Agriculture analysis is an essential aspect of crop growing. Understanding the soil's current nutrient levels is crucial to increase quality and yields.
LaquaTwin's range of portable meters provides in-field analysis for pH, conductivity, sodium, potassium, nitrate and calcium levels.
The example below uses the LAQUAtwin nitrate and potassium meters to analyse plant sap. In addition, information about an App (NutriLab WebApp) that you can use to analyse the resulting data should help track changes and understand when your corps need additional fertilizer.
Plant Sap Analysis
Soil and plant tissue testing is valuable for determining fertilizer needs and maximizing fertilizer efficiency. A soil test is beneficial early in the growing season when plants are too small to collect tissue samples. Plant tissue test for i.e. nitrate and potassium levels during the growing season provides information for diagnosing an issue and managing fertilizer addition effectively. Soil test results, while a valid alternative, can change quickly due to rain or irrigation, and they may not reflect the plant's true nutrient state.
Vegetable Crops - Nitrate and Potassium Measurement using LAQUAtwin
Analysing fresh plant petiole sap using the LAQUAtwin NO3-11 or NO3-11C nitrate pocket meters and the LAQUAtwin K-11 potassium pocket meter provides an easy method to determine plant health. These meters are waterproof and equipped with a built-in thermistor that detects the sample temperature, and a replaceable sensor with a flat membrane that accepts as little as 0.3 ml sample (0.05 ml with sampling sheet B). As a result, they can measure plant sap in just a few seconds with a minimal sample.
When using the LAQUAtwin pocket meters in the field, they ideally work in the shade and frequently need recalibrating throughout the day as the meter is sensitive to temperature changes. Therefore, collect petioles from the field and analyse them with the meters indoors for optimal results.
Meter Calibration
Before measuring your sample you will need to calibrate the meters using the standard solutions included in their kits. All LAQUAtwin ion meters use the same basic protocol for calibration, which is included in the manuals (NO-11C manual and K-11 manual).
Sample values need to be within the calibrated range of the meters. Readings outside the calibrated range will be inaccurate. If the meter reading is above the calibrated range, dilute the sap with deionized or distilled water, and consider the dilution factor when calculating the original sap concentration.
Plant Leaves Collection
The nitrate level in the plant can vary throughout the day. To obtain consistent test results, reasonable standardization of time, temperature, and weather conditions need to be considered when sampling.
Collect the petioles (leaf stems) of about 20 most-recently-matured leaves—those that have reached maximum size and have changed from a juvenile light green colour to a dark green colour. Refer to Figure 1 to help you identify the petioles of some vegetable crops.
Take the leaves from different plants to ensure that the sap sample is representative of the field or tested area.
Source: University of Florida - Plant Petiole Sap-Testing for Vegetable Crops
Press Sap Preparation
The samples of petioles can be stored at room temperature (70°F, 21.1°C) in a plastic bag for up to 2 hours. For longer storage times, work in Florida has shown that fresh, whole (unchopped) petioles can be placed in a plastic bag and stored on ice in a cooler for up to 8 hours or frozen overnight. Remember that cold petioles must be warmed to room temperature before crushing, as the temperature differences between sap and meter would otherwise affect the results.
- Chop and mix the petioles. Take a subsample of chopped petioles for crushing.
- Squeeze the sap from petioles using a garlic press, lemon press, or hydraulic sap press.
- Measure the fresh sap using the LAQUAtwin pocket meters within 1–2 minutes of pressing (see video below).
- Record the readings.
Interpreting the Readings
Over the growing season, vegetable crops differ widely in nutrient needs and uptake patterns. Therefore, good record-keeping of trends in nitrate and potassium concentrations over the season will help gain insight into the crop's nutrient dynamics.
To analyse the readings you obtain, you must compare them to growth standards tables. It is essential to note the plant growth stage at sampling. Guidelines on growth stages nutrient levels are available from universities and research institutes based on their research and field experience. Tables 1 and 2 contain ranges of suggested critical values. The NutirLabApp below is another way to analysis your data using an App.
NutriLab App
LAQUAtwin meters data can be used in conjunction with the NutriLab WebApp. This App was developed by MMM tech support GmbH & Co.KG with support from the BMEL as an interpretation tool for plant press sap readings. The nutrient data values are based on extensive literature research and trials at the Institut für Gemüse- und Zierpflanzenbau. The App comes with the following features:
- The ability to interpret and archive measured values of the plant press-sap based on standard European growth data.
- The App can be used on a computer, tablet or smartphone.
- The comparative data currently includes 75 plant species covering 315 optimum values. These measured values are based on plant species and development stages according to the BBCH scale. The App also includes optimum values for individual crop varieties.
- NutriLab is available with an annual subscription
The video below provide a detailed explanation of how the App works
All blog information was provided courtesy of Horiba Scientific.
Their Laqua range of electrochemistry meters comprises a selection of meters and electrodes with the associated buffers and standards.
- LAQUA Benchtop Water Quality Meters – High-end benchtop meters provide simplicity with excellent on-site usability – from operation and maintenance to troubleshooting.
- LAQUA & U-50 Handheld Water Quality Meters – Designed for one hand and with an IP67 waterproof rating and shock-resistant casing, this meter is ideal for use over long periods, even in dark places, making it optimal for field measurements in rivers and lakes.
- LAQUAtwin Pocket Water Quality Meters – HORIBA's unique pocket meter integrates the electrode, display, and sample container to enable simple, effective on-site testing by direct measurement from a single drop.
- Electrodes, Standard Solutions & Accessories – A wide range of products to compliment these meters – including various electrodes to match any application, standard solutions for ease of calibration, and a variety of accessories to complete your LAQUA experience.
