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Influence Of Nitrogen And Phosphorus Fertilizers On The Quality Of Potatoes
Influence Of Nitrogen And Phosphorus Fertilizers On The Quality Of Potatoes

About the nutritional value of potatoes

growing potatoes
growing potatoes

Both adults and children like dishes made from quality potatoes. That is why it is considered a culture with high vitality. This is a dietary product. The nutritional value of potatoes is that in its tubers there is a large amount of easily digestible starch and vitamin C, which is so necessary for human health, the content of which ranges from 15-25 mg per 100 g of raw material.

In addition, the tubers contain easily digestible complete proteins, as well as phosphorus, iron, potassium and trace elements. Potatoes are also valued for their taste. The content of starch and other nutrients depends not only on the fertilizer applied, but also on the variety, meteorological conditions, cultivation technology and soil properties.

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Starch is the main nutrient and the main energetic material of the tuber, it contains about 70-80% of the dry weight or 9-29% of the weight of the natural tuber. As a rule, late-ripening varieties have a higher starch content than early-ripening ones. In dry summer conditions, potatoes contain more starch with a relatively low yield, and, conversely, in conditions of sufficient moisture, the yield of tubers increases with a slight decrease in starch content. The potatoes grown in the northern regions contain less starch than the same varieties grown in the central and southern regions.

Along with starch, potato tubers contain a lot of sugars, mainly glucose, less sucrose and very little fructose. The amount of sugar depends on the nutritional conditions of the plant, as well as on the variety, its degree of maturity, storage conditions and ranges from 0.17-3.48%.

Many varieties of potatoes are also distinguished by a high protein content (the range of fluctuations is within 0.69 … 4.63%). These are mainly "yellow-meat" or "red-meat" varieties, on the cut of the tuber of which the colored pulp is visible. White meat varieties always contain a small amount of protein. The potato protein, called tuberin, is higher in biological value than the protein of other agricultural crops. An important property of potato protein is that it is characterized by an increased content of lysine, which limits the nutritional value of almost all plant proteins. Tuberin compares favorably with most plant and some animal proteins, it has almost 100% digestibility and assimilability in humans and animals. Therefore, potatoes are of great importance in human protein metabolism,its daily requirement for 40-50% may well be satisfied by good potatoes.

Along with protein, potatoes contain free amino acids, which account for up to 50% of the total non-protein nitrogen substances, the biological value of which is not inferior to the protein itself. Therefore, in potato tubers, it is often not the content of pure protein that is determined, but the so-called crude protein, which includes non-protein nitrogenous compounds in its composition. The content of crude protein ranges from 0.84 to 4.94%, and sometimes its amount is even more than these figures. In terms of protein yield per hectare, potatoes are not inferior to wheat.

Potato tubers contain on average 78% water, 22% dry matter, 1.3% protein, 2% crude protein, 0.1% fat, 17% starch, 0.8% fiber and from 0.53 to 1.87 % ash, which includes potassium, calcium, magnesium, phosphorus, sulfur, iron, bromine, copper, selenium and other mineral elements that are very necessary in human nutrition.

The fat content of potatoes is low, although the fatty acid composition is very valuable. About 50% of them are doubly unsaturated linoleic acid, about 20% is three times unsaturated linolenic acid.

The composition of potato tubers also includes ballast substances, which are understood as indigestible constituents of plant cell membranes such as cellulose (cellulose, pectins, hemicellulose, lignin), which perform important and very different functions in the digestive tract, affecting metabolism. They play a big role in healthy eating. Although the proportion of these substances in tubers is small, a 200 g portion of potatoes provides about one quarter of their daily requirement for humans.

The average content of important macro- and microelements in potatoes is quite high. With a daily consumption of 200 g of potatoes, a person's need is satisfied by 30% of the daily value in potassium, by 15-20% in magnesium, 17 in phosphorus, 15 in copper, 14 in iron, 13 in manganese, 6 in iodine and 3% in fluorine.

With a daily consumption of 300 g of potatoes, you can meet the daily requirement for vitamin C by 70%, vitamin B6 - by 36%, B1 - by 20%, pantothenic acid - by 16% and vitamin B2 - by 8%.

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growing potatoes
growing potatoes

In recent years, in the light of new concepts, potatoes are considered one of the most important crops with a high potential for the content of antioxidants that strengthen the human immune system. In this case, we are talking primarily about the content of anthocyanins and carotenoids. It is these pigments that are of great value as sources of antioxidants due to their ability to release free oxygen radicals in the human body. It is now well known that diets rich in antioxidants help reduce the risk of atherosclerotic disease, certain types of cancer, age-related changes in skin pigmentation, cataracts, etc.

The range of fluctuations in the content of anthocyanins in pigmented potatoes is in the range of 9.5-37.8 mg per 100 g of pulp of tubers. Prospects for further improvement in this area allow pigmented flesh potatoes to be placed on a par with vegetables such as broccoli, red bell peppers and spinach, which are known for their antioxidant properties.

Potatoes with yellow flesh have long been popular in many countries of the world due to their high content of carotenoids (101-250 mg per 100 g of fresh flesh). On soddy-podzolic loamy soils, potatoes occupy one of the first places in the accumulation of dry matter per unit area, second only to beets and corn, and on light sandy soils, the yield of tubers often exceeds the yield of root crops. Therefore, potatoes grown in the country are the main crop that can produce a high-quality harvest and ensure that there are no pesticides or anything harmful in it, only nutrients that are desirable for the grower.

The need for potatoes in nutrients

growing potatoes
growing potatoes

This crop makes the greatest demands on the amount of nutrients needed to form a high yield. The increased need for potatoes in nutrients is associated with its biological characteristics: the presence of an underdeveloped root system and the ability to accumulate a large amount of dry matter per unit area. It was found that 60% of potato roots on sandy loam soils are located in a layer up to 20 cm, 16-18% - in a layer of 20-40 cm, 17-20% - in a layer of 40-60 cm, and only 2-3% of roots penetrate into deeper horizons.

Therefore, relatively high doses of fertilizers are used for potatoes as compared to other vegetable crops. In connection with the noted biological characteristics of this crop, fertilizers have a great influence on both the yield and the quality of potato tubers. Both mineral and organo-mineral fertilizers increase the content of starch, sugars, vitamin C, crude protein, minerals, organoleptic properties in tubers and increase the percentage of marketable tubers. First, let's look at how certain types of fertilizers do it.

Organic fertilizers have a great effect on increasing potato yields. They increase the content of ascorbic acid in tubers, improve the marketability of tubers, but somewhat reduce starch content and the content of minerals. Increasing doses of manure increase the marketability of potatoes - the percentage of large tubers in the crop. The content of large tubers in the crop at a manure dose of 3-4 kg / m2 increases from 20 to 31%, and at a dose of 5-8 kg / m2 - up to 42%. However, in this case, the taste properties decrease, the pulp darkens, and the plant disease susceptibility increases.

The greatest decrease in the starch content of tubers is observed with the introduction of medium doses of manure on light-textured soils. The starch content of potatoes under the influence of manure decreases to a greater extent in the early varieties than in the middle-late and late varieties. With increasing doses of organic fertilizers, the starchiness of the tubers decreases more.

growing potatoes
growing potatoes

If the starch content in tubers without the use of manure was 16.5%, then when 2 kg of manure was applied per 1 m2, its content decreased to 15.9% and 5 kg - to 15.6%. In normally rainy years, organic fertilizers at a dose of up to 5 kg / m2 practically did not have a negative effect on the starch content of tubers, and in dry years, even under the influence of small doses of manure, the amount of starch sharply decreased. This is due to the unbalanced content of nutrients in the manure. This disadvantage is corrected by the joint application of manure with mineral fertilizers.

The decrease in starchiness of tubers under the influence of organic fertilizers can be reduced or even prevented by additional application of phosphorus fertilizers. If, when applying 5 kg / m2 of manure, the starch content in the tubers decreased from 21.8 to 20.7%, then the addition of 10 g / m2 of phosphorus made it possible to increase the amount of starch to 22.1%. The introduction of 5-7 g / m2 of phosphorus into the nests when planting tubers allows increasing starch content up to 22.8%. Therefore, the skillful use of organic fertilizers, especially in combination with mineral fertilizers, allows you to get high yields of potatoes with good quality tubers. The optimal dose of manure is 5-6 kg / m2.

The role of nitrogen fertilizers

growing potatoes
growing potatoes

High quality potatoes can be achieved even with the introduction of only one mineral fertilizer. The starch content in tubers increases from 17.1 to 18.7%, and the marketability of tubers increases to 80-85%.

Nitrogen fertilizers significantly increase the yield. Usually, with a lack of nitrogen, plants develop poorly, have a small leaf surface, which leads to a decrease in starch, since the intake of carbohydrates into the tubers slows down with the death of the leaves. Excessive nitrogen nutrition contributes to a more powerful development of the tops, lengthens the growing season, delays ripening and, like the lack of nitrogen, reduces the yield and starchiness of tubers.

Therefore, to obtain a high yield of potatoes with good taste, the dose of nitrogen fertilizers must be applied differentially, depending on the properties of the soil, the planned yield and the characteristics of the variety. Nitrogen in the early stages of tuberization (immediately after flowering) increases the starch content in tubers. The lowering effect of nitrogen on starch content is observed only towards the end of the growing season of plants.

This effect of nitrogen on the starchiness of tubers is explained by the rate of increase in their mass. The effect of nitrogen on the increase in the average weight of tubers is small at the beginning and significantly increases towards the end of tuberization. Accordingly, the decrease in starch content under the influence of nitrogen affects only by the end of the growing season.

The negative effect of nitrogen fertilizers on the starchiness of potato tubers is enhanced when they are used in conjunction with organic fertilizers. But this applies more to late-ripening varieties. Early varieties of potatoes against the background of manure, increasing the yield, do not reduce the starchiness of the tubers. However, the collection of starch per unit area is always much higher when nitrogen fertilizers are applied against the background of manure.

A slight decrease in starch in potato tubers upon application of nitrogen fertilizers is explained by an increasing supply of nitrogen to plants, as a result of which carbohydrates are spent on binding nitrogen (ammonia), the formation of amino acids and protein. The increased consumption of carbohydrates ultimately causes a slight decrease in their deposition in the form of starch in the tubers.

The optimal dose of nitrogen is 6 g / m2. Different forms of nitrogen fertilizers have approximately the same effect on potato starchiness. Even ammonium chloride (due to the high chlorine content) does not reduce the starchiness of potatoes with a single application. The negative effect of ammonium chloride is manifested only with the systematic application of this fertilizer in the same area. Potatoes fertilized with urea give more tasty tubers than other forms of nitrogen fertilizers.

Nitrogen fertilizers always increase the crude protein content of plants. However, with a lack of trace elements - copper, molybdenum, cobalt, manganese - less protein accumulates and more non-protein forms. Ammonium nitrate and urea have different effects on the amount of crude protein. So, in years with high soil moisture, when urea is applied in tubers, a higher content of crude protein is observed than when ammonium nitrate is applied. In a dry year, ammonium nitrate and urea had the same effect on crude protein content.

The high efficiency of urea in comparison with other forms of nitrogen fertilizers is due to the fact that urea nitrogen quickly converts into the ammonia form, is fixed in the soil and serves as a source of plant nutrition for a long time.

Sodium nitrate has the smallest effect on increasing the yield of potatoes, which can be explained by the rapid leaching of nitrogen from this fertilizer outside the root layer.

Thus, all nitrogen fertilizers have a positive effect on the quality of potatoes, while the digestibility of the tubers is somewhat reduced. However, tubers of better quality and taste are obtained with the introduction of urea, in contrast to other nitrogen fertilizers.

The role of phosphorus fertilizers

growing potatoes
growing potatoes

Phosphorus is one of the most important elements in the diet of potatoes. It is of paramount importance in protein synthesis. A lack of this element in the soil causes a slowed down development of the potato plant, that is, the same phenomenon is observed as with an excess of nitrogen. With a lack of assimilable phosphorus in the soil, the leaves of potatoes acquire a dark green color, which becomes especially noticeable during the budding and flowering period and remains, as a rule, until harvest. Lack of phosphorus in the soil sometimes leads to the formation of glandular spots inside the tubers, which have a rusty-brown color and consist of dead, corked cells. The nutritional value of such potatoes is sharply reduced.

With a good supply of the soil with mobile phosphorus compounds, the growth and development of plants is accelerated, the ripening time of tubers is reduced, which leads to a greater accumulation of starch content in them. On soddy-podzolic sandy loam soils with a lack of mobile phosphorus in the soil, the use of phosphorus fertilizers increases the yield of tubers, increases the content of starch and vitamin C in them, and improves taste. On soddy-podzolic, highly podzolized loamy soil with an average content of mobile phosphorus and exchangeable potassium, when 6 g / m2 of phosphorus was applied, the starch collection increased from 0.318 to 0.355 g / m2, the taste of potatoes increased from 3.5 to 3.8 points. Increasing doses of phosphorus fertilizers increased the content of starch and crude protein and increased the marketability of tubers.

On soddy-podzolic soils, characterized by an acidic reaction of the environment (pH 4.8), low content of mobile phosphorus (3.9 mg P2O5 per 100 g of soil) and exchangeable potassium (8.8-10.3 mg K2O per 100 g of soil), the use of increasing doses of phosphorus fertilizers also increased the content of starch, protein, vitamin C and carotene in tubers. The best results were obtained with the introduction of phosphorus at a dose of 12 g / m2 against the background of NK fertilizers and 3 kg / m2 of manure. On these soils, phosphorus fertilizers increased the starch content in potato tubers from 17.5 to 21.5%.

Thus, the results of studies of domestic and foreign scientists show that the effect of phosphorus fertilizers is, as a rule, opposite to the effect of nitrogen; under their influence, the processes of plant growth and development are accelerated, the ripening time of tubers is reduced, the content of starch and vitamin C in them increases, the taste and keeping quality are improved, and the resistance of tubers to diseases and mechanical damage during harvesting increases.

Read the next part. The influence of potash fertilizers and micronutrients on the quality of potatoes →