Abstract
Grape is one of the major crops produced in California; however, moderate salt concentrations in the soil pore space can affect its growth. Therefore, it is important that the root zone salinity be rigorously monitored and maintained below the threshold limit for grape. Spatial analysis of salt heterogeneity can facilitate site-specific management for the crop. We conducted an electromagnetic salinity survey followed by semivariance modeling and kriging analyses in order to quantify the spatial variability and structure of salt distributions in a central Californian grape field. Soils in the study area had silty clayey texture and the salinity across the root zone remained largely elevated with random variations. Around 78 and 19 % of the salinity values remained in the 3-4 and 4-4.5 dS m-1 ranges, respectively. The 3.5-4 dS m-1 level represented one of the most abundant concentrations across the areas of salt build up in the grape field. Based on our variogram and crossvalidation analyses, the Gaussian model fitted best to the salinity data (r2 = 0.996, RSS = 0.0003). The salt heterogeneity was characterized by high structural variance (99 %) and low nugget effect (C0 = 0.014). The kriging analysis demonstrated a large spatial dependence of salinity that extended beyond a 1000 m radius. The isotropic nature of the spatial correlation structure produced an omnidirectional variogram. The overall salinity levels across the field surpassed the salt tolerance threshold for grape and the spatial analyses identified sensitive zones and their structures that require precise adaptive management.
Highlights
California is one of the most productive agricultural regions in the world growing over 250 crops, including grapes
A dual-dipole EM survey was conducted in a 25-ha grape field of central California, where the soils belonged to the Lethent series characterized by clayey saline properties that became further affected by intensive irrigation and inadequate drainage (Cal EPA, 2006; USDA, 2006 & 2014)
Under continuous global climate changes, it is necessary that root zone salinity be rigorously monitored and maintained below the threshold values for grape with due attention to irrigation water and soil type management
Summary
California is one of the most productive agricultural regions in the world growing over 250 crops, including grapes. In central California, grape is one of the major crops grown, supplying about three quarters of the state production. Many irrigated lands within this area have been undergoing salinization that is subsequently affecting crop production (Cal EPA, 2006). Deteriorations of these lands are attributed to several factors including soil texture, inherent soil salinity, high evapotranspiration, and irrigation with saline water. Land degradation due to salt buildup has already affected many agricultural ecosystems around the globe (Metternicht & Zinck, 2003; Martinez-Beltran & Manzur, 2005)
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