Grain problems: the expert responds on wheat diseases


THE AGRONOMIST ANSWERS ON HOW TO GROW AND CARE FOR PLANTS

WHY ARE OUR SEEDLINGS OF WHEAT DEAD?

QUESTION FROM ADRIANA

I'm Adriana, a primary school teacher from the province of Genoa; I turn to you to explain a problem that has recently arisen in the context of carrying out a learning unit for a second class.
Regarding the sowing of wheat in the garden, carried out by the children on October 24, 2008, we had a nasty surprise: the wheat seedlings died. (the seedlings at the end of November had already reached a height of 13 cm)
Each child tried to give a reason for what happened and almost everyone attributed the responsibility to the large amount of snow that fell this year and the large amount of snow laden with salt that was thrown onto our garden by the snow blower.
To test the salt hypothesis, the children proposed to do an experiment: re-sow the wheat grains in 2 pots; in one when the seedlings are born put the salt and in the other not.
(I would not, however, exclude, as a contributing cause, the weight of the large amount of snow added by the snowplow)
I would be grateful if, as an expert person, you can validate our hypotheses or / and if you can give us other reasons.
I tell you that I have already had this experience of sowing wheat on other occasions and such a thing has never happened.
Waiting for your answer
Thank you for your attention
Adriana

AGRONOM ANSWERS

Dear teacher Adriana,

with pleasure I answer this question because it is a little different from the usual ones that are proposed to me.

First of all, congratulations for the experiments he conducts with the children: nowadays it is not easy to find teachers who make children experience the thrill of seeing the birth of a plant and therefore of life starting from a seed.

Now to answer the question I believe, from the things he writes, that the causes that may have determined the death of your wheat may be different and that the reasons listed may all be valid.

The seedlings were in that phase which agronomically is called "tillering", that is when the plant begins to have 3-4 leaves. In this phase, the environmental factors that influence the success of the cultivation are: availability of oxygen in the soil, temperature, soil humidity, lighting and nutritional conditions and by analyzing the presence / absence of these factors, we can find out what was the cause.

The temperatures have dropped a lot this year and if the ground has frozen for a long enough time this could have caused a swelling of the land mass (the water that turns into ice increases in volume) with an uprooting of the seedlings. Generally the practice that is done when such an emergency is foreseen is a rolling of the soil to re-adhere the soil to the roots but I do not think you have thought of this possibility. If the young roots lose their adhesion to the soil, they are obviously destined to die.

Low temperatures in themselves are not harmful to the grain (within certain limits of course) but become so to the extent that the soil is not adequately prepared for this eventuality.

Now I don't know if and how you worked the soil before planting the seeds, this practice is also very important to ensure good soil permeability. Normally the pre-sowing process is plowing or, in your case, a hoeing at least thirty centimeters deep. The importance of this practice is linked to the fact that the soil does not remain compact and therefore in the case of incessant rains, it favors the drainage of excess water. If this has not been done or has been done partially, it could also have occurred that the water has not managed to leach as it should and therefore has saturated the soil with consequent lack of oxygen at the level of the root system, conditions which generate the death of plants by asphyxiation. In fact, in the areas where the rains are normally abundant, the bedding technique is used, among other things, which consists in sowing on a sort of raised row of land that improves the disposal of excess water, but obviously you could not have foreseen this, as the rains are not normally that intense.

But even if these causes did not occur, surely the distribution of the salt and the addition of sodium chloride caused the seedlings to die. In fact, salt brings with it two types of problems, agronomically speaking: one of a chemical type and one of a physical type.

Chemical modifications can be of two types:

  • one linked to the fact that the salt dissolved in the circulating solution of the soil (generally in the water) retains the water and makes it unavailable to the plants as the force that the plant should exert to? tear? to the salt the water molecules are clearly inferior to those that the salt exerts on the water (in practice there is an osmotic pressure much stronger than that which the root system can exert) and since the plant also has to overcome the strength of the soil that it retains water, in this situation the plant, despite having liters of water available ...? To explain it in other words: it is as if a pump were extended from the ground floor to the third floor of a building and the person on the third floor was told that in order to drink he must suck the water contained in with the force of his lungs. a tank placed on the ground floor;
  • the modification of the ph of the soil due to the fact that the salt raises the ph of the soil to very high levels (therefore a very basic soil) which results in the unavailable yield of the mineral elements useful to the plant as they bind to form other compounds that they are not usable by plants, so the plant ...? Are you starving?

The physical changes are due to the fact that an excess of salt in the soil, due to its high water absorbency, also modifies the structure of the soil, reducing the free spaces for both air and water circulation with the consequences who can imagine.

As for the layer of snow above the ground this is generally not a problem if it is soft snow rained down from the sky but since it tells me that the snowplow has deposited large quantities so it was not soft snow but certainly had bought. a certain compactness, this too could have been a cause creating an asphyxiated environment.

In short, a disastrous situation that could only end with the death of the poor wheat seedlings.

I hope I was clear, if there are any doubts, let me know.

Best regards to her and a hug to her children.

Dr. Maria Giovanna Davoli


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