Method of isolated plant nutrition in agrochemical research and experiments

The split-root method allows for the study of processes hidden within the soil. With its help, agronomists investigate the role of individual roots, the movement of nutrients through the plant, their release into the environment, as well as the interaction of salts in the root zone. For this, the plant is simultaneously grown in two vessels of different diameters, one inserted inside the other. The inner vessel must be at least 2–3 cm lower than the outer one. Water, sand, soil, or their combinations are used as a substrate.

Substrate preparation and transplant/seedling cultivation

When setting up sand cultures, the smaller inner vessel is filled first, followed by the outer one. Gravel, a piece of gauze, and an irrigation tube are placed at the bottom of the outer vessel. Nutrient solutions are distributed unevenly, as the objective of the experiment is to supply specific elements to one vessel and the remaining part of the mixture to the second. When packing the sand, each portion is moistened.

• Root length for planting — at least 4–5 cm
• Growing period on the mesh — 7–12 days
• Sand humidity during packing — 60% of full water-holding capacity
• Liquid volume per 1 kg of sand — 150 ml

During subsequent irrigation, water is added to maintain a constant weight of the vessels. All added water is distributed between the outer and inner vessels in proportion to the amount of sand in each. To grow seedlings, seeds are germinated and then kept on a paraffin-coated mesh above distilled water until roots of the required length are formed.

Planting technique and humidity control

For planting, uniform plants with a well-developed root system are selected, preferably with an even number of roots. In sand cultures, a separate plug is used for each seedling, while in water cultures, a single common wooden plug with holes for the plants, aeration tubes, and funnels is used. The attachment points for the plugs are marked in advance on the walls of the vessels, and deep, oblique furrows are made in the sand.

1. Carefully divide the root system of the prepared plant into two equal strands.
2. Secure the plant in the plug and place it on the wall of the inner vessel at the marked location.
3. Place the root strands into the prepared furrows in the inner and outer vessels.
4. Immediately cover the roots with sand using a strong stream of distilled water from a wash bottle.
5. Fix the stem in the plug opening using cotton wool.

After covering the roots with a stream of water, the sand inevitably becomes over-moistened. This temporary decrease in salt concentration and excess moisture are favorable for plant establishment. Nevertheless, it is necessary to strictly monitor the substrate humidity parameters.

How to properly set up control variants

When using the split-root method, it is important to exclude side factors that may distort research results. The physical separation of roots and their transfer into different vessels is a major stress for the plant. To understand how the division of roots or the deficiency of a specific nutrient element, rather than the transplanting process itself, affected the crop, it is necessary to organize the control system correctly.

For this purpose, two mandatory control variants are set up in the experiment. All plants for these are prepared exactly the same way and planted on the same day. The control setup process consists of the following stages:

1. Nutrient control preparation. The same complete nutrient mixture is applied to both vessels of the control variant. The total volume of nutrients in the control must strictly correspond to the experimental variant.
2. Root division control preparation. To assess the influence of the division procedure itself, a vessel with a classic sand culture is set up. The roots of the plants in this variant are not divided.
3. Planting. All prepared plants are placed in experimental and control vessels simultaneously.