Jun 14, 2018
Walnut is of great economic importance, as its trees perform significant water protection, soil-protective and water-regulating functions and are an ecologically important plant object.
The walnut trees, in comparison with other fruit crops, are distinguished by their durability and regular fruiting. There are trees aged 200-300 years. According to N.V.Sorokin, in the Crimea - Baidarskaya valley - grew a walnut tree , whose age was determined in 1000 years.
Walnut - deciduous plant, monoecious, with dioecious flowers, cross-pollinated and wind-pollinated. Male and female generative organs are located on the same plant, but separately.
Nut leaves are large, complex, odd-pinnate, with 5-9 whole leaves from elliptical to ovate, dark green, slightly faded at the edges, with a specific odor. There are also simple leaves, that is, having one plate and stalk, and also two and four leaves.
Kidneys are divided into vegetative and reproductive. Vegetative include the kidneys forming leaf-sprouting growth shoots, which can be lateral, located in the axils of the leaves along the entire shoot, and the apical, which terminate the shoots.
Staminate kidneys, i.e. male, have an elongated conical shape up to 1.5 cm in length, they are brownish-brown in color with numerous spiral scales, as if faceted. The flowers are placed in straight earrings, which reach 15 cm in length and 1.5 cm in diameter during puberty and are in the fruit-bearing shoot of last year in the lower part of it 1-2 or more together. Flowers in the base of earrings have 20-30 stamens, and located in the upper part of the same earring only -6-8 stamens. First flowers bloom at the base of the earring, then on top.
A staminate flower consists of three bracts, intergrown with bases. In the center of the pericarp there are stamens. Each stamen consists of a short thread attached to the pericarp, a liaison on which the anthers are located. Anthers of stamens have an elongated shape and in the ripening period the pollen is opened on the sides by longitudinal slits. The mature pollen is spread by the wind, bees and bumblebees. The flowering period of staminate flowers is up to 20 days. The differentiation of staminate kidneys occurs during the growing season and ends in May-June.
Pestilent flowers appear on the shoot of the current year and are located singly, 2-3, and the vintage years - 4-5 on one pedicel. There are varieties and forms of walnut, in which the flowers are collected in a brush for 2 or more flowers. The pistil( female) flower is oblong in shape, in the upper part it passes into the column and ends with two large broad-brained stigmas of light, pinkish-yellow color. Blossom pistil flowers soon after the beginning of growth of the shoot and the appearance of 3-4 leaves in time, which in our climatic conditions falls at the end of April - early May. Female flowers retain susceptibility to pollen within two weeks. Differentiation, ie, the laying and formation of pistillate flowers, always occurs in embryonic cells of apical or nearby cells. This process begins in the autumn and ends in the spring.
As a rule, on the same tree flowering of staminate and pistillate flowers occurs at different times. This phenomenon is called dichogamy. Therefore, when planting industrial gardens, pollinators should be selected. A number of varieties and forms first bloom stamen flowers, this type of flowering is called protoandric type.
Due to the fact that the pollen remains receptive for a long time, female flowers can be pollinated by the pollen of their own tree. According to Yu. I.Nikitinsky, in comparison with free pollination self-pollination significantly increases the yield - up to 40%.Such a phenomenon, called homogalya, is very rare.
When under-fertilized, the flowering period increases, and in protogenic forms self-pollination takes place, which is excluded in most cases in protoandric forms. This explains why the protogenic forms are more productive than the proto-anic ones, and that in both forms the yield increases with the coincidence of the periods of flowering.
There are cases when the appearance of fruits in some varieties and forms occurs without pollinators, that is apomictic. Identification and introduction of apomictic walnut forms allows to receive high and guaranteed walnut yields annually, regardless of the conditions of the year in the flowering period.
Walnut pollen is light and nutritious. It contains up to 23% protein, 14% sugar, 32% fiber, 4% water and 3% ash. In connection with this, during the flowering period, the pollen of the walnut attracts a huge number of bees. As a result of research conducted by scientists, it is established that the pollen of walnut in comparison with other fruit crops is the easiest and, according to Kurennoy, it long floats in the air, flying at a distance of 8 km.
The flowering type is not an inherited feature in the offspring and manifests itself in seed reproduction in almost equal proportions of protoandria and protogeny.
It is required to take into account such features as the type of flowering, the degree of self-fertilization, the selection of pollinators, the character of fruiting. All these factors strongly influence the productivity of walnut plantations.
Pistachio flowers on the tree of the nut appear earlier than the staminate, which are laid mostly for only 4-6 years, depending on the characteristics of varieties and forms.
An exception is a number of varieties of the "ideal" type, on which secondary flowering is observed.
The type of fruiting is also an important biological sign of this culture. Most varieties and forms are fruited from the apical buds;the lateral( axillary) buds in them are growth. At the same time, there are trees that are able to bear fruit both on the apical and on the side kidney( apex-lateral type of fruiting).Such forms and varieties are distinguished by higher yields and somewhat restrained growth. Fruits of a walnut are placed as one by one, but more often 2-3 fruits, and sometimes their number reaches 4. There are varieties with fruit-bearing fruit( 8-15 fruits each).
Walnut can successfully grow on soils of various fertility, including humus poor, sandy and skeletal, with a neutral and alkaline reaction. Such soils include chernozem, forest-loamy, chernozem sandy loam, preference is given to deep, loose, superficial and fresh soils. The walnut yields the highest productivity in relatively rich and well drained, as well as alluvial first terraces of river valley valleys. Such soils include, in our territory, more than 600 soil varieties, chernozems of all subtypes and varieties, including: light gray, gray, dark gray, meadow, flood-meadow and chernozem-meadow soils. Nut trees also grow well on carbonate soils.
In all cases, it is necessary to avoid wetlands and soils with close groundwater table( not closer than 2-4 meters).The main indicator of the suitability of walnut lands is the volume weight of the soil, which should be less than 1.45 g / cm3 at a depth of 60 cm.
On walnut slopes and poor, heavy, clay soils, walnut grows very slowly, ages early and practically does not yield harvests.
A prerequisite for good tree growth is soil moisture. Surplus wet, marshy soils, as well as very dry soils are not suitable for the growth of walnut. It tolerates air drought well, but it is especially sensitive to groundwater and salinity, including toxic salts.
Walnut is referred to breeds that survive channel cold-cool flooding, within one month. In the walnut garden, located in the lowland, out of every 5 years 2 are barren due to spring frosts.
Walnut is light-loving and thermophilic.
The critical temperature for walnut is 27 degrees below zero. When frost - 25, 27 degrees, male earrings and part of vegetative kidneys are damaged, at 28, 29 degrees one year with p ost, 30 degrees - skeletal branches and the whole tree to the level of the root neck. Skeletal branches are damaged, as a rule, on the southern side, forming severe burns on the bark of the stem.
The bark of young trees is light gray, later with large cracks.
The weakest resistance to low temperatures are the roots, which must be taken into account when planting trees in the spring, as well as during the digging of seedlings and when storing them. Friable root tissue is damaged at 5-6 degrees below zero and this can lead to complete death of the plant.
Despite the fact that the walnut is thermophilic, an increase in air temperature in summer above 37 degrees causes considerable damage to the fruit placed in the tree crown. With sunburn, the fruits are suspended in development and small, withered kernels are formed.
The duration of the walnut growing season from the dissolution( March) of the kidneys to the leaf fall( October-November) under our conditions is 180 to 210 days in different years.
Walnut does not tolerate shading. This explains why, when standing alone or in low-level plantings, he develops a powerful crown and root system and gives regular and abundant harvests. Shaded plants grow and bear fruit worse. Weakened by shading, part of the skeletal branches is affected by low temperatures, diseases, pests and subsequently dies. Therefore, pruning is a mandatory agro-technique in the cultivation of this culture.
At a young age, when the trees are well lit, they have a large running-off ability. The absolute number of buds on the conductor and skeletal branches go into growth, forming annual increments, which subsequently turn into skeletal branches. For trees left without pruning( 8-10 year olds), up to 20-30 skeletal branches of the first order can be counted.
With strong darkening, only the apical growth of shoots is usually observed;only the apical bud grows and very rarely one or two lateral buds. As a consequence, at the age of 12-15 years, the crown consists of a set of elongated and bare skeletal branches, and the underdeveloped leaf apparatus and crop will be located only on the periphery of the crown.
The most common way to form a walnut is a cup-shaped crown with 3-4 skeletal branches and an altered-leader form of the crown with 5-6 skeletal branches.
When forming trees by the type of a bowl, 3-4 first-order branches are laid in the crowning zone, which have good intergrowth and are evenly distributed. The distance between the branches should be at least 60-80 cm, the bookmarking of the skeletal branches ends at the 3-4th year after planting, after which the central conductor is removed. For optimal illumination from the inside of the crown, the skeletal branches are cut off by transferring to the lower lying beam. Subsequently, pruning is performed mainly to remove diseased, damaged and shaded branches.
The altered-leader formation is as follows: the skeletal branches are also laid single, but the first two, if they are located in opposite directions, should be laid from adjacent buds. During the first year of growth, the seedlings form 3-4 shoots and, therefore, the crown should be started for the second year. This process for creating the required structure takes place during 5-6 years and is considered complete, there remain 5-6 branches of the first order, from which it is necessary to form branches of the second and the following orders.
In the future, the central conductor comes in the same way as in the cup-shaped formation, i.e.is removed. Subsequently, the thinning, sick, damaged, and drying branches are thinned out.
As the tree ages, the natural self-destruction of the crown occurs. First weakened weakened, damaged by frost, pests and diseases branches. On the old tree there are no more than 4-5 branches of the first order.
Thus, a walnut tree can form a powerful crown capable of laying and retaining a large crop, when, by appropriate shaping, good crown illumination is provided.
Walnut is a fast-growing breed with a great shoot-forming ability, especially at a young age in conditions of optimal soil-climatic conditions. When the walnut is sown, the walnut plant retains the core root, resulting in increased winter hardiness. It is not necessary to transplant the nut without prior overcauteration, especially the grafted material.
In the first year of life, the walnut seedling can reach 30-50 cm in height, and in exceptional conditions and above, 1 cm in diameter. The root during this period becomes 4-5 times higher than the length of the trunk. In the second year of life, the growth of the seedling increases, and by the end of the vegetation its height reaches 1 meter, at 6 years of age it is 2.5 meters, at 60-80 years of age it is 15-20 meters.
The root system of the walnut, unlike other fruit crops, is devoid of suction hairs. The process of absorption of mineral substances in the aqueous solution is carried out by mycorrhiza, a symbiosis between soil microorganisms and tree roots, and therefore, when planting trees, it is necessary to make organic fertilizers, which promotes the rapid formation of microflora in the root system, and therefore to the better development of both the root system andunderground part.
The active growth of the stem root lasts only 3-5 years and reaches 3-3.5 m depth by this time. At the age of 20-30 years, the depth of penetration of the stem root reaches 6.5-7 meters. With age, lateral roots greatly thicken, and the radius of their distribution sometimes reaches more than 20 meters. When excavating the root system of a walnut tree 55 years of age( planted along the irrigation canal), powerful lateral roots up to 25 cm in the base were found, which grew apart from the canal. In old trees, the radius of root distribution is 3-4 times the radius of the crown. The powerful development of the root system of the walnut rod type contributes to its high wind resistance and winter hardiness.
Only in cases of unilateral or superficial development of the root system on eroded soils, in the conditions of mountain slopes winded walnut trees are observed. The harmful influence of constantly blowing winds in one direction adversely affects the walnut trees. So, in the regions of Sochi and Tuapse, according to AI.Golikov, a walnut growing on mountain slopes, is characterized by a weak resistance to wind, which is due to the unilateral and superficial development of its roots.
Blowing during the flowering period, intensive dry winds adversely affect the flowering, pollination and fertilization processes of flowers. All this indicates the need to concentrate walnut plantations, including industrial ones, in places well protected from winds. The usual good increment of walnut shoots in young trees in the North Caucasus is from 60 to 100 cm and 1 cm in diameter. In wet years, the increase reaches 200 cm during the growing season. Walnut, in comparison with other fruit crops, is distinguished by its high shoot-forming and run-off ability.
Shoots, respectively, are divided into growth and fertile. Growth shoots have one growth cycle during the growing season. Their normal growth ends in mid-July. Shoots smooth, shiny.
Growth of walnut shoots occurs most rapidly in the first half of summer, fruits - in the first month after flowering, and in early July stops. In the future, the green envelope grows and the kernel ripens. In the second half, temporary decay of the primary meristem of the shoots occurs, as there is an intensive growth in thickness. The second half of growth is characteristic of this culture and it ends usually in August with reference to our conditions. In some, especially wet and warm years, this period is prolonged, and there is a danger of damage to growing shoots by early frost frosts.
The vigorous growth of the walnut lasts up to 40-50 years. Then it gradually dies out, the growth in thickness continues throughout the life of the tree.
The low level of farming often leads to an extension of the period of growth of the tree before it enters into fruiting, i.e., early fertility, to premature decline in growth activity, as well as to drying and death.
The natural crown of a walnut is more often spherical or dome-shaped, it reaches up to 30 meters in length. In thickened plantations of forest type walnut trees are stretched to the height and take an elongated-oval shape of the crown. According to A.A.Strict, the walnut tree, which grew in the village of Kekhvi( Georgia), reached 25.6 meters in height and had a circumference of 8.5 meters. Annually, up to 1600 kg of nuts were collected from it. Its crown was so large that up to 200 horsemen could hide in its shadow.
The walnut tree of seed origin, as a rule, enters fruiting at the age of 6 to 12 years, and reaches full fruiting at the age of 50-60 years. The exception is mainly varieties of Central Asian selection such as "ideal", "Uzbek fast-bodied" and others, derived, among other things, by the breeder Kalmykov. The trees of the varieties described above begin to bear fruit on the 2-3rd year after sowing and have restrained growth, and the fruits retain an important feature of heredity - early fertility.
Unlike ordinary walnut trees, grafted saplings enter fruiting for the 4th-5th year, and some varieties even earlier, fully retain the qualitative features of the mother plant and, in contrast to trees of seed origin, regularly yield a stable yield. There are natural solitary walnut trees, the yield of which reaches 100-400 kg from one tree. Selection, allocation and consolidation of such high-yielding forms are the tasks of fruit-breeders and breeders.
In the valleys the walnut fructifies more abundantly than on the slopes. In lowlands, that is, in low terrain relief, trees are more often exposed to negative climatic factors, which directly affects the productivity of trees.
Fruit is a hard nutty nut, from round to elongated, with a fleshy pubescent or bare green outer shell and a woody endocarp of varying thickness, with a surface from almost smooth or wrinkled to heavily pitted depressions, with blunt or sharp grooves or ribs. The fruit inside is divided by two or four incomplete partitions, as a result of which the seed is two- or four-bladed, with a light-brown shell, cotyledons - two.
Walnut, being a thermophilic crop, is nevertheless able to withstand, without freezing, rather low temperatures during the winter. As the long-term observations conducted both in Crimea, Moldova, and in our region showed, there were cases when he suffered frosts to 30-35 degrees, and just in the near future the frozen parts were completely restored. A significant damage to the development of the nut can bring hail.
Frost resistance in many respects depends on the rhythm of plant development during the growing season. If the walnut tree is well prepared for winter in a timely manner, that is, shoots manage to complete growth, mature and become lighter, it will be more resistant to transferring the conditions of a harsh winter. Young plants are sufficiently resistant to frost, which is associated with an earlier end of vegetation. By careful and timely care of your favorite plants, we can help them and prepare them for overcoming many natural disasters.
All parts of a tree are especially sensitive to sharp temperature fluctuations in the spring period. A sharp drop in air temperature in this period to 2-4 degrees below zero, provided that before there were "plus" temperatures, often leads to the death of most of the pistillate flowers in this period of vegetation. The most sensitive to significant spring frosts and the roots of walnut. The frost resistance of walnut trees falls sharply during the period of bud budding and the growth of shoots. In this connection, it is necessary to plant walnut trees taking into account the forecasts of the end of late spring frosts in one or another natural zone. When planting is required abundant watering. It should be borne in mind that dense and prolonged fogs during the flowering period are destructive for the harvest, since flowers suffer greatly from them, pollination is difficult, which often leads to a mass loss of ovaries.