Assessment of temporal and spatial variability of soil salinity in a coastal saline field

Many coastal tideland areas in southern Hangzhou Gulf in Zhejiang Province of China have been successively enclosed and reclaimed for agricultural land uses under a series of reclamation projects over the past 30 years. The variability of soil salinity was considerably great and an understanding of the temporal and spatial components of soil salinity variability is essential before decisions can be made about the feasibility of site-specific management. In this paper, a 5.35-ha field reclaimed in 1996 was selected as the study site and 112 bulk electrical conductivity (EC_b) measurements were performed in situ by a hand held device in the topsoil (0–20 cm) at regular 20-m intervals across the field over a two-year period. Conventional statistics and geostatistical techinques were used to assess the spatial variability and temporal stability of soil-salinity distribution. The results indicated high coefficients of variation in topsoil salinity over the three samplings. Simple mean EC_b comparison revealed that soil salinity increased from winter to spring. Kriged contour maps showed the spatial trend of salinity distribution and revealed the consistently high and low salinity areas of the field. In percentage terms, the proportions of the moderately saline class, strongly saline class, and extremely saline class were 37, 39, and 24%, respectively. Temporal stability map indicated that more than 60% of the study field was determined as the stable class. Based on the spatial and temporal characteristics, a similarity assessment map was created, which presented 5 homogenous sub-zones, each with different characteristics that can have an impact on the way the field is managed. It was concluded that saline soil land might be managed in a site-specific way based on the clearly defined management sub-regions within the field.