EFFECT OF GLYPHOSATE AND PARAQUAT ON BIODIVERSITY OF SOIL INVERTEBRATE FAUNA AT THE TEACHING AND RESEARCH FARM OBAFEMI AWOLOWO UNIVERSITY ILE

ABSTRACT

This study investigated the effect of glyphosate and paraquat on soil invertebrate fauna biodiversity, soil physico-chemical properties and the relationship between them with a view to determining the ecological effects of chemicals on the environment. 

An experimental field of 19 m by 11 m was mapped out at the Teaching and Research Farm of Obafemi Awolowo University, Ile-Ife, for the study. Plots of 4 m by 3 m separated by 1 m were laid out in completely randomized design with three treatments and four replications. The treatments were cowpea + glyphosate (CG), cowpea + paraquat (CP) and cowpea + water (CW) as control. Herbicides were applied at the manufacturer’s recommended rates of 4 l/h for glyphosate and 2 l/h for paraquat. Soil invertebrates’ fauna were collected pre- and post-application of herbicides as follows: 14, 7 days before application (DBA); 7, 14, 30, 60, 90 and 120 days after application (DAA) using pitfall trap with 4% formalin and a modified Berlese-Tulgren extractor. Earthworms were sampled by taking and examining a soil core of 20 (l) x 20 (w) x 20 (d) cm per plot. Sub-samples of each core was taken and analysed for physico-chemical properties in the laboratory using standard procedures. Data obtained were analysed using analysis of variance (ANOVA) and Pearson correlation coefficients. 

Seven types of soil invertebrate fauna were identified. These were Collembola, Acarina, Formicidae, Aranae, Isoptera, Coleoptera, Diplopoda and Oligocheata. Collembola was the most abundant invertebrate fauna (59.1 %) collected while Oligocheata was the least abundant (0.18%). The population of all the invertebrate fauna was reduced by the application of both glyphosate and paraquat. However, the population grew gradually from 14 DAA for Collembola, Aranae and Isoptera, 30 DAA for Formicidae, Diplopoda, and Acarina, attaining peaks at 60 DAA. The Shannon-Weiner index for glyphosate, paraquat and control were 1.30, 1.50 and 1.54 respectively. Pearson’s correlation coefficient revealed a positive significant relationship at p < 0.05 between soil moisture content, Aranae, Diplopoda, Collembolla, and at p < 0.01 with Acarina. Sodium ion and calcium ion were positively correlated (p < 0.01) with Aranae and Diplopoda while Isoptera only showed significant (p < 0.01) positive correlation with calcium ion. Organic matter was positively correlated (p < 0.05) with Aranae, Collembola and Diplopoda (p < 0.01). Phosphorus showed positive significant correlation at p < 0.01 with Formicidae Aranae, and at p < 0.05 with Isoptera and Collembola. In contrast, soil temperature and soil pH showed significant (p < 0.05) negative correlation with Collembola. Values of most physico-chemical properties did not vary significantly between the treatment and control plots except sodium ion which significantly (P < 0.05) increased in paraquat treated plots.

This study concluded that application of glyphosate and paraquat reduced the population of most soil invertebrate fauna.

TABLE OF CONTENTS

                              Pages 

TITLE PAGE i

CERTIFICATIONii

ACKNOWLEDGEMENTSiii

TABLE OF CONTENTS iv

LIST OF TABLESvii                                                                          LIST OF FIGURESviii

LIST OF PLATESix

ABSTRACTx                                                                                CHAPTER ONE: INTRODUCTION1                                                                          

1.1 Background of Study1                                                                                            

1.2 Objectives of Study2                                                                                                

CHAPTER TWO: LITERATURE REVIEW                                                    

2.1 Soil Invertebrates Commonly Found in the Soil4                                                    

    2.1.1 Classification and Ecology of Protozoans4   

    2.1.2 Classification and Ecology of Nematodes6                                                      

    2.1.3 Classification and Ecology of Collembola7                                                      

    2.1.4 Classification and Ecology of Acarina8         

    2.1.5 Classification and Ecology of Formicidae9

    2.1.6 Classification and Ecology of Isoptera10

    2.1.7 Classification and Ecology of Coleoptera10

    2.1.8 Classification and Ecology of Aranae11                                                              

    2.1.9 Classification and Ecology of Diplopoda12                                                         

    2.1.10 Classification and Ecology of Annelida12                     

2.2 The Use of Soil Invertebrates as Indicator of Stress in the Environments 13

2.3 Classification of Commonly Used Herbicides 14

   2.3.1 Herbicides Commonly Used in Nigeria 15 2.4 Effects of Herbicides on Soil Invertebrate Fauna 22 

CHAPTER THREE: MATERIALS AND METHODS 25

3.1 The Study Area 25

3.2 Experimental Design and Procedures 25

3.3 Herbicides Used 25

3.4 Land Preparation 27

3.5 Sampling Techniques and Sorting Method 27

     3.5.1 Earthworm Sampling Method 27

     3.5.2 Micro-arthropods and other Soil Invertebrate Fauna 27

3.6 Measurement of Environmental Factors 29

3.7 Procedures for Determining Soil Chemical Properties 31

     3.7.1 Determination of Soil pH 31

     3.7.2 Determination of Soil Organic Matter 31

      3.7.3 Determination of Cations 32

3.8 Statistical Analyses 32 CHAPTER FOUR: RESULTS 34

4.1 Abundance and Distribution of Soil Invertebrate Fauna in the 

      Experimental Plots Pre- and Post-Application of Herbicides 34

4.3 Soil Physico-Chemical Properties in Relation to Abundance and Distribution of

      Soil Invertebrate Fauna 41

CHAPTER FIVE: DISCUSSION AND CONCLUSIONS 51

5.1 Discussion 51

5.2 Conclusions 54 

5.3 Future Recommendations 55

REFERENCES 57

APPENDICES 69