Soil pH Mapping with an On-The-Go Sensor

Michael Schirrmann,Jan Seidel,Eckart Kramer,Robin Gebbers

doi:10.3390/s110100573

Michael Schirrmann, Jan Seidel + Show 2 more

Open Access

https://doi.org/10.3390/s110100573

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Abstract

Soil pH is a key parameter for crop productivity, therefore, its spatial variation should be adequately addressed to improve precision management decisions. Recently, the Veris pH Manager™, a sensor for high-resolution mapping of soil pH at the field scale, has been made commercially available in the US. While driving over the field, soil pH is measured on-the-go directly within the soil by ion selective antimony electrodes. The aim of this study was to evaluate the Veris pH Manager™ under farming conditions in Germany. Sensor readings were compared with data obtained by standard protocols of soil pH assessment. Experiments took place under different scenarios: (a) controlled tests in the lab, (b) semicontrolled test on transects in a stop-and-go mode, and (c) tests under practical conditions in the field with the sensor working in its typical on-the-go mode. Accuracy issues, problems, options, and potential benefits of the Veris pH Manager™ were addressed. The tests demonstrated a high degree of linearity between standard laboratory values and sensor readings. Under practical conditions in the field (scenario c), the measure of fit (r2) for the regression between the on-the-go measurements and the reference data was 0.71, 0.63, and 0.84, respectively. Field-specific calibration was necessary to reduce systematic errors. Accuracy of the on-the-go maps was considerably higher compared with the pH maps obtained by following the standard protocols, and the error in calculating lime requirements was reduced by about one half. However, the system showed some weaknesses due to blockage by residual straw and weed roots. If these problems were solved, the on-the-go sensor investigated here could be an efficient alternative to standard sampling protocols as a basis for liming in Germany.

Highlights

The pH value is the negative logarithm of the molar concentration of protons in a solution: pH log aH mol L 1 (1)As a measure of soil acidity or alkalinity, soil pH constitutes one of the most important chemical soil parameters [1]
Preceding tests under controlled conditions demonstrated a high degree of linear relationship between standard laboratory soil pH values and sensor pH values
This is of importance because differences in soil pH of 0.1 units can lead to differences in lime recommendations of up to 400 kg·ha−1 CaO

Summary

Introduction

As a measure of soil acidity or alkalinity, soil pH constitutes one of the most important chemical soil parameters [1]. Soil pH values outside the range of 5.5 to 6.5 are considered as nonoptimum because they can have negative impacts on nutrient availability [2,3], soil structure [4], soil organisms [5], and can make plants more sensitive to diseases [6]. Due to uptake by plants and natural leaching of alkaline soil compounds, acidification is common among soils in temperate climates. The regulation of soil pH by applying alkaline or acid fertilizers can limit effects of extreme acidic or alkaline soil conditions, which in turn improves crop production and resource efficiency [7]. Soil pH regulation becomes a vital strategy within a radically changing world, where globally average crop yields must be increased by 60% to 120% until 2050 to meet the needs of the human population and dietary habits [8]

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