Salinity Problems of Temora
A Case Study on the Salinity Problems of Temora, NSW Isolated outbreaks of dry land salinity have begun to occur on farms in Southern NSW. Strategies to quantify and lower the damage of dry land salinity are reported for a case study in Temora. An electromagnetic survey (The Electromagnetic Method measures earth’s response to electromagnetic signals transmitted by an induction coil. The induction coil produces magnetic field alternating at various frequency. The alternating magnetic field induces electric current in the material under the ground, which in turn produces secondary magnetic field.
The electromagnetic sensor measures intensity of this magnetic field. Response to high-frequency signal comes from shallow part of the ground, while deeper part of the earth responds to low-frequency signal. ) Revealed that a saline scald of about 0. 4 hectares was associated with a further 20 hectares of high subsoil salinity. Crop production losses which had attributed to salinity in 1999 were 100 per cent with the scald, but decreased 30 per cent near the scald.
Lucerne (a flowering plant in the pea family cultivated as important forage for crops) Established in 100 hectares around the scald lowered the water table in one year, and the rain leached surface salt into the subsoil so that in 2000 crops grew in areas where they failed in the previous year. In the winter of 2000, the water table rose under the scald but not under the surrounding lucerne, indicating that control of recharge from higher in the catchment is needed to reduce discharge in addition to reduction of the local water table.
The area of dry land salinity in New South Wales is predicted to increase by 60 within 50 years, affecting both mixed-farming (300-600 mm annual rainfall) as well as permanent pasture regions 0ver 600mm. The reports also propose that there is little or nothing that ‘conventional’ agriculture can do to prevent the spread of salinity and much of the agricultural landscape will need to be returned to woodland. People find these predictions surprising for areas where there is little visible evidence of surface salinity.
In the Temora district of southern NSW (540 mm annual rainfall) there are few saline scalds and landholders believe they can control salinity using perennial pastures to lower the water table. A saline scald on a farm near Temora first appeared in the late 1980’s and by the late 1990s covered two patches with a combined area of 0. 4 hectares where a thin crust of salt covers the soil surface. The affected area is 50 m upslope from a road and at the foot of a 2 km long slope.
In order to lower the water table and reduce the spread of salinity, the landholder established lucerne in 1999 by under sowing it with wheat over 100 hectares next to, and uphill from, the scald. The extent and severity of salinity over the farm was measured as soil electrical conductivity (EC) using a motorbike-mounted electromagnetic induction sensor (EM31) attached to a GPS unit. Impact of salinity on crop and pasture production
Plant establishment was poor for most crop and pasture species within the scald, and the growth and yield of surviving plants was limited The table shows Species and varieties of crops and pastures sown in salted and unsalted land in 1999. Density of the crop species was measured in 1999 and of the pastures in 2000. All crop and pasture species tested established in areas outside the scald where EC was up to 1. 2m. Plant productivity varied according to level of salinity and position in the landscape.
Data for two crops (wheat, canola) are presented in Fig 2. Wheat was more salt tolerant than canola, as shown by the rate of yield decrease with increasing Using lucerne to reduce salinity Piezometers (An instrument for measuring the pressure of a liquid or gas, or something related to pressure (such as the compressibility of liquid) were installed in the scalds and on fence lines beside the established lucerne. Between spring 1999 and autumn 2000 the water table under the scalds fell from the surface to depths between 75 and 150 cm.
The following several weeks of rainfall in winter 2000, the water table rose to close to the surface under the scalds but not under the surrounding lucerne. The salinity of the groundwater under the scalds and lucerne was more stable than the height of the water table over the period of measurement, but with some fluctuations, apparently reflecting pulses of salt or fresh water. This picture shows the water depth and groundwater salinity in 3 piezometers marked on Fig. 1.