The first use of wastewater was reported in Banzelo, Germany, in 1531 and in Edinburgh, Scotland in 1650. In the early of the 20th century most of the countries started to use wastewater. In Palestine more than 70 percent of wastewater was used for agricultural irrigation (Abedi and Najafi, 2001). Nearly, 60 percent of total volume of wastewater in California (432 Mm3) was used for agricultural irrigation too (Tavakoli and Tabatabaei, 1999). In many cities of Iran, municipal wastewater is used for agricultural irrigation. For instance, the water of the Firuzabad canal in Tehran in which a significant part of the municipal and industrial waste is disposed, widely used for irrigation of fruit and vegetables. Of the 9700 hectares of the cultivable lands of Tehran, almost 6900 hectares (nearly 70%) are irrigates with wastewater. It has been reported that in Shiraz, in arid seasons the main discharge of the river is wastewater which is ultimately used in agriculture. In Tabriz, municipal and industrial wastewater enters the Ajichai River and is ultimately used for agricultural irrigation. (Tabatabaei and Liaghat, 2004). Wastewater sludge is also uses as a fertilizer in agricultural lands. The application of wastewater and sludge in agricultural land generates numerous sanitary problems (Abedi and Najafi, 2001). Czyzyk (1996) in his research reported that wastewater irrigation has a significant effect on the groundwater contamination level. Lauver (2000) has evaluated nitrate contamination of the groundwater of Arizona using volume balance approach in the agricultural lands in which wastewater is used for irrigation. He reported that the quality of groundwater contamination potential is increased when uncontrolled amount of wastewater is used for irrigation. Sharmasarkar et al. (2000) has evaluated the nitrate plume in the soil of the sugar beet filed irrigated by wastewater.
When wastewater is continuously used for irrigation, some changes are expected
to happen in soil infiltration. The most important index for evaluation of the
change are Sodium Adsorption Ratio (SAR), Electrical Conductivity (EC) and Total
Dissolved Solid (TDS). Tavakoli and Tabatabaei (1999) reported that the three
indexes should be considered synchronal in evaluation of soil infiltration change.
The acceptable range of SAR and EC in the irrigation with wastewater is presented
by world health organization (WHO) in 1989. In general, irrigation water salinity
makes the soil saline and hard and decreases crop yield. So the salinity effect
must be considered in advance base on the sort of the soil, climate and crop
(Tavakoli and Tabatabaei, 1999). Zadhoush (1998) evaluates the effect of wastewater
both on physical and chemical properties of the soil and on the crop of the
lands in northern parts of Isfahan.
The effect of wastewater on soil, subsurface water and plants completely depend on the type of the wastewater and its content. Industrial sugar beet wastewater has special effects on soil because of its special content.
There is no reference evaluating the effect of the wastewater in irrigation on the physical properties of the soil. A large number of lands in the eastern parts of Isfahan are irrigated with a large amount of industrial sugar beet wastewater. Several years ago, farmers started to use industrial wastewater for irrigation because of the drought season and scarcity of water. The crops of these lands were Alfalfa, grass and sugar beet.
The objective of this research is evaluation of the change in the important
content properties of the soil irrigated with industrial sugar beet wastewater.
These properties are Saturation Percent (SP), Field Capacity (FC), Permanent
Wilting Point (PWP), Gravitational Water Content (GWC) and Total Available Moisture
MATERIALS AND METHODS
Material: To evaluate the effect of the industrial sugar beet waste water on the physical properties of the soil water content, an experiment was carried out in Khorasgan Azad University in Isfahan, Iran in the summer 2005. The soil texture was clay-loam and the soil initial conditions were measured as Table 1. The irrigation water analysis is presented in Table 1, too.
The experiment was conducted in 21 columns of soil as shown in Fig. 1. The columns made by PVC with the diameter of 110 and the height of 400 for each. The first 50 mm part of the column in the lower part was filled with a sand filter, the next 250 mm with soil and the next 50 mm with sand filter. The other remained 50 mm was used for irrigation. The columns of soil are exposed to wastewater using the surface irrigation method during seven interval days. The total numbers of irrigation events was 12 and the volume of the wastewater irrigation was 1.2 L.
The experiment is statistically designed fully randomized with three treatments and three replications. The three treatments were T1, T2 and T3. Soil and water analysis were conducted in three steps of irrigation. Table 2 shows the treatment description and sampling time.
||Soil properties of the experiment filed
||Treatment description and sampling time
||Setup of the experiments
Method: In any sampling time of the research (Table 2), both physical and chemical analyses were conducted on soil and just chemical analysis was conducted on the wastewater. The list and analyses of the physical and chemical properties of the soil analysis are presented in Table 3. Table 3 shows the chemical analysis of the wastewater, too.
The first three columns of soil are selected randomly for the tests of the initial condition. Other nine columns are used for the second steps of the analysis. Other remained columns are also used for final tests. The analysis of the soil is conducted on the disturbed soil.
RESULTS AND DISCUSSION
This research has been carried out to evaluate the effect of industrial sugar beet wastewater on the content properties to the soil during 12 events of irrigation. Figure 2 shows the Saturation Percent (SP) in three steps and three treatments. The SP value in the beginning of the test was 46% and it was the same for all the treatment, because the tests are carried out in the same condition. The SP value is increased during the irrigations events for all of the treatments. Table 4 shows the statistical analysis of the data in the initial conditions compared with the final conditions using a t-test value and a Duncan test. Table 4 shows that there no significant difference of SP value (less than 5%) between all the treatments. All the treatments are categorized in one group in Duncan test.
In the chemical analysis of the soil such as SAR, pH, EC, there is no significant variation during irrigation events (Table 4). It means that the change of SP may not affected by the soil chemical properties. The Organic Matter (OM) of the soil is also tested because it can affect the properties of the soil. Figure 3 shows the OM value in the test.
The analysis of the wastewater shows that there is OM existing in the wastewater
which can increases the OM in the soil. Table 4 shows that
OM is not increased significantly during the test period. It can conclude that
the experiment period (12 events) should be longer to make the variation significant.
||Saturation Percent (SP) in the treatments of experiment (%)
Matter (OM) in the treatments of experiment (%)
So in case that the numbers of events is increased the level of significantly
will be decreased. It means that if irrigation with the wastewater continues
for more than several years, it will cause some significant changes in the OM
of the soil and probably in the SP. The Bulk Density (BD) is also evaluated
as another parameter which is illustrated in Fig. 4. There
is no considerable in BD during the irrigation period. Although no change was
observed in T3 and it was constant during the irrigation. Tabatabaei
et al. (2004) report that irrigation will also increases BD. It can be
concluded that in T3 increasing of OM has prevented increasing of
BD in the soil.
Figure 5 and 6 show Field Capacity (FC)
and Permanent Wilting Point (PWP) of the soil, respectively. The FC and PWP
is seen to be greater in T3 rather than in T2 and T1
and it is same for SP.
analysis of data base on T and Duncan test
|*no replication; a,bDuncan level
||Bulk Density (BD) in the treatments of experiment (g cm-3)
||Filed Capacity (FC) in the treatments of experiment (%)
Table 4 shows that the variation of FC and PWP is significant
during 12 irrigations in 1% level. It can also be concluded that increasing
of OM in the soil also increases the FC and PWP, because of irrigation with
||Permanent Wilting Point (PWP) in the treatments of experiment
||Gravitational water (GW or SP-FC) in the treatments of experiment
As the rate of FC and PWP is low in the light soils (sandy, sandy-loam) irrigation
with the wastewater will improve soil water content properties in these points.
available water (TAW or FC-PWP) in the treatments of experiment (%)
During irrigation, the SP of the soil is increased at first and then it starts to be decrease. FC is also increased. Figure 7 shows the GW in the T1, T2 and T3. Table 4 shows that the GW isn’t varied significantly during the experiment time, although the FC changes significantly. The Duncan test shows that the GW is categorized in one group and confirms the least result.
A very important soil water content parameter is Total Available Water (TAW). This parameter is different from FC and PWP. Figure 8 shows the TAW value in the experiment. The TAW is decreased during the experiment significantly in T2 and T3. Actually it is not like FC and PWP, because their values have been increased but TAW is decreased. It can be conclude that although the FC and PWP has been increased but the rate of increasing in PWP was greater than FC. It means the increasing of OM level in the soil has changed the soil moisture characteristic curve.
In brief irrigation with the wastewater decreases the available water for the plants. Consequently irrigation with the wastewater decreases the irrigation intervals and farmers must irrigate the farm in more events for the same yield. This could be considered as an undesirable effect of the wastewater irrigation. It is clear that the other effects of the wastewater on soil should be evaluated.
We would like to express our appreciation to Khorasgan Azad University for financial support of this research project. The authors wish to thank Mr. Karimzadeh, Mr. Massoudi and Mr. Shahnavazi for their assistant in the filed work.