Abstract

Mapping soil properties, using geostatistical methods in support of precision agriculture and related activities, requires a large number of samples. To reduce soil sampling and measurement time and cost, a combination of field proximal soil sensors was used to predict and map laboratory-measured soil properties in a 3.4-ha pasture field in southeastern Brazil. Sensor soil properties were measured in situ on a 10 × 10-m dense grid (377 samples) using apparent electrical conductivity meters, apparent magnetic susceptibility meter, gamma-ray spectrometer, water content reflectometer, cone penetrometer, and portable X-ray fluorescence spectrometer (pXRF). Soil samples were collected on a 20 × 20-m thin grid (105 samples) and analyzed in the laboratory for organic C, sum of bases, cation exchange capacity, clay content, soil volumetric moisture, and bulk density. Another 25 samples collected throughout the area were also analyzed for the same soil properties and used for independent validation of models and maps. To test whether the combination of sensors enhances soil property predictions, stepwise multiple linear regression (MLR) models of the laboratory soil properties were derived using individual sensor covariate data versus combined sensor data—except for the pXRF data, which were evaluated separately. Then, to test whether a denser grid sample boosted by sensor-based soil property predictions enhances soil property maps, ordinary kriging of the laboratory-measured soil properties from the thin grid was compared to ordinary kriging of the sensor-based predictions from the dense grid, and ordinary cokriging of the laboratory properties aided by sensor covariate data. The combination of multiple soil sensors improved the MLR predictions for all soil properties relative to single sensors. The pXRF data produced the best MLR predictions for organic C content, clay content, and bulk density, standing out as the best single sensor for soil property prediction, whereas the other sensors combined outperformed the pXRF sensor for the sum of bases, cation exchange capacity, and soil volumetric moisture, based on independent validation. Ordinary kriging of sensor-based predictions outperformed the other interpolation approaches for all soil properties, except organic C content, based on validation results. Thus, combining soil sensors, and using sensor-based soil property predictions to increase the sample size and spatial coverage, leads to more detailed and accurate soil property maps.

Highlights

  • Proximal soil sensing is increasingly used for mapping soils with high spatial detail to support land management and precision agriculture [1,2]

  • The combination of proximal soil sensors in these models improved predictions of all soil properties investigated compared to individual sensors, disregarding the portable X-ray fluorescence spectrometer (pXRF) sensor. These results show that proximal sensor fusion is superior to individual sensors for soil property prediction

  • The pXRF sensor produced the best predictions for chemical and physical soil properties among individual sensors and outperformed fusion of the other sensors for soil OC content, clay content, and bulk density (BD) prediction

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Summary

Introduction

Proximal soil sensing is increasingly used for mapping soils with high spatial detail to support land management and precision agriculture [1,2]. It entails the use of geophysical field and laboratory sensors to measure soil properties (mechanical, electromagnetic, optical, etc.) to directly or indirectly predict and map soil properties of interest. Other sensor characteristics like portability, ease of use, measurement support, and the capacity to predict multiple soil properties are considered, as well as interfering factors and other limitations

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