the redung-project: appropriate fertilizer selection and model … · 2019. 2. 3. · standard...

The REDUNG-project:appropriate fertilizer selection and model-based irrigation as measures to reduce nitrate leaching in soil-bound greenhouse butterhead lettuce cultivation

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Situation

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Plant nutrients, i.e. nitrate, can leach to deeper soil layers due to:

• excessive irrigation• rinsing between cultivation rounds to halt salt accumulation

They become inaccessible for superficial rooting system• financial loss for grower• elevated environmental risk


Project objectives

3

- Prevention of salt accumulation by using fertilizers reduced in ballast salts

- Irrigation according to model-calculated actual evapotranspiration (ET)


Part 1 – Fertilizer selection

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Trial set-up:

12 consecutive cultivation rounds

Standard fertilizer (Blaukorn premium or Floranid permanent)15-3-20 16-7-15

Fertilizers with reduced ballast salts (Cl-, SO42- ) Floranid summer (COMPO), DCM Unimix A (DCM), new fertilizer (Everris)

16-0-25 10-5-15 23-0-30


5

Results:

Use of fertilizers low in ballast salts results in:

– a smaller increase of chloride and sulphate content in the upper soil layer and a smaller increase of EC

– equally heavy, high quality crops

– an elevated risk of glassiness

Part 1 – Fertilizer selection


Part 2 – Model-based irrigation

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Starting point:Adjusted PM-model developed by Pollet (1998) including:– submodel for vertical projection instead of LAI– submodel for stomatal resistance

λ𝐸𝐸𝐸𝐸 = ∆ .(𝑅𝑅𝑛𝑛 −𝐺𝐺 )∆+ 𝛾𝛾∗

+(𝜌𝜌 .𝑐𝑐𝑝𝑝 .

𝐷𝐷𝑟𝑟𝑏𝑏

)

∆+ 𝛾𝛾∗met 𝛾𝛾 ∗ = 𝛾𝛾 . (1 + 𝑟𝑟𝑐𝑐

𝑟𝑟𝑏𝑏)

Challenges:– Only validated in winter conditions– Only heading state: high percentage of crop coverage

and low evaporation rate



7

Experimental set-up

Small-scale hydroponic systems serving as lysimeters



8

Experimental set-up

Optimal rhizosphere conditions: optimal water- and nutrient availability

High repeatability

Mimicking evaporating soil surfaceby using flannel cloth(compared with soil object)



9

Experimental set-upModel requires measurements of 5 variables

» Rn (net radiation)

» PAR (irradiation)

» Ta (air temperature)

» Tl (leaf temperature)

» RH (relative humidity)



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Adaptations to the model of Pollet

– Adding term for evaporation (Ritchie 1972)

λE =∆

∆ + γ ∗. 𝑅𝑅𝑛𝑛 . 𝑒𝑒−0,398 . 𝑆𝑆

– Adaptation of the submodel for transpiring surface

surface vertical projection surface hemisphere with same radius as vp



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Results:

• Good diurnal fitting during all growing seasons• Good estimation of total evapotranspiration

R²=82,7

94%

R²=88,4

104%



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Results:

• Good diurnal fitting during all growing seasons• Good estimation of total evapotranspiration

R²=82,7

97%



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Challenge: Reduction of application costMethod: Reduction of amount of sensors

Calculation of:• Rn out of PAR• Tl out of Ta and PAR

Decision based on:• high correlation• sensor cost



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Results:

• Deduction of Tl and Rn is possible• Accurate estimation of daily and cumulative ET

R²=94,3

104%



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Results:

• Deduction of Tl and Rn is possible• Accurate estimation of daily and cumulative ET

R²=84,2

95%



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Validation in soil-bound cultivation

Round Irrigation quantity (L) Crop weight (g) ~Model Standard Model Standard

1* 9,5 10,0 359 a 337 a2 41,2 41,0 442 a 458 a3 55,5 40,0 542 a 508 b4 91,3 95,5 532 a 530 a

* modelling started only halfway cultivation round

~ means in each row, not followed by the same letter are significanty different at the P

Part 3 – On-farm implementation

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sensors

collector application / user interface

gateway webserver

RF GPRS



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• Use of data from climate computer is possible

• Requires determination of light transmission rate

• Possibilities (+ cost) for data export vary betweencomputer manufacturers



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User interface(Screenshot)


Final remarks

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- Appropriate fertilizer selection candelay salt accumulation by reducing the increase in EC, and consequently lowering the rinsing frequency

- A homogeneous irrigation pattern is primordialto avoid spatial variation in salt accumulation

- Excessive irrigation can be avoidedby deducting the irrigation quantity from ET-calculationusing the REDUNG-application


Sara Crappé (Project coordinator)

Peter Bleyaert & Simon Craeye

Isabel Vandevelde & Stefaan Fabri

Stefaan De Neve

Aknowledgements

21


Questions?


Slide Number 1SituationProject objectivesPart 1 – Fertilizer selectionPart 1 – Fertilizer selectionPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 2 – Model-based irrigationPart 3 – On-farm implementationPart 3 – On-farm implementationPart 3 – On-farm implementationFinal remarksAknowledgements Slide Number 22

the redung-project: appropriate fertilizer selection and model … · 2019. 2. 3. · standard...

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