Impact of spatially variable soil salinity on crop physiological properties, soil water content and yield of wheat in a semi arid environment

In the Birchip region of the Victorian southern Mallee, Australia, subsoil salinity is an important factor determining crop growth and yield. Crop simulation models have performed poorly in this region, presumably due to their inability to account for subsoil constraints, mainly salinity. The objective of this work was to study the impact of subsoil salinity on crop physiological properties, growth, water use and yield of a wheat crop. From a calibrated electromagnetic survey (EM 38) over an area 7 m wide by 100 m long, three sites of low, medium and high salinity levels were identified. For each site, soil electrical conductivity was measured and the values averaged for the depth 0-70 cm were 0.25, 1.14 and 1.63 dS/m at the sites with low, medium and high salinity, respectively. Further, at different stages of crop growth, radiation interception by the canopy as well as soil water content were measured while plant samples were collected to estimate crop physiological properties. Grain yield at each salinity site was also measured. All the physiological properties and yield were negatively affected by increasing salinity levels due to less water use and radiation interception. Compared to the low salinity level, medium and high salinity levels reduced the above-ground dry weight of the crop at harvest by 40% and 41%, accumulated intercepted radiation by 23% and 37%, radiation use efficiency by 25% and 52%, water use by 18% and 35% and grain yield by 41% and 48%, respectively