SUBSURFACE DRIP IRRIGATIONFOR SUGARCANE

What is subsurface drip Irrigation (SDI)?

ASAE (S526.1) defines subsurface drip irrigation as “application of water below the soil surface through emitters, with discharge rates generally in the same range as drip irrigation.”

SDI have been in use for 15-20 years. It began in Hawaii for Sugarcane. South Africa, Swaziland, and Zimbabwe have been covering large areas for the last 10 years. Some 30 crops- Vegetables, Sugarcane, Corn, Wheat – are irrigated by SDI.

Basic requirements

n Placement of drip laterals below specified depths – at the normal tillage depth or any suitable depth that would en-sure repeated use of the laterals for many years.

n Placement of drip laterals is either manual or with the aid of installation equipment.

Why we need subsurface installation of laterals?

n To facilitate the use of Mechanical cane harvesters and still achieve a high irrigation efficiency. Harvester blades will not damage the laterals buried subterranean.

n To avoid damage to the drip laterals during harvest (even in manual harvest conditions).

n To facilitate the use of drip laterals for many seasons (7-10 years) even in conditions of heavy lodging of cane.

Irrigation of sugarcane

Installation of subsurface drip line

While installing SDI, there are some factors those need to be considered.

1. Depth of placement of Drip line. n Research reports are limited but are of great value for

any field operation. n Drip lines have been placed at 30 cm below the surface

(Huang et al. 1982) in Taiwan; at 10 cm below the surface by Moore and Fitschen, 1990 in Hawaii and Sirode et al. 2004 in Thailand.

n The main factors are soil type and volume of maximum root spread of cane. The possibility of cane root intrusion into the drip line or roots coiling over the drip line are main threats those need to be managed for the success of SDI performance.

n It is recommended to place the drip line at 10-15 cm below the surface. The two rows of cane setts are to be placed on either side of the drip line at 5-7 cm below the drip line (fig 1). This way the wetting area will fully encompass the root system and the drip line is protected from root intrusion to the extend possible.

Fig 1. One drip line for two lines of cane setts in a row at 4’ or 5’ placed at 10 cm depth

Drip Line

Placement of Drip Lateral in SDI

7cm

15cm

25cm 25cm95cm120cm

Two Rows of Cane Sett

One Drip Line for 2 Rows of Cane Pair to Pair At 4’ (120cm)

2. Distance between drip lines

n Distance between drip lines depend on the spacing of cane rows which is to suit the spacing of the cutting blade of the harvester.

n A row to row spacing of 120 cm (4’) or 150 cm (5’) are practiced.

n Places where twin rows of cane on each 4 or 5’row is practised we recommend keeping one drip line in the middle of the twin setts (fig 1).

n Where a single line of setts are planted in each row the drip line is placed on one side of the setts (fig 2)

n If mechanical harvesting is not practiced drip lines can be placed in the middle of each pair of paired row planting.

3. Emitter spacing

n Emitter spacing depends on soil texture as is the case with surface drip systems; 20 or 30cm for light / sandy soils, for loamy/ medium soil 40 or 50cm and 60 or 70 cm for Heavy clayey soils.

4. Emitter discharge

n Discharge is chosen based on the infiltration capacity of the soil and the root volume that needs to be wetted.

n 2 or 4 lph emitters are recommended.n 2 LPH for 30 cm to 40 cmn 4 LPH for 50cm to 60cm

INSTALLATION AND MAINTENANCE OF SUBSURFACE DRIP

5. Additional Precautions at the time of SDI installation

n Inclusion of collector pipe at the open end of lateral. A PVC pipe line of suitable pressure rating and diameter is installed in the trench at the open end of laterals and all laterals are connected to this PVC pipeline.

n The trench level of the collector pipe should be deeper than the trench level of the submain (should be 15-20 cm) giving rise to a gradual slope along the lateral lines from submain pipe.

n Both at the submain end and collector pipe end Air cum vacuum breaker (AVBV) along with a flush valve should be provided at each section.

n Provide a pressure check points at each section both at the submain side and collector pipe side.

n As much as commercially possible reduce the area under each section. This would bring in more check points and vacuum break points. Short sections can easily and effectively be flushed also.

n If such sections are not possible divide the sections and provide a flush valve and AVBV assembly at each section. This would help in increasing the velocity of flushing.

n Encourage farmers to obtain water meters for each SDI system.

n In case where long running laterals are essential try using 20 mm lateral.

n Farmer shall be given a chart noting the flow through every section and pressure at various check points.

n If possible farmer shall be supplied with pressure check assembly. These things are necessary to diagnose the system performance.

6. Position of the orifice

n When installing Turbo aqura care should be taken to keep the yellow line and hence the orifices facing above

Irrigation schedule for Sugarcane in SDITable 1. A model irrigation schedule for SDI

S. No. Month Net daily ETP, mm

Daily water requirement,

mm/day

Daily water require-ment @ 90% ef-ficiency, mm/day

Daily WR litre l/ac

Lit/AC

Pumping timemts/section

(1 sect =1 ac)

rounded to nearest

5 minutes

1 JAN 4.74 0.37 0.42 1706 6 5 mts

2 FEB 5.78 0.78 0.86 3512 13 15 mts

3 MAR 6.80 2.04 2.26 9182 34 35 mts

4 APRIL 7.66 4.02 4.47 18099 67 1hr 10mts

5 MAY 7.74 5.26 5.84 23673 88 1.5 hr

6 JUNE 5.60 5.04 5.60 22663 84 1.5 hr

7 JULY 4.67 5.14 5.71 23136 86 1.5 hr

8 AUGUST 5.16 6.19 6.88 27850 103 1hr45 mts

9 SEPT 5.03 5.53 6.15 24897 92 1.5 hr

10 OCT 5.35 4.28 4.75 19263 71 1hr 10mts

11 NOV 4.83 3.62 4.02 16300 60 1hr

12 DEC 4.35 2.35 2.61 10574 39 40 mts

# Sectional area is 1 ac. Design discharge is 4.5 lps.

The irrigation schedule may be changed according to location and different sowing dates based on the pan Evaporation of the Location.

Irrigation schedule to be followed after germination of setts to reach saturation

FERIGATION SCHEDULE FOR SUGARCANE

FERTIGATION IS RECOMMENDED ONCE IN TWO DAYS

S.No Duration in Days

DOSE of UREA once in 2 days

kg/ac

Total UREA Doses

DOSE of MAP once in 2 days kg/ac

Total MAP Doses

DOSE of MOP once in 2 days

kg/ac

Total MOP doses

1 15 to 30 5.14 7 0 0 0.4 7

2 31 to 105 2.75 38 0.74 38 0.4 38

3 106-207 1.44 50 0 0 0.46 50

4 207-255 1.2 25 0 0 1.8 25

5 256-265 0 0 0 0 2.8 5

MAP; Monoammonium phosphate

MOP; Muriate of Potash.

Fertigation

Fertigation should be practiced for high yields and quality. In SDI application of solid fertilizers to the surface soil will be of little use; as the wetting zone is subterranean. Therefore except for initial basal dose of P which gets mixed in the top soil during final ploughing, all subsequent doses have to be injected through the drip system.

Fertigation of sugarcane –plant cane

n 10-15 t of organic manure should be applied at land preparation to the soil

n Fertigation schedule can be modified for each Sugar Factory recommendation as and when required.

n Fertigtation period is from planting to 265 days. Fertigtation is to be done every 2 days.

n The nature of Subsurface drip needs phosphate also in soluble form. Therefore total P is given part as SSP (basal soil application) and rest as MAP thru fertigation.

Fertigation Schedule For Sugarcane

n N and K from conventional sources of urea and white potash.

Fertigation of Sugarcane-Ratoon

n 10-15 t of organic manure to be applied at first earthing- up in each ratoon.

n A 25% increase of fertilizer quantities are generally recommended for the ratoon crops.

n Keeping the same fertigation schedule the fertilizer doses have to be increased accordingly for the ratoon crop.

n In case of multiple ratoons (up to 9) a soil test is recommended after every 3 ratoons and fertilizer quanta needs to be adjusted based on available nutrients in the soil.

Maintenance of Subsurface drip system

Subsurface drip system needs all the maintenance measures as the surface system and more. In SDI adjustments of flow

rate and pressure are not possible after installation.

A. Regular Flushing and cleaning

n Flush submain and lateral open end collector pipe (A PVC pipe to which all lateral free ends are connected ) every 3 days.

n Check the pressure of the system on laterals and tally with the design pressure. Any pressure difference of Inlet & Outlet will indicate filter blockage. Take steps to remedy the situation.

n Clean the screen/disc filter daily before or after the irrigation.

n Backwash sand filter daily depending on the dirt load in the water.

n Drain the sand collector of Hydrocyclone filter daily.n Clean the fertilizer tank of all debris after each event of

fertigation.n Undertake a well planned acid (for hard water irrigation)

and Chlorine (for algal or bacterial slime).

B. Treatment Schedule

n Treat with Chlorine to ward off root intrusion into the tubes Or inject root guard (TRIFLORALIN) in the system.

C. Acid injection to remove salts settled into the system

n Dilute hydrochloric acid/Phosphoric acid are recommended. The procedure is same as for surface drip system. Acid injection for removal of salt from the system should be done as per existing plan.

n Acid & chlorine should not be injected on the same day. n In case of regular fertigation the frequency of acid

injection can be reduced.

D. Chlorine Injection

n Periodical injection of chlorine (50 ppm solution) (using bleaching powder) is recommended for preventing root intrusion. Initially a frequency once in 15 days is recommended. Chlorine concentration is 50 ppm at Ventury and +5 ppm at the emission point.

E. Treflan (Trifloralin) treatment

n If the drip lines are already incorporated with treflan (root guard) no need for injection of the chemical.

n In all cases at least one treatment with treflan is required at the beginning of a new crop (ratoon).

n Treflan is a chemical which will get fixed in soils. In clayey soils the fixation is very rapid. Therefore higher concentration is required for root inhibition to get sufficient free treflan available around the emitting orifice.

n 0.125 ml of Trifluralin (Commercial sample of Treflan contains 477g/l of Trifloralin) per emitter is the required concentration. If there are 3000 emitters are available in an acre then 0.125 x 3000 = 375 ml treflan is require for one injection.

n For sugarcane crop an injection at the end of germination period (3 weeks after first irrigation) and a second at the end of growth or after harvest is recommended.

n Each time inject for short period of 5-10 minutes only.

n Irrigate only after 24 hours of Treflan treatment.

F. What is the remedy if root has intruded into the emitters ?

n If root intrusion has already occurred first inject chlorine at higher concentration; 20 ppm at dripper point.

n Follow this with an injection of Hydrogen peroxide (at the rate of 1 ml for 20 emitters) which will decompose the intruded root mass which was killed by the chlorine.

n Flush the system at higher pressure to get the root debris out of the system.

Benefits of SDI

n SDI will result in a dry soil surface and inhibits weed germination

n Reduces water consumption as evaporation is reduced.n Maintains optimum soil moisture and Nutrients around

the roots. n Creates a low humid environment in the surface and

results in low infection of crop by disease agents.n Practically eradicates all chances for run off.n Avoids soil crusting and surface compaction n Prevents mechanical damage to the lateralsn Saves labour- low incidence of weed; provision for

fertigation

Issues and Precautions

n Difficult to repair damages to lateralsn Accumulation of salinity on the top soil –re-translocation

to deeper depths during rainy periods. n Blocking of flow due to root entanglement –Preventive

measuresn Root intrusion into emitting points- Preventive measures

to be followed

Client Information

Considering the issues and the novelty of the technology in Indian conditions a detailed discussion with the client/user should be done before installing the SDI system.

MAINTENANCE OF SUBSURFACE DRIP DRIP SYSTEM

STAGES OF INSTALLATION AND CROP STAND

Wetting bulb development from Subsurface drip line

Germination Irrigation using Subsurface drip line

Uniform crop stand of cane with SDI

Installation of drip line using the Mechanical Device

Installation of drip line using the Mechanical Device

Drip line excavated after installation

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