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An ASABE Meeting Presentation

Paper Number: 096487

Suction of Soil Particles under Vacuum Conditions inSubsurface Drip Irrigation: Comparative Test of Emitters

Prof. Rubens Duarte Coelho (University of Sao Paulo / USP - INCT [email protected])

Eng. Jorge Luis Copquer dos Santos (Graduated Student ESALQ / USP)

Eng. Christian J. Mendoza Castiblanco (Graduated Student ESALQ / USP)

Prof. Marconi Batista Teixeira (University of Goias State - Ipameri)

Written for presentation at the2009 ASABE Annual International Meeting

Sponsored by ASABEGrand Sierra Resort and Casino

Reno, NevadaJune 21 June 24, 2009

Abstract.Subsurface drip irrigation (SDI) presents an inherent risk of suctioning soil particles fromthe surrounding porous media due to vacuum occurrence inside lateral lines underground that canresult emitter clogging. This work aims to evaluate the vacuum occurrence effect on 25 drip modelsunder SDI conditions. The treatments consisted in the application of four vacuum levels -10, -15,-20and -40 kPa in two soil textures: sandy and clay. The obtained values of flow rate were used tocalculate average flow rate (qm), discharge variation coefficient (CV) and uniformity distributioncoefficient (UD). Random block was the statistical delineation adopted, F tests was used to thevariance analysis and Tuckey test with 5% probability to averages comparisons and regressionanalysis. Subsurface drip emitters performance was influenced by the soil texture. The highestvacuum level -40 kPa present the major emitters obstructions with reduction in the flow rate for bothsoil textures. Some emitters presented variable results according to soil texture and constructivedesign.

Keywords. Clogging, emitters, drip irrigation.

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Introduction

Sugar cane irrigation for biofuels production in Brazil is a huge potential market for SDI

application in the next 20 years (6 million ha / forecasted expansion area). However, subsurface

drip irrigation is increasing slowly in the brazilian irrigated agriculture, due to limitations that the

method presents in some recent field experiences: clogging problems, emitters with trifularin

protection (Geoflow / rootguard) are unavailable at the local market and lack of scientific

researches indicating its technical and economical viability (DALRI & CRUZ, 2002).

Drip irrigation it is extensively used on soil surface. The evolution of the hydraulic

characteristics of emitters resulted in the use of drip irrigation underground, with the perspective

of obtaining some advantages compared to the traditional form (superficial drip): larger lifetime

and higher water efficiency use (GOMES & SOUSA, 2002).

Subsurface drip irrigation (SDI) system is characterized by the application of water in

form of drops, directly inside the soil, allowing the application of water in small quantities, next to

the roots of the plants, not moisturizing the inter-row area and soil surface. The consumption of

water is reduced compared to other irrigation systems. When it is well managed, it allows a

higher efficiency of water application, in consequence of a better control of the applied depth,

minor lost by evaporation and practically none lost due to percolation and run-off (RESENDE,

2003).

Subsurface drip irrigation compared to superficial conventional system presentsadditional advantages, as applying water and nutritious directly in the root area, reducing

evaporation losses, avoiding mechanical damages during the cultivation operations and rodents

attack, providing larger growth of the root system, reducing moisture at soil surface and

minimizing the incidence of diseases (CAMP, 1998; SILVA et al., 1999).

According to Phene & Ruskin (1995), subsurface irrigation system increases the

application efficiency once the volume of water stored is larger than superficial systems.

Subsurface drip irrigation systems have been compared to other overhead irrigations for

different crops and in all cases the production is same or superior (CAMP, 1998).

Subsurface drip irrigation is subject to most of the problems of the traditional superficial

system, adding the obstruction of emitters from suctioning of soil particles and penetration of

root systems from crops and weeds, causing increment of localized head loss in the lateral lines

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(roots inside lines), harming lateral line flow rate downstream to the intrusion point (Ruskin

1992; FARIA, 2002).

Vacuum events in the irrigation parcels are related to the closure of the hydraulic valves

in steep slopes topographic conditions, when water inside lateral lines is drained toward of lower

areas, generating a negative pressure inside the hydraulic net that promotes suction of soil

particles under saturated conditions in lateral lines at higher elevations (WEATHERHEAD,

2002). Emptying of drip lines can result high values of negative pressures collapsing the

secondary lines (PVC), being indispensable the use of anti-suction valves of double effect at

parcels located in steep slopes inside the irrigation area, in order to prevent vacuum occurrence

in the hydraulic system.

The objective of this work is to evaluate the effect of vacuum occurrence on the hydraulic

performance of 25 commercial emitters, operating under subsurface drip conditions, for two soil

texture (clay and sandy) and four vacuum levels.

Material and Methods

The experiment was carried out at a test bench with 11.0 m long and 4.0 m wide and

1,30 m height, installed under indoor conditions at the Irrigation Laboratory, of the Agricultural

Engineering Department, College of Agriculture "Luiz de Queiroz " ESALQ, University of So

Paulo, Piracicaba-SP, Brazil. (Figure1).

Figure 1 - Illustrative picture of the bench trial, where the experiment was developed

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The application system allowed the recirculation of the applied water in accordance with

the following sequence: reservoir pump drippers gutter reservoir.

The treatments consisted of applying suction levels -10, -15, -20 and -40 kPa in two soil

textures, sandy and clay loam texture in 25 dripper models. The characteristics of the soils

used are described in Table 1. The soils used in the experiment were sieved with mesh

openings of 2 mm, after pre-drying and griding.

Table 1 - Physical characteristics of soils used in the experiment

Soil % clay % silt % sand

Clay 49,34 18,96 31,70

Sandy 20,08 7,99 71,93

Each emitter model was represented by 10 drippers (replications) that were evaluated at

each test carried out. A total number of 260 emitters were monitored during this trial.

Because of emitters tested are commercial products, data and analysis presented here

were coded to avoid any commercial speculation of the results, once there is no standard test

procedure available to this trial condition. The numbers used in the encoding of the models

emitters (1,2,3, .., 26) has no connection with the trade names of products and or the sequence

of emitters in Table 2. Decodification of emitters for academic purposes can be requested to the

correspondent author.

Table 2 - Drips characteristics used in testes

ModelNominal Flow Pressure

FlowL h-1 kpa

Azud 1,4 150 normal

Carbodrip 2,0 150 Self-compensating

Carborundum CD/AC 2,3 150 Self-compensating

Drip In 2,5 150 Self-compensating

Dripnet 1,6 150 Self-compensating

Hydro Drip 2,0 150 normal

Hydro PC 2,0 150 Self-compensating


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Hydro PCND 2,35 150 Self-compensating

Hydrogol 3,0 150 normal

Irridrip Plus 2,5 150 Self-compensating

Irriloc 1,1 150 normal

Naan Paz 2,0 150 Normal

Naan PC 2,1 150 Self-compensating

Naan PC 3,8 150 Self-compensating

Naan Tif 1,6 150 Normal

Petrodrip 1,5 150 normal

Ram 2,3 150 Self-compensating

Ram 2,3 150 Self-compensating

Super Typhoon 2,0 150 normal

Tiran 2,1 150 normal

Twin Plus 1,8 150 Self-compensating

Uniran 1,6 150 Self-compensating

Vip Line 3,6 150 Self-compensating

Emitters were surrounded by soil particles in this experiment using an artificial procedure:

lines were not buried in the soil; lines were hanged in the air inside the test bench and emitters

outlet were involved by small amounts of soil surrounded by porous synthetic textile (Bedin),

like a air layering design.

Emitters used in the test were running previously a complex sequential test procedure for

developing drip irrigation standard procedures in Brazil (previous results are not showed in this

article). The previously sequential procedure is described as following:

a) Application of CaCO3 and MgCO3 solution (ISL: 1,439 - 100% maximum solubility with

pH equal to 8.84) for 12 hours with the rest of the product inside driplines for 36 h,

totaling 360 h of application. The water used in this test was prepared by addition of

CaCO3 and MgCO3,in order to obtained a Ca: Mg rate of 1,7:1 (prevailing conditions in

the major sources of underground water available for irrigation in the Northeast Brazil).

b) After this test, drippers were exposed to a 12 h application of nitric acid (pH in the range

of 2,0 to 3,0) with the rest of the product inside the line for 12 h to verify the flow rate

recovery

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c) Performed the cleaning procedure described above, a new treatment, using 75% of the

solubility of CaSO4 was imposed.

d) After this test, driplines rested for 58 days and from this point, it started the

implementation of CO2 . This was applied for 8 hours continuously without a break of the

solutions on the lines of drip and was reading the manual flow gives final application.

The limit of the gas was injected to maintain the pH between 5,0-6,5 being monitored to

the same 30 minutes each (pH meter).

e) Treatment using water with high organic load (green algae). The procedure for

application of this water was as follows: 12 h on + 36 h off. The system worked for 15

weeks totalizing 528 hours, whereas at the end of the last application was the recovery

of the flow of the chemical treatment used drips with sodium hypochlorite (150 ppm free

chlorine) in 4 applications of 15 minutes with rest of the chlorine solution in the interior of

the line for an hour and subsequent implementation of clean water for 24 hours to wash

the inside of the same at a pressure of 150 kPa.

f) After the previous test the applications of nitric acid at pH 2.0 for 48 continuous hours,

followed by a cleaning of drips with the end of each line open side to facilitate the

removal of fouling.

The main reason for not using new emitters in this test was the impossibility of ready

access to all 26 emitter models to run this trial (some models are not sold in the Brazilian

irrigation market) and because after running the preliminary procedures described above, it was

noticed that almost all emitters were in good conditions (CV < 5 %).

The experiment consisted in the application of 4 vacuum levels -10, -15, -20 and -40

kPa for two soil textures (sandy and clay) for the selected 26 emitters. Before each vacuum

application, the irrigation system was activated for a period of 30 minutes, enough to cause

saturation of the soil volumes; after that, each dripline was connected to a electric vacuum

pump for 5 minutes for each vacuum level described above. After three days of the vacuum

application, the flow rate of each emitter was measured by weighing the volume collected during

5 minutes on a certified scale (0.01g).

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Figure 2 -Driplines hanging inside the test bench and emitters involved by small amounts

of soil surrounded by porous synthetic textile (Bedin).

The pump system used in the trials was composed of a small centrifugal pump. Drip

lines were joined at a manifold using PVC connections and the water flow an each line was

controlled by individual registers. The operation of the experiment was carried out manually,

following strictly the ON / OFF hours of water application scheduled. At the entrance of each

manifold section it was installed an analogical pressure gauge (0 - 700 kPa), allowing at each

flow rate measurement, pressure to be controlled.

The procedure for measuring individual emitters flow rate was the pressurization of the

system at 150 kPa, positioning of containers (1 liter) under respective drippers with a lag of 5

seconds, sequential removal of the containers after 5 minutes, weighing of containers and

tabulation of data.

The gravimetric method was used for determining the water volume collected from each

emitter tested. Flow rate values were expressed in L h-1. It was used a certified precision scale

(OHAUS) with accuracy of 0.01 g. Flow rate readings of drip lines were conducted with potable

water.

After data tabulation it was calculated flow rate, coefficient of variation and distribution

uniformity using equations 1, 2 and 3.

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601000t

Pq

(1) 100

q

sCVq

(2) 100

%25

q

qUD

(3)

P weight of collected water, g;

T collecting time, min;

q emitters flow rate, l h-1;

CVq flow rate variation coefficient, %;

s standard deviation of emitter discharge, l h-1;

UD uniformity distribution coefficient, %

%25q average flow rate of of the smallest values; l h -1;

q average flow rate of emitter, l h-1.

The empirical distribution was used to calculate the percentage of emitters for different

ranges of flow rate reduction. It was adopted the random block experimental delineation, test

"F" for the analysis of variance and Tuckey test (5%), for average comparison and regression

analysis.

Results and Discussion

The 25 emitters models were separated in four groups according to the flow rate range

that operate according to the Table 3.

Table 3 Classification of the emitters models according to the flow rate.

Group 1: Flow rate from 1,0 at 1,6 Emitters: 23 - 19 - 21 - 1 - 25 - 26

Group 2: Flow rate from 1,8 at 2,05 Emitters: 15 - 2 - 8 - 12 - 13 - 18 - 14

Group 3: Flow rate from 2,1 at 2,35 Emitters: 3 - 9 - 10 - 22 - 6 - 7 - 11

Group 4: Flow rate from 2,5 at 4,0 Emitters: 17 - 20 - 5 - 16 - 4

Table 4 shows the average flow rate values of emitters, submitted to different vacuum

levels and soil textures; Tukey test (5%) interpretation it also presented.

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Table 4a - Average flow rate of emitters (L h-1

) subject to various vacuum levels and soil textures (Sandy / Clay): Emitters groups 1 and 2.

Test

Vaccum

(kPa)

Emitters: Group 1

1 19 21 23 25 26

Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy Clay

1 0* 0.89bA

0.88bcA

1.70aA

1.70aA

1.45bA

1.49aA

1.21aA

1.13aA

1.62aA

1.52aA

1.52aA

1.50aA

2 0** 1.09B

1.27A

1.62A

1.39B

1.86A

1.60B

0.78bA

0.92A

1.68A

1.58A

1.42A

1.49A

3 10 0.75cA

0.74cA

1.37bA

1.54A

1.91A

1.42B

1.25A

1.16A

1.56A

1.37aA

1.39A

1.42A

4 15 0.80bcA

0.84bcA

1.04cA

1.23bA

1.61bA

1.36B

1.04A

1.02A

1.49A

1.20bA

1.50A

1.39A

5 20 0.89bA

0.97bA

1.09bB

1.38A

1.61bA

1.40B

1.12A

1.04A

1.65A

1.14bB

1.36A

1.29A

6 40 0.78bcA

0.60dB

1.20bA

1.33aA

1.60bA

0.91bB

0.74bA

0.46bB

1.44aA

1.62aA

1.31aA

1.35A

TestVaccum(kPa)

Emitters: Group 2

2 8 12 13 14 15 18

Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy C

1 0* 1.79abA

1.63B

1.88cA

1.84cA

1.42cA

2.08bB

2.08bA

1.63cB

2.13A

1.92bB

1.68bA

1.76A

2.11A

1.

2 0** 2.00aA

1.58B

1.85cB

2.08bA

1.95bA

1.99bA

2.35A

2.24A

2.28A

2.38A

2.11A

1.55B

1.85A

1.

3 -10 1.80abA

1.37bB

2.54bA

1.94bcB

1.87bA

1.84bcA

2.35A

1.68cB

2.09A

1.67cB

2.07A

1.60B

1.88A

1.

4 -15 1.84A

1.37bB

3.10A

2.84B

1.92bA 1.71cA

2.32A

1.74cB

2.03bA

1.62cB

1.65bA

1.67A

1.58bA

1.5 -20 1.91

A1.48

B1.85

cB2.10

bA2.27

A1.98

bB2.27

A1.98

bB1.84

bA1.90

bA1.32

cB1.59

A1.79

bA1.

6 -40 1.70bA

1.37bB

1.62dA

1.69cA

1.79bB

2.88aA

2.18bA

2.12aA

1.43cB

2.15aA

1.23cB

1.57aA

1.67bA

0.

0* No vacuum (0 kPa) and flow rate measured without soil surrounding emitters (before starting the trial);

0** No vacuum (0 kPa) and flow rate measured with soil surrounding emitter (just after installation of the trial).

1* Average with the same lowercase letter for each column indicates no significant difference by Tukey test (5%).

2*Average with the same capital letter between columns (Sandy / Clay) for each model for each test number, are notsignificantly different (5%) by Tukey test.

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Table 4b Average flow rate of emitters (L h-1

) subject to various vacuum levels and soil textures (Sandy / Clay): Emitters groups 3 and 4.

est Vaccum (kPa)

Emitters: Group 3

3 6 7 9 10 11 22

Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy C

1 0* 2.14A

2.12A

2.37B

2.61A

2.09bA

2.16A

1.62bA

1.77cA

2.03bA

2.08A

1.65A

1.74abA

2.18A

2.

2 0** 2.15A

2.16A

2.25A

2.00cB

2.11bA

2.05A

2.06B

2.40A

2.21A

2.28A

1.74A

1.83A

1.80bA

2.

3 -10 1.90bB

2.04A

2.10abB

2.31bA

2.61A

1.32bB

2.24A

1.98bB

2.37A

2.09B

1.47A

1.56bA

1.99A

2.1

4 -15 2.19A

1.92bB

1.75cA

1.88cA

2.69A

2.01B

1.40cB

2.26A

1.99cA

1.90bA

1.29bB

1.97A

2.06B

2.

5 -20 1.88bA

1.66cB

1.94bB

2.27bA

2.22bA

1.94cA

1.78bB

2.01bA

1.77cA

1.82bA

1.38abA

1.32cA

1.73bB

2.1

6 -40 1.64cA

1.59cA

1.83bcB

2.07cA

0.92cB

1.94cA

1.39cB

1.92bA

1.85cA

1.73cA

1.16bB

1.46bcA

1.55cB

2.

est Vaccum (kPa)

Emitters: Group 4

4 5 16 17 20

Sandy Clay Sandy Clay Sandy Clay Sandy Clay Sandy Clay

1 0* 2.57cA

1.84dB

2.32bA

2.30abA

2.49A

2.41A

2.52A

2.55A

2.25A

2.23bA

2 0** 3.88bA

3.92A

2.58A

2.41abB

1.54cA

1.71cA

2.46A

2.29bA

2.22A

2.27A

3 -10 3.83bB

4.01A

2.63A

2.61A

1.98bA

2.05abA

2.55B

2.79A

2.35B

2.58A4 -15 4.01

A3.86

bB1.70

cB1.99

cA1.66

cB2.17

abA2.07

bB2.51

abA2.43

A2.44

A

5 -20 3.70bA

3.53cB

1.90bcB

2.26bA

2.07bA

2.28A

2.51A

2.44bA

2.33A

2.47A

6 -40 3.73bB

4.04aA

2.11bB

2.53aA

2.10bA

1.91bA

2.21bB

2.48bA

2.32aA

2.36A

0* No vacuum (0 kPa) and flow rate measured without soil surrounding emitters (before starting the trial);

0** No vacuum (0 kPa) and flow rate measured with soil surrounding emitter (just after installation of the trial).

1* Average with the same lowercase letter for each column indicates no significant difference by Tukey test (5%).

2*Average with the same capital letter between columns (Sandy / Clay) for each model for each test number, are notsignificantly different by Tukey test (5%).

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It is possible to notice in Tables 4a and 4b that emitters 3, 7, 8 and 10 were the ones that

presented the greatest reductions in flow rate for vacuum tension of - 40 kPa for both soil.

Emitters 20 and 26 does not presented any flow rate disturbance for the application of different

vacuum levels for the two soil textures studied. Emitter 25 also presented a good uniformity of

flow, differing statistically only for the clay soil at vacuum levels of -15 and -20 kPa. For emitters

2, 18 and 21, non-compensating drippers, soil texture influenced on the flow rate of emitters,

confirming the initial hypothesis that different soil particles sizes can disturb flow rate in different

magnitude.

The highest increase in the original flow rate (for both soil textures) was observed for the

model 8 after the application of -15 kPa vacuum level.

Figures 3 to 6 show the flow rate average values (L h -1), quantified by measuring

individual flow for different emitter models analyzed in this test. ot being presented, while the

data concerning the background of drips to facilitate interpreting the behavior of the flow.

0.0

0.5

1.0

1.5

2.0

0 1 2 3 4 5 6

evaluations

qm

(lh-1)

23 19 21 1 25 26

0.0

0.5

1.0

1.5

2.0

0 1 2 3 4 5 6

evaluations

qm

lh-1)

23 19 21 1 25 26

Sandy Clay

Figure 3Flow rate average values (L h-1

) for Group 1 emitters.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5 6

evaluations

qm

(lh-1)

15 2 8 12 13 18 14

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5 6

evaluations

qm

(lh-1)

15 2 8 12 13 18 14

Sandy Clay

Figure 4 - Flow rate average values (L h-1


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0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5 6

evaluations

qm

(lh-1)

3 9 10 22 6 7 11

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5 6

evaluations

qm

(lh-1)

3 9 10 22 6 7 11

Sandy Clay

Figure 5 - Flow rate average values (L h-1) for Group 3 emitters.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6

evaluations

qm

(lh-1)

17 20 5 16 4

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6

evaluations

qm

(lh-1)

17 20 5 16 4

Sandy Clay

Figure 6 - Flow rate average values (L h-1


Figures 7 through 10 show the values of the coefficient of variation (flow rate) for

emitters evaluated in each group flow.

0

20

40

60

80

100

120

0 1 2 3 4 5 6

evaluations

CV

(%)

23 19 21 1 25 26

0

20

40

60

80

100

120

0 1 2 3 4 5 6

evaluations

CV

(%)

23 19 21 1 25 26

Sandy Clay

Figure 7

Flow rate coefficient of variation for Group 1 emitters.

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0

20

40

60

80

100

0 1 2 3 4 5 6

evaluations

CV

(%)

15 2 8 12 13 18 14

0

20

40

60

80

100

0 1 2 3 4 5 6

evaluations

CV

(%)

15 2 8 12 13 18 14

Sandy Clay

Figure 8 - Flow rate coefficient of variation for Group 2 emitters.

0

20

40

60

80

100

0 1 2 3 4 5 6

evaluations

CV

(%)

15 2 8 12 13 18 14

0

20

40

60

80

100

0 1 2 3 4 5 6

evaluations

CV

(%)

15 2 8 12 13 18 14

Sandy Clay


0

20

40

60

80

100

0 1 2 3 4 5 6

evaluations

CV

(%)

17 20 5 16 4

0

20

40

60

80

100

0 1 2 3 4 5 6

evaluations

CV

(%)

17 20 5 16 4

Sandy Clay


Figures 11 to 14 present values of uniformity distribution coefficient (UD) for all model dripsevaluated according to emitters flow rate Groups.

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0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

avaliaes

UD(%)

23 19 21 1 25 26

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

avaliaes

UD(%)

23 19 21 1 25 26

Sandy Clay

Figure 11 - Uniformity distribution coefficient for Group 1 emitters.

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

avaliaes

UD(%)

15 2 8 12 13 18 14

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

avaliaes

UD(%)

15 2 8 12 13 18 14

Sandy Clay


0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

avaliaes

UD(%)

3 9 10 22 6 7 11

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

avaliaes

UD(%)

3 9 10 22 6 7 11

Sandy Clay


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0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

avaliaes

UD(%)

17 20 5 16 4

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

avaliaes

UD(%)

17 20 5 16 4

Sandy Clay


It is notice a good performance for almost all emitters (flow rate coefficient of variation

CV < 5 %), at the beginning of the experiment, before starting the imposition of vacuum

treatments.

Higher values of CV were found with the application of the tension of -40kPa for both

soils. Group 3 of emitters was the most sensitive.

In Figure 8 it is presented the CV graphs for Group 2 emitters. It was observed that

emitters performance for different soils was differentiated: soil texture influences flow rate

disturbance under vacuum .

Self-compensating models 8 and 15 (Group 2) were influenced by sandy soil. Emitter 8

presented a flow rate increase in response to the application of vacuum levels -10 and -15 kPa

for the clay soil, possibly due to the positioning of soil particles on the settlement border of the

flexible membrane (pressure compensating mechanism). For higher levels of vacuum (-20 to -

40 kPa) it was observed a flow rate reduction.

Emitter model 12 (Group 2) presented a flow rate increase for sandy soil in proportion to

the vacuum level applied. For the clay soil, flow rate disturbance occurred only for vacuum level

of -40 kPa.

Figure 9 shows the graphs of CV for Group 3. In general, for the sandy soil, increasing

the vacuum level resulted in higher CV values for emitter models in this group.

The largest increase in flow rate, for both soils, was observed for model 8 after theapplication of the weak vacuum of -15 kPa.

For emitter models 5, 16, 17 and 20, the effect of the vacuum levels of -10, -15, -20 and -

40 kPa was of small magnitude for the clay soil. For the sandy soil, model 16 presented the

greatest reduction in flow when subjected to vacuum levels of -10 and -15 kPa, with a reduction

in the vacuum of 20 and 33% respectively.

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Resende & Coelho (2003) studying the effect of 5 vacuum levels in the flow rated of

underground emitters (SDI), detected higher levels of flow reduction for lower levels of flow (-13

and -20kPa). It seems that at higher levels of suction (-53 and-80kPa), soil moisture

immediately adjacent to the water outlet decreased rapidly, forming a rigid porous seal,

preventing the suction of the soil paste more distant from the hole, which reduces the total

amount of soil particles suctioned.

Emitter model 4 presented a flow rate increase with the application of vacuum. The

highest percentage of emitters clogged, was achieved by the emitter 7, with gradual increase of

the clogging from the tension of -15 kPa to -40 kPa (Table 4b). Figure 15 shows the percentage

of the total range drips by reducing flow, using the tensions of 0 and 40 kPa (sandy texture).

0 kPa

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100

Reduo de vazo (%)

Totaldegotejadores(%)

40 kPa

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100

Reduo de vazo (%)

Totaldegotejadores(%)

Figure 15Percent distribution of drippers (n = 15) by flow rate range reduction for emitter

7 (sandy soil) to vacuum levels of 0 and - 40 kPa.

Conclusions

The obtained results in this trial led to the following conclusions:

a. The performance of drip emitters (SDI) under vacuum conditions depends on soil

texture;

b. For the majority of emitters analyzed, vacuum level of -40 kPa caused higher levels of

flow rate disturbance for both soils.

c. The higher increases in the flow rate (for both soils) was observed after the application

of vacuum level of -10 kPa, for emitter 9 and vacuum level 15 kPa for emitter model 8.

d. The proposal methodology could be refined to become an ASABE standard procedure,

in order to help SDI farmers to run lower risks in the field.

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Acknowledgment

These writers are grateful to the following Brazilian Institutions for their financial support:

Federal Department of Science and Technology (MCT), National Scientific and Technological

Development Council (CNPq), Sao Paulo State Scientific Foundation (FAPESP) and National

Institute of Science and Technology in Irrigation Engineering (INCTEI / ESALQ - USP).

References

CAMP, C.R. Subsurface drip irrigation: a review. Transactions of the ASAE, v. 41, n. 5, p.1353-1367, 1998.

DALRI, A. B.; CRUZ, R. L. Efeito da freqncia de irrigao subsuperficial por gotejamento nodesenvovimento da cana-de-acar (Saccharum spp.). Irriga, Botucatu, v. 7, n. 1, 2002.

FARIA, L. F. Variao de vazo de gotejadores enterrados na irrigao de citros e caf.2002,87 p. Tese (Doutorado em Agronomia). Piracicaba: ESALQ/USP, 2002.

GOMES, E. P.; SOUSA, A. P. Produtividade da alface ( lactuca sativa L.) em funo dos valoresde lminas de gua aplicados por gotejamento superficial e subsuperficial. Irriga, Botucatu, v. 7,n. 1, 2002.

PHENE, C.J.; RUSKIN, R. Potential of surface drip irrigation for management of nitrate inwasterwater. In: INTERNATIONAL MICROIRRIGATION CONGRESS, 5, 1995, Orlando,Proceeding St Joseph: American Society of Agricultural Engineers. 1995.p.155-167.

RUSKIN, R. Reclaimed water and subsurface irrigation. St. Joseph: ASAE, 1992. 12p. (ASAE.Paper, 922578).

SILVA, W.L.C.; GIORDANO, L.B.; MAROUELLI, W.A.; FONTES, R.R.; GORNAT, B. Responseof six processing tomatoes cultivars to subsurface drip fertirrigation. Acta Horticulturae, n. 487,p. 569-573, 1999.

RESENDE, R. S Intruso radicular e efeito de vcuo em gotejamento enterrado na irrigao decana-de-acar. 2003, 124 p. Tese (Doutorado em Agronomia). Piracicaba: ESALQ/USP, 2003.

WEATHERHEARD, K. PC drip tube and vacuums.http://www.microirrigationforum.com/new/archives/pvvac.html (17 out 2007)

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