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

Transcription

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

2 Situation 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 2

3 Project objectives - Prevention of salt accumulation by using fertilizers reduced in ballast salts - Irrigation according to model-calculated actual evapotranspiration (ET) 3

4 Part 1 Fertilizer selection Trial set-up: 12 consecutive cultivation rounds Standard fertilizer (Blaukorn premium or Floranid permanent) Fertilizers with reduced ballast salts (Cl -, SO 4 2- ) Floranid summer (COMPO), DCM Unimix A (DCM), new fertilizer (Everris)

5 Part 1 Fertilizer selection 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 5

6 Part 2 Model-based irrigation Starting point: Adjusted PM-model developed by Pollet (1998) including: submodel for vertical projection instead of LAI submodel for stomatal resistance λeeee =.(RR nn GG ) + γγ + (ρρ.cc pp. DD rr bb ) + γγ met γγ = γγ. (1 + rr cc rr bb ) Challenges: Only validated in winter conditions Only heading state: high percentage of crop coverage and low evaporation rate 6

7 Part 2 Model-based irrigation Experimental set-up Small-scale hydroponic systems serving as lysimeters 7

8 Part 2 Model-based irrigation Experimental set-up Optimal rhizosphere conditions: optimal water- and nutrient availability High repeatability Mimicking evaporating soil surface by using flannel cloth (compared with soil object) 8

9 Part 2 Model-based irrigation Experimental set-up Model requires measurements of 5 variables» Rn (net radiation)» PAR (irradiation)» Ta (air temperature)» Tl (leaf temperature)» RH (relative humidity) 9

10 Part 2 Model-based irrigation Adaptations to the model of Pollet Adding term for evaporation (Ritchie 1972) λe = + γ. RR 0,398. SS nn. ee Adaptation of the submodel for transpiring surface surface vertical projection surface hemisphere with same radius as vp 10

11 Part 2 Model-based irrigation Results: Good diurnal fitting during all growing seasons Good estimation of total evapotranspiration R²=82,7 R²=88,4 104% 94% 11

12 Part 2 Model-based irrigation Results: Good diurnal fitting during all growing seasons Good estimation of total evapotranspiration R²=82,7 97% 12

13 Part 2 Model-based irrigation Challenge: Reduction of application cost Method: Reduction of amount of sensors Calculation of: Rn out of PAR Tl out of Ta and PAR Decision based on: high correlation sensor cost 13

14 Part 2 Model-based irrigation Results: Deduction of Tl and Rn is possible Accurate estimation of daily and cumulative ET R²=94,3 104% 14

15 Part 2 Model-based irrigation Results: Deduction of Tl and Rn is possible Accurate estimation of daily and cumulative ET R²=84,2 95% 15

16 Part 2 Model-based irrigation Validation in soil-bound cultivation Round Irrigation quantity (L) Crop weight (g) ~ Model Standard Model Standard 1* 9,5 10,0 359 a 337 a 2 41,2 41,0 442 a 458 a 3 55,5 40,0 542 a 508 b 4 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<0,001 level 16

17 Part 3 On-farm implementation RF GPRS collector gateway webserver application / user interface sensors 17

18 Part 3 On-farm implementation Use of data from climate computer is possible Requires determination of light transmission rate Possibilities (+ cost) for data export vary between computer manufacturers 18

19 Part 3 On-farm implementation User interface (Screenshot) 19

20 Final remarks - Appropriate fertilizer selection can delay salt accumulation by reducing the increase in EC, and consequently lowering the rinsing frequency - A homogeneous irrigation pattern is primordial to avoid spatial variation in salt accumulation - Excessive irrigation can be avoided by deducting the irrigation quantity from ET-calculation using the REDUNG-application 20

21 Aknowledgements Sara Crappé (Project coordinator) Peter Bleyaert & Simon Craeye Isabel Vandevelde & Stefaan Fabri Stefaan De Neve 21

22 Questions?