Tencho Cholakov

Institute for Vegetable Crops ‘Maritza’ Plovdiv 4003, Bulgaria

 

Abstract

 

The results from the research work concerning the influence of the windbreaks and the distance between them over some parameters of the phitoclimate were summarized.

It was found out the maize windbreaks help for rising the temperature in the ground air layer. After a careful estimation from the researched variants for practical purposes the variant with distance of 24m between the windbteaks is better.

Parallel with its influence over the phitoclimate the windbreaks are analyzed as well as a factor capable of reducing the plant protecting work when growing tomatoes in field conditions.

 

Key words: ecological conditions, tomato, windbreaks

 

In the basis of the modern theory of increasing the agricultural crop yields underlies the definition optimisation of the environmental factors. In essence it is the achievement in a higher or lower degree of a certain correspondence between the necessities of plants and the values characterising the environmental conditions. One of the ways for achieving to some extent this goal is the use of two or more crops one of which must be high-growing /wind-break crop/. As windbreak crops are used sunflower, maize, rye ect. The aspiration is by using them to create natural plant barrier situated under angle of 30-90° towards the direction of the prevailing wind. This human intervention causes redistribution in the values of the microclimatic elements ranging widely but this does not disturb the natural condition of the ecosystems.

It is an old practice in agriculture to create forest belts and to use windbreaks as a factor of sowing protection from dangerous meteorological phenomena and for improvement of the microclimate of the agricultural fields /5, 6, 8, 9/. In number of scientific articles it is stated that the conditions for plant development become more favourable /10, 12, 13/. In this connection it is also reported of received higher yields by using compound sowings with windbreak cultures /1, 7, 14/.

Now agriculture in Bulgaria is being reorganized and the necessity of research work in this field is topical for the newly established farms. This applies even more to the priority for the country direction of vegetable growing for which the available information is insufficient and the existing in Bulgaria is already outdated /11, 15/.

The aim of this article is to add to the information from the carried out researches on the influence of the maize windbreaks on the phytoclimate and also to summarize the received results and to reveal a new element of the ecological significance of the windbreaks for the practice.

The orientation of the windbreaks /cross type/ was such that the angle between them and the orientation of the prevailing wind ./west-east/ varied from 55-80° . Each windbreak consisted of three rows of maize plants (row-distance 30cm and inter row-distance 5-10cm). The length of the rows of tomatoes and the windbreaks was from 140 to 160m (10 rows) -1-st variant, 24m (15 rows) -2-nd variant and a control variant without windbreaks. Each of the variants was in four repetitions / 14 x 10 m² / situated according to the long parcel method. The sowing of the tomatoes and the maize was done almost simmultaneously during the third decade of April.

The supervision of the temperature and the relative air humidity was put through in the stages of blossoming, fruit-setting and ripening with mercurial thermometers with exactness to 0.1° C and termohigrographs in 7¹⁵ and 14¹⁵h situated in meteorological boxes in the middle of the high row. The sensores were at heght of 25-30cm over the soil surface and at a distance of 1/2 from the distance between the windbreaks at both the variants. The readings from the control variant and between the windbreaks were taken simmultaneously. Periodically was measured the height of the windbreaks and the beginning of the phenological stages in tomatoes was given an account of.

The averaged for the period results from the made microclimatic observations in the tomatoe sowing are produced in table 1.. We are not going to publicate the data for the blossoming stage because of the low values of the temperature differences. In our trial this stage was registrated in the period 15-20 June at height of the maize plants of 91-108cm and this is the reason for the weaker effect of the windbreaks. In the fruit-setting stage the height of the maize plants was more than 110 cm. The settled during this period average day temperature differences between the control and the variants are greater ( 0.3 and 0.5° C ). The greater difference is for the variant with less distance /16 / between the windbreaks. This trend is retained also in the period of ripening /table 1/. In this case the differences are greater 0.5 and 1.1° C and they can be explained with the influence of the windbreaks which height is over 190cm. This data shows that between the windbreaks are created conditions for the ground air to be held longer over the sowing, as a result of which the air warms up more than in the control plot. This process is better revealed in the variant with less distance between the windbreaks.

The presence of windbreaks creates conditions for the development of tomatoes at higher values of the average day temperatures of the air. As a result of this in the spaces between the windbreaks for the period fruit-setting -beginning of ripening additionally can be gathered effective temperature sum of over 10° C , from 15-20° C. It is sufficient to accelarate the phenologic development of plants with 1-2 days.

From the carried out experiments the influence of windbreaks on the dynamic of the relative air humidity was not determined. The received between the control and the variants differences of 1-4% coinside with the utmost precision of the measuring instruments.

The analysis of the air temperatures shows that in the space between the windbreaks they are higher. This is a premise for accelarated running of the periods between the stages, especially in the variant with 16m distance between the windbreaks. In this variant the wind velocity weakens more than in the variant with 24m between the windbreaks /4/. The latter, however, is characterized with a number of advantages -better conditions of soil humidifying /3/ higher yield /2/ and greater economical effectiveness of the windbreak application /16 /.

 Apart from the microclimatic significance finding expression in improvement of the conditions for tomatoe growing the windbreaks have also influence on the plant protection. On one hand as a high-growing plant, to a certain extent maize prevents from spreading the virus carrier Hyalestes obsoletus /11 / and on the other hand it protects sowings from wind by adverting or reducing the degree of plant damaging. As a result of these damages on tomatoe plants appear black spots and it becomes necessary to do prophylactic spraying to prevent from plant diseases.

Table 1. Values of the temperature and the relative air humidity 25 cm over soil

 As our observations show, at an average twenty-four-hour velocity of over 5m/s in the period from budding till tomato plants become flattened on the soil surface, wind causes damages to plants. In connection to this was carried out the research as a result of which are the figures in table 2 They show that during the successive five years for Plovdiv’s region wind velocity in at least one solar day had been between 6 and 9m/s and there had been a real danger of plant damaging.

Observed for the velocity of the wind in the region of Plovdiv is the period after 10 July. On this date the average height of the maize is 84cm and the windbreaks to some extent begin, though faintly,to decelarate the speed of the air flow/4 /.

The use of windbreaks of maize provides considerably better conditions in the period of forming and ripening of tomatoe fruits in comparison to the control variant.It was found out from the observed distances between the windbreaks 16 and 24m, that the summary effect is greater in the second variant and it is recommended for applying in the practice.

Maize windbreaks can be used as a means of reducing the damages on mid-early tomatoes in regions where often blow winds with an average twenty-four-hour velocity of over 5m/s. For this reason in many cases their application is also a possibility for reducing the number of chemical treatings of the sowing.

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2. Cholakov,T.,G.Pevicharova. Quantity Characteristics of the Yield of Mid-early Tomatoes from Windbreak Sowing.Higher Institute of Agriculture- Plovdiv. Anniversary Scientific Session.Miscellany of The Reports And Summaries. October 1995, vol 2, book 1,243-245.

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