Abstract
Efficient water use planning is crucial for the sustainability of irrigated agriculture in California, where alluvial geological materials with indigenous salts impinge on crop growth. To facilitate irrigation scheduling and cultivation planning, it is necessary to determine water percolation quotients (WPQ) required for removal of excess salts from the rhizosphere. In order to estimate real-time WPQ, we conducted electromagnetic geophysical surveys at a saline farmland followed by stochastic computations. Results showed a wide variability in salinity that reached 16 dS m-1 in some locations. About 95% of the surveyed samples surpassed 2 dS m-1. Despite spatially dependent asymmetric variability and skewness (-0.13 to 1.90), the WPQ distribution patterns were consistently quantified with low errors (< 0.06). The sensor responses in the fields reached 100% cumulative frequency at a threshold of 13.6 dS m-1. Up to 49% of WPQ data ranged from 0.1 to 0.2. The WPQ decreased with increasing salinity and the zones with low quotient values represented areas where plant growth could be impaired. High WPQ levels demarcated zones with potential solute dissolution and dispersion. Overall, evaluation of WPQ can benefit irrigation planning and crop management practices while enhancing water use efficiency for agricultural production in farms that have been affected by drought and water shortage, and crop growth can be sustained at WPQ level that maintains salts below the crop tolerance threshold.
Highlights
Geological parent materials in many agricultural lands of California are predominated by alluvial geomorphic structures that are primarily composed of shale and sandstone deposits containing elevated levels of indigenous salts (McNeal & Balisteri, 1989)
Water shortage and terrestrial upsurge of salts are persistent problems around the globe including in Californian agricultural lands (FAO, 2011; Howitt et al, 2014)
Our geophysical method offered non-invasive estimation of soil salinity and water percolation quotient (WPQ) with high resolution, and the results showed their spatial distributions and frequencies within the rhizosphere
Summary
Geological parent materials in many agricultural lands of California are predominated by alluvial geomorphic structures that are primarily composed of shale and sandstone deposits containing elevated levels of indigenous salts (McNeal & Balisteri, 1989). Shallow clay layers and inadequate drainage in these areas result in reduced water percolation and salinity buildup that impair soil structure and crop growth (USGS, 2015). Agricultural productivity of these farmlands is heavily dependent on irrigation. 45% of irrigated agricultural lands in California are impacted by soil or water-induced salinity (Letey, 2000). For mitigating these adverse conditions, it is necessary to develop a precise water percolation quotient (WPQ) in order to remove salts from the rhizosphere and maintain a tolerable salinity for plants. The sensing approach allows for real-time above-ground measurements and provides a better, rapid and economical option as compared to the invasive traditional methods (Hendrickx et al, 1992; Diaz & Herrero, 1992; McKenzie et al, 1997; Sudduth et al, 2003)
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