Abstract: This study was carried out to determine the effects of different fertigation practices on irrigation system performance in in-line emitters using Samandag region well water. The experiment was conducted at the research field of the Samandag Vocational College, University of Mustafa Kemal, Hatay, from 2001 to 2002. In the experiment, three different emitters (1.7, .75 and 4.0 L h-1), three different fertilizer treatments (no-fertilizer, MKP+Ca(NO3)2+KNO3+KSO4+NH4NO3 and NH4NO3+KSO4+MKP) combinations with flushing and no flushing management groups were tested in three replications. Emitter discharge rates were tested at the beginning and end of every season to determine emitter flow variations. The effect of the different fertilizer treatments on system performances was found to be statistically significant. Fertilizers which included both calcium and sulfates resulted in lower system performance than the others. Emitters that have the lowest flow rates had the lowest performance. The acid treatment and flushing management increased the system performance slightly, but it was found not to be statistically significant.
INTRODUCTION
Drip irrigation method provides plant water requirement more regularly and frequently when compared to the other irrigation methods (Özekici and Sneed, 1995). It has important advantages over other irrigation methods; nutrients and other chemicals could be applied with water more frequently and regularly as needed by plants, which result in more healthier and higher yielding plants (Nakayama and Bucks, 1981).
Efficiency of drip irrigation system depends on uniformity of water coming from all emitters of the system. Any alteration of emitter discharge rates can result in lower application uniformity than expected. Clogging of drip-lines results in a significant decrease in both the average emitter discharge and the distribution uniformity, such that these fall below the acceptable ranges identified earlier (Marcu et al., 1992).
In a growing season, the highest irrigation efficiency is only possible with a good planning and management (Smajstrla et al., 1990). System uniformity can be lower due to equipments defects such as valves and pressure regulators and clogging of emitters (Hochmuth and Smajstrla, 1991).
Emission uniformity of a drip irrigation system should be tested regularly by measuring emitter discharge rate and calculating efficiency value of the system. When fertigation is preferred the emission uniformity should be 95% or higher (Smajstrla et al., 1990).
The clogging of drip emitters is the largest maintenance problem with drip systems (Keller and Bliesner, 1990). It is difficult to detect and expensive to clean, or replace, clogged emitters. Partial or complete clogging reduces emission uniformity and as a consequence, decreases irrigation efficiency (Capra and Scicolone, 2004).
Quality of irrigation water also effects the degree of emitter clogging (Bucks et al., 1979). High concentrations of soluble salts in the water is the most important factor of clogging. Hills et al. (1989) examined the four management schemes and three water qualities with electrical conductivities of 0.59, 1.12 and 2.02 dS m-1 for lessening the chemical clogging effects of high calcium content water in drip-tape. Results showed that partial and full clogging due to chemical precipitation occurred in all management schemes for the water with the highest salt content. Flow values in the laterals had decreased between 20 and 40% for this water. Corresponding f1ow reduction for the lowest salt content water varied between 3 and 15%. Of the management modes evaluated, reduction of water pH from 7.6 to 6.8, by sulfuric acid injection provided the least clogging for all three water qualities.
The most important disadvantage of fertigation is precipitation of chemical materials and clogging of emitters (Papadopoulos, 1993). In some cases, a combination of carbonate precipitates and fertilizers are responsible for severe clogging of drip irrigation systems (Sagi, 1990).
Hebbar et al. (2004) were declared that, in fertigation, use of 100% water-soluble fertilizer is recognized to safe guard the drip system in a long run. The normal fertilizer generally tends to clog the emitters and cause uneven distribution of fertilizers. However, in the study of 2 years, no clogging of emitters was observed.
An experimental trials carried out on the behaviour of six kinds of filters (gravel media, disk and screen) and four types of drip emitters (vortex and labyrinth) using five kinds of municipal wastewater that have not undergone previous advanced treatment. Results showed that of the emitters with a similar discharge, vortex emitters were more sensitive to clogging than labyrinth emitters. In-line labyrinth emitters in pipes with a smaller diameter were more sensitive to clogging than the same kind of emitter in pipes with a greater diameter (Capra and Scicolone, 2004).
Flushing of irrigation system pipelines is an essential part of the maintenance program required for long-term success with microirrigation. Flushing will prevent accumulation of small particles and their buildup to a size that can plug emitters. Flushing frequency can vary according to both amount of flushing material and quality of the irrigation water, because of this laterals should flushed at least once a month (Smajstrla and Boman, 1999).
The emitters on the trickle irrigation systems could be easily clogged by poor management, resulting in loss of energy and water. This makes irrigation system, which has a high investment cost ineffective in a short time. Growers may return back to the other irrigation systems which have lower irrigation uniformity (Özekici, 1998).
The objectives of this research were to determine the effects of different fertilizers used in drip irrigation with different emitters on system performance and also to find solutions to increase the performance of drip irrigation systems.
MATERIALS AND METHODS
The research was conducted at a greenhouse located at the research station of Samandağ Vocational College, University of Mustafa Kemal, Hatay, in three consecutive seasons (spring 2001, fall 2001 and spring 2002).
| Table 1: | Average Values of Irrigation Water Quality in Seasons |
| Table 2: | Technical properties of lateral and emitters |
| *Found by measurements | |
The research station is located in the coastal area of Samandag, 600 m away from the Mediterranean Sea (36°08' N; 35°54' E ) and a altitude of 3 m above sea level. During the study, average, maximum and minimum temperatures inside of the greenhouse are 22.9, 42.2 and 2.4°C, respectively.
The water source was a 9 m deep well. The irrigation water was analyzed at the beginning of each growing season (Table 1). The irrigation waters, which effects drippers performance, were classified by Bucks et al. (1979) according to their clogging effects. The irrigation water used in this experiment fall into high risk class with regard to pH, hydrogen sulfide and bacterial population and average risk class with regard to dissolved materials and low risk class with regard to Mn, total Fe and suspended materials according to Bucks et al. (1979) classifications.
Drip irrigation system was set up with sand separator, screen filter with 200 mesh, fertilizer tank with 100 L capacity and a pump, water meter, valves and manometers. Submain pipeline which had ball valves and pressure regulators at the inlets were located for applying each fertilizer forms separately. In the system, three different laterals with different in-line emitters were used (Table 2).
The experimental design was set up in a split-strip plots with three replication. Main plots were included fertilizer treatments (F0, F1, F2). Main plots were splinted by two different managements which included (M1) and with no included (M0) flushing and acid injections. In these plots, three different laterals (L1, L2 and L3) were placed with three replications (Fig. 1). All factors in the experiment is given in detail below.
| Table 3: | Applied fertilizer quantity based on treatments (kg ha-1 season-1) |
F0, control plots, included only irrigation water application.
F1, total nitrogen was given as 25% sulfate and 75% nitrate forms with Ammonium Nitrate (NH4NO3), Calcium Nitrate (Ca(NO3)2), Potassium Nitrate (KNO3), Potassium Sulfate (KSO4) and Mono Potassium Phosphate (MKP).
F2, total nitrogen was given as 50% sulfate and 50% nitrate forms with Ammonium Nitrate, Potassium Sulfate and Mono Potassium Phosphate.
M0, no acid injection and flushing were performed.
M1, acid injection and flushing were used to keep the pH value of fertilized water about 6-6.5, depending on the titration test results, a concentration of 1 mg L-1 phosphoric acid were applied. Moreover, at the end of the each season, laterals were flushed with 5 mg L-1 phosphoric acid solution.
L1, a lateral with 2.75 L h-1 discharge rate and with emitters at every 20 cm.
L2, a lateral with 4.0 L h-1 discharge rate and with emitters at every 25 cm.
L3, a lateral with 1.7 L h-1 discharge rate and with emitters at every 20 cm.
Lengths of all laterals were 23 m and they were placed 50 cm away each other.
Fertigation was applied according to guidelines recommended by Bar-Yosef (1991) where, for greenhouse tomatoes, amount of NPK should be 450, 95 and 943 kg ha-1200 day-1, respectively.
Fertilizers were applied with every irrigation application. Fertigation was achieved by Burt et al. (1995) method which is called “quarter”. Total applied amount of fertilizers in F1 and F2 treatments were given Table 3. Because of the control treatment, irrigation water was applied in F0 treatment but no fertilizer was applied.
The amount of irrigation water applied was based on free surface evaporation from a Class A Pan. Manufacturing, placement and management of this pan was based on rules of Richard et al. (1998). Irrigation was started by tensiometer value, which was placed 30 cm deep from soil surface, not exceeding -25 cb.
| Fig. 1: | Graphical layout of the experiment plan |
The first growing season (S1) was 145 days. In this season, total of 309.1 mm irrigation water given with twelve irrigations. The second growing season (S2) was 165 days and a total of 216.4 mm irrigation water given with eleven irrigations. Third growing season (S3) was 101 days and a total of 292.1 mm irrigation water given with ten irrigations.
Performance of emitters were tested at the beginning of the experiment according to ASAE Standards (1998). Laterals were raised 20 cm from the ground without elevation differences, irrigation water pressures in the lateral were adjusted according to manometers value at the beginning and end of the laterals by placing ball valves. Emitter flow variations were determined twice at the beginning (BS) and at the end of the (ES) each season for predetermined 50 emitters for each laterals. To determine the flushing effects, emitters discharge rates were tested at the end of the season before (ESBF) and after (ES) the flushing. During the tests, water temperatures were measured but since the emitters has turbulent flows, the effects of water temperature on discharge rates were neglected according to literature (Peng et al., 1986).
Emitter flow variation, qvar, (WU et al., 1986), coefficients of manufacturing variation, CVm, (Solomon, 1977), statistical uniformity, Us, (Bralts et al., 1981), emission uniformity, EU and design emission uniformity, EUd, (Keller and Karmeli, 1974) equations were used for evaluation of the system performance according to ASAE standards (1998).
RESULTS AND DISCUSSION
Emitters flow tests: At the beginning of the experiment, a series of the tests related to the emitters were performed and qmean, CVm, qvar, Us EU and EUd performance values were determined (Table 4).
Results showed that, the CVm values of L1 and L2 were in the category of Excellent. CVm values of L3 were in the category of Poor.
| Table 4: | Some performance indicators of the laterals at the beginning of the experiment |
| Table 5: | Classification of the CVm, Us and EU indicators of laterals at the beginning of the experiment according to ASAE (1998) standards |
| Table 6: | Duncan’s Multiple Range Test Results of Flow Rate Decreases in SeasonxFertilizerxFlushingxLateral Interaction |
| *Treatments marked with the same letter are in the same group at the p≤0.05 level | |
According to the other criteria’s (Us and EU) L1 and L2 were in the excellent category and the L3 was in the good category (Table 5).
Emitter discharge rates at the end of the each season were lower than the values at the beginning of the each season, particularly, at the end of the laterals. In agreement with this, some studies have pointed out similar findings (Adin and Sacks, 1991; Ravina et al., 1992; Puig-Bargues et al., 2005). Although flushing application had reclaimed some of the clogged emitters and increased the emitter discharge rates, this was not found to be statistically significant. It was observed that, at the end of the flushing applications, clogging of some emitters at the end of the laterals were increased as a result of dragged materials.
| Fig. 2: | Emitter discharge rate variations in the experiment |
L1 and L2, in general, had showed consistent discharge rate variations in themselves. The highest emitter discharge rate decrease was in F1 and the lowest emitter discharge rate decrease was in F0 resulted emitter clogging (Fig. 2A and B). However, there were high and inconsistent variations of emitter discharge rates in comparison with other laterals in L3. CVm values of L3 which had the lowest discharge rate were the highest because of this, their values of qmean were inconsistent in all treatments compared to the others (L1 and L2). In this group, it was determined that the highest emitters discharge rate decrease was in F1 and the lowest emitters discharge rate decrease was in F2 (Fig. 2C). In control treatment (F0M0) 74% of L1 emitters, 95% L2 emitters and 49% L3 emitters showed 0-5% discharge rate decrease however emitters of L3 showed up to 50% discharge rates decrease.
The maximum (25-100%) discharge decrease were determined; 4% of L1 in F1M0 groups, 0.67% of L2 in F2M0 and 0.67% of L2 in F2M1 groups, 14.02% of L3 in F1M0 and 13.34% of L3 in F1M1 groups.
When the emitters which had clogging and decreased flow rate at some percentages were evaluated the highest clogging and thereby lower flow rates were observed in F1 applications. The flushing management, although not statistically significant, was efficient in preventing clogging and increased flow rates. These results are in good agreement with the findings of Hills et al. (1989).
| Table 7: | Average performance values of the laterals at the end of the seasons (%) |
Moreover, the L3 emitters which had relatively smaller holes tend to have more clogging and lower flow rates. As emitters have bigger holes, the clogging was less and the flow rates were higher. Similar relationships were also reported by Keller and Bliesner (1990) and Chigerwe et al. (2004).
Emitter discharge rate variations based on both seasons and treatments were tested statistically by using MSTAT-C computer software. Fertilizer, lateral, seasonxlateral, fertilizerxlateral, seasonxfertilizerx flushingxlateral interactions were significant at 1% and seasonxflushing, seasonxfertilizer x flushing, seasonxfertilizerxlateral, flushingxlateral and fertilizerx flushingxlateral interactions were significant at 5% level by variation test. Treatment means were evaluated and compared with Duncan multiple range test (Table 6). The highest flow rate decreases were observed in S2F1M0L3 and S2F1M1L3 and the lowest flow rate decrease was in S2F1M1L1. This results indicated that emitter flow rates were more important factor than the others for emitter discharge rate decreasing caused by clogging.
Evaluation of emitter performances: The system performance indicators (qvar, Us, EU and EUd ) were calculated at the end of the each season by using emitter flow test results (Table 7). The lowest emitter flow variation (qvar) was found in F0M1L2 interaction in second (S2) season and the highest emitter flow variation was found in F1M0L3 interaction in second (S2) and third (S3) seasons.
Percentage statistical uniformity variation among the seasons were calculated and these values were analyzed statistically. Lateral and seasonxlateral interactions was significant at 0.1% level and fertilizer, fertilizerxlateral and seasonxfertilizerxlateral interactions were significant at 5% level by variation test. To determine the effect of treatments on Us variations, values of mean were tested with Duncan test. Seasonxfertilizerxlateral interactions had twelve statistical groups with in 95% confidence level. The highest variation was in S2F1L3 interaction and the lowest variations were in S2F2L2, S3F0L2, S1F0L1, S3F0L1, S1F0L2, S2F2L1, S2F0L1, S2F1L2 and S2F0L2 interactions.
The effect of treatment on EU variation were analyzed with Duncan test. Fertilizer, lateral, seasonxlateral, fertilizerxlateral and seasonxfertilizerxlateral interactions were significant at 0.1% level and, seasonxfertilizer interactions was significant at 5% level. There were nine different Duncan groups in seasonxfertilizerxlateral interactions 95% confidence level. The biggest EU variation was in S2F1L3 interaction with the lowest flow rates and the lowest variation was in S2F1L2 interaction with the highest flow rates. Similarly, Chigerwe, et al. (2004) reported that a well designed micro-tube systems with high flow rates generate high uniformity, even at extremely low head (0.1 m) and present lower clogging problems and higher placement flexibility than the low flowing systems.
Since the minimum emitter flow rates in the system were used in calculation of design emission uniformity (EUd), fully or partially clogged any emitter in the system could lower the EUd values of the system. Therefore this is a not good method for evaluating system performance in the field. As indicated in literature, this evaluation method should only be used when more than one emitters used per plant or when multiple outlets emitters were used. Since one emitter per plant was used in this experiment and there were also fully clogged emitters, the variation tests were not performed.
As a result of this study, It can be concluded that in drip irrigation systems fertigation effects the emitter flow differences. The type of applied fertilizers effected the performance. The lowest performance was observed in F1 (Calcium and sulfate forms were used together) treatments. The pH adjustments and flushing particularly gains importance when these forms of fertilizers were used. There were no significant differences between flushing applications statistically but these applications increased emitter discharge rates. Further research should be conducted to determine the effect of flushing frequency on emitter clogging.
By the end of the experiment, L2 laterals which had the highest discharge rates, had the highest performance and L3 laterals which had the lowest discharge rates, had the lowest performance. Thus, choosing emitters with the higher discharge rates must be important for resistant to emitter clogging.