PENILAIAN KESESUAIAN LAHAN UNTUK IRIGASI

PENILAIAN KESESUAIAN LAHAN

UNTUK

IRIGASI

EVALUASI LAHAN UNTUK IRIGASI

Di daerah iklim arid dan semi-arid, di daerah penelitian, menurut hasil klasifikasi iklim, metode yg paling relevan

untuk memperbaiki produksi pertanian adalah “IRIGASI”.

To decide where and how to irrigate, natural conditions, available types of crops and technology, previous

experience, costs and benefit analysis, should be considered.

Untuk meminimumkan dampak negatif akibat praktek irigasi, seperti erosi tanah dan salinisasi, maka diperlukan

sistem evaluasi untuk tujuan irigasi.

Sumber: http://www.iao.florence.it/training/geomatics/BenSlimane/Marocco21_4_2_3.htm

LAHAN IRIGASI

Irigasi merupakan upaya yang dilakukan manusia untuk mengairi lahan pertanian.

Irigasi Permukaan merupakan sistem irigasi yang menyadap air langsung di sungai melalui bangunan bendung maupun

melalui bangunan pengambilan bebas (free intake) kemudian air irigasi dialirkan secara gravitasi melalui saluran

sampai ke lahan pertanian. Dalam hal ini dikenal saluran primer, sekunder, dan tersier.

Pengaturan air ini dilakukan dengan pintu air.

Prosesnya adalah gravitasi, tanah yang tinggi akan mendapat air lebih dulu.

Sumber: https://id.wikipedia.org/wiki/Irigasi

LAHAN IRIGASI

Di lahan kering, air sangat langka dan pemanfaatannya harus efisien. Jumlah air irigasi yang diberikan ditetapkan

berdasarkan kebutuhan tanaman, kemampuan tanah memegang air, serta sarana irigasi yang tersedia.

Ada beberapa sistem irigasi untuk tanah kering, yaitu:

(1) irigasi tetes (drip irrigation),(2) irigasi curah (sprinkler irrigation),(3) irigasi saluran terbuka (open ditch irrigation), dan(4) irigasi bawah permukaan (subsurface irrigation).

Sumber:

LAHAN IRIGASI

Irigasi adalah suatu rekayasa teknik dalam usaha penyediaan, pengaturan,

pemanfaatan, dan pembuangan air irigasi untuk menunjang pertanian yang jenisnya meliputi irigasi permukaan, irigasi rawa,

irigasi air bawah tanah, irigasi pompa dan irigasi tambak.

(PP Irigasi no 20/2006)

Sumber:

LAHAN IRIGASI

Irigasi adalah usaha penyediaan dan pengaturan

air untuk menunjang pertanian yang jenisnya meliputi irigasi air permukaan,

irigasi air bawah tanah, irigasi pompa dan irigasi rawa

PP 77/2001

Sumber:

EVALUASI LAHAN UNTUK IRIGASIMetodologi

Sistem Parametrik digunakan untuk mengevaluasi kesesuaian lahan bagi penggunaan irigasi (Sys et al., 1991); metode ini didasarkan atas

granulometrical baku dan karakteristik fisika dan kimia tanah.

Evaluasi dilakukan untuk estimasi kesesuaian lahan untuk irigasi permukaan sekala kecil, sehingga tidak melibatkan teknik-teknik seperti “drop irrigation”, yang mungkin akan

memberikan hasil evaluais yg berbeda.

Only potential land characteristics were taken into account but nothing is here reported about effective irrigation possibilities, i.e.

about irrigation water availability.



Faktor-faktor yg mempengaruhi kesesuaian tanah untuk irigasi dapat dikelompokkan menjadi empat golongan:

1. Ciri-ciri Fisika tanah, that determine the soil-water relationship in the soil such as permeability and available water content (both related to texture, structure, soil depth and calcium carbonates status);

2. Ciri-ciri Kimia Tanah, that interfere in the salinity/alkalinity status, such as soluble salts and exchangeable Na;

3. Ciri-ciri Drainage;4. Faktor Lingkungan, seperti lereng.


During heavy rainfall the upper soil layers become saturated and pools may

form. Water percolates to deeper layers and infiltrates from the

pools.

Sumber : http://www.fao.org/docrep/R4082E/r4082e07.htm

SOIL WATER RELATIONS

ABSORPTION OF WATER: Water in the soil is mostly and abundantly, under normal conditions, is available in the form of Capillary water. In the soil the space in between soil particle forms a

network of spaces, which normally is filled with water. The water that is present in such spaces is called capillary water.

Sumber: http://preuniversity.grkraj.org/html/4_PLANT_AND_WATER_RELATIONSHIP.htm


Most of the water is absorbed by the plants

is through root hair zone.

The figure shows the pathway of soil water

into root system.

Sumber: http://preuniversity.grkraj.org/html/4_PLANT_AND_WATER_RELATIONSHIP.htm


Availability of Water in the Soil

Soil is the major source of water for plants. The plants absorb water

through root hairs from the soil. The total water content present in

the soil is called holard. Out of this, the water which can be

absorbed by plants is chresard and remaining is called echard.

Diagram Showing Different forms of Soil Water and their Possible Relationship with Soil and Plant

Water Status.

Sumber: http://www.tutorvista.com/content/biology/biology-iv/plant-water-relations/availability-water-soil.php


Jadwal irigasiSome irrigation water is stored in the soil to be removed by crops and some is lost by evaporation, runoff, or seepage. The amount of water

lost through these processes is affected by irrigation system design and irrigation management. Prudent scheduling minimizes runoff and

percolation losses, which in turn usually maximizes irrigation efficiency by reducing energy and water use. (Of course, in situations where not

enough water was being applied, proper irrigation scheduling will increase energy and water use.)

When water supplies and irrigation equipment are adequate, irrigators tend to overirrigate, believing that applying more water will increase

crop yields. Instead, overirrigation can reduce yields because the excess soil moisture often results in plant disease, nutrient leaching,

and reduced pesticide effectiveness. In addition, water and energy are wasted.

Sumber: http://www.bae.ncsu.edu/programs/extension/evans/ag452-4.html


Jadwal irigasiThe quantity of water pumped can often be reduced without reducing yield. Studies have shown that irrigation scheduling

using water balance methods (to be discussed later) can save 15 to 35 percent of the water normally pumped without reducing

yield. Maximum yield usually does not equate to maximum profit.

The optimum economic yield is less than the maximum potential yield. Irrigation scheduling tips presented in popular farm magazines too often aim at achieving maximum yield with too little emphasis on

water and energy use effficiencies. An optimum irrigation schedule maximizes profit and optimizes water

and energy use.



MENGHUBUNGKAN AIR-TANAH DENGAN CEKAMAN TANAMAN

Jumlah air yg harus diberikan pada setiap aktivitas irigasi tergantung pada sifat tanah dan jumlah air-tersedia yang dapat disimpan dalam tanah.

Jumlah air-tanah yg diserap tanaman sejak irigasi atau hujan terakhir disebut sebagai “depletion volume”.

Irrigation should begin when the crop comes under water stress severe enough to reduce crop yield or quality. The level of stress that will cause a

reduction in crop yield or quality depends on the kind of crop and its stage of development; the level varies during the growing season as the crop matures. For example, corn will tolerate more stress without causing a yield reduction

when the stress occurs during the vegetative stage as opposed to the pollination stage. Thus, determining when to irrigate is a scheduling decision

that should take into account the crop's sensitivity to stress.


SOIL WATER RELATIONSThe relationship between water distribution in the soil and the concept of irrigation

scheduling when 50 percent of the PAW has been depleted.



Determining When to Irrigate

There are three ways to decide when to irrigate:

1. measure soil-water 2. estimate soil-water using an accounting

approach (the check-book method) 3. measure crop stress.



Irrigation scheduling is simply knowing when to irrigate and how much irrigatzon water to apply. An effective irrigation schedule helps to maximize profit while minimizing water

and energy use.

The following factors contribute to developing a workable and efficient irrigation schedule:

1. soil properties 2. soil-water relationships 3. type of crop and its sensitivity to drought stress 4. stage of crop development 5. availability of a water supply 6. climatic factors such as rainfall and temperature.


SOIL WATER RELATIONSRelationship between plant-available water and water distribution in the soil.

Plant-available water, PAW, is the volume of water stored in the soil reservoir that can be used by plants. It is the difference between the volume of water stored when the

soil is at field capacity and the volume still remaining when the soil reaches the permanent wilting point (the lower limit)



Most crops will recover overnight from temporary wilting if less than 50 percent of the PAW has been depleted. Therefore, the allowable depletion volume generally recommended in North Carolina is 50 percent (Figure 9). However, the recommended volume may range from 40 percent or less in sandy soils to greater than 60 percent in

clayey soils.

The allowable depletion is also dependent on the type of crop, its stage of development, and its sensitivity to drought stress. For

example, the allowable depletion recommended for some drought-sensitive crops (vegetable crops in particular) is only 20 percent during

critical stages of development.


SOIL WATER RELATIONSThe relationship between water distribution in the soil and the

concept of irrigation scheduling when 50 percent of the PAW has been depleted.


SOIL WATER RELATIONS. Effective Root Depth

Rooting depth is the depth of the soil reservoir that the plant can reach to get PAW. Crop roots do not extract water uniformly from the entire root zone. Thus,the

effective root depth is that portion of the root zone where the crop extracts the majority of its water. Effective root depth is determined by both crop and soil

properties.Plant Influence on Effective Root Depth. Different species of plants have different potential rooting depths. The potential rooting depth is the maximum

rooting depth of a crop when grown in a moist soil with no barriers or restrictions that inhibit root elongation. Potential rooting depths of most agricultural crops

important in North Carolina range from about 2 to 5 feet. For example, the potential rooting depth of corn is about 4 feet.

Water uptake by a specific crop is closely related to its root distribution in the soil. About 70 percent of a plant's roots are found in the upper half of the crop's

maximum rooting depth. Deeper roots can extract moisture to keep the plant alive, but they do not extract suffficient water to maintain optimum growth. When

adequate moisture is present, water uptake by the crop is about the same as its root distribution. Thus, about 70 percent of the water used by the crop comes from the

upper half of the root zone (Figure 10). This zone is the effective root depth.


SOIL WATER RELATIONSThe amount of water extracted by plants is influenced by the

distribution of the root in the soil.


SOIL WATER RELATIONS. Root zone soil water extraction and plant root development patterns.

Sumber: http://www.ianrpubs.unl.edu/pages/publicationD.jsp?publicationId=1004

SOIL PERMEABILITY

Permeabilitas tanah merupakan sifat tanah untuk dapat merembeskan air dan udara , dan sifat ini sangat penting

dalam kaitannya dengan IRRIGATION. Banyak faktor mempengaruhi permeabilitas tanah. Sometimes they are extremely localized, such as cracks and holes, and it is difficult to calculate representative values of permeability from

actual measurements. Observations on soil texture, structure, consistency, colour/mottling, layering, visible pores and depth to

impermeable layers such as bedrock and claypan* form the basis for deciding if permeability measurements are likely to be

representative.

Sumber: ftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e09.htm

SOIL PERMEABILITY

Soil permeability relates to soil texture and structure

The size of the soil pores is of great importance with regard to the rate of infiltration (movement of water

into the soil) and to the rate of percolation (movement of water through the soil).

Pore size and the number of pores closely relate to soil texture and structure, and also influence soil

permeability.


SOIL PERMEABILITY

Rataan permeabilitas berbagai tekstur tanah (cm/hour )


PASIR = Sand 5.0

Sandy loam 2.5

Loam 1.3

Clay loam 0.8

Silty clay 0.25

LIAT = Clay 0.05

SOIL PERMEABILITY

Struktur tanah sangat ememodifikasi laju permeabilitas:


Tipe Struktur Tanah Permeability1

Platy

- Greatly overlapping

Dari sangat lambat menjadi sangat cepat

- Slightly overlapping

BlockyPrismaticGranular

SOIL PERMEABILITY

Soil permeability classesPermeability is commonly measured in terms of the

rate of water flow through the soil in a given period of time. It is usually expressed either as a permeability rate

in centimetres per hour (cm/h), millimetres per hour (mm/h), or centimetres per

day (cm/d), or as a coefficient of permeability k in metres per second (m/s)

or in centimetres per second (cm/s).


SOIL PERMEABILITYKelas Permeabilitas Tanah untuk Pertanian dan Konservasi


Kelas Permeabilitas TanahLaju Permeabilitas1

cm/hour cm/day

Sangat Lambat - Very slow Less than 0.13 Less than 3

Slow 0.13 - 0.3 3 - 12

Moderately slow 0.5 - 2.0 12 - 48

Moderate 2.0 - 6.3 48 - 151

Moderately rapid 6.3 - 12.7 151 - 305

Rapid 12.7 - 25 305 - 600

SANGAT CEPAT - Very rapid More than 25 More than 600

SOIL PERMEABILITY

Permeability also varies with soil texture and structure. Permeability is generally rated from very rapid to very slow. This is the mechanism by

which water reaches the subsoil and rooting zone of plants. It also refers to the movement of water below the root zone. Water that

percolates deep in the soil may reach a perched water table or groundwater aquifer.

Sumber: http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447039&topicorder=10&maxto=10

SOIL PERMEABILITY

Infiltration and permeability describe the manner by which water moves into and through soil. Water held in a soil is

described by the term water content. Water content can be quantified on both a gravimetric (g water/g soil) and

volumetric (ml water/ml soil) basis. The volumetric expression of water content is used most

often. Since 1 gram of water is equal to 1 milliliter of water, we can easily determine the weight of water and

immediately know its volume. The following discussion will consider water content on a

volumetric basis.


SOIL PERMEABILITY

Water holding capacity designates the ability of a soil to hold water. It is useful information for irrigation scheduling, crop selection,

groundwater contamination considerations, estimating runoff and determining when plants will become stressed. Water holding capacity

varies by soil texture .


http://passel.unl.edu/UserFiles/File/Crp.%20Prod.%20Nat.%20Res.%20Mngmt/Soils%20lesson%202/2.6.gif

SOIL WHC

Medium textured soils (fine sandy loam, silt loam and silty clay loam) have the highest water holding capacity,

while coarse soils (sand, loamy sand and sandy loam) have the lowest water holding capacity. Medium textured soils

with a blend of silt, clay and sand particles and good aggregation provide a large number of pores that hold water

against gravity. Coarse soils are dominated by sand and have very little silt and clay. Because of this, there is little aggregation and few

small pores that will hold water against gravity. Fine textured clayey soils have a lot of small pores that hold

much water against gravity. Water is held very tightly in the small pores making it difficult for plants to adsorb it.


SOIL PERMEABILITYSince soil texture varies by depth, so does water holding capacity. A soil may have a

clayey surface with a silty B horizon and a sandy C horizon. To determine water holding capacity for the soil profile, the depth of each horizon is multiplied by the available water for that soil texture, and then the values for the different horizons

are added together.Calculation of water holding capacity for a soil profile:


SOIL DRAINAGE

Well-drained soils also are preferred for many nonagricultural uses. Home sites and housing developments should be located in well-drained soils, especially if basements are to remain dry and septic

systems are to function efficiently.

One of the best indicators of drainage class is soil color. The more redoximorphic features (mottling due to wetness) and gray in the

subsoil, the poorer the soil drainage, the longer and higher the water tables stand in a soil profile, the more intense is the mottling and the

higher it occurs within the profile. Soil scientists recognize six drainage classes in the field. Figure 23 shows the relationship

between topography or position on the landscape and the resulting soil drainage. The water table, as indicated on the figure, is

shown as it might appear during wet seasons.

Sumber: http://faculty.msmary.edu/envirothon/current/guide/soil_structure.htm

Kelas drainage dan lokasinya pada landskap Maryland.


SOIL DRAINAGE

DRAINAGE BERLEBIHAN Water is removed from the soil very rapidly because of either coarse textures (such as sand and loamy sand) or

shallow, porous profiles on steep slopes. Excessively drained soils are suited poorly to agriculture unless irrigation is

practiced. No drainage mottles occur in these soils.

DRAINAGE BAIK. Aerasi tanahnya bagus. Subsoil colors are bright and the

profile lacks redoximorphic features above 1 m (40 in.). Brown, yellowish brown and reddish brown colors

are common.Sumber: http://faculty.msmary.edu/envirothon/current/guide/soil_structure.htm

SOIL DRAINAGE

DRAINAGE CUKUP BAIK

In these soils, redoximorphic features are present above 1 m (40 in.) indicating that saturated conditions or water tables

occur above this depth at various times during the year. Mottles are restricted to the 0.5 to 1 m (20 to 40 in.) zone for

classification in this category. These soils may retard crop growth in wet years, but crops may do very well during

drought periods. Artificial drainage may be beneficial during wet periods.

Septic systems may experience periodic failure during saturated conditions.


SOIL DRAINAGE

DRAINAGE AGAK BURUK

Redoximorphic features occur within the 10 to 20 in. zone, indicating prolonged periods of saturation or high water

tables.

Gangguan atau kegagalan tanaman yg serus dapat terjadi selama tahun-tahun basah. Kalau ridak ada drainage buatan,

produksi tanaman terhambat dan sistem septik biasanya gagal.


SOIL DRAINAGE

Poorly drained. These soils have dark surface horizons and gray subsoils with redoximorphic features occurring

above 25 cm (10 in.). They have high water tables or are ponded for long

periods or both. These soils usually occupy level areas or footslope positions and are productive only if they are artificially drained. Development of

these soils for home sites should be avoided.


SOIL DRAINAGE

DRAINAGE SANGAT BURUK

Water is removed so slowly that the water table remains at or on the surface much of the year. These soils usually

occupy low-lying and concave or depressed positions on the landscape.

They normally have very dark or black, thick surface horizons with relatively high organic matter contents. The

subsoils usually are gray. These soils can be used for agriculture, but only if intensive drainage is practiced.


SOIL DRAINAGE

The soil drainage class and some characteristic features associated with each class are depicted in the following

figure (from Soil Survey).

One characteristic feature in the figure is the depth of rooting that typically occurs in each drainage class, providing there are no other restrictions (i.e., compacted layer) to root

penetration.

Deeper rooting depths are associated with well drained soils, because the depth of the water table below the

surface is not restricting root growth and oxygen exchange.

Sumber: http://nrcca.cals.cornell.edu/soil/CA3/

SOIL DRAINAGEAlthough not all plant species respond the same, for most common agricultural

crops, a deeper and healthy root environment translates into higher biomass productivity. Studies in New York have shown 2 to 3 fold yield increases in corn and forage production on well drained soils as compared to those grown on somewhat

poorly to poorly drained soils.

Sumber: http://nrcca.cals.cornell.edu/soil/CA3/

LAHAN IRIGASI

Sumber:


The different land characteristics that influence the soil suitability for irrigation are rated and a capability index for irrigation (Ci) is

calculated according to the formula:

Ci = A/100 * B/100 * C/100 * D/100 * E/100 * F/100

dimana: Ci: Indeks kapabilitas untuk irigasi; A: nilai tekstur tanah; B:

nilai kedalaman tanah; C: nilai status CaCO3 ;D: nilai salinitas/alkalinitas; E: nilai drainage dan F: nilai

slope.

Kelas kapabilitas didefinisikan menurut nilai indeks kapabilitasnya (atau kesesuaian) (Ci) (Table 28).


EVALUASI LAHAN UNTUK IRIGASITable 28 - Capability indexes for the different capability classes


Indeks Kapabilitas Class Definition Symbol

>80 I Excellent S1

60-80 II Suitable S2

45-60 III Slightly suitable S3

30-45 IV Almost unsuitable N1

<30 V Unsuitable N2


For slope class, texture, soil depth, calcium carbonate status, salinity and alkalinity,

drainage, a weighted average was calculated for the upper 100cm of the soil profile then the considered factors were rated according

to Table 29-Table 34.


EVALUASI LAHAN UNTUK IRIGASITable 29 - Rating of slopes (after Sys et al., 1991)


Slope class (%) RatingNon terraced Terraced

0-1 100 1001-3 95 953-5 90 955-8 80 95

8-16 60 8516-30 50 70>30 30 50

EVALUASI LAHAN UNTUK IRIGASITable 30 - Rating of textural classes for irrigation (after Sys et al., 1991)


KELAS TEKSTUR TANAHRating

<15%Gravel

15-40%Gravel

40-75%Gravel

Clay – LIAT 65 65 55Loam – LEMPUNG 90 80 70

Sand – PASIR 30 25 25Silt – DEBU 90 80 70

Sandy clay loam 95 85 75Silty clay loam 100 90 80

Loamy sand – PASIR BERLEMPUNG 55 50 45Sandy clay – LIAT BERPASIR 75 65 60Silty clay – LIAT BERDEBU 85 95 80

Clay loam – LEMPUNG LIAT 100 90 80Sandy clay – LIAT BERPASIR 80 90 75Silt loam – LEMPUNG DEBU 90 80 70

EVALUASI LAHAN UNTUK IRIGASITable 31 - Rating of soil depth (after Sys et al., 1991)

Table 32 - Rating of CaCO3 (Sys et al., 1991)


Soil depth (cm) Rating CaCO3 (%) Rating

<20 30 >50 3020-50 60 25-50 6050-80 80 10-25 85

80-100 90 0.3-10 100>100 100

Table 33 - Rating of salinity and alkalinity (after Sys et al., 1991)


Na+ (%)Electric conductivity (mS)

0-4 4-8 8-16 16-30 >30

0-8 100100*

9590*

9080*

8570*

8060*

8-15 9590*

9080*

8570*

8060*

7550*

15-30 9080*

8570*

8060*

7550*

7040*

>30 8570*

8060*

7550*

7040*

6530*

(*) Clay, Silty clay, and Sandy clay

Table 34 - Rating of drainage classes (after Sys et al., 1991, modified)Results and discussion


Kelas Drainage

Rating

Clay, silty clay, sandy clay, silty clay loam

other textures

Excessively drained 100 100

Somewhat excessively drained 80 100

Well drained 85 95Moderately drained 65 80

Somewhat poorly drained 55 70

Poorly drained 45 55

Very poorly drained 30 50

EVALUASI LAHAN UNTUK IRIGASIFigure 24 - Land suitability for irrigation


EVALUASI LAHAN UNTUK IRIGASITable 35 - Absolute and relative extent of different classes of

suitability for irrigation


Class Land unitArea

km2 %S2 10, 12, 22, 23, 6, 31 42,65 6,59

S3 1, 8, 9, 11, 13, 14, 18, 34 229,73 35,51

N1 7, 4, 17, 19, 20, 21, 25, 26, 27, 28, 29, 32, 35, 37, 33

157,55 24,35

N2 2, 3, 5, 15, 16, 24, 30, 36 168,40 26,03

Not Relevant U, R, Q 12,04 1,86


Di lokasi penelitian tidak ada area yg sangat sesuai untuk irigasi.

Moderately suitable land units are located in the alluvial valley (western part of the study area), and in the forest of Ben Slimane, where, of course, irrigation transformation is purely theoretical.

The largest part of the agricultural areas were classified as marginally suitable, the most limiting factors being physical parameters such as

slope, soil texture, and soil depth. This does not exclude the presence of small favoured areas where

conditions can be much better.

Faktor kimiawi seperti salinitas dan kandungan CaCO3 umumnya bukan faktor pembatas di lokasi penelitian.



Pada lokasi dataran, banyak area yang tidak sesuai karena faktor pembatas sifat fisika tanah :

Faktor pembatas tidak dapat diatasi dengan tingkat pengelolaan yanag ada sekarang, tetapi masih dimungkinkan

untuk irigasi dengan menerapkan teknik-teknik mirigasi lainnya.

In fact, some scattered spots of trees and vegetable orchards with drop irrigation are occasionally present, demonstrating the feasibility of

these techniques.

In the eastern escarpments, steep slopes and shallow soils lead to permanent unsuitable conditions for surface irrigation.


STELA – smno-fpub-mei2013

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PENILAIAN KESESUAIAN LAHAN UNTUK IRIGASI