The condition of winter plantations against the backdrop of current weather conditions
Weather has been unfavourable for farmers for a good few months now. The harvest of 2017 was uniquely long and difficult in most areas of Poland – rainfall prevented the harvest of cereals, rape or maize. Many farmers had made the very difficult decision to forgo the harvest and leave the plants on the field.
This was caused by the lack of technical possibility to perform the harvest or very high losses caused by extensive rains – with shattering and overgrowth. The beginning of the new 2018 season was also difficult, excessive rainfall towards the end of summer and in autumn caused difficulties in sowing of winter rape and winter cereals. Hence, many farmers made the decision to forgo winter species favouring summer ones, especially in terms of cereals that can be replaced by maize.
In relation of the difficulties in sowing, winter plants moved to their resting phase in broadly varied development stages. Winter rape sown according to agricultural periods created very well expanded rosettes made up of 8-10 or even 12 leaves, meaning, they reached the winter rest period at an appropriate stage. Such a condition of one's plantation, with correctly executed insecticidal and fungicidal protection during autumn, gave farmers good hopes of a good harvest. A different group are plantations of winter rape sown in unfavourable soil conditions and outside of the required period. The rosettes are weakly developed – with the leaf count frequently lower than six or seven.
Development stages of cereals are also broadly varied. Even if plantations of winter barley, rye and triticale are usually in the phase of full tillering – most plantations were sown on time, hence the advanced development stages. However, the the period of sowing of winter wheat in practice usually differs broadly from optimum agrotechnical periods – late sowing in the autumn following the harvest of sugar beet or maize. Winter wheat, depending on the sowing period, may be in phases between two-three leaves to full tillering.
The ability of winter plants to survive the winter conditions depends on many factors. One of the very important ones are the genetic properties of the species, including frost resistance, which to a certain extent conditions winter resistance. One needs to remember that frequently, improved crop yield potential is related to a reduction of the above parameters. Frost resistance is the ability of the crop to survive negative temperatures at a suitable level. Wintering ability is the ability to survive the winter, as per the following conditions: temperature, insolation, wind, precipitation and other events.
Literature data is inconclusive and indicates that wheat and triticale are able to „survive” even up to -20 ᵒC, rye -30 ᵒC, barley -15 ᵒC. The indicated limit temperatures are frequently theoretical, as they depend on many factors: time of sowing, infestation by pathogens, species properties or thickness of the show cover. In the winter, winter plants are at risk of freezing over or cold wind burning, smothering.
Freezing is damage to parts of the plant caused by long-term influence of low temperatures. Plants die out when the tillering node (in cereals) or the root neck (rape) freezes over, whereby freezing over of leaves will delay the speed of growth in the spring. However, this is not hazardous for the further maintenance of the plantation.
Cold wind burning occurs in case of no snow cover at strong and very cold winds, which cause the overground part of the plants – the leaves – to dry out. In extreme cases, the root neck and the tillering node can also be damaged.
Smothering occurs if snow falls on unfrozen soil and remains for a longer time. Under the snow cover, the temperature does not drop below 0 °C, resulting in the breathing process not halting – meaning, the plants do not move to the resting phase. In such a case, the plants use up the collected reserve material and are significantly weakened, as a result of which snow mould can develop intensely.
Uncovering of roots – visible particularly in soils able to collect a lot of water or following heavy rains and sudden frost. The ground freezes due to the negative temperatures – it increases its volume and is raised; if temperatures increase, the phenomenon progresses in the reverse direction. Due to such processes repeating, the root system may be interrupted or broken up.
The winter of 2018 was up to now quite mild and, despite the lack of snow cover, did not negatively influence winter crops. Temperature dropped significantly below 0 °C only locally, not causing heavy damage to crops, even those in worse condition. However, the present temperature drops may negatively influence winter plantations. The weather in Poland has one common factor – low temperatures, but it is diverse, hence analyses of the threats to farmed plants from unwanted winter phenomena should be considered regionally.
Region 1. No snow cover across the entire region, air temperatures did not drop below -10 °C, but at the ground – they did. Broadly varied condition of winter crops, some plantations 'lose colour', others show no signs of negative influence of the low temperatures.
Region 2. No snow cover save for the northern part, however, the cover thickness is not particularly high. Night temperatures drop below -15 °C, during the day they remain in the range of -5 to -12 °C. Single plantations 'lose colour'.
Region 3. No snow cover, temperature drops to below -20 °C, accompanied by wind.
Region 4. No snow cover, temperature drops to below -10 °C accompanied by strong winds. Some crops, particularly of winter barley, 'lose colour' across certain areas.
Region 5. No snow cover, air temperature below -5 °C, feeling of cold exacerbated by fairly strong winds. Some plantations 'lose colour'.
Region 6. Local snow cover, however not particularly thick, temperatures below -10 °C.
Region 7. No snow cover, day temperatures around -10 °C, dropping sharply in the night. Individual plantations 'lose colour'.
Region 8. Varied when it comes to the snow cover, south of Kraków and Tarnw a few centimetres of snow, remaining areas of Małopolska under a snow cover of 1-2 cm; no snow in Silesia.
Region 9. Snow found locally, susceptible to blowing off by wind, night temperature drops to below -15 °C.
Region 10. Snow cover, in some parts of the southern area of the Lublin region, resent already during the heavy frosts, air temperature below -10 °C.
Region 11. Presently very thin snow cover, temperature drops below -13 °C.
Region 12. No snow cover, night temperatures drop below -10 °C, no wind or signs of heavy damage to crops.
Condition of winter crops against the backdrop of current weather conditions
Most of the country is left without a snow cover, which, at temperature drops below -10 °C, will certainly worsen the condition of winter plants – particularly barley. The plants most susceptible to damage caused by low temperatures are winter barley and winter wheat in low development stages at two-three leaves. Wheat, rye and triticale at full tillering are less prone to temperature influences, and the tillering node is better protected by the leaves. If the cereal plants, at full tillering, lose a small portion of the leaves, then if the plantation is properly taken care of, they should recover quickly.
One thing is certain, the wintering conditions are extremely difficult. Despite this, it is currently difficult to estimate the extent of damage due to frost on plantations, because the conditions do not permit the execution of a wintering trial without damaging the plants if removing them from the ground. The ultimate wintering of the plants in worse conditions will be influenced by the further part of the growing season – the weather following heavy frost and whether, following a temporary period of warmer temperatures, temperature drops will occur.
Bartosz Waniorek, CIECH Sarzyna S. A.