EM-38 for assessing surface and sub-soil salinity and its relationship to establishment and growth of selected perennial pasture species
NSW Agriculture, Yanco Agricultural Institute, Yanco, NSW 2703, Australia. Email: email@example.com
Geonic electromagnetic induction equipment (EM-38) is now commonly used for mapping soil salinity of agricultural fields or landscape due to its rapid and cost-effective in situ measurements. However, its use in quantitative diagnosis of surface (0-15 cm or 0-30 cm) soil salinity is limited notwithstanding its importance to predict establishment and agronomic growth of most agricultural crops. This investigation was thus aimed at evaluating the use of EM-38 to measure surface and sub-surface salinity both in space and time, and relationship of EM-38 readings to observations on growth and establishment of selected perennial pasture species on two different soils underlain with shallow and saline water table. Notwithstanding significant relationships of EC1:5 with ECe (r2 = 0.98) and ECP (r2 = 0.95), the relationships between ECe of surface (0-15 cm or 0-30 cm) soil layers and EM-38 readings were not significant. In addition, ECe predicted from EM-38 calibrations were highly variable and less accurate both in space and time. Hence, the predictability of ECe from EM-38 readings (ECa) values seems less promising as the latter is very sensitive to changes in soil moisture profiles both in space and time. In addition, the relationships of ECa with observations on establishment and growth of perennial pasture species were of low magnitude. However, ECa values, showed relatively better relationship with ECe or EC1:5 of sub-soil layers especially 60-90 cm and 90-120 cm layers. Field soil moisture, clay content of soils and their saturation percentage as measured in laboratory were found to influence ECa readings significantly. Intensity and magnitude of moisture fluctuations are generally greater in the surface than sub-soil layers under field situations and may probably be responsible for observed poor relationships. These observations construe that although EM-38 is a useful instrument for mapping soil salinity of a landscape or paddocks into different soil salinity categories, its potential to test surface soil salinity for the desired agronomic accuracy is limited.