Distribution patterns of soluble salts and gypsum in soils under large-scale irrigation agriculture in Central Asia

Figures & data

Table 1 Outline of the soil sampling plots

Irrigated farms studied	Land use and crop rotation	Soil profiles investigated			Sampling year	Spatial analysis on salt distribution
		Cropland	Adjacent uncultivated land	Semi-natural soil
R. Ili watershed
BK farm	Rice-based	BK101, BK103, BK34	BK104	BK105	1992	+
BBT farm	Rice-based	BBT203			1993	+
R. Syr-Darya watershed
KS farm (Shimkent)	Rice-based	KS35			1994	–
KR farm (Kzylorda)	Rice-based	KR301	KR303		1995	–
Fergana region	Cotton	FG2, FG3, FG4, FG5, FG6			1996	–
SD farm	Cotton	SD11, SD12, SD13			1997	+
Syr-Darya region	Cotton	SY1			1996	–
R. Amu-Darya watershed
KK farm (Nukus)	Cotton	KK11, KK12, KK13			1997	+

Figure 1  Locations of the sample sites.

Figure 2  Distribution of salts in the surface layers of soils in and around the irrigated fields.

Table 2 Chemical composition of samples of irrigation and drainage water

Irrigated farms studied	pH	Electrical conductivity (dS m^−1)	Na	Mg	Ca	Cl	SO4	Sum of cations	Sum of anions	Sodium adsorption ratio (mmol L^−1)^1/2	Sampling time
			(mmolc L^−1)
BK farm
Irrigation water from R. Ili	8.19	0.60	1.6	1.6	2.5	1.0	2.2	5.8	5.9	1.1	1994/7
Drainage water from the farm	8.03	0.85	3.2	2.4	3.4	1.4	3.5	9.1	9.2	1.9	1994/7
KS farm
Irrigation water from R. Syr-Darya	8.25	1.04	3.0	3.0	3.2	1.6	5.4	9.3	9.5	1.7	1994/7
Drainage water from the farm	8.01	2.02	7.9	6.3	5.4	4.7	11.5	19.6	20.3	3.3	1994/7
KR farm
Irrigation water from R. Syr-Darya	7.69	1.64	5.9	5.2	4.5	2.5	11.5	15.8	16.3	2.7	1995/7
Drainage water from the farm	7.55	4.44	24.3	19.2	14.0	10.9	37.8	57.6	53.3	6.0	1995/7
Fergana region
Irrigation water from R. Soh (FG4 and FG5)	7.81	0.32	0.3	0.8	2.2	0.1	1.4	3.4	3.4	0.3	1996/7
Irrigation water from R. Syr-Darya	7.58	1.34	4.3	4.5	5.9	2.2	9.5	14.8	14.6	1.9	1996/7
(FG3, FG6, and SD farm Drainage water from whole the basin to R. Syr-Darya)	7.50	2.89	9.4	11.3	13.2	4.6	27.3	34.4	34.5	2.7	1996/7
Syr-Darya region
Irrigation water from R. Syr-Darya	7.67	1.34	3.7	4.5	5.4	1.9	8.7	13.7	13.0	1.7	1996/7
Drainage water the farm	7.57	2.38	8.9	8.4	9.6	3.9	20.2	27.1	27.1	3.0	1996/7
KK farm
Irrigation water from R. Amu-Darya	7.72	1.35	6.7	3.8	4.8	7.5	9.5	15.5	17.1	3.2	1997/7

Figure 3  Distribution pattern of water-soluble cations and gypsum in soil profiles subjected to rice-based irrigation systems. SAR, sodium adsorption ratio.

Figure 4  Distribution pattern of water-soluble cations and gypsum in soil profiles subjected to cotton-based irrigation systems. SAR, sodium adsorption ratio.

Figure 5  Degree of surface accumulation of (a) soluble cations and (b) gypsum and (c) comparison of them in soils under different land uses. Soils were arbitrarily classified into four groups, I, II, III, IV, based on the abundance of soluble cations and gypsum in (c).