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Agrochemistry

The role of water in the physiology of productivity and plant development

For students

4 min read

AGROCHEMISTRY A

Physiological role of water: how moisture manages crop productivity

Water is the main limiting factor in crop production. Neither temperature, nor light, nor soil composition determines the potential for crop development as much as the availability of moisture. In a plant organism, water forms an inseparable system with all components of the protoplasm, ensuring vital activity and continuous coordination of all plant organs.

The physicochemical properties of water determine its key functions in the cell:

  • Serves as an intracellular medium for all biochemical reactions.
  • Stabilizes the structure of proteins, nucleic acids, and cell membranes through hydrogen bonds.
  • Protects tissues from overheating due to its high heat capacity and performs thermoregulation through evaporation.
  • Provides capillary transport of substances, adsorption of enzymes on the membranes of cell compartments, and ion uptake.
  • Directly participates in respiration, hydrolysis, and photosynthesis, where the OH– ion acts as an electron donor for the oxidative center of chlorophyll.
  • Dissolves and transports assimilates and nutrients.

Water maintains the state of turgidity (turgor) of cells. It is this specific degree of turgor that is necessary for cell expansion during growth, stomatal opening, maintenance of the form of herbaceous plants, and the orientation of their organs in space.

To perform these functions, tissues must be sufficiently hydrated. The degree of hydration is assessed by the relative water content (RWC) in cells. This indicator is calculated using the formula:

RWC = ((Mfresh — Mdry) / (Mturgid — Mdry)) × 100 %

where: Mfresh — fresh mass of the tissue; Mdry — dry mass of the tissue; Mturgid — fresh mass of the tissue when fully saturated with water.

Water balance and mineral nutrition: how to reduce unproductive moisture loss

Crop productivity depends directly on their water balance. Due to high transpiration, plants consume significantly more moisture than they contain. To quantitatively assess this process, the transpiration coefficient is used — the volume of water in grams that a plant evaporates to accumulate 1 gram of dry matter.

  • Transpiration coefficient — amount of evaporated water in grams per 1 g of dry matter
  • Reduction in water consumption with good nutrition — by 15–30 %
  • Main factor of natural selection — lack of water

The transpiration coefficient fluctuates depending on environmental conditions, but an agronomist can influence it artificially. Full supply of plants with mineral nutrition elements reduces the transpiration coefficient by 15–30 % depending on soil moisture. This optimizes water consumption, increases the productivity of fertilizer use, and boosts yield.

With poor supply of nutrients, a plant consumes moisture unproductively. Timely application of fertilizer helps to reduce transpiration by 15–30 %, enabling the crop to use the available stock of soil moisture more economically and to form a harvest even under conditions of precipitation deficit.

Crop Transpiration coefficient Crop Transpiration coefficient
Corn 180–400 Barley 370–520
Oats 440–880 Wheat 350–650
Rice 300–550 Potato 330–640
Sugar beet 300–420 Cabbage 450–550
Cucumber 655–750 Red clover 500–760
Fava bean 600–800 Pea 600–800
Rapeseed 600–800 Buckwheat 400–600
Sorghum 300–400 Millet 350–450
Bean 600–850 Soybean 550–900

The transpiration coefficient is used to determine potential yield if the soil moisture reserves, amount of precipitation, and their proportional contribution to supplying plants with water are known.

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