Spatial variability of bulk soil electrical conductivity in a Malaysian paddy field: key to soil management

Dryland pastures in the Alentejo region, located in the south of Portugal, normally occupy soils that have low fertility but, simultaneously, important spatial variability. Rational application of fertilizers requires knowledge of spatial variability of soil characteristics and crop response, which reinforces the interest of technologies that facilitates the identification of homogeneous management zones (HMZ). In this work, a pasture field of about 25 ha, integrated in the Montado mixed ecosystem (agro-silvo-pastoral), was monitored. Surveys of apparent soil electrical conductivity (ECa) were carried out in November 2017 and October 2018 with a Veris 2000 XA contact sensor. A total of 24 sampling points (30 × 30 m) were established in tree-free zones to allow readings of normalized difference vegetation index (NDVI) and normalized difference water index (NDWI). Historical time series of these indices were obtained from satellite imagery (Sentinel-2) in winter and spring 2017 and 2018. Three zones with different potential productivity were defined based on the results obtained in terms of spatial variability and temporal stability of the measured parameters. These are the basis for the elaboration of differentiated prescription maps of fertilizers with variable application rate technology, taking into account the variability of soil characteristics and pasture development, contributing to the sustainability of this ecosystem.

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TDR estimation of the resident concentration of electrolyte in the soil solution

Soil Research ◽

10.1071/s96089 ◽

1997 ◽

Vol 35 (3) ◽

pp. 515 ◽

Cited By ~ 15

Author(s):

I. Vogeler ◽

B. E. Clothier ◽

S. R. Green

Keyword(s):

Electrical Conductivity ◽

Soil Solution ◽

Electrolyte Concentration ◽

Time Domain Reflectometry ◽

The Other ◽

Bulk Soil ◽

Small Scale ◽

Soil Electrical Conductivity ◽

Soil Columns ◽

Leaching Experiments

In order to examine whether the electrolyte concentration in the soil solution can be estimated by time domain reflectometry (TDR) measured bulk soil electrical conductivity, column leaching experiments were performed using undisturbed soil columns during unsaturated steady-state water flow. The leaching experiments were carried out on 2 soils with contrasting pedological structure. One was the strongly structured Ramiha silt loam, and the other the weakly structured Manawatu fine sandy loam. Transport parameters obtained from the effluent data were used to predict the transient pattern in the resident electrolyte concentration measured by TDR. The electrolyte concentration was inferred from the TDR-measured bulk soil electrical conductivity using 2 different calibration approaches: one resulting from continuous solute application, and the other by direct calibration. Prior to these, calibration on repacked soil columns related TDR measurements to both the volumetric water content and the electrolyte concentration that is resident in the soil solution. The former calibration technique could be used successfully to describe solute transport in both soils, but without predicting the absolute levels of solute. The direct calibration method only provided good estimates of the resident concentration, or electrolyte concentration, in the strongly structured top layer of the Ramiha soil. This soil possessed no immobile water. For the less-structured layer of the Ramiha, and the weakly structured Manawatu soil, only crude approximations of the solute concentration in the soil were found, with measurement errors of up to 50%. The small-scale pattern of electrolyte movement of these weakly structured soils appears to be quite complex.

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