Vegetable refrigeration

The vegetable refrigeration is a continuous activity in almost all crops in summer. The strong heat input in the summer season could not be overcome without natural cooling mechanisms.

Plants use water to transport their nutrients. First, water carrying ions such as nitrogen, calcium or phosphorus is transported from the roots to the leaves... Then water is used to transport nutrients through the phloem. carbohydrates generated during the photosynthesis.

Water in the plant has different functions, all equally important, although not all of them consume the same amount of water.

• Turgidity maintenance and universal solvent.

Herbaceous plants do not have bones, nor do they have a cambium to produce a strong wood. Two elements are used to maintain its structure. The water cells have a small layer of cellulose that gives them some resistance. On the other hand, they are filled with liquid water, which is what generates enough consistency to keep them upright. This water is also the liquid in which all nutrients are dissolved and all metabolic reactions of the plant take place.

The water retained by the plant is estimated at only 5% of the total water flowing through the plant over its entire life span.

In reality, water consumption to maintain turgor and carry out its metabolic functions is not very high, only the amount of water contained in the plant is continually renewed by the following functions of water in the plant.

• Gas exchange.

Water together with O2 are two molecules that in their gaseous form help to maintain adequate CO2 concentrations in the leaf cells. Both the water vapour as the O2 come out of the plant through small orifices called stomata. The stomata are both entry and exit gates, opening according to the needs of the plant. The most adapted plants are better able to keep their stomata closed during dry periods.

For gas exchange to take place, water has to evaporate and generate a potential that allows CO2 to enter the plant, but this is not naturally favoured. Water molecules are smaller than CO2 molecules and therefore more water comes out of the CO2 than goes in. On the other hand, the atmospheric concentration of CO2 is very low. It represents less than 0.04% of the total gas concentration in the atmosphere. So the potential input is very low, compared to the potential outflow of water into the atmosphere. This is because air is generally not saturated and always demands more water.

Hydrogen is the smallest element there is, which makes water a very small molecule.

• Starring in the photosynthesis.

To generate the glucose the plant needs to complete its metabiolism, the plant uses water as an electron donor to enable the CO2 fixation reaction. Water is a very weak reducing agent, but with energisation by photons and chlorophyll it allows the conversion of CO2 into chemical energy.

6 CO2 + 6 H2O → C6H12O6 + 6 O2

Water consumption by this method is moderately small. The largest water expenditure is considered to be due to cooling.

• Cooling by perspiration.

This is where the bulk of water consumption in crops is. Plants have their own cooling system, which is based on the evaporation of water and is responsible for most of the water consumption. The change from liquid water to gaseous water requires a large amount of heat, and that heat is taken from the plant. It is the same system we humans use to cool ourselves, sweat. So the water vapour and the energy needed to evaporate it are released into the atmosphere.

The orography of the field is also important when it comes to cooling needs. As is evident, sunny areas will increase their needs much more than shady areas.

Stressed areas can sometimes be revived with a light refreshment irrigation. This type of irrigation consists of applying a very light rain administered either with a sprinkler head or with a nozzle that delivers a very fine droplet.. This small amount of water will act as sweat and cool the turf.

This technique is very simple and has a great impact on the health of the plant and will cool the surface more quickly than through transpiration alone.

 Each gram of water absorbs about 590 calories.

Like every organism itself, it is another universe, and the magnitude of transpiration varies from one plant to another. Water loss in cereals, e.g. maize which loses 2 to 3 kg of water daily, is very different from that of a large cactus which can only lose 25 g of water daily, which is why it is important to know the rate of water loss and the rate of transpiration. evapotranspiration of each crop.

On high performance turf other techniques are used such as forced ventilation which reduces the risk of fungus, but increases the risk of fungus. evapotranspiration and has a high energy cost.

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