PLANNING PHASE

“ A row crop drip system does not make a farming operation good. On the contrary, one needs to START with a farming operation and then adopt row crop drip irrigation and properly adjust farming practices ( and implements) around the new irrigation methods to ensure success.” - ITRC

Planning and Design considerations Type of system Water quality/quantity Clogging/Filter system Fertilizing/Chemical injection Soil moisture distribution Layout/Emitter application/Germination Distribution lines/zones Miscellaneous control devices Costs Maintenance Automation

Type of System

Max Slope

Max soil intake rate (in/hr)

Shape of field

Adaptable to Sown, drilled, sodded crops

Labor (hr/ac)

Cost ($/ac)

Orchards/vineyards

Row crops

Drip

Point-source

No limit

Any Any Yes No No .10 1000-1800

Line-source No limit

Any Any Yes* Yes No .10 1000-1800

Subsurface 5 1.5 Any Yes* Yes Yes .10 1000-1800

Bubbler 5 3 Any Yes No No .10 800-1000

Spray No limit

any any Yes No No** .10 1000-1800* Can be made to work** Will work for low cover crops

Water qualityWater quality is usually the most

important consideration when determining whether a micro irrigation system is physically feasible.

PHYSICAL FACTORS(Suspended solids)

CHEMICAL FACTORS(Precipitates & others)

BIOLOGICAL FACTORS

(Bacterial growth)Inorganic particles Sand Silt Clay Plastic Metal

Calcium &/or magnesium carbonates

Calcium sulfateHeavy metals Hydroxides Carbonates Silicates Sulfates

Filaments

Organic Particles(Aquatic organisms) Zooplankton Snail Fish

Oil and other lubricants Slimes

Organic Particles(Non-aquatic

organisms) Insect larva Ant Fish Spider

Fertilizers Phosphate Aqueous Ammonia Iron, copper, zinc Manganese

Microbial ochres Iron Sulfur Manganese

TYPE OF FACTOR MINOR MODERATE SEVERE

Physical Suspended solidsa 50 50-100 >100

Chemical pH Dissolved solidsa

Manganesea

Total irona

Hydrogen sulfidea

Carbonate+bicarbonatea

7.05000.10.20.250.0

7.0-8.0500-2,000

0.1-1.50.2-1.50.2-2.050-100

>8.0>2000>1.5>1.5>2.0>100

Biological Bacterial

populationb10,000 10,000-

50,000>50,000

Water quantityCrop ETMAD/stress – Root zone Salt Tolerance – leaching

requirementFrost controlGermination

System capacity.

◦….shall be adequate to meet the intended water demands during the peak use period

◦….shall include an allowance for reasonable water

losses (evaporation, runoff, and deep percolation) during application periods.

◦…shall have the capacity to apply a specified amount

of water to the design area within the net operation period.

System capacity Continued

◦should have a minimum design capacity sufficient to deliver the peak daily irrigation water requirements in 90% of the time available, but not to exceed 22 hours of operation per day.

ET for TreesBig tress need more water than small

trees

Mature tress on close spacing need same amount of water per acre as large trees on wider spacing

If there is several blocks of the same type of tree using the same flow rate per tree, but on different spacing. Each block needs to be design for a different number of hours per week.

Cover crop come in all sizes shapes and types and may have an additional ET component – upwards 15 - 20%

For cover crop grown all season long, the micro/drip system needs to be a microspray that wets a large percentage of the surface area

To crop or not to cover crop?

Drip systems – ◦the ground surface is moist almost

all the time which increase evaporation

◦The small frequent irrigations contribute to little or no plant stress

These two factors may increase the ET by as much 15% above published rates.

Considerations on Published ETLoam or heavier textured soil with at least 60%

wetted volume◦ Design for the peak month of a normal year

Situations of low soil water capacity◦ Design flow rates may need to be 10 -15% higher

Low water holding capacities are caused by:◦ Small percentage wetted area◦ Sand or rocky soils◦ Shallow soils◦ Shallow root systems (e.g. avocadoes or some produce

crops)

Transpiration ratios - Unavoidable losses

Table 7-15. Seasonal transpiration ratios for arid and humid regions with various soil textures and rooting depths.

Climate zone and root depth TR1 for indicated soil texture

Very course

Coarse Medium Fine

Arid <2.5 ft (.75 m) 2.5 to 5.0 ft (.67-1.5 m) >5.0 ft (1.5 m)

1.151.101.05

1.101.101.05

1.051.051.00

1.051.001.00

Humid <2.5 ft (.75 m) 2.5 to 5.0 ft (.67-1.5 m) >5.0 ft (1.5 m)

1.351.251.20

1.251.201.10

1.151.101.05

1.101.051.00

1Seasonal transpiration ratios (TR) are for drip emitters. For spray emitters add 0.05 to TR in humid climates and 0.10 in arid climates

Designing for less than Peak ETRegulated Deficit Irrigation (RDI)

◦Wine grapes (increase sugars)◦Alfalfa seed◦Almonds (start of hull split)◦Tomatoes (increase solids)◦Regulate early growth of trees and

vines ( trying to avoid spindly mature trees)

Auxiliary needsLeachingFrost protection

Leaching Process of applying irrigation water in

excess of soil moisture depletion to flush salt from the root zone. Excess water percolates below the root zone carrying the salt with it.

Types of leaching Maintenance - maintain soil salinity at a

more or less constant level over time Reclamation - periodic leaching to reduce

accumulated salts in the soil to an acceptable level

0 1 2 3 4 5 6 70.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

Salinity of Applied Water (dS/m)

Crop

Sal

t To

lera

nce

Leac

hing

Val

ue (

dS/m

)

LR=0.05

LR=0.10

LR=0.15

LR=0.20

LR=0.30

Frost control

Crop Data Summary Basic Crop Data Crop to be Irrigated

Rooting Depth (feet)

Plant Spacing

(feet)

Row Spacing (inches)

Threshold Salinity1

(mmhos/cm)

Net Water Requirement

(inches/yr)

Peak Daily ETc

(inches /day)

1 Threshold salinity, ECe(ct), is the maximum mean root zone soil salinity at which yield reductions will not occur.

Computed Qmax = 23 x ETmax = 23 x _____ in/day = _______ gpm/acre

where: Qmax = max. water requirement, gpm/day , and ETmax = highest peak daily ETc, inches/day, from above. (assumes a maximum operating period of 22 hours/day and a design efficiency of 90%)

Soils Data Basic Soil Data Soil Type/Name

Dominant

Texture

Design Soil Intake Rate

(Inches/hour)

Available Water Holding Capacity

(inches/foot)

MAD1

(%)

ECe(ave)

2 (mmhos/cm)

1 MAD is Management Allowed Deficit 2 ECe(ave) is Average Soil Extract Electrical Conductivity

WaterIrrigation Water Electrical Conductivity, ECw ______ mmhos/cm. Compute Leaching Fraction, LF, where:

_______________

__________

1794.01794.00417.30417.3

)(

LFUse

ECEC

LF

wcte

Attach Supporting Documentation that includes: (check all that apply) Method for determining net annual water requirement and peak daily ETc

Rationale for selected Management Allowed Deficit (MAD)

Rationale for selected leaching fraction

Laboratory analysis of irrigation water with suitability assessment for drip irrigation including analysis to determine filtration requirements

Proposed chemical treatments of irrigation water

Filter systemsAll water must be screened and filtered

to some degree before use in a micro irrigation system.

Clogging of emitters is the most difficult problem encountered in micro systems

The type of filter depends on the micro system and the particulate matter in the water supply

Filters

InjectionAll systems should be designed with

injection in mind. Chemical injection is essential for long-term sustainability of drip irrigation.

Reasons for chemical injection◦Water treatment◦Emitter plugging◦Enhancing water infiltration into soil◦Fertigation◦Pesticides◦Soil pH modification

Soil Moisture distributionMicro irrigation normally wets

only a part of the potential plant root zone in a soil.

Distribution and extent of soil wetting should be a major consideration in the design of any micro irrigation system.

The volume of soil wetted is a function of the emitter type, emitter discharge, distance between emitters, time of set, and soil texture.◦Fine textured soils have low absorption rates

but the water will move farther from the emitters and this reduces the number of emitters required

◦Coarse texture or high intake soils will require more emitter to obtain the necessary wet area and higher discharge emitters.

For agricultural crops, typically half to three-fourths of the potential root development should be wetted

Slope and topography

8200

8200

8100

8100

8000

8000

7900

7900

7800

7800

7700

7700

7600

7600

7500

7500

7400

7400

7300

7300

7200

7200

7100

7100

7000

7000

6900

6900

6800

6800

6700

6700

62006200

61006100

60006000

59005900

58005800

57005700

56005600

55005500

54005400

53005300

52005200

SlopeSlope less than 5% any type of

micro system may be used5% or Greater subsurface and

basin are generally not suitedLay lateral along contour to

reduce pressure variationSteep slopes may require

pressure regulators at the head of each lateral

Type of System

Max Slope

Max soil intake rate (in/hr)

Shape of field

Adaptable to Sown, drilled, sodded crops

Labor (hr/ac)

Cost ($/ac)

Orchards/vineyards

Row crops

DripPoint-source

No limit

Any Any Yes No No .10 1000-1800

Line-source No limit

Any Any Yes* Yes No .10 1000-1800

Subsurface 5 1.5 Any Yes* Yes Yes .10 1000-1800

Bubbler 5 3 Any Yes No No .10 800-1000

Spray No limit

any any Yes No No .10 1000-1800

* Can be made to work

Salinity

Salts tend to concentrate at the soil surface and below the surface at the perimeter of the soil volume wetted by each emitter.

Hose and seed placement

Germination

Soil Characteristics such as texture, structure, and salinity determine upward movement.◦ Shallow placement (8-10”) course soils work better◦ Deep placement of hose (14-24”) fine texture soils works

better◦ Beds need to be firm

sprinkler or furrow irrigation may be needed to germinate field and vegetable crops.

Layout continuedCrop row spacing and orientationBed spacing raised or ground

levelPlant spacing – row or individual

plantsSoil texture and stratification

Distribution/ZonesWhere is the water coming from How is the water delivered to

each manifoldHow many zonesHow many zones can be water

concurrently

EconomicsThe decision to purchase an

irrigation system is often based on an inadequate economic analysis.

The management ability and performance of the operator are probably the most important factors in determining the feasibility of irrigation or making a change in an existing irrigation system.

If the water user is an average surface irrigation system manager, chances are he/she will be an average sprinkler or micro irrigation system manager.

Automated systems typically require higher levels of management

Each NRCS employee should be aware of the economics of irrigating in the general area and be familiar with the procedure used in analyzing data to determine feasibility.