Soil Reclamation

UDC 626.8:631.4(575.172) Eurasian Soil Science, 28(10),1996

Translated from

Pochvovedeniye, No.7, 1994, 91-97

Alteration of Soils in the Irrigated Zone of the Amu Darya River Delta

B. Jollibekov

Karakalpak Branch

Uzbek Academy of Sciences

The soil in the irrigated part of the Amu Darya River delta is being altered by human impact. Increased irrigation has everywhere caused a rise in the level of high-salinity ground-waters. Increasing salinity of irrigation water and the re-use of drainage waters in relatively low-water years have led to salinization of all irrigated soils and have accelerated secondary salinization. On rice plantations, Irrigated Rice-Paddy Solonchak soils that are difficult to restore have developed in low areas of relief.

Key words: Soil alteration, irrigated zone, Amu Darya River delta

The Karakalpak Republic is one of richest areas of Uzbekistan in terms of resources. As of 1 November 1989, it had total of 16.24 million ha of land, of which agricultural land accounted for 439,000 ha; 419,700 ha was sown on crops, 6,700 ha was used for orchards, vineyards, and the like; and about 165,000 ha was sown on cotton.

Flooding irrigation is used on 260,000 ha. The irrigation standards, broken down by salinity of the soil, are: 2000 to 3000 m³/ha for low-salinity or unsalinized soil; 3000 to 3500 m³/ha for moderately saline soils; and 4000 to 6000 m³/ha for highly saline soils. The salinity of the Amu Darya River is rising and has reached 2.1 to 2.3 g/liter. With rising salinity, the amount of water withdrawn from the river has increased 10 to 20 percent.

The annual water loss in the irrigation networks is 4900 m³; the field loss is 2400 m³; and the amount of water taken in by the irrigation system averages 17,200 m³.

Of 485,200 ha of irrigated land, 90.1 percent is saline, compared with a figure of 50.9 percent for the republic as a whole. The breakdown is slightly saline soils, 184,000 ha; moderately saline soils, 180,000 ha; highly saline soils, 73,300 ha.

Some 55 km³ of water from Amu Darya and Syr Darya rivers is used for irrigation; the amount of water used in the Karakalpak Republic is between 8.5 and 9.1 billion m³.. In some regions, the irrigation standards are as high as 4500 to 8500 m³/ha. Overuse of irrigation of water occurs as a result of inadequate planting and unwarranted increases in authorized irrigation levels, without allowance for the salinity of the soil or of the irrigation water. The Karakalpak Republic has the lowest water to land index (about 80 percent).

With decreasing water resources, increasing ecological degradation, the rapid rise in the salinity of the Amu Darya and its contamination by effluent, and the decline in the water level of the Aral Sea, the approach to land reclamation and improvement is being altered. The area sown to cotton is being decreased. It had declined by 53,000 in 1990 and should decrease by 125,000 ha in 1995 and by 173,000 in 2000; the introduction of cotton-alfalfa rotations should bring the figure for the year 200 to 263,000 ha [2].

One of the ironies of aridization is that, alongside the progressive decrease in the natural supplies of water in the soil and the air, with increasing salt content of the soil solution, the plants cannot use the moisture that is present in the soil [1, 4].

Beginning in 1990, we made field studies of the chemistry and degree of salinization of Alluvial-Meadow-Irrigated soils, highly salinized Alluvial-Meadow-Irrigated soils, Irrigated Rice Paddy soils, and Solonchakous Irrigated Rice Paddy soils, and of their alteration by human impact.

The alteration of soil in the irrigated part of the Amu Darya delta was studied in semipermanent tracts located on the Raushan Sovkhoz, Kungrad Rayon; the Madaniyat Sovkhoz, Karauzyak Rayon; and the Nukus Botanical Garden, Karakalpak Branch, Uzbek Academy of Sciences, in Nukus. The groundwater levels had begun to rise throughout the lover Amu Darya region in 1969 as a result of a great increase in the irrigated areas. In a well at Nukus near the botanical garden, beginning in May of 1967, the groundwater level rose, reaching a depth of 0.51 m. The highest groundwater level was at a depth of only 0.14 m, in 1971. High levels again occurred in 1977 (0.19 m). In 1985 and 1986, the groundwater level was relatively stable at 1.57 to 1.58 meters.

Highly salinized Irrigated Rice Paddy soils are formed by rice growing in low areas of terrain. These soils, which occur throughout the rice-growing sovkhozes of the Karakalpak Republic, have low productivity and are expensive to reclaim.

The change in the chemistry and salinity of these soils was studied on the Raushan Sovkhoz between 1987 and 1990 and on the Madaniyat Sovkhoz beginning in 1984.

Section 2 on the Madaniyat Sovkhoz, about 500 m east of the central facilities, was dug on 31 May 1984, before sowing the rice. The soil had the following structure:

0-29 cm. Dark yellow to gray, moist, compacted, fine-grained, sandy-loam texture, abundant dove-gray patches and small plant rootlets.

29-71 cm. Reddish to chocolate color, loam texture, highly compacted, moist, abundant rusty patches with root inclusions.

71-137 cm. Dove-gray to light gray with yellow sand, interstratified loam and sandy loam, compacted, moist, in some places with rootlets.

137-200 cm. As above, moisture, live plant roots. Groundwater appears at 180 cm.

Table 1

Annual and Seasonal Changes in Chemistry and Salinity of Highly Waterlogged Rice-Paddy Irrigated Soils

Layer, cm	1987	1988	1989	1990
	Spring	Autumn
0-10	SC .	CS .	CS .	CS .
	3.27	1.78	1.05	0.71
10-30	CS .	CS .	CS .	CS .
	2.55	1.77	1.08	0.86
30-50	CS .	CS .	CS .	CS .
	1.83	2.22	1.22	1.01
50-100	S .	C .	SC .	CS .
	1.19	2.76	1.14	0.48
100-200	CS .	C .	CS .	CS .
	1.99	1.07	2.06	0.94
0-100	2.21	2.13	1.12	0.76
0-200	2.17	1.92	1.31	0.86

Note.. Here and in Tables 2 and 5, type of salinity is given above bar (C, chloride; S, sulfate; CS, chloride-sulfate; SC, sulfate-chloride); figure below bar is mean salt content, percent.

The soil was highly startified. The salt concentration was highest in the plow year (2 percent total salts). The salinity was of sulfate type in the upper layer and changed with depth to the chloride-sulfate type. The bicarbonate content was constant at 0.043 percent throughout the section except the subplow layer. The upper layer contained little chloride (0.088 percent) but the concentration rose to 0.107 percent in the lower horizons. The upper layer contained 1.3 to 1.37 percent of sulfate ion owing to the application of large amounts of ammonium sulfate. The sulfate concentration was between 0.33 and 0.15 percent in the deeper layers. The calcium content was between 0.027 and 0.08 percent and that of magnesium between 0.04 and 0.83 percent. The concentration of sodium declined with depth to a value of 0.49–0.47 percent. The concentration of mobile phosphorus was 9.5 ppm in the upper plower course and 6.5 ppm deeper in the profile. The compacted subplow horizon contained 330 ppm of exchange potassium; lower concentrations occurred in the upper and lower horizons (100 to 200 ppm).

Tract 2 was laid out in the spring of 1987 on the waste fields (formerly used for rice) of he Raushan Sovkhoz. Samples were collected for analysis before plowing. The water-soluble salts occurred chiefly in the top 10 cm of the profile (3.27 percent); at depths of 50 to 100 cm, the concentration was only 1.19 percent (Table 1). The concentrations of salts in the upper layer fell to 0.71 percent after the cultivation of rice (1990). The weighted mean percentage of salt in the top 1-meter layer fell by two-thirds over the course of 4 years, and that in the top 2-meter layer fell by a factor of 2.7 in the same period.

Table 2

Annual and Seasonal Changes in Chemistry and Salinity of Solonchakous Irrigated Rice-Paddy Irrigated Soils

Layer, cm	1984	1986	1989	1990
	Spring		Autumn
0-10	SC .	CS .	SC .	CS .
	9.05	4.27	4.15	3.08
10-30	SC .	CS .	SC .	CS .
	6.53	2.62	4.11	2.66
30-50	SC .	CS .	SC .	S .
	2.52	1.13	3.11	3.09
50-100	SC .	CS .	C .	CS .
	2.85	0.80	1.49	1.47
100-200	Not det.		SC .	CS .
			2.06	1.94
0-100	5.24	2.20	3.21	2.57
0-200	Not det.		2.98	2.37

In the top 10 cm, the salinity was of the sulfate-chloride type in 1987 subsequently changing to the chloride-sulfate type. In the plow layer, the salinity was constantly of the chloride-sulfate type.

The highest salt concentration occurred in 1987, in the top 10-cm layer; in 1988, the maximum was in the 50-100 cm interval, and in 1989 it had descended to a depth of more than 100 cm.

Solonchakous Irrigated Rice-Paddy soils are found on rice plantations at the sites of former-like depressions and are of heavy texture. They are local accumulators of water-soluble salts. The groundwater is at a high level (depth 1 m) and is strongly saline. The salinity is of the sulfate-chloride sodium type, with high magnesium content.

Tract 1 was laid out on the Madaniyat Sovkhoz 1.5 km north of the central facilities on 2 June 1986 before inundation. This soil had the following structure:

0-10 cm. Light gray blocky-granular heavy clay, dry and slightly compacted.

14-38 cm. Dark gray clay, highly compacted, blocky, moist, small plant roots. Sharp color transition.

38-60 cm. Reddish-brown to gray clay, highly compacted, structureless, moist, with some rusty patches. Pronounced color transition.

Table 3

Chemical Compositions and Level of Groundwater in Nukus Botanical Garden

Section number	Depth of groundwater, m	Concentrations of ions, g/liter						Salinity, g/liter
		HCO3	Cl	SO4	Ca	Mg	Na+K
14 November 1960
1	4.25	0.195	0.106	0.168	0.640	0.24	0.103	0.562
2	4.25	0.798	0.851	0.954	0.112	0.204	0.754	3.220
3	5.00	0.390	0.155	0.308	0.132	0.64	0.124	0.977
4	5.00	0.538	0.272	0.616	0.172	0.165	0.163	1.656
22 May 1986
1	0.65	1.098	2.165	3.240	0.631	1.202	4.685	18.961
2	0.78	0.683	2.698	2.073	0.378	0.404	1.955	8.191
3	0.63	0.756	1.917	2.030	0.388	0.488	1.435	6.874
4	1.30	0.902	1.491	1.435	0.396	0.371	0.902	5.487
5	0.93	2.074	7.100	5.491	0.705	1.363	5.025	21.758
6	0.68	0.854	4.615	7.180	0.617	1.443	3.312	18.022
7	1.31	0.585	0.923	1.034	0.193	0.588	0.039	3.362

*Data from laboratory of branch of Uzgiproselstroy Agricultural Planning and Design Institute.

60-100 cm. Dove-gray to light clay, highly compacted, moist, structureless, with some rusty patches. Groundwater appears at a depth of 100 cm.

The water-soluble salts were most abundant in the top 10 cm, reaching a maximum of 9.05 percent in 1984(Table 2); the concentration was only a third as great in 1990.

The concentration of salts in the plow layer ranged from 2.62 percent to 6.53 percent in various years. The weighted-mean salt concentration in the top 1-meter layer fell by half from the summer of 1984 to 1986. In the period of out investigation, the salts were chiefly in the top intervals of the soil and the salinity was of mixed type, varying both with time and with depth. Both sulfate types and chloride types appeared at various times in the middle part of the profile. The concentration of salts in the top 1-meter layer after the annual cultivation of rice fell by half over the course of 7 years.

In 1986, when there was a large-scale dieoff of the trees and shrubs, a soil melioration survey was made at the Nukus Botanical Garden. A total of 9 section, extending down to the water table, were dug in an area of 40 ha. It was found that, in low areas of relief (section 1,2,3), the saline groundwater was located at a depth of only 0.69 m.

The salinity of the groundwater ranged from 6.8 to 18.9 g/liter and was of mixed type (chloride and sulfate-chloride), with sodium and magnesium predominant. The chloride content ranged from 1.9 to 8.1 g/liter and that of sulfate from 2.0 to 3.2 g/liter (Table 3).

In high areas of relief (sections 4, 5 and 7) on a ridge adjoining the river, the water level was somewhat deeper (0.93–1.31 m). The salinity of the groundwater ranged from 3.23 to 21.7 g/liter. The salt composition was of mixed type (chloride-sulfate and sulfate-chloride), with magnesium predominating.

Table 4.

Concentrations of Water-Soluble Salts and Humus in Soils of Nukus Botanical Garden
(percent of air-dried soil)

Section	Depth, cm	HCO3	Cl	SO4	Ca	Mg	Na+K	Total salts	Humus
14 November 1960
3	0-50	0.043	0.057	0.140	0.024	0.015	0.065	0.322	––
6	0-50	0.043	0.019	0.049	0.020	0.010	0.010	0.129	––
8	0-30	0.043	0.170	0.076	0.020	0.010	0.169	0.566	––
22 May 1986*
4	0-10	0.732	1.182	2.469	0.343	0.566	0.759	6.061	0.876
	10-38	0.122	0.197	0.964	0.157	0.136	0.194	1.770	0.109
	38-78	0.231	0.078	0.740	0.078	0.056	0.295	1.478	0.058
	76-140	0.090	0.019	0.127	0.023	0.013	0.055	0.327	––
Well 3	0-10	0.052	0.177	0.241	0.044	0.032	0.137	0.683	0.11
	10-30	0.036	0.159	0.225	0.050	0.029	0.112	0.611	0.95
	30-50	0.104	0.124	0.336	0.039	0.023	0.190	0.816	0.041
	50-100	0.078	0.085	0.354	0.050	0.034	0.131	0.732	––
	100-150	0.091	0.042	0.204	0.022	0.014	0.106	0.479	––
8	0-1	0.338	1.913	1.94	0.264	0.320	1.386	6.162	0.569
	1-14	0.586	0.730	1.209	0.202	0.143	0.771	3.641	0.679
	14-49	0.112	0.208	0.408	0.081	0.059	0.160	1.028	0.040
	49-110	0.072	0.125	0.175	0.015	0.019	0.137	0.543	––
	110-142	0.067	0.156	0.489	0.033	0.058	0.212	1.015	––
	142-180	0.045	0.104	0.760	0.076	0.055	0.255	1.295	––

Note. Dash indicates "not determined."

The concentrations of chloride and sulfate in the groundwater ranged from 0.92 to 8.16 and from 1.03 to 7.18 g/liter, indicating that the salinity and ionic composition of the groundwater depended on the level of the water table and on irrigation conditions.

Irrigated Alluvial-Meadow-Tugai soils, Irrigated Alluvial-Meadow soils, and Solonchaks occur on the grounds of the Nukus Botanical Garden.

The Irrigated Alluvial-Meadow-Tugai soils (section 4) were formed by the direct influence of woody vegetation (Ulmus foliacea, maple, turanga, oleaster) and occur chiefly in the western and northern areas of the botanical garden. They have a slight sod horizon.

These soils now remain only on elevated ridges adjoining the river, where the groundwater level is at a depth of less than 1 meter. The sod horizon contains 0.87 percent humus; in the lower horizons, the concentration declines to 0.05 percent (Table 4).

Water-soluble salts accumulate chiefly in the upper layer, reaching a concentration of 6.0 percent. The high concentrations result from secondary salinization, the high groundwater level, and the exudational water-salt regime of the soils in the absence of leaching irrigation. The salinity is of the chloride-sulfate, sulfate, and magnesium-sodium type. The chloride content is highest (1.18 percent) in the upper horizon and decreases to 0.019 percent in the profile. The sulfate content of the top layer is 2.46 percent, and it declines to 0.13 percent in the lower horizons. The sod horizon contains 0.56 percent magnesium and 0.79 potassium and sodium; the concentrations of these elements in the lower horizons are between 0.01 and 0.05 percent.

Alluvial-Meadow-Irrigated soils (well 3) occur in the eastern part of the botanical garden, where the nursery is located. They are relatively poor in humus (0.51) owing to the annual cultivation addition of organic fertilizer.

Table 5

Annual and Seasonable Changes in Chemistry and Salinity of Highly-Salinized Alluvial-Meadow-Irrigated Soil

Later, cm	1986	1987	1988		1989
	Autumn	Spring	Autumn	Winter	Winter	Spring	Summer	Autumn
0-10	CS .	CS .	CS .	CS .	CS .	CS .	Not det.	CS .
	3.2	0.68	3.15	1.86	2.21	0.48		2.30
0-30	CS .	CS .	CS .	CS .	CS .	CS .	CS .	CS .
	3.61	0.64	2.64	1.47	1.58	0.53	1.10	1.85
30-50	CS .	CS .	CS .	CS .	CS .	CS .	CS .	CS .
	1.48	0.82	2.13	1.07	0.95	0.84	0.80	0.98
50-100	CS .	CS .	CS .	CS .	CS .	CS .	SC .	CS .
	1.24	0.73	1.26	1.11	1.07	0.91	0.51	0.61
100-200	CS .	S .	CS .	CS .	CS .	S .	S .	CS .
	0.95	0.51	0.95	0.93	1.13	0.45	0.71	0.56
0-100	2.38	0.72	2.30	1.38	1.45	0.69	0.80	1.43
0-200	2.10	0.68	2.03	1.29	1.39	0.64	0.78	1.26

Water-soluble salts are uniformly distributed through the top 1-meter layer of the soil (0.61-0.81 percent). The salinity is of the chloride-sulfate type, or of sulfate type at greater depths, with magnesium and sodium predominant. The chloride concentration reaches 0.17 percent in the top layer and falls to 0.04 percent in the lower horizons (Table 4). Sulfate ion is concentrated in the subplow horizon (0.33 percent) and is uniformly distributed in the lower part of the profile (0.20-0.26 percent). The magnesium content is lower than in the Irrigated Alluvial-Meadow-Tugai soils. Sodium is uniformly distributed through the profile.

Highly Salinized Alluvial-Meadow-Irrigated soils occur widely in the irrigated part of the Amu Darya delta owing to regular irrigation with high-salinity waters. The highly salinized Alluvial-Meadow-Irrigated soils differ from the other soils by having a high concentration of water-soluble salts throughout the profile and by the presence of saline groundwater relatively close to the surface.

On tract 3, which was laid out near the main entrance of the botanical garden on 22 May 1986, changes in the composition of water-soluble salts and in the level and salinity of the groundwater were monitored.

The soil is a highly salinized Meadow-Alluvial-Irrigated soil without vegetation and with the following structure.

Soil surface covered by a salt crust 3 to 5 cm thick.

0-10 cm. Light gray sandy loam, slightly compacted, structureless, dry, abundant small and medium roots, sharp color transition.

10–38 cm. Dark gray sandy loam, moderately compacted, structureless, fresh, salt inflorescence in the 28-32 cm interval, small roots present. Sharp textural transition.

38-74 cm. Dark gray to reddish-brown, sandy-loam, moderately compacted, horizontally stratified, blocky-granular, abundant small roots and salt inflorescence. Sharp texture and color transitions.

74-108 cm. Dark gray micaceous sand, slightly compacted, moist, a few dead plant roots. Gradual textural transition.

108-139 cm. Dark gray ochraceous light sandy loam, highly compacted, blocky, moist, some dead plant roots and salt inflorescence. Distinct color transition.

139-169 cm. Dark gray ochraceous sandy loam, highly compacted, blocky, wet. Sharp textural transition.

169-198 cm. Dark gray, micaceous, stratified sand, compacted, wet, abundant rusty patches, dead plant roots and white salt inflorescence. Groundwater appears at depth of 190 cm.

We found a strong, persistent salinization of the top layer (0-10 cm) in autumn. All of the soils were salinized (Table 5).

The concentration of salts in the upper layer declined from 3.2 percent in the spring of 1986 to 2.30 percent in the autumn of 1989. The lowest salt concentrations occurred in the spring of 1987 and 1989 (0.48-0.68 percent).

In the plow layer, the concentration of water-soluble salts decreased by half during the period of the investigation.

In the autumn of 1986, 1988, and 1989, the salt concentration in the top 1-meter and top 2-meter layers reached its maximum values (Table 5).

The chloride-sulfate salinity in the top layer (0-10 cm) of the Highly Salinized Alluvial-Meadow-Irrigated soils, in the plow layer (10-30 cm), and in the subplow layers persisted over the entire period of the investigation. In the spring and summer, a sulfate type of salinity occurred in the second 1-meter layer (Table 5). The spring desalization of the entire profile resulted from heavy irrigation in order to leach out salts and from the subsequent preparation for planting. In the winter, the salinity is restored by precipitation and by the lack of evaporation from the surface.

The soil horizons of light texture contain the smallest amounts of salts.

In spring, strong winds carry away the upper evaporite horizon [3], so that the top layer contains smaller amounts of salt than at other times of year.

Solonchaks most often form in low areas of relief in the central part of the botanical garden, in areas where the groundwaters are close to the surface. Tree plantings, primarily North American species, died between 1977 and 1989. In some areas, Meadow Solonchak patches occurred. Slightly and moderately saline groundwaters occur at depth of 0.5 to 0.8 m.

In the top soil layer (0-14 cm), the humus content is 0.56 percent and the concentration of water-soluble salts reaches its maximum (6.16 percent). The salinity is one of the sulfate-chloride, chloride-sulfate, and magnesium-sodium types. The lower part of the profile is highly salinized (section 8).

The chloride concentration decreases with depth in the profile, and the sulfate content increases in the upper and middle parts of the profile, depending on the texture. Carbonates occur chiefly in the upper part of the profile.

In the last 15 years, the area occupied by Solonchaks and salinized soils in the Nukus Botanical Garden has increased. After planting of introduced species, certain species died, including shrub Amorpha, white acacia, and spiny Gleditshia. Plants that could not tolerate the increased salinity included eastern willow, Populus boleanus, Pennsylvania ash, Catalpa bignonioides, and Cercis canadensis. Trees planted along the shores of ariks on the embankment adjoining the river were somewhat more resistant, including Ulmus and Gleditshia and such shrubs as Derza and Adelia.

The rise in groundwater level was harmful to woody plants whose natural habitat is mountain or piedmont areas. These plants are in depressed condition everywhere in the botanical garden. They include Crataegus, Derza, and Adelia.

In high relief areas, including the ridges adjoining the river and their slopes, where alluvial-Meadow-Tugai Irrigated soils occur, the groundwater level was somewhat higher (93-100 cm). In the fifth and sixth years of the survey, woody plants in these areas became desiccated and died.

On Irrigated Alluvial-Meadow-Tugai soils in areas where the groundwater was at a depth of 130 cm, 122 introduced species of trees had died by 1987.

Conclusion

Heavy human impact has altered the soil cover in the irrigated part of the Amu Darya delta.

Increased use of irrigation and leaching waters has caused a ubiquitous rise in groundwater levels. The increasing salinity of irrigation waters and re-use of high-salinity drainage waters for irrigation have set in motion a ubiquitous salinization of irrigated soils and have accelerated secondary salinization.

Rising groundwater levels have killed fruit trees, ornamentals, and natural trees and shrubs. Low-productivity, hard-to-reclaim Solonchakous Irrigated Rice-Paddy soils have developed in the plantations of low areas of relief.

Bibliography

1. Kovda, V. A. 1977. Aridizatsiya sushi i bor'ba s zasukhoy (Aridization and efforts to combat drought). Nauka Press, Moscow.

2. Medetullayev, Zh. 1987. Agropromyshlennyy potential Karakalpakskoy ASSR (Agroindustrial potential of the Karakalpak Republic). Karakalpakiya, Nukus.

3. Orlova, M. A. 1983. Rol' elovogo faktora v solevom rezhime territorii (Effect of wind on soil salinity). Nauka, Alma-Ata.

4. Rozanov, B. G. 1984. Aridization and human caused desertification. Pochvovedeniye, No. 12.