Autumn fertilization of winter cereals

Renata Gaj, Ph.D.

Poznań University of Life Sciences

 

The success of cereals and other crops’ cultivation measured by the yield, i.e. the amount of grain, roots or tubers harvested, depends largely on obeying basic principles of proper agricultural practices, among which the most important are the choice of appropriate position, its preparation and fertilization. The preparation of the position for growing winter crops requires the consideration of the fact that this group of plants remains in a field from 9 to 10 months. Farmer's task is to create optimal conditions for nutrient uptake for such a long time, starting from the selection of a position with a regulated soil pH, at least average abundance of assimilable forms of phosphorus and potassium, removing compacted layers of soil by subsoiling (mechanical or biological) and ending with the selection of a suitable variety adapted to changing habitat conditions. To achieve the goal of high and stable cereal yields and a good quality of grain, one should consistently eliminate all factors limiting the growth of plant roots. Each manufacturer of cereals should be aware that the weaker the position is, the bigger and more important the scope of necessary agrotechnological efforts increasing its fertility is.

Correct determination of doses of P and K

 

Correct determination of nutritional needs of plants is an essential element of the fertilization scheme of winter cereals. Individual accumulation of components by cereals is presented in Table 1.

Plants that are well nourished with phosphorus and potassium are more tolerant to the stress factors such as drought, high temperatures and disease and, as a result, produce better crops. In fact, the protective role of phosphorus comes down to its role in the process of plant growth, in which a key role is played by energy bonds, and the impact on the growth of roots. Phosphorus is a component of plants feeding and cannot be replaced by any other element. It is best to use the estimated dose of P before sowing plants. In the case of the need for high doses of P and K, it is advised to divide them into autumn and spring dose. In the case of soil rich in phosphorus, approximately 30% of the nutritional requirements of the plantation should be applied.

 

Expert’s opinion:

The main aim of introducing a “fresh” phosphorus in the form of nitrophoska to the soil in the spring is to provide a sufficient quantity of this ingredient in the initial phases of plant growth and stimulation for accelerated development.

 

The plant gets phosphorus from the soil, precisely from the soil solution in the form of orthophosphoric anion H2PO4, which is present in a wide range of pH, but the optimum range is in the range between 5.5 and 7.2. The presence of easily accessible phosphorus compounds in the soil determines the development of the root system. The element even stimulates the root growth. Even in soils rich in phosphorus, the dynamics of phosphates uptake is significantly reduced in conditions of water scarcity. A factor that limits the uptake of phosphorus during the spring growing season is low temperature. The impact of low temperature on the availability of soil phosphorus for plants results from:

  • lower pace of mineralization of organic phosphorus;
  • lower activity of microorganisms involved in the process of making phosphorus available for crops;
  • lower rate of plants’ metabolism (less developed root system);
  • higher viscosity of water, which reduces the diffusion rate, reducing the amount of phosphorus coming to the surface of the root.

Another critical stage of development of cereal in terms of phosphorus is the period of filling the seed, the so called filling phase. At this stage of development plants use nutrient reserves previously accumulated in vegetative organs, as well as the ones contained in the soil.

 

Stabilization of cereal yield and potassium fertilization

Accurate diagnosis of the factor limiting yield, which is often a potassium deficiency, is the basis of success for any farmer. Particularly worrying is the fact that in Poland the deepening decline in potassium and calcium fertilizer use is observed, which soon will become important factors limiting the stability of yield of most crops. The deficiency of potassium in the soil over a considerable area of ??the country is so large that it does not guarantee an efficient processing of applied nitrogen into yield and at the same time does not provide adequate quality of grain. The lighter the soil is, the lower potassium content in the soil is. The optimum level of potassium in cultivated soil destined to grow crops should be at least an average level of affluence. A sufficiently high level of K in the soil enables the plant to effectively manage water, which has a significant impact on the process of flowering and caryopses formation  during the growing season in spring. The importance of potassium in the feeding of cereals is very diverse, but the most important functions of this element include the regulation of water management, the impact on the nitrogen management, the influence on the growth of plant cells, the activation of a number of enzymes that catalyze the processes of photosynthesis, energy production and the synthesis of carbohydrates, proteins and fats. Potassium deficiency entails primarily the reduction of protein content in the plant and, consequently, a decrease in yield. As a result of protein biosynthesis disruption, the plants with a potassium deficiency accumulate large quantities of free amino acids and amides, which constitute a direct medium for the development of pathogens. Inadequate supplies of potassium also reduces plants’ resistance to frost.

Unlike rapeseed and sugar beet, cereals are among the plants that tolerate potassium fertilization. The type of potassium fertilizer does not matter in the technology of cereals fertilization. The potassium salts (60% and 40%) and compound fertilizers are used most frequently. The cereals’ nutritional needs for potassium are varied during the growing season and generally the greatest demand falls on the vegetative growth phase.

 

The first symptoms of magnesium deficiency already in autumn

Cereals are the indicator plants in autumn, when it comes to magnesium deficiency. Mg deficiency symptoms first appear in the phase of 2-3 leaves and often disappear in later stages of cereals’ development. This reaction of the cereals is associated with the specifics of the development of their root system. In the first stage the cereal root system develops just below the surface of the soil, and only later the plant strikes roots in deeper layers, where it can take up magnesium that was formerly washed out. Polish soils are naturally poor in magnesium and this condition stems from the origins of their creation. Most of the soils were formed from poor postglacial rocks, hence the low amount of the element therein. The factors significantly influencing the content of assimilable magnesium in the soil also include: acidification of cultivated soils, low abundance of the component, meteorological conditions during the growing season, differences in organic matter content, the level of mineral and organic fertilization, overliming and crop rotation. Magnesium fertilization strategy requires the identification and consideration of the following factors such as soil pH, the degree of sensitivity of the plant to acidity (barley is particularly sensitive to acidity), soil abundance in assimilable magnesium, critical phases of plants. Very acidic and acidic soils require the use of fertilizers that deacidify the soil and at the same time supplement the shortage of this component in the soil. In this case, an optimal solution is the use of calcium-magnesium fertilizers, such as dolomite, magnesium oxide, magnesite. In the case of magnesium carbonate or dolomite, one should be aware of the dependency of availability of the fertilizer component on the soil pH and the degree of fertilizer’s grinding. The lower soil pH and the larger degree of rock grinding is, the greater the release of magnesium is. In the absence of liming, magnesium reserves need to be supplemented with natural or mineral fertilizers, such as kieserite, or with both groups of fertilizers at the same time. When using 100 kg of kieserite for 1 ha, additional macrocomponent should be added, which is the sulfur in the amount of 22 kg. Compound fertilizers NPKMg or potassium fertilizers Korn-Kali®, which in addition to basic ingredients also contain magnesium, are an alternative for kieserite. Taking into account the concentration of magnesium in the group of compound fertilizers in the range of content from 2% to 6%, one should keep in mind additional complementary treatment during the growing season.

 

In autumn cereals need micronutrients

Cereals should be supplied with micronutrients already during the autumn growing season. The use of micronutrients in winter cereals is justified only if their yield potential is planned at the level of 70-80% of yield model. The reaction of winter cereals for fertilization with microelements decreases towards barley > wheat > triticale > rye. The demand for a wider range of micronutrients increases especially on farms focused only on plant production. In the current economic situation of Polish agriculture an increase in micronutrient deficiency is expected due to increased share of cereals in crop structure, insufficient fertilization with manure, use of highly concentrated mineral fertilizers, simplification of cultivation and high nutritional needs of a new generation of plants.

A plant which is well nourished with microelements launches certain mechanisms that increase its resistance to disease. Starting from the moment of sowing until harvest, cultivated plants, are exposed to the attack of pathogens and pests that is continuous but varied over the whole process of growth. Especially during the warm autumn a good supply of copper, manganese and zinc increases the resistance of plants to fungal attacks, mainly in the case of root system and stem base. Manganese and zinc allow the plant to cope with autumn water scarcity better, while zinc and copper increase the resistance of plants to low temperatures. Oats is the most sensitive to Mn deficiency among all the cereals, and the absence of this component can cause a disease called grey leaf spot.

 

Expert advises:

Microelement fertilizers can be applied both to the soil, foliarly, as well as together with the seed.

 

A special way to supplement the deficiency of microelements is their provision with seed treatment. This method of application meets the dietary plants, but only in the initial stage of growth. The use of micronutrients in autumn should also have a preventive nature and aim at avoiding potential effects of deficiency at later dates. One should be aware that soil application of micronutrients does not give a full guarantee of meeting the nutritional requirements of crops, due to insufficient using of fertilizer component. Soil application also entails an increased dose of the component in the fertilizer. Cultivated plants often suffer from the state of micronutrient deficiency that results from the limited mobility of micronutrients in the soil. The mobility of microelements is controlled by the content of organic matter, iron and aluminum compounds, carbonates and the soil pH. The increase in pH above 5.0 leads to a strong decrease in the content of manganese and zinc.

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