Subsurface Drip Irrigation as a Factor Ensuring Productive and

Ecological Functions of Soils

Nadiya Maksymenko, Olena Gololobova and Oleksiy Shovkun

Department of Environmental Monitoring and Nature Use, Karazin Institute of Environmental Sciences, V. N. Karazin

Kharkiv National University, Svobody sq., 6, 61022, Kharkiv, Ukraine

Keywords: Subsurface Drip Irrigation, The Ecological and Reclamation Condition of the Soil, The Ecological and

Reclamation Monitoring of the Irrigated Soil.

Abstract: Irrigation is a powerful factor influencing soil. Given the accelerated and significant change of ecosystems

under the influence of reclamation load and prevention of degradation processes, soil monitoring using

modern innovative methods becomes especially important. Soil fertility management for irrigated land should

be aimed at developing models of sustainable, environmentally friendly and cost-effective use of natural

resources. It is also essential to preserve and enhance soil productivity and its environmental and social

functions for the long term. This has set high demands for energy efficiency, environmental safety and the

economic feasibility of irrigation technologies, including in urban landscaping. The aim of the study was to

investigate the ecological and reclamation condition of the soil during long-term subsurface drip irrigation of

ornamental grass plot, linden (Tilia cordata Mill.), and white cedar 'Brabant' (Thuja occidentalis 'Brabant').

The experiment was conducted during 2018–2021. Research methods: the assessment was carried out on a

set of diagnostic indicators following the recommendations for the survey of ecological and reclamation

conditions of lands under drip irrigation. The recommendations were developed by the National Scientific

Center “Institute for Soil Science and Agrochemistry Research named after O. N. Sokolovsky”. The results

of the study show that the scoring of diagnostic agrophysical indicators is the most favorable. Subsurface drip

irrigation does not change the content of organic matter; there is no direct dependence of humus content on

irrigation. Subsurface drip irrigation does not change the nutrient status of the soil; the determining influence

of soil genetic characteristics on the content of mineral nutrients is observed. Assessment of diagnostic

indicators for the cation-anion composition of the aqueous soil extract revealed a poor soil condition in terms

of the percentage of Na++K+ from the amount of absorbed alkaline cations. The soil condition in terms of

the content of toxic salts was rated to be close to good. The degree of soil salinization by the Ca/Na ratio was

> 2.5 for both irrigated and natural grass plots. The soil condition in terms of this indicator was rated to be

good. The total pollution rates Zc under subsurface drip irrigation was similar to that for uncontaminated soils.

Assessment of the soil microelement status indicated probable excess of zinc and manganese under the

influence of irrigation. Conclusion. The scoring of the ecological and reclamation condition of the studied

soil according to diagnostic indicators showed the possibility of using subsurface drip irrigation with

compulsory further ecological and reclamation monitoring of the irrigated soil

1 INTRODUCTION

Recognition of the fundamental role of soil in climate

change adaptation and mitigation has made it one of

FAO's top priorities. This should contribute to improving

environmental security and social development,

understanding the importance of maintaining productive

and ecological functions of soils, in particular for the

functioning of terrestrial ecosystems (Baliuk & Drozd,

2017). At the same time, in the context of ecological

reconstruction of the green infrastructure of many

Ukrainian cities, preservation of existing cultivars and

hybrid forms of ornamental plants and introduction of

new ones make actual the introduction of modern

innovative technologies of landscape irrigation, including,

of course, subsurface drip irrigation.

Given the accelerated and significant change of

ecosystems under the influence of reclamation loads and

the need to prevent degradation processes, monitoring of

land in the area of these loads becomes especially

essential, with the obligatory involvement of modern

126

Maksymenko, N., Gololobova, O. and Shovkun, O.

Subsurface Drip Irrigation as a Factor Ensuring Productive and Ecological Functions of Soils.

DOI: 10.5220/0011345200003350

In Proceedings of the 5th International Scientiﬁc Congress Society of Ambient Intelligence (ISC SAI 2022) - Sustainable Development and Global Climate Change, pages 126-134

ISBN: 978-989-758-600-2

innovative and methodological approaches. Irrigated land

fertility management should be aimed at developing

models of sustainable, environmentally safe, and cost-

effective use of natural resources (Baliuk & Drozd, 2017,

Baliuk, Kucher & Maksymenko, 2021,), preserving and

increasing productive, environmental and social functions

of soils for the long term, which puts high demands on

energy efficiency, environmental safety, and economic

feasibility of irrigation technologies, including in urban

landscaping (National soil protection program of Ukraine,

2015, Maksymenko et al., 2021).

Irrigation is a powerful factor influencing agro-

ecosystems in general and soils as their main

component in particular. All constituents of the soil as

a whole system are more or less subject to the

transformative effect of irrigation. The

transformation causes the disequilibrium of the

system with the further stabilization at a qualitatively

and quantitatively new level. These changes are as

follows: the transformation of water, air, thermal and

redox regimes; intensification of biological

processes; increase in the mobility and reactivity of

minor and major plant nutrients and toxic pollutants;

increase in the dynamism and variability of some soil

physical parameters (density, hardness, stickiness,

structural properties, permeability, etc.); in some

cases, redistribution of granulometric particles of

different sizes throughout the soil profile; and

quantitative and qualitative changes in the colloidal

part (Baliuk et al., 2018).

The analysis of literature sources indicates a

water-saving effect when applying subsurface drip

irrigation: for example, water consumption has

decreased to 25–50% compared to surface irrigation

(Camp, 1998; Sinobas & Rodríguez, 2012; Camp et

al., 2020). According to USDA-NASS calculations,

the use of subsurface drip irrigation in the United

States in 2006–2016 increased by 89% (Lamm,

2016).

With the long-term use of drip irrigation,

diagnostic agrophysical indicators in moistened areas

have been favorable for plants and soils (Usatova &

Ryabkov, 2018).

The microbial soil coenosis structure was

determined in the Sector of Soil Microbiology in the

National Scientific Center “Institute for Soil Science

and Agrochemistry Research named after O. N.

Sokolovsky”. The results have proved that

microorganisms that take up organic forms of

nitrogen for 0–30 cm soil layer increased their

number from 9.25 to 10.68 million CFU/g under the

influence of subsurface drip irrigation. Organotrophic

microorganisms activation indicates that subsurface

drip irrigation has created conditions contributing to

more active assimilation of nutritious organic

substrate. According to the assessment proposed by

Zvyagintsev, the degree of enrichment of soil with

microorganisms was high without irrigation and very

high with irrigation. The number of microorganisms

assimilating nitrogen of mineral compounds was also

higher under subsurface drip irrigation: 10.29 million

CFU/g versus 7.25 million CFU/g without irrigation.

According to Zvyagintsev, the variant without

irrigation is moderately enriched; with irrigation, it is

highly enriched. Under subsurface drip irrigation, the

number of actinomycetes increased from 5.10 million

CFU/g to 6.68 million CFU/g. This indicates a

favorable trophic regime of soil. According to the

calculation, the oligotrophic index of soil was 0.37

without irrigation and 0.50 with subsurface drip

irrigation. The oligotrophic index indicates that the

studied agricultural method provides a higher content

of easily assimilable nutrients in the soil. Nitrogen

mineralization and immobilization rate characterizes

the intensity of nitrogen mineralization and

assimilation of nitrogen compounds by microbial

coenosis. In both variants, namely in the control

without irrigation and in the variant with subsurface

drip irrigation, the processes of organic matter

synthesis were found to prevail over the processes of

its destruction: in particular, this rate was 0.86 in the

control and 0.95 in the variant with subsurface drip

irrigation (Gololobova, 2020).

About 80% of arable land in Ukraine (over 24

million hectares) has such types of water regime of

soils, which form the dominance of deficient (or

periodically deficient) moisture. This makes the water

regime an extremely important factor. Irrigation is a

cardinal measure of optimization and stabilization.

However, it should be noted that the introduction of

subsurface drip irrigation into the nature management

system is possible according to the monitoring

results, subject to compliance with technological

processes of crop cultivation, environmental

reclamation monitoring (ERM) and its variety – soil

reclamation monitoring (SRM) on irrigated areas

(Recommendations for the survey, 2012).

2 RESEARCH METHODOLOGY

The study area is situated within the scientific and

experimental functional zone of the Dendrological

Park of national importance in Kharkiv National

Agrarian University named after V. V. Dokuchaiev

(Fig. 1). A field experiment was established in

autumn 2017 to survey the ecological and reclamation

Subsurface Drip Irrigation as a Factor Ensuring Productive and Ecological Functions of Soils

127

condition of the soil with long-term subsurface drip

irrigation.

Figure 1: Geographic location of study area - Dendrological

Park in Kharkiv National Agrarian University named after

V. V. Dokuchaiev.

The experiment involved experimental sites under

ornamental grass plot, with plantings of small-leaved

linden (Tilia cordata Mill.), white cedar 'Brabant'

(Thuja occidentalis 'Brabant'), and control sites

without irrigation.

The assessment was carried out on a set of

diagnostic indicators according to the

recommendations for the survey of ecological and

reclamation condition of land under drip irrigation

(Recommendations for the survey, 2012). Ecological

and reclamation condition of irrigated land is the land

condition, which is assessed by hydrogeological

(level, hydrochemical composition and

mineralization of groundwater), environmental

engineering (porosity coefficient and degree of

manifestation of exogenous geological processes),

soil reclamation (degree of salinization, alkalinization

and salinity of soils, their water-salt and nutrient

regimes, and irrigation water quality according to

agronomic criteria), ecological-toxicological (the

content of heavy metals and pesticides in the soil and

water pollution) and agronomic criteria (Baliuk &

Drozd, 2017).

Diagnostic soil indicators were determined in the

Laboratory of Instrumental Methods of Soil Research

and the Laboratory of Soil Geoecophysics in the

National Scientific Center “Institute for Soil Science

and Agrochemistry Research named after O. N.

Sokolovsky” according to certified methods (Soil

quality, 2005; Soil quality, 2009; Method of soil

sampling, 2013).

Soil diagnostic indicators were determined by

conventional methods:

- soil density was determined according to

Kachinsky’s method in 0–10 cm, 10–20 cm, 20–30

cm and 30–40 cm soil layers in spring at the

beginning of the growing season;

- macroaggregate analysis was carried out by the

dry sieving method according to Savinov; water

stability of soil aggregates was investigated by wet

sieving method in soil layers of 0–10 cm, 10–20 cm,

20–30 cm, and 30–40 cm;

- content of nitrate and ammonium nitrogen was

determined according to DSTU (State Standards of

Ukraine) 4729:2007 Soil Quality. Determination of

Nitrate and Ammonium Nitrogen in Modification

of NSC ISSAR named for O.N. Sokolovskiy;

- content of mobile compounds of phosphorus

and potassium was determined following DSTU

4114–2002 Soils. Determination of Dynamic

Compounds of Phosphorus and Potassium by the

Modified Method of Machigin;

- cation-anion composition in the soil-water

extract was determined according to DSTU

8346:2015, DSTU 7943:2015, DSTU 7908:2015,

DSTU 7909:2015, DSTU 7944:2015, and DSTU

7945:2015;

- content of mobile fractions of heavy metals in

a buffer ammonium acetate extract (pH 4.8) was

defined using atomic absorption

spectrophotometry, following DSTU 4770.1:2007,

DSTU 4770.2:2007, DSTU 4770.3:2007, DSTU

4770.4:2007, DSTU 4770.5:2007, DSTU

4770.6:2007, DSTU 4770.7:2007, DSTU

4770.8:2007, and DSTU 4770.9:2007.

Scoring of diagnostic indicators of soil was

carried out by the recommendations for the survey of

ecological and reclamation conditions of lands under

drip irrigation (Recommendations for the survey,

2012).

3 RESEARCH RESULTS

Among the physical conditions for the fertility of

medium- and heavy-textured soil, the soil density

andstructural status should be considered the most

important.

Soil density was determined at the experimental

sites according to the Recommendations for the

ISC SAI 2022 - V International Scientiﬁc Congress SOCIETY OF AMBIENT INTELLIGENCE

128

survey (2012) before the start of the irrigation period;

the results are presented in Tables 1–2.

The equilibrium density for the soil under the

grass plot had the optimal values after each irrigation

season during 2019–2021 for both 0–15 cm and 15–

30 cm soil layers.

The average values of soil density over the years

of the study were 1.10 g/cm

for the 0–15 cm layer

and 1.13 g/cm

for the 15–30 cm layer.

The equilibrium soil density recorded at the

beginning of the 2021 growing season showed the

optimal values after three years of subsurface drip

irrigation for white cedar both for all 10 cm soil layers

and for the 0–40 cm layer.

The score of the diagnostic indicator

(Recommendations for the survey, 2012) was

maximally positive both for the control and for the

studied variant (Table 2).

Table 1: Soil density in the experiment with subsurface drip irrigation of the grass plot, g/cm

, 2019–2020.

Soil layer, cm 2019 2020 2021

Average over

years

Scored ecological and

reclamation assessment

0–15 1.08 1.11 1.12 1.10 0

15–30 1.12 1.12 1.14 1.13 0

Table 2: Soil density in the experiment with subsurface drip

irrigation of white cedars, May 2021.

Variant

Soil

layer,

Soil

density,

/cm

Scored ecological

and reclamation

assessment

Control

0–10 1.08 0

10–20 0.91 0

20–30 1.01 0

30–40 1.01 0

0–40 1.00 0

Subsurface

drip

irrigation

0–10 0.91 0

10–20 0.95 0

20–30 1.06 0

30–40 0.94 0

0–40 0.96 0

Thus, long-term use of subsurface drip irrigation

during 2018–2021 did not result in soil compaction.

In particular, an optimal value of this diagnostic

indicator of the soil agrophysical condition was

recorded both under the grass plot and white cedars.

The absence of soil compaction contributed to the

soft and porous top layer preservation, promoting the

growth and development of both the root system and

the aboveground part of ornamental plants.

In modern sustainable agriculture, the structure of

soil is considered as a kind of regulator of the

processes occurring in it. It is the final result of

natural processes of soil formation and development

and therefore determines the suitability of the soil as

the habitat of the entire agrobiocenosis.

The top layer of the soil should be maintained to

have a high level of soil aggregation. Such conditions

improve moisture conservation and enhance the

efficiency of water consumption by plants (Baliuk et

al., 2018).

Table 3 shows the soil structural condition

assessed by the content of air-dry

agronomically

valuable particles with a size of 0.25–10 mm. The

subsurface drip irrigation provided an excellent

structural condition according to the classification

proposed by Dolgov in terms of the content of air-dry

agronomically valuable particles with a size of 0.25–

10 mm (Dolgov et al., 1983).

The average content of air-dry aggregates was

86.24% in the control, whilst it was 88.36% under

subsurface drip irrigation. Thus, subsurface drip

irrigation has maintained excellent soil condition by

this diagnostic soil indicator. The soil structure index

was 6.35 in the control and 8.55 in the studied variant.

It has been demonstrated that the most effective

moisture consumption occurs at the following ratio of

structural fractions: from 20 to 5 mm – 20–25%, from

5 to 0.25 mm – 60–65%, less than 0.25 – up to 15%

(Baliuk et al., 2018).

Subsurface Drip Irrigation as a Factor Ensuring Productive and Ecological Functions of Soils

129

Table 3: The content of air-dry aggregates in dry sieving in the experimental variants with white cedar plantings, May 2021.

Variant Soil layer, cm

Amount of air-dry

aggregates (0,25–10 mm),

Soil structure

index

Scored ecological and

reclamation assessment

Control

0–10 87.53 7.02 0

10–20 86.87 6.62 0

20–30 83.60 5.10 0

30–40 86.96 6.67 0

0–40 86.24 6.35 0

Subsurface drip

irrigation

0–10 88.87 7.98 0

10–20 83.14 4.93 0

20–30 93.25 13.81 0

30–40 88.18 7.46 0

0–40 88.36 8.55 0

Therefore, the assessment of the ratio of soil

structural fractions will be relevant in analysing the

soil structural composition. The ratio of structural

fractions in the soil under the white cedar plantings at

the above ranges is presented in Table 4.

Table 4: The ratio of the soil structural fractions at the specified ranges, %, May 2021.

Variant Soil layer, cm <0.25 mm 0.25–5 mm 5–10 mm >10 mm

Control

0–10 6.50 70.97 16.56 5.97

10–20 3.96 72.77 14.1 9.17

20–30 0.99 63.37 20.23 15.41

30–40 2.02 65.62 21.35 11.02

0–40 3.37 68.19 18.06 10.39

Subsurface drip irrigation

0–10 3.90 74.62 14.25 7.24

10–20 2.11 61.61 21.53 14.76

20–30 2.15 73.43 19.82 4.61

30–40 1.35 68.45 19.73 10.47

0–40 2.38 69.53 18.83 9.27

The results show that the ratio of soil structural

fractions at the specified ranges corresponds to the

optimal parameters for the soil structural composition

both in the control and under the subsurface drip

irrigation; in particular, the fraction of 0.25–5 mm is

68.19% in the control and 69.53% in the studied

variant. The established optimal ratio of structural

fractions is a factor improving the moisture balance

and the efficiency of its consumption by plants. The

score of the structural condition is the most favorable.

The results on the number of waterproof

aggregates (7–0.25 mm) in wet sieving are presented

in Table 5.

The results indicate that subsurface drip irrigation

provided the good structural condition of the soil in

terms of the content of waterproof aggregates sized

0.25–7.00 mm, according to Dolgov. The average

values of this indicator for the 0–40 cm soil layer were

51.65% in the control and 54.20% under irrigation.

The score of waterproof aggregates (0.25–7 mm)

content is also the most favorable.

The study of diagnostic agrophysical indicators

therefore showed that subsurface drip irrigation

preserved the soil structure. In this case, the ratio of

structural fractions corresponded to the optimal

parameters, equilibrium density was within optimal

values, and the scoring was the most favorable.

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Table 5: Content of waterproof aggregates (0.25–7.00 mm) according to the experimental variants with white cedar plantings,

May 2021.

Variant Soil layer, cm

Content of waterproof

aggregates (0.25–7.00 mm),

Scored ecological and

reclamation assessment

Control

–

10 42.00

–

20 49.52

–

30 57.88

–

40 57.22 0

–

40 51.65

Subsurface drip irrigation

–

10 47.54

–

20 56.56

–

30 62.76

–

40 49.94 0

–

40 54.20

The soil indicators describing the soil nutrient

status are presented in Table 6.

The content of mineral nitrogen according to the

grouping of soils by this indicator is very low for both

irrigated and natural grass plots, amounting to 9.78

and 13.59 mg/kg, respectively.

In the variant with subsurface drip irrigation of

white cedar, the mineral nitrogen content is medium

and makes 18.14 mg/kg.

The results indicated good phosphate status for

the grass plot with subsurface drip irrigation, as well

as for the control site of natural grass plot.

In the soil under the white cedars, the availability

of labile phosphorus forms was very high, accounting

for 88.7 mg/kg. The availability of labile potassium

forms was high for control and irrigated sites (187.21

and 187.18 mg/kg, respectively).

Table 6: Diagnostic indicators for soil nutrient status under subsurface drip irrigation and their scoring, 0–30 cm soil layer,

2019–2020.

Variant

content,

mg/kg

Score

О content,

mg/kg

Score

Mineral nitrogen

content, mg/kg

Score

Grass plot with subsurface

drip irrigation

54.05 0 269.51 0 13.59 5

White cedars, subsurface

drip irrigation

88.70 0 187.18 0 18.14 2

Control 53.47 0 187.21 0 9.78 5

Thus, the determining influence of soil genetic

characteristics on mineral nutrient contents was

observed. Poor nitrogen status was due to the natural

characteristics of the soil and the peculiarities of

nitrogen uptake by ornamental plants. It is obvious

that the studied soil requires the application of

nitrogen fertilizers on the grass plot to maximize the

potential of the ornamental plants, in particular not

only at the beginning of the growing season but also

after each mowing. As for the nitrogen status of the

soil under the white cedars, small amounts of nitrogen

fertilizers should be applied once during the period of

active needle growth.

A special function of soil humus is that it

contributes to the formation of close to optimal soil

properties, even at unfavorable chemical composition

(Baliuk et al., 2018). Subsurface drip irrigation did

not change the content of organic matter: in

particular, the content values were 2.06 and 2.33% for

the control and irrigated grass plots, respectively.

According to the grouping of soils by humus content,

it is assessed as medium (Fateev & Samokhvalova,

2012b). Such humus content is a characteristic natural

feature of the studied soil, i. e. there was no direct

dependence of the humus content on irrigation during

the observation period.

Diagnostic indicators of the cation-anion

composition in soil-water extract for the grass plot

with subsurface drip irrigation and the control

(without irrigation) in the 0–40 cm soil layer are

presented in Table 7, as well as their scoring. The

degree of soil salinity by the Ca/Na ratio has a value

Subsurface Drip Irrigation as a Factor Ensuring Productive and Ecological Functions of Soils

131

above 2.5 for both irrigated and natural grass plots.

That is, the subsurface drip irrigation did not

cause a noticeable transformation in the qualitative

composition of water-soluble salts towards the

narrowing of the calcium-to-sodium ratio. The

condition of the soil on this indicator was rated to be

good.

Table 7: Scoring of diagnostic indicators for the cation-anion composition in soil-water extract when using subsurface drip

irrigation, 2020.

Variant

pH aqueous

Score

∗

Ca/Na

Score

∗

HCO





–Ca



, mEq/100 g

Score

∗



,%oftot

absorbed cations

Score

∗

Content of toxic

salts, mEq/100 g

Score

∗

Grass plot with

subsurface drip

irrigation

8.18

3.18

0.45

16.00

0.35

Control

(natural grass

plot without

irri

ation

)

8.24

3.48

0.51

15.79

0.37

*According to Recommendations for the survey (2012).

By the content of toxic salts, the soil condition

was rated to be intermediate between satisfactory and

good (close to good) in both cases.

Secondary soil alkalinity was estimated by the

percentage of Na

+ K

of the amount of absorbed

alkaline cations. According to this indicator, the

condition was unsatisfactory both for the control site

and for the studied agricultural practice.

The speed and extent of the detected process are

determined by the quality of irrigation water (the

content of alkaline salts of sodium and potassium in

an equivalent ratio exceeds the content of calcium,

magnesium, and iron salts), the initial properties of

the soil, including the carbonates content and calcium

ions activity, and condition of the irrigated land. For

the soil with shallow carbonates (40–50 cm), the

effective environmental and economic practice would

be deep reclamation plowing, which is an alternative

to gypsum treatment (Baliuk et al., 2018).

The alkaline reaction of the soil solution was

preferred by the white cedars: the plants developed

well and rapidly, the annual growth of the studied

Thuja occidentalis was 25–30 cm.

The content of heavy metals in the 0–30 cm soil

layer in the experimental variants is presented in

Table 8.

Table 8: Content of heavy metals in the experimental variants, 0–30 cm soil layer, 2020, mg/kg.

Variant Cu Fe Mn Ni Co Pb Cr Zn Cd Z

Scor

White

cedars with

subsurface

drip

irrigation

0.09 2.07 13.95 0.14 0.02 0.61 0.66 0.68 0.12 2.11

Grass plot

with

subsurface

drip

irri

ation

0.24 2.86 8.92 0.14 0.11 2.29 0.49 0.70 0.08 4.54

Control 0.26 0.86 5.80 1.30 0.13 2.61 0.40 0.17 0.06 4.59

Threshold

limit value*

3.0 - - 4.0 5.0 6.0 6.0 23.0 0.7

Background

value*

min 0.01 0.02 0.89 0.01 0.01 0.02 0.04 0.01 0. 02

max 2.91 32.16 59.47 2.2 1.08 5.3 2.82 4.28 1.12

mean 0.36 3.22 14.9 0.94 0.2 0.62 0.5 0.38 0.15

*According to Fateev and Samokhvalova (2012b)

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132

The results indicate that heavy metals content in

the soil in none of the variants exceeded the threshold

limit value (Fateev & Samokhvalova, 2012a).

The calculations of the total pollution rates Z

(Gutsulyak, 2001), which are presented in Table 8,

indicate that subsurface drip irrigation does not cause

soil contamination with heavy metals; the soil of the

experimental site, according to the polyelement

contamination indicators, belongs to the

uncontaminated (Z

< 16) (Gutsulyak, 2001). The

expected scoring is presented in Table 8.

According to the gradation provided by

Medvedev, chemical degradation of soils is absent if

zinc content < 11 mg/kg, copper content < 1.5 mg/kg,

cobalt content < 2.5 mg/kg, lead content < 3.0 mg/kg,

and cadmium content does not exceed three times the

background content (Medvedev, 2012).

The comparison indicates no probability of

chemical degradation of the soil for any of these

chemical elements.

The resistance of plants to biotic and abiotic

factors is determined both at the cellular level and by

the processes that take place under the harmonious

influence of all plant organs. Micronutrients play an

essential role in that regard as cofactors of various

enzymes, which have their specific action in redox

processes; in some cases, there is their

interchangeability. Bobko, Vlasyuk, Peive, Shkolnik,

Gedz, Toma, and others drew attention to the positive

effect of micronutrients on the resistance of plants to

adverse conditions and, in particular, to drought, due

to changes in the chemistry of the plant body (Baliuk

et al., 2018).

The microelement status of the soil in the

experimental sites was assessed using the grouping of

soils by the content of labile forms of micronutrients

extracted with acetate-ammonium buffer (pH 4.8),

mg/kg of soil (Fateev & Samokhvalova, 2012b). The

results showed that the availability of micronutrients

in the soil from the experimental site with subsurface

drip irrigation of white cedars was as follows: high

for Mn, very low for Cu and Co, and very high for Zn.

In the soil from the experimental site with subsurface

drip irrigation of the grass plot, the availability of

micronutrients was as follows: medium for Mn and

Co; very low for Cu, and very high for Zn. In the

control site, the micronutrients content was low for

Mn and Cu and medium for Zn and Co.

The assessment provides an opportunity to predict

possible changes in soil conditions in the context of

determining the lack or excess of micronutrients.

Irrigated soil will be characterized by a high content

of zinc and manganese, and in the future, they are

likely to be in excess. At the same time, subsurface

drip irrigation does not contribute to the accumulation

of labile forms of copper and cobalt.

4 CONCLUSIONS

The presented findings of the 2019–2021 study

allowed us to draw the following preliminary

conclusions.

1. The equilibrium soil density showed the

optimal values at the beginning of the growing season

in 2020–2021 for all soil layers: 1.08–1.16 g/cm

for

grass plot and 0.91–1.08 g/cm

for white cedar

plantings.

2. The use of subsurface drip irrigation provided

an excellent structural condition in terms of air-dry

agronomically valuable particles with a size of 0.25–

10 mm; the ratio of structural fractions corresponded

to the optimal parameters. The average content of air-

dry aggregates was 86.24% in the control, whilst it

was 88.36% under subsurface drip irrigation. The soil

structure index was 6.35 in the control and 8.55 in the

studied variant.

3. Subsurface drip irrigation provided good

structural condition of the soil in terms of the content

of waterproof aggregates sized 0.25–7.00 mm. The

average values of this indicator for the 0–40 cm soil

layer were 51.65% in the control and 54.20% under

irrigation. The score of diagnostic agrophysical

indicators is the most favorable.

4. Subsurface drip irrigation did not change the

content of organic matter: in particular, the content

values were 2.06 and 2.33% for the control and

irrigated grass plots, respectively. This humus content

value was a characteristic natural feature of the

studied soil, i. e. there was no direct dependence of

the humus content on irrigation during the

observation period.

5. Subsurface drip irrigation did not change the

soil nutrient status, namely the content of mineral

nitrogen, labile phosphorus and potassium; the

scoring was the same for both the irrigated and the

control sites. No direct dependence of nutrient

content on irrigation was observed. There was the

determining influence of soil genetic characteristics

on the content of mineral nutrients. Poor nitrogen

status was due to the natural characteristics of the soil

and the peculiarities of nitrogen uptake in ornamental

plants. The studied soil requires the application of

nitrogen fertilizers on the grass plot to improve

fertility, in particular not only at the beginning of the

growing season but also after each mowing. As for

the nitrogen status of the soil under the white cedar,

the application of small amounts of nitrogen

Subsurface Drip Irrigation as a Factor Ensuring Productive and Ecological Functions of Soils

133

fertilizers once during the period of active needle

growth is relevant.

6. Assessment of diagnostic indicators for the

cation-anion composition of the aqueous soil extract

revealed a poor soil condition in terms of the

percentage of Na

from the amount of absorbed

alkaline cations in both variants. By the content of

toxic salts, the soil condition was rated to be

intermediate between satisfactory and good (close to

good) in both cases. The degree of soil salinization by

the Ca/Na ratio was more than 2.5 for both irrigated

and natural grass plots. The soil condition in terms of

this indicator was rated to be good.

7. The results indicate no probability of chemical

soil degradation for any chemical element. The total

pollution rates Zc in both white cedar sites and the

grass plot were similar to that for uncontaminated

soils.

8. The assessment of the microelement status of

the soil enables forecasting of possible changes in soil

status in the context of determining the lack or excess

of micronutrients. The content of zinc and manganese

may increase due to the irrigation, and their excess is

likely to continue. At the same time, subsurface drip

irrigation does not contribute to the accumulation of

labile forms of copper and cobalt.

9. Score assessment of the ecological and

reclamation condition of the studied soil by

diagnostic indicators revealed subsurface drip

irrigation utility with compulsory further ecological

and reclamation monitoring of the irrigated soils.

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