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Soil Salinity Distribution as Affected by Drip Irrigation System, Land Slope and Water Application
Abdullah S. Aljughaiman
Department of Environmental and Natural Resources College of Agriculture & Food Sciences King Faisal University, Alahsa, Saudi Arabia
E-mail: [email protected] Tel: 966-595114110
Abstract
This study was conducted in a sandy loam soil plot at King Faisal University Research Station, Saudi Arabia, with an aim to investigate the effects of an automated drip irrigation system (ADIS), field capacity (FC), and land slope on soil salinity distribution.
The water amounts used were 60%, 80%, and 100% FC, on non-sloped (0% grade) and sloped (5% grade) land. According to salt concentration data, FC treatments were arranged in the following order: 80% FC>60% FC>100% FC before and after irrigation on the 0%
slope. On the 5% slope, the order was 100% FC>80% FC=60% FC before irrigation and 100% FC=80% FC=60% FC after irrigation. On non-sloped land, significant differences were observed in soil salt accumulation under 80% FC, 100% FC, and 60% FC before and after irrigation (p<0.01). The salinity distribution recorded on the 5% slope improved under the 60% and 80% FC treatments. The salt concentration decreased with depth before irrigation and increased with depth after irrigation. Under the 5% slope condition, the mean soil salinity increased by 20.1%, 7.4% and 11.2% before irrigation and 21.7%, 13.1% and 17.3% after irrigation under 100% FC, 80% FC, and 60% FC, respectively. The findings of this study illustrated the importance of slope and attaining salt balance when using an ADIS, especially in heavy soils.
Keywords: Automation controller, field capacity, soil salinity distribution, vegetative growth, faba bean
1. Introduction
Drip irrigation has several advantages and thus is used widely in arid and semi-arid areas. It is characterized by simultaneous rationalization of the amount of water and energy used. However, one of its disadvantages is the spreading of salt on the soil surface, which leads to damage to plants including permanent wilting (Aragüés et al., 2014; Aragüés et al., 2015).
Gencoglan et al. (2006) studied the effect on green bean yield of conventional subsurface drip irrigation (SDI) and alternate partial root-zone surface drip irrigation (SPRD). They found that the overall irrigation water saving was 16% for the SPRD irrigation treatments compared with the SDI treatments, and that SPRD increased the water use efficiency (WUE) and the slope of the yield relationships. Huang et al. (2010) reported similar findings when investigated potato yield using SDI and SPRD. Wang et al. (2008) studied the effect of alternate partial root-zone irrigation (APRI) on soil microorganisms during maize cultivation. They obtained a higher number of soil microorganisms in APRI compared to conventional irrigation and fixed partial root root-zone irrigation.
Land Slope and Water Application 122 Determining water and salinity distribution under APRI for a wide range of soil types, crops, design features, and irrigation strategies is costly and time-consuming. The investigation of successive wetting and salinity patterns and root water uptake under APRI requires detailed soil water monitoring and a large number of measurements (Meerbach et al., 2014). In contrast, numerical modeling is an inexpensive, rapid, and labor-saving tool for the simulation of water and solute dynamics under different irrigation techniques. Phogat et al., (2010) revealed that HYDRUS-2D precisely simulates water and solute movement under different irrigation methods in sand soil types. Therefore, HYDRUS- 2D can be used as an effective design and management method.
The planting area has expanded rapidly since the 1990s after the introduction of drip irrigation, plastic mulching, and high planting density to Xinjiang region, China (Wang et al., 2004). Drip irrigation, with its low rate and frequent irrigation application over a long period, can maintain high soil matrix potential in the root zone (Kang et al., 2010).
The distribution pattern of soil salinity under drip irrigation depends on soil properties, differences in water and fertilizer management, and the design of the irrigation system (Li et al., 2015).
Several design and evaluation standards for drip system uniformity have been developed in different countries (ASABE, 2003; Chen et. 2009). Moreover, many studies have investigated the effect of drip irrigation parameters on water and salt distribution in soils (Chen et al., 2010; Wang et al., 2011).
Nightingale et al. (1991) studied the effects of trickle irrigation rates on soil salinity distribution in an almond orchard and concluded that increasing irrigation amounts reduced the depth-weighted mean soil salinity beneath the trickle line.
Field experiments for water and solute distribution from a point source conducted by Khan et al. (1996) indicated that solute concentrations in soil increased with input concentration, applied volume, and application rate. Greater system uniformity can potentially lead to a uniform distribution of water and salt in soil; however, the initial installation cost of systems with greater uniformity are relatively high, although the long-term ownership costs might be reduced (Wilde et al., 2009).
Moreover, a low level of drip system uniformity might not permit sufficient leaching of salts out of the root zone at locations with low emitter rates, what hinders plant growth to some extent.
The objective of the current study was to evaluate the impact of an ADIS and the amount of irrigation water (FC), applied on the salt distribution in the soil of faba bean crops grown in an arid region of the Al-Hassa oasis in eastern Saudi Arabia.
2. Materials and Methods
This study was conducted at Al Hassa Governorate, Al Hassa City, Hofuf State, Kingdom of Saudi Arabia (elevation: 147 m, latitude: 25° 24′ N, longitude: 49° 36′ E in sandy loam soil). The aim was to study the effect of an ADIS, different slope conditions, and different field capacities on soil moisture distribution patterns, water amounts, and faba bean yield. Ground water was used as the source of the irrigation water for the study.
Field experiments were performed under drip irrigation by an automated system, and three field capacity (FC) treatments were used specifically: 100%, 80%, and 60% FC, with 100% FC used as a control. The soil of the experimental field had (Nile alluvial) clay loam texture. Faba bean seeds (Vicia faba; Giza 461, G461) were planted in the second week of October and the growing season lasted 141 days.
Soil particle size distribution test was determined using the Pipette method of Gee and Bauder (1986) as shown in Table 1. Soil bulk density was measured according to Black and Hartage (1986).
Soil moisture content at FC and permanent wilting point were measured according to Walter and Gardener (1986) as shown in Table 1. The available water was calculated using the following equation:
Soil sample Depth (cm)
Particle size distribution (%) Texture class
*FC *WP *AW BD
(g/cm3)
HC (cm/h) Coarse sand Fine sand Silt Clay (V/V %)
0-15 3.7 54.5 25.2 16.6 SL 0.22 0.11 0.11 1.45 1.11
15-30 3.8 55.8 24.6 15.8 SL 0.22 0.11 0.11 1.43 1.28
30-45 4.6 53.7 26.0 15.7 SL 0.22 0.11 0.11 1.43 1.28
45-60 4.6 55.9 25.5 14.0 SL 0.21 0.10 0.11 1.42 1.53
(*) Determined as a percentage in (v/v %) cm3 water/cm3. BD, bulk density; HC, hydraulic conductivity; SL, sandy loam PWP
FC
AW = − (1)
Where:
AW = available water ( aw %), FC = field capacity ( f.c %), and
PWP = permanent wilting point ( pwp %).
Soil aggregate stability aggregation percentage (Agg. %) and mean weight diameter (MWD) were determined using the wet sieving technique without using a dispersion agent according to Kemper and Rosenau (1986). Soil hydraulic conductivity (HC) was determined under the constant head technique of Klute and Dirksen (1986). HC was calculated using the following equation:
)...
. /(
) (QL AtH
HC = (2)
where,
Q = volume of water flowing through the sample per unit time (L3/T), A = cross sectional flow area (L2),
L = length of the sample (L), and
H = differences in the hydraulic head across the sample (L).
Soil intake rate was determined using the double wall ring infiltrometer technique described by Kohnk (1968). The Kostiakov equation was used to represent the infiltration process:
...
ktn
I = (3)
where,
I = infiltration rate at time t (mm/min);
t = time that water is on the surface of the soil (min);
k = intercept of the curve representing the infiltration rate at unit time, i.e., instantaneous infiltration rate (mm/min); and
n = the slope of the curve representing the relationship between log I and log t ...
ktn
D = (4)
where:
D = is accumulative intake rate (mm/min), and
n = is the slope of the curve representing the relationship between log D and log t.
Some soil chemical characteristics were determined as follows:
Soil pH and EC were measured in 1:2.5 soil water suspensions and in soil past extract, respectively, according to Jackson (1967). CaCO3 and soluble cation and anion content were measured using a Scheibler calcimeter (Soil Survey Staff, 1993) as shown in Table 2. Irrigation water analysis is given in Table 3.
Land Slope and Water Application 124 Table 2: Chemical analysis of the soil
Soil Sample Depth (cm)
Cations (MEq/l) Anions (MEq/l) EC
pH (dS/m) Ca++ Mg++ Na+ K+ CO3--
HCO3-
Cl- SO4--
0-15 6.43 4.89 185.0 18.84 0 5.64 6.65 58.7 8.10 1.97
15-30 11.53 6.49 237.1 25.01 0 5.21 10.53 62.6 8.13 2.98
30-45 12.15 7.97 279.1 26.63 0 3.68 11.48 64.0 8.11 3.61
45-60 12.56 4.17 307.1 32.28 0 3.62 5.6 66.9 8.03 3.76
The Bougioukou method was used for determination of the soil’s mechanical properties, pH was measured with a pH electronic meter, while organic matter content was determined by combustion of the sample with sulfuric acid. Additionally, the distance between the drippers and the drip lateral length enabled high uniformity of irrigation approaching 95–97%. Throughout the entire irrigation season, the volumetric soil moisture (v/v %) was measured in the experimental plots daily from soil at depths of 0, 10, 20, 30, and 40 cm and at 5, 10, 15, and 20 cm from the dripper.
Table 3: Chemical analysis of irrigation water
Cations (MEq/l) Anions (MEq/l)
pH EC
(dS/m)
Ca++ Mg++ Na+ K+ Co3=
HCO3-
Cl- SO4=
0.7 1.72 128 13 0.0 3.4 1.8 67 7.48 2.0
The rapid, reliable and non-radioactive time domain reflectometry (TDR) method, was used irrespective of soil type. The working principle of TDR is based on the direct measurement of the dielectric constant of soil and its conversion to water volume content (Fig. 1).
Figure 1: TDR device and probe with five sensors
Testing of the soil moisture content is a complex process and the placement of a sensor at the root level of the crop is, in most cases, not sufficient for satisfactory performance. As a solution to this problem, it is recommended to use two or more sensors at various depths such that a greater area of the root level is covered. To achieve this and to ensure greater accuracy, soil moisture probes with five sensors each were permanently installed in the 12 experimental plots, where they were kept in a continuous contact with the soil. Each probe equipped with sensors to measure the soil moisture content at five different depths: 0–10, 10–20, 20–30, 30–40 cm, and 40–50 cm. An average was calculated for the measurements taken at each position within the five depths for each treatment.
The mean values for the treatments were compared by analysis of variance (ANOVA) and the least significant difference (LSD) between systems at p<0.01 was also determined. A randomized complete block design according to Steel and Torrie (1980) was used.
3. Results
The salt distribution pattern under a lateral length of 60 m from the ADIS was analyzed (Table 4 and Figs. 2 and 3). It has been found that the salt concentration has decreased with depth before irrigation and increased with depth after irrigation. On the 0% slope before irrigation, the mean soil salinity was recorded as the lowest under 100% FC (0.36 dS/m), followed by 0.39 dS/m under 60% FC, and 0.41 dS/m under 80% FC. In contrast, after irrigation, the mean soil salinity was observed to be the highest under 80% FC (0.40 dS/m), followed by 60% FC (0.38 dS/m), whereas the lowest value (0.36 dS/m) was observed under 100% FC. Similarly, on the 5% slope, the salt concentration also decreased
Table 4: Effect of slope and FC under ADIS on soil salinity EC (dS/m) distribution patterns
Slope (I)
Soil Depth (cm) (II)
100% FC Soil EC (dS/m) 80% FC 60% FC
(III)
Before After Before After Before After
(IV)
0 0.47 0.26 0.50 0.33 0.48 0.34
10 0.43 0.28 0.46 0.35 0.39 0.35
0% 20 0.34 0.35 0.38 0.37 0.38 0.37
30 0.27 0.44 0.36 0.45 0.36 0.41
40 0.24 0.49 0.34 0.51 0.35 0.47
Mean 0.36 0.36 0.41 0.41 0.39 0.38
0 0.58 0.35 0.55 0.38 0.55 0.38
10 0.54 0.38 0.51 0.38 0.51 0.39
5% 20 0.41 0.41 0.40 0.41 0.40 0.41
30 0.37 0.55 0.37 0.53 0.38 0.53
40 0.36 0.63 0.37 0.61 0.37 0.57
Mean 0.45 0.46 0.44 0.46 0.44 0.46
LSD 1% 0.02 0.03 0.01 0.02 0.03 0.01
Interactions 1%:
(I) X (II) 0.04 0.06 0.03 0.02 0.05 0.02
(I) X (IV) 0.02 0.03 0.02 0.01 0.06 0.04
(II) X (IV) 0.03 0.04 0.05 0.02 0.04 0.03
(III) X (IV) 0.02 0.02 0.03 0.04 0.01 0.05
(I) X (III) 0.01 0.01 0.02
(II) X (III) 0.03 0.04 0.01
with depth before irrigation and increased with depth after irrigation. The mean soil salinity before irrigation was the highest under 100% FC (0.45 dS/m), and the values were lower and equal under the two other irrigation water amounts (0.40 dS/m). After irrigation, the values of mean soil salinity were equal (0.46 dS/m) under all treatments. The mean soil salinity increased by 20.1%, 7.4%, and 11.2%
before irrigation and 21.7%, 13.1%, and 17.3% after irrigation under 100% FC, 80% FC, and 60% FC, respectively, for 5% slope.
Land Slope and Water Application 126
Figure 2: Contour maps for soil salinity EC (dS/m) distribution patterns under different drip irrigation treatments before and after irrigation on the 0% slope
Distance from dripper (cm) Distance from dripper (cm) Distance from dripper (cm)
Soil depth (cm) Immediately before irrigation
Soil depth (cm) 24 h after irrigation
100% from FC 80% from FC 60% from FC
Figure 3: Contour maps for soil salinity EC (dS/m) distribution patterns under different drip irrigation treatments before and after irrigation on the 5% slope
Distance from dripper (cm) Distance from dripper (cm) Distance from dripper (cm)
Soil depth (cm) Immediately before irrigation
Soil depth (cm) 24 h after irrigation
100% from FC 80% from FC 60% from FC
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
0
5
10
15
20
25
30
35
40
0 5 10 15 20
The mean soil salinity under closed-circuit irrigation was in the following ascending order:
100% FC<60% FC<80% FC before and after irrigation on 0% slope and 60% FC=80% FC<100% FC before irrigation and 100% FC=80% FC=60% FC after irrigation on the 5% slope.
The differences in mean soil salinity under the 0% slope condition between any two irrigation treatments were found to be significant at (p<0.01) before irrigation, however, it weren’t significant after irrigation, whereas the differences were insignificant between any two treatments before and after irrigation under the 5% slope condition. The differences in mean soil salinity between any two soil depths were significant at (p<0.01), except for the depth of 0–10 cm before and after irrigation under 100% FC and 80% FC with respect to 0% slope condition. Under the 5% slope condition, the differences in mean soil salinity between any two soil depths were significant at p<0.01, except for the difference at a depth of 0–10 cm after irrigation under 80% FC and 60% FC and at 30–40 cm before irrigation under all irrigation treatments. The interaction effect at the 1% level (Table 4) indicated that 80% FC treatment was greater than 100% FC and 60% FC treatments with decreased depth. The interaction effect of irrigation treatment and soil depth on soil salinity under 0% slope was maximal (0.50 dS/m) for 80% FC with 0-cm soil depth, and the minimum mean soil salinity was 0.36 dS/m under 100% FC before and after irrigation. In contrast, under the 5% slope condition, the maximum soil salinity value was 0.63 dS/m under 100% FC with a soil depth of 40 cm after irrigation. The minimum mean value on the 5% slope was 0.44 dS/m for 60% and 80% FC before irrigation. These data agree with the guidelines set forth by ASABE 2003 and Chinese Standard 2009. Under the 0%
slope condition before irrigation, the maximum and minimum salt content values (dS/m) were 0.50 (0 cm depth) and 0.24 (40 cm depth) under 80% FC and 100% FC, respectively, whereas after irrigation, the maximum and minimum values were 0.51% (40 cm depth) and 0.26% (0 cm depth) under 80% FC and 100% FC, respectively. On the 5% slope before irrigation, the maximum and minimum salt content values (dS/m) were 0.58% (0 cm depth) and 0.36% (40 cm depth) with 100% FC, whereas after irrigation, the values were 0.63 (40 cm depth) and 0.35 (0 cm) under 100% FC. Contour maps for the soil salinity distribution when the lateral length was 60 m under different field capacities and slope conditions (after and before irrigation) are shown in Figures 2 and 3.
4. Discussion
The present study aimed to determine the effects of an ADIS on salt distribution in the plot growing faba bean on sandy loam soil in an arid region of Saudi Arabia. Two different land types were used for the study: non-sloped (0% grade) and sloped (5% grade) land.
The results showed that the salt concentration decreased and increased with soil depth before and after irrigation, respectively. In particular, irrigation with 60% to 80% FC under a 5% slope gives better salinity distribution than other treatments. Furthermore, using the 5% slope, a marked increase in the mean soil salinity was observed after irrigation compared to that before irrigation. These data agree with the findings of Simunek and Hopmans (2009) and Souza et al. (2009).
In a previous study, Meerbach et al. (2000) investigated the effects of drip irrigation layout on soil water and salinity and showed that salt accumulation within the root zone of cotton under every- row irrigation was higher than that under alternate-row irrigation. The present study’s findings clarified that the interaction among the slope, soil depth, and irrigation had a considerable impact on salt accumulation in soil and distribution within the root zone of faba beans irrigated by automated drip irrigation. This finding reflects the importance of the slope in determining how automated drip irrigation should be implemented.
In conclusion, our study findings indicated the importance of attaining salt balance using ADIS and improving drainage system in farms to facilitate salt leaching, especially in heavy textured soils.
Land Slope and Water Application 128
AcknowledgEment
This research project supported by the Deanship of Scientific Research at King Faisal University.
Research Project number: 150006.
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