phosphorus (P) in overland flow from horticulture farms in coastal Queensland, Australia, could eutrophy coastal freshwater and marine habitats environments nearby. The potential for such eutrophication was investigated in a coastal macadamia plantation under commercial production. During the 13-month study, P losses in overland flow were quantified in a 0.24-ha farm catchment with a 3.1% gradient, during five consecutive storm events. These events were within expected short- and long-term episodic rainfall frequencies and intensities. Runoff occurred when such storms generated between 20-40mm/h of rainfall for >9min. Calculated annual losses of total P were 0.32kg/ha.year, comprising dissolved inorganic P (DIP, 0.28kg/ha.year), particulate P (0.03kg/ha.year), and dissolved organic P (0.01kg/ha.year). DIP represented 88% of all losses and this was attributed to excessive fertilisation and untimely applications. Losses of total P were generally higher than those reported in comparable studies. Concentrations of DIP in runoff were 20200-fold higher than those found in other coastal catchments in Queensland. High concentrations of DIP were present in the topsoil of the non-fertilised, inter-row areas of the farm catchment and this was attributed to transfer and deposition of DIP from adjacent fertilised tree beds during storm flow. Therefore, it can be expected that farm runoff will be enriched with DIP from these areas for an indeterminate period despite any future remediation to fertiliser management. The weighted average of DIP in farm runoff was 2.01mg/L, whereas it was 0.005mg/L in a catchment stream bordering the farm, showing a steep concentration gradient between the two ecosystem compartments. Together with nitrogen (N) losses in runoff, reported previously, an N:P molar ratio of 2:1 was contained in the farm runoff. This was well below the growth-limiting threshold for aquatic organisms, as determined by the Redfield ratio of 16:1 (N:P). The entry of nutrient-enriched farm runoff, as detailed in this study, into the catchment stream and the proximity of such waterways (8km) to the coastline may also have implications for the near-shore (oligotrophic) marine environment during periods of storm flow. Altogether, this work revealed the high risk of eutrophication from farming landscapes such as the one under study. © 2012 CSIRO.
Ahmad W.,University of Sydney |
Singh B.,University of Sydney |
Dijkstra F.A.,University of Sydney |
Dalal R.C.,1 Boggo Road |
Dalal R.C.,University of Queensland
Soil Biology and Biochemistry | Year: 2013
Lime is commonly used to overcome soil acidification in agricultural production systems; however, its impact on inorganic and organic soil carbon dynamics remains largely unknown. In a column experiment, we monitored rhizosphere effects on lime dissolution, CO2 effluxes, and the concentrations of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in leachate from an acidic Kandosol. The experiment consisted of four treatments viz: soil only (control), soil + lime, soil + wheat, and soil + lime + wheat. We measured CO2-C effluxes at 7, 43 and 98 days after planting (DAP) and leachate was collected at 56 and 101 DAP. The soil CO2-C efflux rate increased significantly with lime addition at 7 and 43 DAP compared to control. At 43 DAP, the largest increase in CO2-C effluxes was observed in the lime + wheat treatment. However, at 98 DAP similar CO2-C effluxes were observed from wheat and lime + wheat treatments, suggesting that most of the lime was dissolved in the lime + wheat treatment. Both DOC and DIC concentrations in the leachate increased significantly with lime and wheat only treatments (cf. control). In contrast to DOC, there was an increase in the DIC concentration in the soil leachate from lime + wheat treatment columns at 101 DAP (significant wheat × lime interaction), thus, accentuating the pronounced role of wheat roots. We conclude that plant mediated dissolution of lime increased the concentration of DIC in the soil leachate, while both liming and presence of plants enhanced DOC leaching. © 2012 Elsevier Ltd.
Mankad A.,CSIRO |
Chong M.N.,CSIRO |
Gardner T.,1 Boggo Road |
Water Resources Management | Year: 2012
This study examines biophysical and socio-demographic factors potentially affecting water use patterns of households with mandatory rainwater tanks in South East Queensland (SEQ). The Queensland Development Code (QDC) MP 4.2 promotes the use of rainwater tanks at the domestic level to reduce direct reliance on mains water supply. A sample of 1,134 mandated rainwater tank households were surveyed across SEQ. Results indicated that the majority of participants (78%) had tanks of 5 kL in capacity or larger, with 35% of householders having at least half of roof catchment area connected to their tanks. Also, the majority of participants utilised their rainwater for toilet flushing (97%), clothes washing (94%) and garden irrigation (77%). These biophysical findings indicate a high level of compliance with the QDC MP 4.2 code. Social factors affecting potential yields from mandated rainwater tanks were also examined, to complement the biophysical data obtained. It was found that the majority of tank users were happy to use rainwater as an alternative water supply option for non-potable uses. However, most participants reported being unaware of past or present water restrictions to their water supply, highlighting important social implications for total mains water savings. In conclusion, this study presents important biophysical and social descriptions about mandated water users in urban SEQ, as well as providing a foundation for future modelling of actual yields from mandated rainwater tanks to facilitate improved assessment of mains water savings due to the implementation of mandated rainwater tanks. © Springer Science+Business Media B.V. 2012.