Soil pH and nutrient testing options explained

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Soil pH depends on many environmental factors. Alkaline soils are characterized by the accumulation of soluble salts and carbonates, and are often found in areas that are rich in limestone. Acidic soils are characterized by the presence of free hydrogen and aluminum ions, and may be caused by acid rain, fertilizer application, or decomposing organic matter.

Most natural soils have a pH ranging from pH 4.0-8.0, depending on the geology of the area. One of the key factors in plant growth is the availability of macronutrients and micronutrients. The availability of both macro and micronutrients is directly related to pH. The pH soil and nutrient solutions will determine the solubility of the nutrients. 

Soils that have a pH of 4.0 to 5.0 are considered to be strongly acidic; within this acidic range, the solubility of minerals such as aluminum, iron, and manganese increases and can become toxic to plants.

Soils that have a pH greater than pH 8.0 or 9.0 are considered to be strongly alkaline; at this pH range, the nutrients that plants need to grow are not soluble and available for uptake. While the optimum pH value for nutrient uptake is dependent on the species of plant being grown, the majority of plants thrive in a soil that is slightly acidic.

It is also important to note that there are optimum pH values for beneficial soil bacteria, such as bacteria that convert atmospheric nitrogen (N₂) into plant available soil nitrogen (NH₄+). These nitrogen-fixing bacteria live on the root hairs of legumes and thrive at an optimum pH range between pH 6.0 and 8.0.

Soil pH Testing Options

A nursery contacted Hanna Instruments looking for a portable pH and total dissolved solids (TDS) meter.

The customer wanted to monitor the nutrient solution that was distributed to their plants through a drip irrigation system and periodically check soil pH and TDS values by making a soil slurry. The customer preferred a simple meter that was capable of measuring pH and TDS with a single probe.

The pH / EC / TDS / Temperature Meter – HI9814 was recommended due to the simple, single-point calibration. The customer appreciated the meters easy-to-use manual calibration feature for both pH and EC/TDS calibration.

Our solution

HI9814 is a durable, portable pH, conductivity, total dissolved solids and temperature meter for most measurements encountered in hydroponics, aquaponics or general agriculture applications. All operations and settings, are made through only two buttons and the housing is waterproof and rated for IP67 conditions. User-selectable features include selectable TDS factors of 0.5 and 0.7 as well as auto-off after 8 minutes or 60 minutes to prolong battery life.

The supplied HI1285-7 multiparameter probe measures pH, EC/TDS, and temperature in one convenient, rugged probe.

Multiparameter Probe

The specially engineered HI1285-7 pH/ EC/TDS/temperature probe utilizes a fiber junction and gel electrolyte which provides a fast response and reduced potential for contamination. These features make this probe ideal for use in fertilizer solutions.

A solid-state preamplifier is integrated into the probe to protect the pH measurement from transient electrical noise. Sources of electrical noise include ballasts used in lighting and pumps to circulate water and nutrient solutions.

The H1285-7 probe features a Quick Connect DIN connector that makes a waterproof connection with the meter.

Calibrate pH and EC with one solution

The HI9814 offers a quick calibration feature that allows for calibration of both parameters with a single solution. Simply enter calibration mode and the meter will automatically detect and calibrate pH and EC sensors. EC calibration is automatically applied to TDS readings.