..• cirad CHOPART J.-L. & LE MEZO L.

(1)

CHOPART J.-L.

1 _{& LE MEZO L.}

2 [email protected]

Agroocotogy ln tropks Ground C watw ,,.,.na�nMnt

Energy from biomus Renew•bl• Enl1rge the fitld of posslbilit,es

1AGERconsult F-34090, Montpellier, France

cirad

2CIRAD, UPR 115, F-97410, Saint-Pierre, La Réunion, France

We present the findings of

a

study testing the PRER (Potential Root Extraction Ratio) mode/ (Chopart 1999,

Leifi et al., 2011) to estimate the maximum avai/able soi/ water (MASW) depending on the sugarcane root

system in a deep soi/ of La Réunion. The aim is to optimize sugarcane irrigation, especially deficit

irrigation, by adjusting irrigation rates and intervals according to root distribution in the soi/.

Methods

Measurements where done on a deep soil in La Réunion, in a R570

nine months after harvest of the previous crop.

Root distribution was studied using the trench-profile method by

mapping root intersections (RI) in four soil profiles to a depth of

four meters using a grid (5 x 5 cm mesh). From RI, we inferred

root length densities (RLD) (Chopart et al., 2008) and root distances

(RD), (Newman, 1969).

The PRER is the ratio of volume of soil potentially accessible to a root for water

uptake (Vu) and the whole volume of soil assigned to that root. Modelling Vu took

RD into account & a max distance of water movement from soil to roots (5 cm).

The conventional max. available soil water (MASWlab, cm of water in cm of soil)

had a value of 0.1cm/cm from the soil surface to the four meter depth.

Results & Discussion

../ There was a wide variability in RLD distribution between the surface and the

rooting front (4 m), with many competing roots and rootless zones (Fig.1 ).

../ PRER values ranged from 80% near the surface to values ranging from 30%

to 1% between the 1 - 3 m depth (Fig.2& 3).

../ The biological MASW (MASWbiol) depending on PRER( Fig.3) and MASWlab

ranged from 0.8 mm/cm near the surface to 0.01 mm/cm at 3 m. The total

MASWbiol was 86 mm (SD.: 14).

0.5

I 1 {; � 1.5 • u -·2S - O:ZS-04 - .... .tCM

Fig.1: RLD (cm/cm

l

₎

0 0.2 0.4 0.6 1 2 ' 2.5 -PRER/5 cm muh

../ When only rooting depth and conventional MASWlab (cm/cm) were used,

value of total MASWlab was 300 mm for a 3 m rooting depth (Fig.4) .

../ MASWbiol appeared to provide a better estimate than conven_ti��al.

_{MASWlab for crop modelling and irrigation, especially for def1c1t 1mgat1on .}

../ Deficit Irrigation requires a good estimate the soil water storage.

1 -o-

RLD

F;g.Jc 'Pmfiles of RLD (omkm') &

P

RER(O

�

Max Avallable Soli Water (mm/cm of soil depth)

••

I,

� 15

"

0..2 0 4

..•

-

MASWb1ol

-MASW!ab

01 10 1 2

Fig.4: Profiles of biological and conventional

MASW

(mm/cm soil depth)

References

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_c

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