Plant and Soil Testing

A review of advanced soil and plant testing technologies in agriculture

Accurate soil and plant testing is essential for maintaining sustainable crop production and effective ecosystem management. Understanding soil fertility, plant health and nutrient availability is critical for optimizing crop yields, minimizing environmental impact and promoting long-term soil health.

Traditionally, soil and plant testing relied heavily on laboratory methods, but advances in technology have revolutionized the way testing is conducted. Today, innovative tools such as infrared (IR) spectroscopy, remote sensing, electrochemical sensors, smartphone-based tools and soil data management platforms provide faster, more efficient, and real-time solutions.

Traditional Soil and Plant Testing Methods

Wet chemical extractions (including Mehlich-3). Wet chemical extraction methods, such as Mehlich-3, Bray-1, Olsen and ammonium acetate, are essential for determining macronutrient availability, including phosphorus, potassium, calcium and magnesium. These methods dissolve soil nutrients using specific reagents, and the resulting solution is analyzed through spectrophotometry or colorimetry.

Mehlich-3 is the most versatile of these extractions — it is applicable across a wide range of soil pH levels and is highly accurate (R 2 > 0.95 for P and K). However, as with most wet chemical methods, the process is time-consuming and labor-intensive, often taking days to produce results. This limits farmers’ ability to respond quickly to soil nutrient changes during critical growing periods.

Physical soil properties. Traditional methods like gravimetric techniques, pressure plates and pycnometers are used to measure physical soil properties such as bulk density, porosity and moisture retention. These metrics are vital for understanding soil structure and water retention, particularly in irrigation-dependent regions. However, these tests are labor-intensive and do not provide real-time data, making them less feasible for large-scale or continuous monitoring.

Dry combustion and Kjeldahl methods. Dry combustion and Kjeldahl methods are widely used to measure total nitrogen (N) and organic carbon (C) in soils. Dry combustion quantifies organic carbon by burning soil samples and measuring carbon dioxide, while Kjeldahl digests samples in sulfuric acid to convert organic nitrogen into ammonia for measurement. Both methods are highly accurate (R 2 > 0.95), but they are costly and time-consuming, and they require specialized equipment, limiting their use for rapid or large-scale soil assessments.

Plant tissue analysis. This traditional method assesses nutrient uptake and plant health by collecting, drying, grinding and chemically extracting nutrients from plant tissues. Techniques like atomic absorption spectrometry (AAS) and inductively coupled plasma (ICP) spectrometry provide high precision in measuring micronutrients and heavy metals, but the process can take several days, limiting its practicality for time-sensitive agricultural decisions.

Advanced Soil and Plant Testing Technologies

Recent advancements in soil and plant testing technologies have made it possible to obtain real-time, field-based data with minimal sample preparation. These technologies include near-infrared (NIR) and mid-infrared (MIR) spectroscopy, remote sensing, electrochemical sensors, smartphone-based tools and soil data management platforms. Together, they represent a shift towards precision agriculture, enabling farmers to make more informed decisions based on data collected in real time.

Near-infrared (NIR) spectroscopy. NIR operates in the 700-2,500 nm wavelength range and is effective for assessing soil organic carbon (SOC), nitrogen content and moisture levels. NIR works by analyzing how soil and plant samples absorb and reflect light at different wavelengths, predicting organic matter with an accuracy of R 2 = 0.89 and total nitrogen at R 2 = 0.85. NIR is portable, fast and cost-effective, making it ideal for large-scale soil testing.

Mid-infrared (MIR) spectroscopy. MIR, covering 2,500-25,000 nm, excels in detecting soil minerals and trace metals. It has demonstrated high accuracy in measuring calcium, magnesium and heavy metals, with R 2 values as high as 0.99 for organic carbon. MIR is also valuable for analyzing plant biomass components such as lignin and cellulose, providing insights into plant growth and resilience.

The ChrysaLabs field probe (Figure 1) is an example of spectroscopic testing that integrates VisNIR, capacitance technology and Attenuated Total Reflection (ATR) spectroscopy to deliver real-time, in-field results. VisNIR measures the interaction of visible and near-infrared light with soil particles to assess properties like organic matter, moisture and nutrients, while capacitance gauges soil moisture and texture. ATR focuses on soil composition, detecting chemical bonds in organic matter and nutrients. Machine learning enhances the accuracy of this multi-technology approach, allowing rapid assessment of nitrogen, phosphorus, potassium, pH, organic matter and cation exchange capacity (CEC), making it a powerful tool for precision agriculture.

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Remote sensing and field sensors. Remote sensing technologies have transformed large-scale soil and plant testing by allowing non-invasive monitoring of soil conditions, plant health and nutrient levels over extensive areas. Hyperspectral imaging and LiDAR (Light Detection and Ranging) are two commonly used remote sensing tools.

Hyperspectral imaging captures data across a broad spectrum of wavelengths, providing detailed information about plant stress, soil organic matter, and chlorophyll content. Hyperspectral imaging has an accuracy of R 2 = 0.80 for predicting soil organic matter, making it a valuable tool for monitoring soil health over time.

LiDAR technology uses laser pulses to create high-resolution maps of soil texture and topography. It can accurately distinguish between soil and plant materials, with an accuracy of R 2 = 0.72 for mapping soil structure.

Electrochemical sensors. Electrochemical sensors are another advanced tool used in precision agriculture. These sensors measure key soil parameters, such as pH, electrical conductivity (EC) and nutrient levels (N, P, K) in real time. By providing immediate feedback, electrochemical sensors enable farmers to make timely decisions about irrigation and fertilization. These sensors are cost-effective and portable, and they have shown accuracy levels of R 2 = 0.85 for measuring pH and EC.

Smartphone-based soil testing. The integration of smartphones into soil testing has opened up new possibilities for field-based testing. With apps and sensors designed specifically for soil analysis, smartphones allow farmers to test soil properties on-site and receive instant results. For example, smartphone-based tools can measure soil pH, organic matter and nutrient levels through colorimetric tests or camera-based algorithms that assess soil color.

Smartphones are increasingly being used for image-based plant testing as well. Farmers can photograph plant leaves, and the app can analyze the images to detect nutrient deficiencies or disease symptoms. Although smartphone-based analysis tends to be less accurate than laboratory methods (with R 2 values ranging from 0.66 to 0.79 for soil organic carbon), it is much faster and more accessible, particularly for small-scale farmers or those in remote areas.

Soil Data Management Platforms

Modern agriculture increasingly relies on soil data management platforms to integrate and analyze data from various sources, such as soil sensors, remote sensing tools and smartphone-based testing. These platforms provide farmers with real-time insights into soil conditions and enable them to make data-driven decisions for irrigation, fertilization and pest control.

For instance, the AGRIVI platform collects data from soil sensors (e.g., moisture, pH and nutrient sensors) and aggregates it in a user-friendly interface. Farmers can monitor their soil conditions in real time and adjust farming practices based on the data. EarthOptics’ SoilMapper combines remote sensing with machine learning to create detailed maps of soil compaction, carbon sequestration and nutrient profiles, offering a more comprehensive view of soil health across large areas.

Cloud-based platforms like Microsoft Azure’s Data Manager for Agriculture enable farmers to manage vast amounts of soil and crop data by integrating satellite imagery, weather data and AI analytics. These platforms allow users to track changes in soil conditions over time and implement strategies to optimize resource use and improve crop yields.

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Applications in Plant and Crop Testing

Advanced technologies like NIR, MIR and smartphones are increasingly being used for plant testing. For example, NIR spectroscopy can monitor chlorophyll content, nutrient uptake and plant stress, with an accuracy of R 2 = 0.92 for estimating chlorophyll in wheat leaves. These tools enable farmers to assess plant health more quickly and accurately than traditional tissue analysis methods.

Smartphones have also found applications in crop health monitoring. Using apps to photograph crops, farmers can detect nutrient deficiencies or diseases based on color analysis. While less accurate than lab-based tests, smartphone tools offer a low-cost, accessible option for real-time decision-making.

Advanced soil and plant testing technologies — including NIR and MIR spectroscopy, remote sensing, electrochemical sensors, smartphone-based tools and soil data management platforms — are revolutionizing agriculture by providing faster, more cost-effective and scalable solutions. Although traditional methods remain essential for high-precision analysis, advanced technologies allow farmers to collect real-time, in-field data and make more informed decisions.

The rise of smartphone-based soil testing and the integration of data management platforms like AGRIVI and EarthOptics’ SoilMapper illustrate how digital tools are enhancing farmers’ ability to monitor and manage soil and crop health. As these technologies continue to evolve, their adoption will likely expand, contributing to greater agricultural efficiency, sustainability and productivity.

Patrick Freeze is a soil health scientist, research and development manager, and technical specialist at Ward Labs. He earned his Ph.D. in soil chemistry from Washington State University where he studied soil health and heavy metal chemistry as a USDA NIFA Needs Fellow and in Thailand as a U.S. Fulbright Scholar.