Measurement. Agronomy 1

The most relevant directly measurable agronomic variables for sports surfaces are the following:

Humidity

Moisture monitoring in the profile of sports surfaces is crucial for efficient agronomic management and also affects other biomechanical and playability parameters.

In soil profiles, mineral and organic materials and pore spaces are found. These pore spaces are divided into macropores and micropores, the distribution of which is mainly determined by the texture of the substrate, compaction levels and organic matter content. Moisture accumulates mainly in the micropores and temporarily in the macropores during periods of saturation.

Buried sensors and its continuous data logging as available for the WatchDog station.

Measurements of this variable can be made continuously over time, through buried sensors or discrete measurements with portable monitoring devices.

Agrodit also offers a customised solution of buried sensor systems in which we obtain accurate and representative humidity, temperature and salinity data for areas such as greens or football pitches.

Measurements can be based on the soil matrix potential, where the suction pressure is determined using porous ceramic sensors. Alternatively, measurements can be based on the volumetric percentage of water present in the soil.

Electrical methods are the technology TDR (Time Domain Reflectrometry), based on the measurement of the delay of an electrical signal sent through the ground, or through FDR or coaxial impedance technology, measuring the energy that is dissipated and stored in the ground.

The two most notable advantages of coaxial impedance is that it does not require calibration, the measurement is very accurate, and it can measure apparent electroconductivity with true precision. A device such as POGO measures humidity using the coaxial impedance method, providing highly reliable results.

Matrix suction probes.

TDR technology

FDR technology

Both electrical technologies are based on the determination of the dielectric constant of the soil to calculate the volumetric percentage of water in the soil by different mechanisms. Although both tools are very useful, it is important not to mix their measurements; the readings should always refer to the same type of instrumentation. For turf in cold climates, suitable ranges are 25-35%, while for hot climates they are 20-25%.and adjusted according to individual needs.

These tools can also measure electrical conductivity simultaneously. The relationship between electrical conductivity and soil moisture allows the estimation of soil salinity, known as the salt index. It is recommended that salt index measurements are always carried out at constant humidity values. There are also handheld devices specific to the measurement of EC.

pH

pH is a measure of the acidity or alkalinity of an aqueous solution, specifically the concentration of hydrogen ions. For the greenkeeper, the pH of pore water in turf soils is of particular interest. The hydrogen ion concentration is multiplied or divided by 10 each time the pH decreases or increases by one unit. For example, if the pH decreases by 2 units, the hydrogen ion concentration will increase 100 times and vice versa, exponentially.

What factors affect these concentrations in the soil? It is not just the addition of acids or bases, but multiple processes interconnected with the soil reaction. Soils can have an acidic or basic reaction depending on the moisture present, i.e. pore water, and this will be influenced by several factors such as the nature of irrigation water, fertilisers used, microbial activity, decomposition of organic matter producing CO2, nutrient holding capacity, limestone content, among others.

One of the main importance of pH is its relation to the solubility of different nutrients and its influence on the soil microbiota.

Solubility ranges as a function of pH

Diseases such as Spring Dead Spot (SDS) in Bermuda and Take All Patch or Microdochium Nivale in Agrostis thrive in soils with alkaline pH. Therefore, maintaining a slightly acidic pH in these soils can be an effective strategy for their control.

There are several devices available to measure the Soil pH. The choice of the appropriate device depends on the preferred measurement method.

Those pH meters that are used by measuring directly on the wet soil sample are very convenient and nowadays quite accurate.

pH meter direct measurement

It is also possible to measure the pH without taking a sample, by inserting a probe at the desired depth. This methodology is more precise, as it takes into account the CO2 that is constantly produced due to the rich soil atmosphere on sports surfaces.

pH measurement without sample extraction

Very high CO2 levels, up to 3 or 4%, compared to 0.03% in the atmosphere, have been recorded in the profiles of greens or football fields (Lee et al., 1997). . Dissolved CO2 forms carbonic acid when combined with water, leading to an acidification of the pore water. Consequently, in situ pH measurements tend to be more acidic than those obtained by extracting samples, as the extracted samples equilibrate with the ambient atmosphere.

In addition, a pH measurement can be made by diluting the soil with water and then pouring a few drops of the supernatant water, either distilled or irrigation water, onto the measuring device.

pH meter for measuring liquid solutions

In turfgrasses with sandy substrates and low buffering capacity, the measured pH is often highly dependent on the pH of the irrigation water, especially in the absence of fertilisation.