Changes in flax yield and quality in response to various mineral nutrition

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Introduction
According to Food and Agriculture Organization of the United Nations (FAO) statistics, today a limited number of countries grow fiber flax for commercial purposes: in polyunsaturated fatty acids (Omega-3 and Omega-6) is produced from the seeds. Flax seeds and linseed oil are used for food, medical, and technical purposes.
Harsh competition in the sales market, including in the flax sector, has set domestic producers the task to obtain high-quality fiber, seeds, and oil, end ensure strict control of their finished product quality and chemical composition (Belopukhov et al., 2010;Enakiev et al., 2018;Man et al., 2021;Dmitrevskaya et al., 2022).
Given the above, the objective of our research was to adapt the fiber flax, Voskhod variety, to the soil and climatic conditions of the Moscow region and to study the chemical composition of flax seeds and flaxseed oil in response to the application of mineral and organic fertilizers and without fertilizers.

Material and Methods
The studies were carried out in 2013-2016 as part of the long-term field experiment of Russian State Agrarian University, Moscow Timiryazev Agricultural Academy, started by Professor A.G. Doyarenko in 1912 (Filippova et al., 2018;Mazirov et al., 2021). The soil of the experimental plot is sod-medium and slightly podzolic, old-arable (more than 200 years under arable land), naturally acidic and floating (according to the FAO classification -Podsolluvisol). The soil characteristics of the experimental site are presented in Table 2.
Since 1949 (7th crop rotation), liming has been introduced into the experiment, as one of the essential factors in the cultivation of acidic soddy-podzolic soils. Lime is applied to half of each field, in the form of dolomitized limestone -once per crop rotation (the dose is based on the values of the hydrolytic acidity of the soil).
The rise of the flax-growing branch of agriculture in Russia in recent years has been facilitated by the adoption of the State Program for the Development of Agriculture until 2025 (Molajou et al., 2021a). This program significantly has deepened and expanded the economic measures of influence on the processes in the agrarian and agri-food spheres of the country, among which a significant place was and is given to subsidies and subsidies that stimulate the growth of production, including the flax-growing subcomplex (Molajou et al., 2021b;Afshar et al., 2022). However, in the global production of natural and synthetic fibers, flax occupies a limited market segment, as Table 1 shows. This corresponds to the fact that only 0.1 kg of flax fibers produced per year per inhabitant of our planet, which, of course, is extremely low (Rozhmina et al., 2018).
Despite the high productivity of modern fiber flax varieties, their maximum biological capabilities and potential of the variety in production conditions can be 30-50%, which is largely due to the insufficient use of mineral fertilizers in the optimal ratio of nutrients. The use of environmentally friendly, biologically active products can also increase the economic efficiency of flax cultivation through a natural positive effect on productivity. Consequently, with the rational use of soil resources, fertilizers, plant protection products, the results of selection and technological methods of cultivation of flax, it is possible to obtain high yields of fiber and seeds (Du et al., 2015).
The value of fiber flax is due to the variety of its uses (Duman, 2022;Dundar et al., 2021;Ahmad et al., 2021). Fabrics for various purposes are produced from flax fiber: clothing (linen fabrics), household, furniture-decorative, industrial, as well as special-purpose fabrics (medical and defense industries). In the EU countries and China, 30-50% of the production of linen fabrics is textile fabrics for the production of clothing, in Russia the production of technical fabrics accounts for about 50% (Grishina et al., 2016;Grigoryeva et al., 2021).
Flax seeds are a valuable source of various substances: proteins (18-23%), fats (30-40%), phospholipids, macro-and microelements (Abu-Zaid et al., 2022). Flaxseed oil rich Doses of mineral fertilizers in 1973 were increased and amounted to N 100 , Р 150 , К 120 for food elements. Phosphorus and potash fertilizers are applied at the same time for pre-sowing treatment, and nitrogen fertilizers -in 2 periods: in the fall (N 50 ) and in the spring as top dressing (N 50 ).
Since 1973, to study the aftereffect of fertilizers, their plot application was stopped on even fields (132,134,136) of the main crop rotation, and each field has been fertilized with a continuous single dose of N 100 Р 150 К 120 . Manure also has not been applied to these fields. For permanent winter rye, 20 tons of manure are applied annually per hectare in 8 and 10 variants.
The area of the plots was 50 m 2 , the registration plot area was 25 m 2 . The predecessor in all the years of research is the first-year clover. Nitrogen fertilizers were applied in the spring before sowing; phosphorus, potash, and manure -in the fall. Liming has been carried out once every 4-5 years based on the hydrolytic acidity of the soil, during the years of our research it was not carried out. The soil is soddy-podzolic, medium and light loamy, old arable, according to agrochemical indicators (average values during the years of research): soil density 1.5-1.6 g/cm 3 , humus content (Tyurin) -2-2.5%, P 2 O 5 (Kirsanov) -170-180 mg/kg, K 2 O (Maslova) -90-100 mg/kg, N, readily hydrolysable (Tyurin) -5-5.5 mg/100 g, pH (water) -5.5-6. Agroclimatic conditions of the growing seasons 2013-2016 did not have a negative effect on the growth and development of fiber flax, the yield of which was mainly determined by the studied factors. The HDC (hydrothermal coefficient), which characterizes the degree of moisture in the growing season, was 1. The fiber and seed yield data were calculated for the variants of the experiment in accordance with the existing guidelines and recommendations (Mikhailouskaya and Bogdevitch, 2009;Berezovsky et al., 2020;Dudarev, 2022;Rihaczek et al., 2020). Samples of seeds and oil were obtained from Voskhod fiber flax (Russian selection).
Chemical analysis of seeds for the content of the total amount of lipids and proteins, as well as the fatty acid composition of flaxseed oil was performed by near infrared spectroscopy (NIR), SpectraStar XL 2500XL-R, in accordance with GOST 32749. Flaxseed oil was obtained by cold pressing in accordance with GOST 5791.
Determined linseed oil yield, acid number according to GOST 50457 and peroxide number according to GOST 51487. Elemental analysis of seeds was determined by atomic absorption spectroscopy (AAS) (KVANT-Z ETA instrument model). All tests were performed in triplicate, confidence intervals with a significance level of 95% were calculated in Excel.

Result and Discussion
The productivity of agricultural crops is closely dependent on the presence of the basic elements of mineral nutrition in the soil. Therefore, the forms and doses of fertilizers applied under flax directly affect the yield of flax and the quality of the resulting flax products.
In our studies, the field experiment was carried out on the territory of the "Long-term field experiment of Russian State Agrarian University, Moscow Timiryazev Agricultural Academy", known abroad as the "Moscow permanent study area". Fiber flax has been grown in this experiment for over 100 years. The multifactorial experience of long-term use of fertilizers, both individually and in various combinations, is a method of understanding the basic patterns of the formation of flax yields and soil fertility conditions in the Non-Black Earth Zone of Russia (Mikhailouskaya and Bogdevitch, 2009).
Our data show high yields of flax from plots with a full range of mineral fertilizers, together with the introduction of manure and liming, both in fiber (18.5-18.9 hwt/ha) and in seeds (7.9-8.3 hwt/ha) (Table 4).
Plots with N 100 P 150 K 120 , without liming (variant 3) produced higher yield by 6.1 hwt/ha of flax straw, by 0.8 hwt/ha of fiber, by 0.3 hwt/ha of seeds relative to zero level plots (without fertilizers, without liming) (variant 1). A similar increase in yield was on plots with liming. The average yield increase over three years of research on plot with N 100 P 150 K 120 , with liming (variant 4) was by 5.6 hwt/ha of flax, by 1.1 hwt/ha of fiber, by 0.9 hwt/ha of seeds relative to the zero-level plot (without fertilizers, with liming) (variant 2). The introduction of organic fertilizers (manure) together with mineral fertilizers (variant 5, 6) contributed to an average increase in yield by 3.5 -6.1 hwt/ha of flax straw, by 0.4 -1.1 hwt/ha of fiber and by 0.4 -0.5 hwt/ha of seeds relative to options with a full complex of fertilizers (variants 3, 4) over three years of research.
Liming promoted an increase in the yield of flax straw by 1.4 -5.5 hwt/ha, fiber by 0.4 -1.6 hwt/ha and seeds by 0.1 -1.1 hwt/ha relative to plots without liming.
Thus, the use of mineral fertilizers together with manure and liming (variant 6) has led to the increase in the yield of flax straw by 30%, fiber by 17%, and seeds by 21% compared to the variant without fertilizers and liming (variant 1).
The harvested flax seeds were analyzed for the content of the total amount of proteins and lipids (Table 5).
Plots treated with a full set of mineral fertilizers together with manure and liming (variant 6) produced seeds with the higher content of protein by 2.7% and lipids by 5.1% relative to plots without fertilizers and liming (variant 1). Liming of plots contributed to the higher content of protein and lipids in flax seeds by 0.3%-0.9% and 0.3-1.8%, respectively, relative to plots without liming on average over three years of research.
An important feature of the quality of the obtained flaxseed oil is its yield (%), acid (AN) and peroxide (PN) numbers. We have determined these indicators when obtaining flaxseed oil from seeds (Table 6).  Hydroperoxides are the main primary oxidation products of unsaturated fatty acids. The peroxide number, which characterizes the content of organic hydroperoxides in the oil, is one of the most important indicators of oil quality for its oxidation state (Tables 6). The primary oxidation products of oils and fats are unstable and easily decompose, transforming into secondary oxidation products, which are a complex group of compounds including various aldehydes and ketones, hydrocarbons, epoxy compounds, relatively stable alcohols, acids, hydroxy acids, and others. Aldehydes and ketones impart unpleasant taste, odor, and toxicity to fats. It should be noted that, although usually for edible vegetable oils, maximum admissible level of PN is 10 mg-eq O 2 /kg, a change in taste (rancidity) and odor of highly unsaturated linseed oil usually begins at PN less than 3-5 mg-eq O 2 /kg oil. The acid number (AN), which characterizes the content of free fatty acids, should not exceed 2 mg KOH/g oil (Bozan and Temelli, 2008;Mohanan et al., 2018;Cheng et al., 2019).
The flaxseed oil yield ranged from 19.5-35.7% on average for different variants of the experiment. The yield of oil of flax seeds increased significantly on experimental plots with the use of a full set of mineral fertilizers (variant 3, 4) 5 -10.4% relative to plots without fertilization (variant 1, 2). Plots treated with a full set of mineral and organic fertilizers (variant 6) showed an increase in the yield of flaxseed oil by 14.9-16.2% relative to the zero level plots (variant 1) The PN was 2.5-1.5 mg-eq O 2 /kg and the AN was 1.1-1.9 mg KOH/g, which corresponds to the production of high-quality linseed oil in accordance with quality standards (TU U 15.4 -32448339 -001: 2005) for all variants of the experiment. Both AN and PN were lower in the fertilized variants relative to the variants without fertilizers.
The fatty acid composition of flaxseed oil is represented by the content of the total of saturated fatty acids 9.0-14.1%, the total of unsaturated fatty acids -85.9-91.0%; the composition of unsaturated fatty acids had a high content of diet-essential α-linolenic acid -46.9-60.9% (Table 7). The application of fertilizers, according to the variants of the experiment, contributed to a decrease in the amount of saturated fatty acids and an increase in the amount of unsaturated fatty acids in linseed oil. Variants treated with the full set of mineral fertilizers (variant 3, 4) had a decrease in saturated fatty acids and an increase in unsaturated fatty acids -2.1-2.5% relative to the zero level plots (variant 1, 2). The same changes were in the composition of fatty acids of flaxseed oil in variant 6 (4.1% -4.8%) relative to variant 1. Liming slightly influenced the fatty acid composition of the oil according to the variants of the experiment.
A wide variety of the content of elements in flax seeds provides a wide range of their medico-biological properties, which allows the seeds to be used as additives for the production of various food products. Table 8 shows the results of elemental analysis of long flax seeds.
the content of chemical elements in seeds can be grouped as follows:

Conclusion
Thus, as a result of our studies conducted in the conditions of the Moscow region on the territory of the Long-term stationary experiment of Russian State Agrarian University, Moscow Timiryazev Agricultural Academy, where fiber flax has been grown for more than 100 years, with the maintained crop rotation and the introduction of a full range of mineral and organic fertilizers, we obtained high yields of flax fiber (18.5-18.9 hwt/ha) and flax seeds (7.9-8.3 hwt/ha).
The content of protein and lipids in seeds was 16.9-19.5% and 33.5-39.4%, respectively. Acid and peroxide numbers of linseed oil meet quality standards. In the fatty acid composition of flaxseed oil, the content of the total of saturated fatty acids is 9.0-14.1%, the content of unsaturated fatty acids is 85.9-91.0%. There was a high content of essential α-linolenic acid is 46.9-60.9%. The content of chemical elements in flax seeds was high for magnesium, calcium, iron, potassium (1500-5620 mg/kg), medium for zinc, manganese, chromium, silicon, aluminum (3.0-25.1 mg/g), and low for copper, lead, cadmium, and mercury (0.01-0.5 mg/kg).