Winter wheat has been and remains the most important grain crop in Ukraine. To get a good harvest, an agrarian should:
- Use varieties with high tillering potential and good resistance to lodging;
- Promptly monitor and control weeds, pests, diseases;
- Use modern, serviceable equipment, modernize it as far as possible.
Growing winter wheat is not easy, among all cereals it is the most demanding to the availability of nutrients in the soil. The entire vegetation period lasts 300 days and is divided into 12 stages of organogenesis, each of which has its own requirements for the choice of mineral fertilizers.
In terms of duration, the following stages are distinguished:
- Germination and initial development – 30 days;
- tillering – 150 days;
- Stem development – 48 days;
- Spiking – 6 days;
- Flowering – 11 days;
- Maturation – 50 days.
If the sowing dates are observed, the soil has enough moisture and all necessary minerals, then winter wheat starts tillering already on 15 days after germination. Usually, tillering and tube emergence take place in the fall. In case of late sowing, lack of moisture and mineral substances, the process of tillering takes place mainly in spring.
In the fall, most of the roots are in the arable layer of soil (15-30cm). By the beginning of winter, primary roots reach a depth of 1 m, secondary roots – 0.6 m. Usually, the formation of the root system continues until the phase of milk ripeness of grain.
It should be noted that it is the agrarian who is interested in ensuring that the wheat has enough moisture and nutrients. If there is not enough moisture or minerals, the plant will throw out one ear with the maximum number of grains possible in a given situation – this is genetically programmed for reproduction. But if there are no nutritional problems, you can expect many spikelets with many grains on each spikelet.
Lack of nitrogen at early stages is critical for the crop, excess is also harmful
On poor soils and after unplowed predecessors, part of the nitrogen should be applied in the fall, necessarily together with potassium and phosphorus.
If sowing is carried out after clean fallow, then on the contrary – it is necessary to protect the wheat from excessive nitrogen intake, for this purpose phosphorus and potassium nutrition is intensified.
Potassium increases cold tolerance and strengthens tillering. Phosphorus – growth of root mass.
The optimal ratio of phosphorus and nitrogen stimulates the growth of green mass, the development of the root system and helps the plant to accumulate enough sugars for winter, which increases the plant’s resistance to low temperatures.
In case of excess nitrogen and phosphorus deficiency at the stage of grain germination, root growth is inhibited, which subsequently reduces yield. Plants have active development of loose large-cell tissue structure with increased water content.
As a consequence:
- wheat mildew is more common;
- root rot;
- brown leaf rust;
- reduced resistance to frost.
That is, in the fall it is important that there is enough nitrogen, but not excessive.
If nutrients are insufficient, winter wheat may not overwinter, sprouts have pale green color (due to lack of chlorophyll) and tillering process slows down, up to stopping.
In general, two critical stages can be distinguished for winter wheat:
In the fall – from the moment of sprouting to the stop of the fall vegetation. Plants are sensitive to nitrogen and phosphorus deficiency;
Spring – from the time vegetation resumes until the tubing phase, when wheat is vulnerable to nitrogen deficiency.
Sufficient nitrogen increases resistance of winter wheat to lodging (excess – on the contrary), promotes good development of leaves and ear, so we can say with certainty that it is nitrogen fertilizers that play a decisive role in complex measures to increase yield.
How nitrogen deficiency will manifest itself at different stages of growth:
- In case of nitrogen deficiency during the tillering phase, shoots will develop poorly;
- During the tube emergence phase, some shoots will be left without spikelets;
- In the phase of grain formation – the spikelets’ lakeiness and grain size are disturbed.
Experience shows that it is impossible to apply the entire nitrogen dose needed by winter crops for the entire development period at one time – it is necessary to divide it into several applications. The higher the expected application dose, the more careful you should be about the uniformity of its distribution over the field area.
Wheat consumes up to 90% of all nitrogen in the spring, after vegetation has resumed. Lack of nitrogen before the sprouting of a dormant bud leads to the cessation of growth of this shoot. During the tillering phase, wheat favors already growing leaves and shoots, so no new ones are formed.
If a nitrogen deficiency is detected during the formation of the 4th and 5th leaves on the main stem, it is likely that the plant will no longer have time to produce the first and second shoots. To partially solve the situation, foliar application of nitrogen should be used. If the fertilizer is applied at this stage, the third and following shoots will be able to grow, so the plant will consist of one main stem and two or three shoots, which will significantly reduce the yield.
In spring, during the resumption of vegetation, winter crops face a situation when the need for nutrients is higher than the capacity of the root system, for example, due to low ground temperature. In this case, the way out of the situation is foliar application of UAN-32. The active ingredient from the drops on the leaves will very quickly appear inside the plant and provide winter crops with nitrogen reserves. UAN fertilizer contains three forms of nitrogen at once, so it starts working at once plus it has a prolonged effect.
Winter wheat forms new shoots when:
- she’s getting enough nitrogen;
- no limiting factors;
- until the signal for stem elongation has arrived (length of daylight hours or sum of active temperatures).
New shoots stop appearing at the beginning of the tube emergence phase. Nitrogen reserves are directed to the growth of the main stem and new leaves on existing shoots.
What is the benefit of applying nitrogen at different stages of growth:
Nitrogen application at the end of the stem growth phase (provided that the plant has assimilated it) leads to an increase in the number of flowers and protein content in grains, but has no effect on the number of spikelets – they were laid earlier.
Nitrogen application at the end of the tube emergence phase increases the protein content of grains. But if there was a nitrogen deficiency earlier, the grain size will be smaller, the spikelet differentiation is completed earlier and its size is smaller than normal.
It makes no sense to apply nitrogen fertilizers on the soil surface after flowering, but leaf application of nitrogen at this stage will increase the protein content in grains, which is very good for wheat – the more protein, the better the bread (this rule does not apply to rye – the situation there is almost the opposite)
The main amount of nitrogen will be assimilated by winter wheat in spring until earing begins. At the beginning of ear formation, if nitrogen is assimilated, it will be used only to improve grain quality (protein content).
At the 12th stage of organogenesis (phase of waxy and full grain ripeness), nutrient supply to the grain stops. Grains mature, simple organic substances are transformed into complex ones – the main reserves of starch, proteins, fats are formed. It makes no sense to apply fertilizers at this stage.
The mass of grains depends on the size of the top two leaves on the shoot. Fertilization at the beginning of the tube phase has a powerful effect on the growth of these leaves, so it will positively affect the yield in general. Untimely, delayed single fertilization can be ineffective if it was preceded by a long period of mineral deficiency and the plants have not formed a sufficient fund of assimilants.
Sulphur is necessary for the complete assimilation of nitrogen
Protein molecule consists of several macronutrients, but separately it should be said about sulfur. It is one of the most important “partners” of nitrogen – with a lack of sulfur, the reduction and assimilation of nitrogen by plants stops. Therefore, when applying nitrogen, sulphur should also be applied to ensure that the nitrogen is properly assimilated. Soil with less than 12mg/kg of sulphur is considered to be deficient.
It is recommended to apply sulphur either in the proportion of 14:1 to nitrogen or at a dose of 50-80 kg SO3/ha.
Of the nitrogen assimilated by the plants, 70% will be taken away from the field as yield. For potassium this value is 10%, but for phosphorus it is already 80%. In addition to nitrogen, the phosphorus content of the field should therefore be monitored.
Phosphorus – metabolism, signs of deficiency
Phosphorus absorption is uneven – 30% of the total dose will be absorbed before the tillering phase, and the remaining 70% during the tillering and tube emergence phases. During tillering, the bulk of phosphorus is in the leaves, then it moves to the stem and almost all of it goes into the grain.
Potassium – importance, signs of deficiency
This element is assimilated from the soil from the very first days of growth. Its maximum amount is assimilated in the phases of tube emergence and earing. Potassium increases the cold tolerance of winter crops, increases stem strength, which is especially important for varieties prone to lodging and increases resistance to pathogens. Thus, potassium indirectly increases the yield of winter wheat.
In case of potassium deficiency during the period of intensive growth, the first thing to be detected are yellow spots on the upper leaves, and then the lower leaves and stem turn yellow. If the deficiency at this stage is not eliminated, the yellowed leaves will dry up, starting from the upper part of the stem. The root system also suffers with a lack of potassium – the roots of side shoots appear, but do not grow. These symptoms are often seen after plant stress or during drought.
Excess nitrogen can increase winter wheat lodging and rust damage, while potassium increases plant resistance to these issues.
Soil acidity is between 6 and 7 units
Wheat is sensitive to soil pH – a pH value of 6-7 units is best, so acidic soils should be alkalized.
On average, winter wheat will take from the soil at harvest:
Nitrogen: 25-35 kg;
Phosphorus: 10-12 kg;
Potassium: 20-30 kg.
If phosphorus was insufficient at the very beginning of vegetation (in the fall), the root system is underdeveloped, leaves are smaller, darker than usual, and grain ripening is delayed. Leaf color may change to reddish or purple.
Phosphorus deficiency for the first two weeks of the growing season reduces yield by 42% of the maximum yield, due to underdevelopment of the root system and reduced stem number (Boatwrsght, Viets, 1966).
Also, grain development is impaired under phosphorus deficiency. The total number of spikelets in the plant and the number of flowers on each spikelet are reduced. Phosphorus is important for the formation of ATP, sufficient amounts of which are necessary for the synthesis of carbohydrates and their delivery to the grain.