II - Readily Available Water (RAW) as Requirements For Crops Water Irrigation Schedule

Lect. (8)

حساب األحتاجات المائة للمحاصل وجدولة ماه الرى: متطلبات

1

2 2

انحاضشج انصايح

ذطثقاخ انحاعة االن ف يجال انضساػح 01441 يقشس

(I) Water Software

1-ETC – Calculator

2- Climwat

(II) Excel

Readily Available Water : RAW (Depletion Fraction or

Deficit Fraction l

Requirements For Calculation of Crops

Water Irrigation Schedule

Requirements For Calculation of Crops Water Irrigation Schedule

See Lect.(5) and Lect. (6)

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انثشيجاخ انائح : أال

تشايج حغاب انثخش رح انحصن ( 1)

تشايج انثااخ اناخح انضساػح( 2)

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انش يا نجذنكرطهة (RAW) تغنح انراحح انا:شاا

(اخ انش ت انفرشج : انش يافاخ أضا اػذي ذحذذ جذل )

(1) Introduction : Definition

Readily available water (RAW) is the water that a plant

can easily extract from the soil. RAW is the soil moisture

held between field capacity and a nominated refill point

for unrestricted growth ( or welting point for the case

of water-stressed crops ) .

Field capacity is the maximum amount of water a soil can hold after drainage

Refill point is when the plant has used all readily available water 5

Readily available water(RAW). RAW is expressed in

millimetres per meter (mm/m) and indicates the depth

of water (mm) held in every meter (m) of soil depth that can

be readily removed by the plant. RAW should be calculated

for the plant's effective root zone.

It is used to schedule irrigation with confidence that you

are providing the crop with enough water

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(1) Introduction : Definition ( Cont.)

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انش يا نجذنكرطهة (RAW) تغنح انراحح انا:شاا

(اخ انش ت انفرشج : انش يافاخ أضا اػذي ذحذذ جذل )

تغنح انراحح انا (RAW)) أ نهثاخ ك انر انا

انغؼح ت تا انحرفظ انرشتح سطتح .انرشتح ي تغنح غرخشجا

ػه يائئ ضغظ ا جذ جد ػذو حاالخ ف ) انش إػادج قطح انحقهح

(انائ اإلجاد ي ذؼا انر انحاصم حانح ف انزتل قطح أ انحاصم

انغؼح انحقهح أكثش كح ي انا ك أ ذحها انرشتح تؼذ انصشف

(حاالخ ػذو جد جذ ا ضغظ يائئ ) إػادج انش قطح

تغنح انراحح اان ػ ؼثش RAW إن شش (و / يى) يرش نكم تانههرش

أيرصاص ك انز انرشتح ػق ي (و) يرش كم ف انجد (يى) اناء ػق

.نهثاخ انفؼانح سانجز نطقح RAW ذحغة ،انثاخ تاعطح تغنح

انا انراحح تغنح ( غثح ) قح غرخذو ذRAW) ) جذنح انش ف حغاتاخ

Total Available Water (TAW)

Refill point

soil water percent determining the time of application water IT is defined by user , according availability of irrigation water

Refill point :

Readily Available Water (RAW) Vs Total Available Water (TAW)

Readily Available Water (RAW)

8

Refill point

Relationship between soil water and crop stress

https://www.agric.wa.gov.au/citrus/calculating-readily-available-water

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(2) Steps for determination of Readily

Available Water

Step 1: Dig a hole Step 2: Identify the effective root zone Step 3: Identify different soil layers Step 4: Identify gravel/stone in each layer Step 5: Identify soil texture(s) Step 6: Calculate RAW

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حفش حفشج: 1

ذحذذ يطقح انجزس انفؼانح: 2

ذحذذ طثقاخ انرشتح انخرهفح: 3

انحجش ف كم طثقح/ ذحذذ انحص : 4

ذحذذ قاو انرشتح: 5

RAWحغاب : 6

انراحح انا:خطاخ حغاب كرطهة (RAW) تغنح

انش يا نجذن

Steps in identifying Readily Available Water

Step 1: Dig a hole Dig a hole within the root zone of your crop. For perennial crops, dig under the canopy in an area watered by the irrigation system. Try to dig to 1 metre or at least 30 cm past the main root zone (where the fibrous roots are).

The effective root zone is where the main mass of roots is found This is typically one to two-thirds of the depth of the deepest roots

Step 2: Identify the effective root zone

https://www.agric.wa.gov.au/citrus/calculating- readily-available-water 12

حفر حفرة: 1 نهحاصم تانغثح يرش ا يرش ) انحصل انجزس يطقح داخم حفشج أحفش

(انهفح انجزس تانغثح عى 30 أ انجزس انؼقح

تحدد منطقة الجذور الفعالة : 2

https://www.agric.wa.gov.au/citrus/calculating- readily-available-water

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انش يا نجذنكرطهة (RAW) تغنح انراحح انا:خطاخ حغاب

انكرهح ف ذجذ انز انكا انفؼانح انجزس يطقح

شهص إن شهس ك يا ػادج زا نهجزس انشئغح

انؼقح انجزس ػق

Fibrous roots which comprise the effective root

zone may only extend a third as far as the

deepest roots

Step 2: Identify the effective root zone (Cont.)

https://www.agric.wa.gov.au/citrus/calculating- readily-available-water 14

انش يا نجذنكرطهة (RAW) تغنح انراحح انا:خطاخ حغاب

قذ ذرذ انجزس انهفح انر ذرك ي يطقح انجزس

انفؼانح إن انصهس فقظ حر أػق انجزس

Steps in identifying Readily Available Water

Step 3: Identify different soil layers If you have different soil layers within the effective root zone measure the depth of each of these in metres.

Step 4: Identify gravel/stone in each layer Stone and gravel reduce the amount of water that can be held by a soil. A very stony soil will hold much less water than the same soil without stones. Grab three good handfuls of soil and using a 2mm sieve remove all stone and gravel . Place the pile of stones and gravel next to the pile of soil and visually estimate the proportions of each (for example, 60% stone and 40% soil).

Sieving shows the proportions of stone and gravel in soil

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انش يا نجذنكرطهة (RAW) تغنح انراحح انا:خطاخ حغاب

انخرهفح انرشتح طثقاخ ذحذذ :3 كم ػق تقاط فقى ، انفؼانح س,انجز يطقح داخم يخرهفح ذشتح طثقاخ نذك كا إرا

.تاأليراس يا

انرشتح ذحر عف .انرشتح ذحها أ ك انر انا كح ي انحص انحجش قهم

حفاخ شالز أيغك .حجاسج تذ انرشتح فظ ي اناء ي أقم كح ػه انصخشح

انحجاسج كيح ضغ .انحص األحجاس كم إلصانح يى 2 يخم اعرخذو انرشتح ي جذج

حجش ٪60 ، انصال عثم ػه) يا كم غة ترقذش قى انرشتح كيح تجاس انحص

.(ذشتح 40٪

4: ذحذذ انحص / انحجش ف كم طثقح

ظهر الغربلة نسب الحجر والحصى ف التربةت

Steps in identifying Readily Available Water

Step 5: Identify soil texture(s) Identify the texture of each soil layer within the effective root zone

Step 6 : Calculating Readily Available Water

(6-1) Select the crop water tension group from Table 1 and identify the RAW

value for each soil texture layer (mm/m).

(6-2) Select soil texture Table 2

(6-3) Reduce the RAW figure(s) by the % stone/gravel in the soil.

(6-4) Multiply the thickness of each soil layer by its adjusted RAW value.

(6-5) Add up the RAW for each soil layer to obtain the total root zone RAW.

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انش يا نجذنكرطهة (RAW) تغنح انراحح انا:خطاخ حغاب

: انرشتح قاو ذحذذ :5 انفؼانح انجزس يطقح داخم ذشتح طثقح كم قاو حذد

حغاب انا انراحح تغنح: 6

RAW قح حذد 1 انجذل ي نهحاصم انائ انرذش يجػح حذد (6-1)

.(و / يى) انرشتح غج طثقح نكم

2 انجذل انرشتح غج حذد (6-2)

.انرشتح ف انحص / انحجش تغثح٪ RAW (أشكال) سقى ذقهم (6-3)

.انؼذنح RAW تقح ذشتح طثقح كم عك اضشب (6-4)

.RAW انجزس يطقح إجان ػه نهحصل ذشتح طثقح نكم RAW أضف (6-5)

Water tension (0kPa at saturation point)

To –20kPa To –40kPa To –60kPa To –100kPa

Water-sensitive

crops such as

vegetables and

some tropical

fruits

Most fruit crops

and tablegrapes,

most tropical

fruits

Lucerne, perennial

pastures, crops such as

maize and soybeans,

wine grapes (except

where partial root

zone drying is being

practiced on wine

grapes)

Annual pastures

and hardy crops

such as cotton,

sorghum and

winter crops

kPa = kilo Pascal Water tension (0kPa at saturation point)

Readily Available Water ( for different crops ) as a function of suction

https://www.agric.wa.gov.au/citrus/calculating-readily-available-water

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مدى السعة ) التى ستطع المحصول أمتصاصها من التربة بسهولةالجهد معبرا عن الرطوبة

وهو أحد مدخالت برنامج حساب األحتاجات المائة للمحصول ( الحقلة الى نقطة اعادة الرى (بتحدد نوع المحصول ) ، وتم أدخاله بطرقة غر مباشرة

الدول النظام من مشتقة وحدة ه Pa ( الرمز (pascal) باسكال

على العمودة للقوة قاس وهو ، ،اإلجهاد أو للضغط للوحدات

زالمساحة وحدة

وحدة وه ، ( N/m2) 1 المربع المتر على نوتن 1 = باسكال 1

. للضغط جدا صغرة .باسكال 100,000 نحو تعادل (بار) جوي ضغط 1 1 = باسكال1000

تعرف بسكال

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Soil Texture Readily Available Water (mm/m)

To –20kPa To –40kPa To –60kPa To –100kPa

Sand 30 35 35 40

Loamy sand 45 50 55 60

Sandy loam 45 60 65 70

Loam 50 70 85 90

Sandy clay loam 40 60 70 80

Clay loam 30 55 65 80

Light clay 25 45 55 70

Table : Select soil texture ( when you run CropWat Software )

Relationship of Readily Available Water (mm/m) to soil suction

Water tension (0kPa at saturation point) 22

أحذ ( يذ انغؼح انحقهح ان قطح اػادج انش ) نهحصل انجذ يؼثشا ػ انشطتح انراحح

ترحذذ ع ) يذخالخ تشايج حغاب األحراجاخ انائح نهحصل ، رى أدخان تطشقح غش يثاششج

(انرشتح

conversion soil water content from m3/m3 to mm Guess, 1 m3/m3 can be converted to 1000 mm of water, if 1mm of water content is defined as 1mm of water drawn from 1m deep soil. Assuming in an unit area (S, m^2) of soil, amount of water in depth (h, m) can be extract from soil of a depth (H, m) volumetric water content (m3/m3) = S*h/S*H = h/H so: h (m)= volumetric water content * H (m) So if my guess of the definition of mm is right, H = 1m =1000mm, h (mm)= 1000 * volumetric water content.

Volumetric water content is a numerical measure of soil moisture. It is simply the ratio of water volume to soil volume

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Example calculation A citrus crop growing in a sandy loam soil containing 20% stone, with an effective root depth of 0.3m and a strategy to irrigate at -40kPa would have the following

calculations: 1. From Table 2, the RAW for a sandy loam soil at -40kPa =

60mm/m. 2. As the soil contains 20% stone, reduce the RAW by 20%. To

do this, multiply by 0.8. 3. Adjusted RAW = (60mm/m) x 0.8 = 48mm/m. 4. Hence, for a rooting depth of 0.3m: 5. Total root zone RAW = ( 48mm/m )x 0.3m = 14.4mm.

https://www.agric.wa.gov.au/citrus/calculating-readily-available-water

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Converting Readily Available Water to litres for drip irrigation

Drip irrigation is common in modern orchards. For this method of irrigation it is easier to use litres rather than the more traditional unit of millimetres when describing readily available water in the plant root zone. Using litres also allows simple calculation of irrigation time.

Where irrigation water and plant roots are evenly distributed over the whole planting area, water storage and plant water use can be measured in millimetres. Drip irrigation distributes water over a small part of the whole block and roots follow this water distribution. In these cases, it is often easier to use litres to describe both water use and storage in the plant root zone. This also allows simple calculation of irrigation time as the discharge from drip systems is commonly reported in litres per hour.

Introduction

https://www.agric.wa.gov.au/spring/converting-readily-available-water-litres-drip-irrigation?page=0%2C1 25

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األعم ي ، ز انش طشقح إن تانغثح .انحذصح انثغاذ ف شائغ تانرقظ انش

انراحح انا صف ػذ انههرشاخ ي انرقهذح انحذج ي تذالا انهرشاخ اعرخذاو

.انش نقد تغطاا حغاتاا انهرشاخ اعرخذاو رح كا .انثاخ جزس يطقح ف تغنح

، تأكها انضساػح يطقح ػه تانرغا انثاذاخ جزس انش يا ذصغ رى حس

اناء تانرقظ انش صع .تانههرش انثاخ يا اعرخذاو انا ذخض قاط ك

، انحاالخ ز ف ، انا ذصغ انجزس ذرثغ تأكها انكرهح ي صغش جضء ػه

ف ذخضا انا اعرخذاو نصف انهرشاخ اعرخذاو األعم ي ك يا غانثاا

.انثاخ جزس يطقح

ا غح زا أظح ي انرصشف ػ اإلتالؽ رى حس انش نقد تغظ تحغاب أضا

.انغاػح ف تانهرش ػادج انرقظ

Rule to remember 1mm depth of water = 1L applied to 1 square metre.

The volume of root zone that is wetted by the drip system will depend on the size and shape of the wetting pattern.

Water held in root zone

Overlapping drippers

Volume stored (L) = wetted width (m) x wetted length (m) x root zone RAW (mm)

For example, for a width of 1.5m wetted, 3m

tree spacing and root zone RAW of 14mm, the

volume of Readily Available Water = 1.5 x 3 x 14

= 63 litres of RAW per tree. 27

https://www.agric.wa.gov.au/spring/converting-readily-available-water-litres-drip-irrigation?page=0%2C1

Non-overlapping drippers

or example, if a root zone with a RAW of 14mm is wet by a dripper with a cylindrical wetting pattern and a radius of 0.2m, the volume of readily available water will be:

πr2 x root zone RAW (mm) (πr2 is the area of a circle where pi (π) equals 3.14.) 3.14 x (0.2 x 0.2) x 14 = 1.8L/dripper.

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