Determining soil salinity and plant biomass response for a farmed coastal cropland using the electromagnetic induction method

Apparent electrical conductivity (ECa) measured by electromagnetic induction (EM) instruments has been successfully used as an ancillary variable to estimate soil salinity from field to watershed scales. It is particularly useful in the case of coastal farming area where reliable estimates of soil salinity aid farmers and researchers in understanding the development of salinization and establishing appropriate management practices. The objectives of this research were to estimate soil salinity (ECe) using intensive EM survey data and prediction equations relating soil salinity to ECa, to determine the optimal data interval in EM survey and to validate the prediction reliability using plant biomass response to soil salinity. This study was conducted in a typical coastal rain-fed farmland in north Jiangsu Province, China. The results indicated that apparent electrical conductivity showed significant correlation with ECe and EM readings from the horizontal coil orientation can be used as the sole predictor in a linear mixed model. Field EM survey data exhibited directional trend resulting from the impact of anthropogenic activities on soil salinity. An optimal sampling interval of 16 m in the survey transect essentially meets the need of spatial prediction when field EM survey is performed. Soil salinity increased with depth and higher soil salinity mainly occurs in areas where rice was previously planted, particularly in lower-lying regions and areas adjacent to the aquaculture plant. Plant biomass is negatively related to both, measured and estimated soil salinity. The relation to measured soil salinity was closer than to estimated soil salinity. Boundary line analysis shows that root zone salinity (ECe) causes a 4.4% and 6.4% plant biomass reduction per dS/m for rice and cotton, respectively. Such results allowed us to conclude that a larger data interval of EM survey than the present could produce satisfactory estimation accuracy of field soil salinity, and the relationship between soil salinity (or ECa data) and plant biomass could help to derive site specific yield goals and management practices in the farmed coastal cropland.