Evaluating the Sustainability of Azolla-Rice Farming in Northern Senegal 公开

Abstract

A sustainable agricultural system is essential for the creation of a secure, sufficient, and equitable global food supply. Farmers worldwide rely on expensive and synthetic fertilizers to produce food. Unfortunately, excess fertilized application can waste these expensive resources and cause nutrient pollution and degradation of aquatic habitats and drinking water sources. Therefore, strategies that recapture and recycle excess or lost nutrients could combat malnutrition while limiting economic and environmental costs. One promising strategy that captures nutrients involves an aquatic fern, Azolla. Farmers in Southeast Asia are using Azolla successfully to recover nitrogen in agricultural runoff and reuse it as input for rice and other crops. However, Azolla’s use remains understudied compared to other farming practices, despite its ecological relevance to sustainable rice agriculture globally. Using diverse methodologies drawn from disciplines in ecology, sociology, and anthropology leveraged by the social-ecological systems framework, I characterized the potential of Azolla-rice farming as a sustainable practice in Senegal. First, I evaluated the potential of this sustainable practice by determining the suitability of Azolla in Africa using present and future climate models. I determined that most of Africa is suitable for Azolla growth and development in rice fields, with slight differences in regional suitability for different Azolla species. Then, I collaborated with Senegalese rice farmers to explore the effect of 1) adding Azolla to existing farmers’ practices and 2) replacing urea, a dominant synthetic N source, with Azolla in irrigated rice fields in the Senegal River Valley. Lastly, I evaluated their attitudes and perceptions of the practice before and after the Azolla trials on their plots. I demonstrated that maintaining farmers’ inputs while adding Azolla as an intercrop modestly increases rice yield. I also showed that omitting half of the urea input and substituting it with intercropped Azolla produces little change to the overall rice yield, signifying an opportunity for farmers to save on input costs. Overall, Senegalese rice growers had a positive perception of the Azolla-rice practice and have started adopting it in the next rice growing season. The results obtained from this experiment suggest that using Azolla in the Senegal River Valley has a potential as an organic fertilizer that can improve overall rice productivity and livelihoods.

Table of Contents

Table of Contents

Chapter 1: Introduction.….………………………………………………………………….....................….1

 1.1. Overview……………..………………………………………………………………………1

1.2. References………………………………………………………………….….…………..….7

Chapter 2: Mapping current and future habitat suitability of Azolla spp., a biofertilizer for

small-scale rice farming in Africa ……………..…………………...………………………….10

2.1. Introduction……………………………………………………………………………...…..10 

2.2. Materials and Methods………………………………………………………………………14

2.2.1. Mapping Habitat Suitability……………………………………………………....14

2.2.2. Mapping Current and Projected Suitability for Azolla…………………………....17

2.3. Results……………………………………………………………………………….……....18

2.3.1. Thermal Performance Curves…………………………..........................................18

2.3.2. Current and Future Projections of Azolla spp. in Africa…………………….........19

2.3.3. Visualizing the Difference Between Current and Future Climate Projections of Africa.......…………………………....………………………...........................................20

2.4. Discussion………………………………………………………….....………………….….22

2.4.1. Comparing Performance Curves……………………………………………….....22

2.4.2. Future projections for A. pinnata…………………………………………....……24

2.4.3. Future projections for A. filiculoides……………………………….......................25

2.4.4. Comparing Methods to Evaluate Azolla Suitability……………………………….25

2.4.5. Recommendations………………………………………………………………....26

2.5. Conclusion………………………………………………………………………….........….28

2.6. References………………………………………………………………………….....….….30

2.7. Chapter 2 Supplementary Material…………………………………………….....................36

Chapter 3: Urea-ka: Replacing inorganic nitrogen fertilizer with Azolla pinnata maintains

rice yields with reduced input costs in the Senegal River Valley …………………………....38

3.1. Introduction………………………………………………………………...………..............38

3.2. Materials and Methods……………………………………………………….….............…..41

3.2.1. Field experiment………………………………………………………………......41

3.2.2. Measurement of rice yield and its components,,,,.………………………………...44

3.2.3. Statistical analysis…………………………………………………………………45

3.3. Results…………………………………………………………………..…………...............45

3.3.1. Investigating percent change in rice grain yield with Azolla additions...................45

3.3.2. Investigating percent change in rice grain yield with Azolla substitutions.............46

3.3.3. Explaining variation in yield….…………………………………………...............47

3.4. Discussion……………………………………………………………………….............…..48

3.4.1. Azolla as a substituted intercrop…………………………………..........................50

3.4.2. 100-grain weight as a proxy for yield………………………………..................…51

3.5. Conclusion……………………………………………………………......…………………52

3.6. References …………………………………………………………….............…………….53

Chapter 4: An In-depth Examination of Senegalese Farmers’ Experience and Perception of Azolla Rice Farming ……………………………………………………………………………56

4.1. Introduction…………………………………………………………………..……...............56

4.2. Materials and Methods……………………………………………………………................58

4.2.1. Perceptions before the Azolla-rice trial...................................................................58

4.2.2. Azolla-rice trials…………………………………………………………………...59

4.2.3. Perceptions after the Azolla-rice trial…………………………………………….59

4.3. Results and Discussion ………………………………………………………………...…...60

4.3.1. Farmer demographics and farm description……………………………………....60

4.3.2. Farmer motivations, goals, and challenges……………………………………….60

4.3.3. Farm management and innovation……………………………………………...…63

4.3.4. Innovation...……………………………………………………………………….66

4.3.5. Knowledge of Azolla……………………………………………………………….67

4.3.6. Focal vs. non focal experience and perceptions of Azolla-rice farming.................68

           4.3.6.1. Learning and experimenting………………………………….................68

4.3.6.2. Farmers’ social environment influence...……………………………….69

4.3.6.3. Characteristics of the practice..................………………………………70

                       4.3.6.3.1. Relative advantage………………………………….................70

           4.3.6.3.2. Trialability…………………………………..............................71

4.4. Conclusion……………………………………………………………………….…….........72

4.5. References. .………………………………………………………………………................74

Chapter 5: Conclusions and Future Directions…………………………………….…...…….77 

5.1. Future Directions and Broader Implications...……………..……………………..................77 

 

 

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School	Laney Graduate School
Department	Biological and Biomedical Sciences
Subfield / Discipline	Population Biology, Ecology & Evolution
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Environmental Sciences
关键词	Azolla rice farming sustainability
Committee Chair / Thesis Advisor	David J. Civitello, Emory University Gonzalo Vazquez-Prokopec, Emory University
Committee Members	Debjani Sihi, Emory University Julie Clennon, Emory University Michael E. Cox, Dartmouth College

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