In 2022, potatoes in many regions of the Russian Federation were significantly affected by a prolonged drought, which led to a noticeable decrease in yields compared to the average level of recent years. Over the course of three summer months, for example, only 47% of precipitation fell in the Moscow region compared to the long-term average values (see table).
At the same time, the drought was accompanied by high air temperature, especially in August, as well as overcompaction of the soil. In terms of their impact on productivity, these factors are unequal. Soil compaction limits both horizontal and vertical root growth, which ultimately reduces tuber numbers and yields. Smaller root systems gain access to a smaller volume of soil, thereby limiting water and nutrient uptake, resulting in smaller plants with less leaf area.
Weather conditions of the growing seasons 2016-2022 in the Dmitrovsky district of the Moscow region
|Month||Average daily air temperature, оС|
|Avg. many L.||2016||2017||2018||2019||2020||2021||2022|
|Average / sum||12,5||12,6||11,0||13,4||12,9||12,4||13,3|
|Avg. many L.||2016||2017||2018||2019||2020||2021||2022|
|Average / sum||460||493||605||403||417||612||449|
At the same time, recent studies have shown that soil compaction does not reduce the intensity of photosynthesis. Potato is also generally considered a cool climate plant. It was once believed that the photosynthesis of potato plants was almost completely suppressed at temperatures above 30оC. Odbut it is now known that this effect causes mainly a deficiency water. In fact, potatoes can adapt to high temperatures (~40оC) and continue photosynthesis, but only if there is sufficient moisture, which is confirmed by the practice of successful cultivation of potatoes for irrigation in the southern regions of the Russian Federation. For example, in 2021, a higher potato yield was obtained in the Moscow region, although an increased air temperature was also noted throughout the summer, a drought was recorded in July, but heavy rainfall fell in August (table). Therefore, the most significant factor among those listed is the drought itself, which will be the focus of this article, prepared on the basis of publications of the last period (1-7).
Drought is recognized as one of the main abiotic stresses, as it affects the morphology, physiology, ecological, biochemical and molecular characteristics of plants. In agriculture, drought refers to a period of water scarcity that leads to a lack of moisture in the soil, which ultimately negatively affects crop yields. Drought is not something new for mankind: in the early 20s of the last century, it caused famine in Russia and China, in the 30s in the USA; the consequences of the anomalous 1976 are still remembered in Europe. In the first decade of the 2003st century, the Australian continent suffered from a long-term drought. European countries faced this phenomenon in 2006 and 2005, in 2010 and 2008 the lack of rain led to a massive reduction in vegetation in the Amazon rainforest. Since 2010, a multi-year drought has covered the Iberian Peninsula. A very hot year XNUMX went down in history in Russia.
Several climate models predict a decrease in annual rainfall and an increase in temperature with frequent droughts, negatively impacting crop yields around the world. Drought stress periods are expected to increase over the next 30-90 years due to reduced precipitation and increased evaporation in many regions of the world, including Europe. With the ever-increasing threat of drought, it is important to study and take into account the response of potatoes, as one of the main agricultural crops, to drought stress.
Potatoes are considered water-saving crops (i.e. those that produce more calories per unit of water used). The production of a kilogram of potatoes requires 105 liters of water, which is significantly less than that of rice (1408 liters) and wheat (1159 liters).
Another visual comparison: it takes 25 liters of water to produce one large tuber, 40 liters to produce one slice of bread or a glass of milk, 70 liters to produce one apple, 135 liters to produce one egg, and 2400 liters to produce one hamburger. water. Despite their high water use efficiency, potatoes are very susceptible to drought stress because they can produce very high yields and the crop has mostly shallow root systems.
Moisture from the leaves evaporates through open stomata. This cools the canopy, keeping the temperature below ambient temperature, but also results in moisture loss. The first physiological response to water stress is the closure of stomata on leaves. When the plant closes its stomata to reduce moisture loss, the intake of carbon dioxide into the leaf is also reduced. This inhibits photosynthesis by limiting the accumulation of starch and sugars. Potato yield and quality (eg specific gravity) depend on photosynthesis to exceed the plant's daily energy requirements, allowing excess carbohydrates to accumulate in the developing tubers. Water deficiency also reduces the internal pressure required for cell expansion and growth. Leaf canopy and root growth can be greatly reduced. Although tuber development resumes when water becomes available, disruption can result in misshapen tubers with narrow spots or pointed ends. Lack of moisture also increases the likelihood of tuber cracking. It is well known that insufficient water at any stage leads to reduced yields. Recent studies have shown that potato susceptibility to drought also depends on the type, stage of development and genotype morphology, as well as on the duration and severity of drought stress.
The physiological development of potato plants is usually divided into five stages: 1 - rooting, planting and germination (from 20 to 35 days); 2 - stolon initiation, early vegetative growth and stolon development (from 15 to 25 days); 3 - tuberization, the formation of tubers at the end of stolons (10-15 days); 4 - growth or swelling of tubers, tubers fill up and increase (from 30 to 60 days); 5 - maturity, ripening of tubers and death of tops (15 days or more). Water deficiency at the first stage does not play a significant role, germination occurs due to water reserves in the mother tuber.
Drought in the second stage can reduce the number of stolons produced, as well as negatively affect the growth and maturation of plants. Water stress at the tuber stage can delay tuber development by several weeks (Figure 1). The effects are often most significant for indeterminate (continuous-growing) varieties, extending the growing season and potentially creating maturation and firm skin problems.
In contrast, determinate (plant growth stops after flowering) varieties are relatively insensitive to water stress during this period and will mature normally. Although water shortages during tuber initiation can affect yields, the impact on quality is the most significant. The scab settles on tubers at this particular time; dumbbell shape, cracks and other deformations are all the result of uneven soil moisture during tuber initiation and early development. Another potential effect of water stress, especially when combined with high temperatures, during tuber initiation and early swelling is the development of a "translucent end" or "sugar end". Dry conditions mean that the sugars produced by photosynthesis are not fully converted to starch.
Lack of water during tuber growth usually affects yield more than quality. During this period, the effect of drought cannot be compensated by anything, the productivity of plants will decrease.
Drought reduces potato yield by affecting vegetative growth, plant height, number and size of leaves, and leaf photosynthesis by reducing chlorophyll, reducing leaf area index or leaf area duration. In addition to vegetative growth, drought can affect the reproductive stage of potatoes by shortening the growth cycle or reducing the size and number of tubers produced by plants. In addition, drought also affects the quality of the resulting tubers.
Effect of drought on above ground potato growth. Leaf canopy development is one of the most drought-sensitive stages of plant development. The development of the canopy means the formation of leaves, stems, as well as an increase in the area of individual leaves and the height of the plant. Drought has an inhibitory effect on stem height, new leaf formation, number of stems, and area of individual potato leaves. Leaf area index (LAI) and leaf area duration (LAD) are considered to be the most important factors in ensuring tuber yield. Drought stress significantly reduces LAI and LAD in potato crops.
Plant growth depends on high turgor pressure, which promotes cell expansion. Plants need a constant supply of water to maintain a high turgor pressure. Under conditions of drought stress, the availability of water for plants decreases, which affects the growth of the canopy. In most plant species, leaf growth stops if available soil water is less than 40-50%. And leaf growth in potatoes stops when available soil water is less than 60%, which indicates an increased sensitivity of potato plants to water shortages. Thus, reduced leaf and stem growth is the first observed effect of water shortage in potatoes. Although the effects largely depend on the timing, duration, and intensity of drought stress, both early and late droughts have an inhibitory effect on canopy growth. Early drought slows it down, thereby increasing the time needed to reach optimal leaf area, while late drought causes mature leaves to die off and new ones to form (Fig. 2).
There are reports of a reduction in the length of the stems of potato plants affected by early drought by 75-78%. The effect of drought also differs in varieties with different precocity. A comprehensive study has shown that late maturing varieties may be less affected by early drought, as they have a longer vegetative growth period. They can delay the achievement of full canopy coverage under late drought stress, thereby minimizing its effects.
On the other hand, the number of stalks of potatoes may be affected to a lesser extent, since the plants already produce the optimal number of stalks before the onset of the late drought.
Plants require water, carbon dioxide and light to complete the normal process of photosynthesis. Drought stress affects the amount and rate of photosynthesis in plants. The reduction in the number of leaves and individual leaf areas affects the amount of photosynthesis. On the other hand, lack of water and CO2 slows down the rate of photosynthesis. Drought stress reduces the relative water content of potato leaves by increasing the intercellular ion concentration. A high intercellular concentration of ions inhibits ATP synthesis, which affects the production of ribulose bisphosphate (RuBP), which is the main carbon dioxide acceptor during photosynthesis. Therefore, a decrease in RuBP production directly affects photosynthesis.
Effect of drought on underground potato growth. The underground parts of potatoes are roots, stolons and tubers. Potatoes have a shallow and weak root system, which makes potato plants susceptible to drought stress. The architecture of the potato root system, the length and mass of the roots are well studied, but it is difficult to speak with confidence about any definite effect of drought stress on the development of underground organs, since the results of studies on this topic are contradictory. A number of specialists reported a decrease in the length of roots under drought stress, while others, on the contrary, drew conclusions about an increase or no change (Fig. 2).
Equally conflicting data were obtained from studies on the effect of drought stress on the dry mass of potato roots and the number of stolons.
Different varieties respond differently to the specific intensity and duration of drought. Some researchers are of the opinion that later varieties produce a deeper and larger root mass than early maturing varieties under the same stress. The root system is significantly affected by the type of soil, the place of the experiment, the physiological age of the tubers and the processing of seed material during planting. The wide variation of all these factors complicates the study of the effect of drought stress on the underground parts of the potato.
Effect of drought on crop yields potatoes. Achieving high yields of tubers is the main task and problem in growing potatoes, so this issue is studied in the most detail. The response of potatoes to water shortages is highly dependent on the variety. In the course of field studies, varieties Remarque and Desiree were under similar conditions of drought stress. The results showed 44% and 11% reduction in yield. At the same time, the weight of fresh tubers is affected by the duration and severity of drought stress. Early stress (from germination to the stage of tuber initiation) leads to a decrease in the mass of fresh tubers of both early and late ripening varieties. However, prolonged drought, lasting from germination to the tuber growth stage, affects early-ripening varieties more severely than late-ripening ones.
Drought also affects the number of tubers produced on potato plants, with the greatest damage occurring in the early stages of plant development, especially at the stage of tuber initiation. But late short-term stress has a more noticeable effect on the formation of dry matter of tubers than on their number.
Dry stress directly affects the dry weight of tubers, reducing leaf growth and reducing their photosynthetic activity. It also changes the relative water content of the leaves, which affects the metabolic activity of the plants. Stomatal conductance decreases, resulting in a decrease in carbon dioxide uptake and a net rate of photosynthesis. In addition, water stress also causes a decrease in chlorophyll content, as well as a decrease in leaf area index and leaf growth duration. All these factors directly affect photosynthesis, which in turn affects dry matter. The reduction in dry matter of tubers is the same in drought-sensitive and drought-tolerant varieties. At the same time, drought-resistant varieties produce smaller, but larger tubers (>40 mm), which makes their yield more marketable than drought-sensitive ones. The reduction in the number of tubers depends on the degree of stress and varietal characteristics. The average dry weight of the tuber under good irrigation, moderate drought stress (50% of available soil water) and severe drought stress (25% of available soil water) is 30,6 g per 1 plant, 10,8 g per 1 plant and 1,6, 1 g per XNUMX plant, respectively. All varieties differed in the production of dry matter of tubers under different water regimes.
Under moderate drought stress, the decrease in the mass of dry tubers in varieties ranged from 49,3% to 85,2%, and under extreme conditions - from 93,2% to 98,2%. Differences between cultivars in tuber dry matter production may be due to differences in their early maturity, as early ripening varieties produce a higher average tuber weight than late ripening varieties.
Drought mitigation opportunities. It would be logical to confine ourselves in this part to the proposal to master various methods of irrigation, as a radical solution to the problem of drought. However, the sharply increased cost of irrigation systems, up to 400 thousand rubles/ha, forces the more purposeful and large-scale use of other waterless, means of mitigating drought damage. These include:
Use of more drought-resistant potato varieties. In recent years, many genes associated with drought stress have been identified, but drought-resistant potato genotypes are still far from being created using genomic editing technology. Indeterminate varieties of the stem type are more resistant to drought, however, with a very long drought, they have problems ripening tubers by the time of harvest (situation in 2021). Early drought reduces the yield of early-ripening varieties to a greater extent than late-ripening ones. Late drought is less important for early varieties, and tubers of late-ripening varieties in this case do not have time to ripen. In conditions of unpredictable drought, the effects of drought stress can be mitigated by growing several varieties of potatoes with different early maturity and type of growth at the same time.
Efficient tillage. Adaptive tillage practices increase water infiltration and reduce soil moisture evaporation and rainfall runoff. Tillage affects water availability by changing the surface roughness and porosity of the soil, but the use of ridges for growing potatoes somewhat limits the possibilities for tillage in potato production. Nevertheless, it is obvious that Compared to the template technology of milling before planting and during ridge formation, which is used unreasonably in many farms, the use of passive working bodies for cultivation, soil deepening, loosening of row spacing, dimples gives a tangible effect of reducing erosion, water and soil washout and improving water accumulation (see photo 1-3, 3 - view of the potato field after 100 mm of precipitation per day).
Against the background of more frequent droughts and taking into account the possibility of climate change, it is advisable to equip potato planters with dimples, especially on sloping fields and at the same time as planting, the formation of full-fledged ridges (photo 4).
soil organic matter mitigates the effects of drought by controlling evaporation, absorbing water vapor in mulch fabrics and increasing infiltration. Animal manure, straw, green manure, rich in carbon, can also improve the nutritional status of soils and their water-holding capacity. Extremely compelling results were obtained comparing five different (but short) potato rotation schemes with and without irrigation (5). The standard two-year or "status quo" (SQ) rotation consisted of barley oversown with red clover as a cover crop, followed again by potatoes the following year, and included regular spring and fall tillage each year.
The Soil Conservation (SC) rotation consisted of a three-year rotation of barley sown with timothy, which continues to grow throughout the next year. In this system, tillage is significantly reduced, while there is no need for additional care and harvesting throughout the year, which significantly improved soil conservation. In addition, straw mulch (2 t/ha) was applied after potato harvest to further conserve soil resources. The Soil Improvement (SI) rotation consists of the same basic tillage (3 years, barley/timothy-timothy-potato, limited tillage, straw mulch) but with annual compost additions (45 t/ha) to provide excess organic matter to improve soil quality. Disease suppression (DS) crop rotation was designed to control soil-borne infections and included the use of disease-suppressing crops, rotation period, crop diversity, green manure. The system was a three-year circulation with a disease-suppressing mustard variety grown for green manure, followed by a first-year mustard seed crop. In the second year, sorghum-sudan grass was sown for green manure, followed by winter rye, with potatoes during the third year. These crop rotations were compared with permanent potato cultivation (PP).
All rotations increased tuber yields compared to the PP control without rotation, and the SI scheme, which included annual composting, produced greater yield increases and a higher percentage of large tubers (Figures 3,4) than all other non-irrigated systems. (increase from 14 to 90%). DS, which contained disease-suppressing green manure and cover crops, produced the highest yields when irrigated (11-35% increase). Irrigation contributed to the increase in tuber yield in all cultivation systems (Fig. 3,4), except for SI (an average increase of 27-37%). It also resulted in significant increases in leaf vegetative time and chlorophyll content (as indicators of photosynthetic potential) as well as root and shoot biomass compared to other cultivation systems, especially under non-irrigated conditions. The SI rotation also increased N, P, and K concentrations in shoot and tuber tissue, but not most micronutrients.
Studies of these farming systems have revealed changes in the physical, chemical, and biological properties of the soil, and these impacts have tended to increase over time. All rotations increased soil aggregate stability, water availability, microbial biomass compared to full rotation (PP), and three year schemes (SI, SC, DS) increased aggregate stability compared to two year (SQ). In addition, three-year reduced tillage rotations (SI and SC) increased water availability and reduced soil density compared to other systems. The SI scheme resulted in greater increases in total and particulate organic matter, active carbon, microbial biomass, water availability, nutrient concentrations, and lower bulk density than in all other cropping systems. SI has also been shown to increase microbial activity and significantly affect soil microbial community characteristics, while PP exhibits the lowest microbial activity with the rest in between. All of these changes are parameters for soil improvement.
In this study, all rotations increased total and commercial tuber yields without irrigation compared to no rotation (PP), but the SI variant produced the highest tuber yield of all systems (both total and commercial): 30-40% higher on average than the SQ and PP systems for all years (Fig.3,4). Yield differences were greatest in drier years (2007 and 2010), when SI yields were 40-90% higher than SQ and PP. In addition, in the SI scheme, the highest content of large and extra large tubers was obtained.
It should be noted that under irrigation, all crop rotations, with the exception of SI, gave significantly higher yields compared to non-irrigated technology, while the total and marketable yields were on average 27 and 37% higher, respectively. Only the SI variant produced comparable (and high) yields in both irrigated and non-irrigated conditions. The data obtained strongly suggest that the increase in yield observed in SI is associated with improved soil conditions, increased water-holding capacity and water available to plants. orochenenie significantly increases growth and yield at normal field conditions but crop rotation schemethat SI, with large organic additives, essentially replaces irrigation, providing comparable results without irrigation.
Rational use of nutrients substances also contributes to increasing the resistance of potatoes to drought, as it affects the water-holding capacity of the soil and plant cells. Some inorganic nutrients such as Zn, N, P, K and Se alleviate drought stress. Foliar and soil application of silicon improves the drought tolerance of potatoes. The maximum application of potassium induces drought resistance by improving growth, gas exchange, nutritional, antioxidant properties. As a stress reliever, potassium alleviates the negative effects of drought by regulating or improving stomatal conductance and photosynthesis rates, CO2 and ATP synthesis. The use of potassium, including directly in the process of drought (foliar feeding), reduced stress, regardless of varieties (1). The introduction of potassium is an effective method for increasing the drought resistance of potato crops.
Foliar application of natural and synthetic growth regulators plants can also mitigate the adverse effects of drought. While this is a new technology in agronomy, which is only becoming part of an effective drought management strategy. In international practice large-scale potato growing for neutralizationThe effects of heat and drought are most actively used by seaweed extracts, protein hydrolysates, humic acids and microbiological preparations. Practical decisions on the use of biostimulants are somewhat different from the theoretical postulates (2). All well-received commercial products against heat and drought are dominated by the amino acid glycine in its pure form and in combination with betaine (a derivative of glycine).
For extracts of algae and humates, the content of organic matter is primary. More concentrated products will be more effective. Humic acids are preferred over fulvic acids. Microbiological preparations must specify the strain composition, efficiency in this area is ensured only by the development of fundamental research institutes, and the authority of strains of beneficial microorganisms is not formed immediately, but over many years. It does not make sense to use preparations with non-specific, incomprehensible composition and unknown content or designation of content in non-standard units of measurement. Unfortunately, there are still enough such non-professional products on the market.
Adjustment of modes of work with seed material. Drought stress, especially when combined with excess heat, worsens the physiological condition of seed tubers. The period of deep dormancy is reduced, the risk of early, literally autumn, germination of tubers of varieties with a short genetic dormancy in storage increases. The effect of drought must be taken into account when preparing seed for specific potato growing purposes. Particular care must be taken to weigh the need for use and the consequences of prolonged germination of seed tubers of each variety at high temperatures.
Council о moving production potato to regions with high rainfall and a lower probability of drought on the scale of the vast Russian Federation is quite justified. Yes, this is irrelevant for most existing enterprises, but it is advisable for startups to treat such opportunities consciously and in a timely manner, i.e. at the project planning stage. Practically effective in most cases is the spatial removal of potato fields within one large enterprise. Often, even at a distance of 5-10-20 km, the amount and timing of precipitation differ significantly. The division of the total area makes it possible to increase the stability of the gross potato harvest.
A severe drought in agriculture has always been considered a force majeure, those. a significant circumstance that negatively affects the ability to fulfill contractual obligations to customers, banks, etc. With true partnerships in the industry and the implementation of government policy to support the stability of food production in such a situation, it is customary to apply economic measures to compensate for the damage from drought to agricultural producers.
So, in 2022, a long drought was observed along with high temperatures in the main potato-producing countries of Europe: Germany, Belgium, France, and England. It has already been calculated that the gross potato harvest in the EU will be the lowest in the last 20 years. The response measures thereare taken promptly: in addition to the guaranteed insurance indemnity, contract prices are being revised - of course, upwards, the tolerances for the size of table potatoes in retail trade are adjusted, of course, downwards. Retail chains inform consumers about the reasons for changing the calibration, the whole society has an understanding that in this situation the share of retailers' earnings in the total price should be reduced in favor of farmers. This style of work of foreign retail chains, actively earning money in the Russian Federation, does not apply to Russian potato growers. Potato purchase prices are currently significantly lower than last year, when there was also a drought (since the drought-2022 did not cover all regions), and it is time for state administration and control bodies, industry unions to pay attention to this. And it is realistic to provide support for potato producers in drought conditions, thereby actually showing concern for food security and import substitution.
Thus, drought becomes the main natural phenomenon that limits the yield of potatoes. The crop's sensitivity to drought is primarily due to its shallow root system. The effects of water stress vary at different stages of growth. Tuber initiation and growth are the most critical stages. Lack of water during the emergence of tubers can seriously affect the quality of shape distortion, scab spread, cracks, hollowness. The lack of water during the swelling of the tubers has the greatest impact on yield. The dynamics of the formation of the leaf surface, the type of variety development determine the level of drought resistance. The effects of drought stress can be mitigated by selecting and growing at the same time several varieties of potatoes with different early maturation and growth patterns. The use of soil deepening, passive working bodies, loosening of row spacings and dimples ensure the conservation of soil moisture reserves and precipitation during the growing season. Increasing the duration of crop rotation, the use of cover crops, green manure, reduced tillage and the application of organic fertilizers significantly improve the growth and yield of potatoes in drought conditions. Effective means of reducing damage from drought are qualified handling of seed material, special anti-stress preparations and foliar feeding with targeted nutrients.
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