HOW DOES IRRIGATION MANAGEMENT AND WEED CONTROL INFLUENCE ON

EXOTIC PLANT ASSEMBLAGES?

Alejandro Juárez, Xavier Solé & Josep Antoni ConesaDepartament d’Hortofructicultura, Botànica i Jardineria Escola Tècnica Superior d’Enginyeria

Agrària. Universitat de Lleida

INTRODUCTION

Catalan western plain:- Strongly contrasted temperatures- Low annual precipitation (380mm)- Summer water deficit

The landscape consists on semiarid plant communities in mosaic with rainfed crops

Implementation and extension of irrigated crops, as fruit tree orchards, have transformed traditional landscape in recent decades

These irrigated crops were established because of their larger productivity compared to traditional rainfed crops

INTRODUCTION

Irrigated fruit tree orchards favor the entry and maintenance of exotic weed species:

1. Water facilitates diaspore entry2. High disponibility of water and nutrients3. Elevated temperatures in summer4. Open structure of the orchards

Consequences:Affect negatively to the crop yield and may develop invasive behaviour in surrounding natural habitats

1 2 3 4

INTRODUCTION

Management of irrigated fruit tree orchards

Irrigation system

Flood irrigation

Weed control

Mecanically on inter-rows

Herbicide application under the trees

INTRODUCTION

Drip irrigation

Hypothesis:

Orchard management determines weed richness and diversity and could favor the presence of exotic flora

Objectives:

1.Find relationships between irrigation system and richness and diversity of native and exotic flora

2.Analyze differences in richness and diversity of native and exotic flora between inter-rows and under the tree lines

3.Assess whether there is a synergistic effect between these two factors on richness and diversity of native and exotic flora

INTRODUCTION

July-September 2009

75 fields with drip irrigation system

75 fields with flood irrigation system

MATERIALS & METHODS

3 X

Phytosociological surveys (Braun-Blanquet)

3 X

1m

10m

2m

5m

MATERIALS & METHODS

DATA ANALYSIS

Origin of species: Natives and exotics (Bolòs & Vigo, 1984-2001)

Richness

-Total

-By family

-Depending on: irrigation system Plot position in field

-By origin

Shannon-Weaver diversity(from cover data for the same groups as richness)

1

·ln

n

i ii

H p p

pi = Ri / R (Ri: relative cover of the i species; R: total cover of all species).

Two-way ANOVA to evaluate the effect of irrigation system , plot position and the interaction between these two factors on richness and diversity

MATERIALS & METHODS

Total: 179 species 40 families

Flood irrigated: 104 species 32 families

Drip irrigated: 157species 36 families

Inter-rows: 86 speciesUnder the tree: 92 species

Inter-rows: 133 speciesUnder the tree: 118 species

RESULTS & DISCUSSION

Flood irrigated orchards Inter-rows % Freq

Under tree %Freq

Trifolium repens 70,22 Sonchus oleraceus 60,70

Taraxacum officinale 64,89 Portulaca oleracea 53,40

Bromus catharticus 61,33 Trifolium repens 52,00

Setaria pumila 46,67 Echinochloa colona 39,07

Rumex obtusifolius 42,22 Euphorbia prostrata 36,57

Sorghum halepense 38,22 Setaria adhaerens 36,06

Cyperus rotundus 34,22 Digitaria sanguinalis 34,96

Echinochloa colona 32,89 Bromus catharticus 28,49

Paspalum distichum 28,00 Taraxacum officinale 24,63

Eleusine indica 27,56 Malva sylvestris 24,36

In bold: exotic species

Bromus catharticusSetaria pumila

Sorghum halepense

Eleusine indica

Cyperus rotundusPaspalum distichum Euphorbia prostrata

Setaria adhaerens

Echinochloa colona

RESULTS & DISCUSSION

In bold: exotic species

Drip irrigated orchards Inter-rows % Freq

Under tree %Freq

Sonchus oleraceus 45,54 Sonchus oleraceus 75,53

Aster squamatus 39,79 Setaria adhaerens 34,36

Taraxacum officinale 36,86 Convolvulus arvensis 27,61

Polygonum aviculare 32,34 Malva sylvestris 25,66

Crepis bursifolia 32,31 Amaranthus albus 21,21

Malva sylvestris 28,74 Chenopodium album 20,71

Conyza bonariensis 26,71 Aster squamatus 19,42

Plantago coronopus 26,35 Cynodon dactylon 15,59

Kochia scoparia 23,90 Heliotropium europaeum 14,75

Plantago lanceolata 20,98 Sonchus tenerrimus 14,72

Conyza bonariensis Cynodon dactylon

Amaranthus albus

Aster squamatus

Crepis bursifolia

Setaria adhaerens

RESULTS & DISCUSSION

Mean richness (number of species) in % Mean Shannon diversity index

FI: flood irrigationDI: drip irrigation

RESULTS & DISCUSSION

VariableDependent variable F P Direction effect

irrigation system

total30,763

<0,001 **

F>D

exotics 261,386

<0,001 **

F>D

natives40,763

<0,001 **

D>F

Position

total80,164

<0,001 **

IR>TL

exotics56,716

<0,001 **

IR>TL

natives84,545

<0,001 **

IR>TL

Irrigation x position

total 2,627 0,105exotics

15,419<0,001 **

IR>TL in D and F

natives17,590

<0,001 **

IR>TL in D and F

TWO WAY ANOVA FOR RICHNESS/PLOT

D: drip irrigationF: flood irrigationIR: inter-rowsTL: tree line

RESULTS & DISCUSSION

VariableDependent variable F P Direction effect

irrigation system

total 66,217

<0,001 **

F>D

exotics 261,46

<0,001 **

F>D

natives 11,182

<0,001 **

D>F

position

total 43,942

<0,001 **

IR>TL

exotics 30,448

<0,001 **

IR>TL

natives 12,299

<0,001 **

IR>TL

Irrigation x position

total 0,284 0,594exotics 18,73

0<0,001 **

IR>TL in D and F

natives8,296 0,004 *

IR>TL in D and F

D: drip irrigationF: flood irrigationIR: inter-rowsTL: tree line

TWO WAY ANOVA FOR SHANNON DIVERSITY INDEX

RESULTS & DISCUSSION

• Drip irrigated orchards have a larger total richness than flood irrigated orchads because they present different environments with contrasting conditions: irrigated under the tree and rainfed in the inter-rows

• Flood irrigated orchards have a higher Shannon diversity because cover of weeds is higher and more homogeneously distributed

• Flood irrigation favors both the presence and diversity of exotic flora to the detriment of native flora

• Exotic weeds presents in orchards are different depending on irrigation system

CONCLUSIONS

• Drip irrigation orchards shelter more native weeds because inter-rows maintain typical mediterranean stress conditions

• Below the tree rows in both irrigation systems, there are the lowest richness and diversity of species because the herbicide application ocurrs there

• There is a synergistic effect between irrigation system and weed management (plot position) over native and exotic weeds that favors exotic weeds in the inter-rows of flood irrigation and native weeds in the inter-rows of drip irrigation

CONCLUSIONS

IMPLICATIONS FOR MANAGEMENT

The choice of irrigation system becomes a crucial aspect in the design of a management system aimed to prevent the establishment of exotic flora in mediterranean areas

Thank you for your attention

Acknowledgements: Financial support provided by AGAUR PhD grants Generalitat de Catalunya