Ethnophytopathology: Rice Fields Free of Diseases, from the Culture of Producers in a Nuquí, Chocó-C...

Karen Silva, Jairo Castaño-Zapata

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Ethnophytopathology: Rice Fields Free of Diseases, from the Culture of Producers in a Nuquí, Chocó-Colombia´s Community

Karen Silva1, Jairo Castaño-Zapata2,

1Department of Agronomy, Universidad Nacional de Colombia, Bogotá , Colombia

2Department of Agricultural Production, Universidad de Caldas, Manizales, Colombia

Abstract

In addition to inquiring about the knowledge of Nuquí producers, the goal of this research was to prove that the fields of healthy rice plants were set in a specific landscape, which is different to the landscape where rice plants managed with fungicides are located; the composition and structure of the landscapes were determined through participant observation, bibliographic resources and photographic records. The study variables were defined in order to perform correspondence and conglomerate/cluster analysis, both univariate and bivariate. There are two clusters, Nuquí and Lerida, and the index number of different species for Nuquí-Chocó was higher compared with that of Lerida-Tolima, which indicates that Nuquí producers usually establish their rice fields among vegetable species such as weeds, shrubbery, and trees and preserved a very particular structure of landscape, allowing them to maintain their crops free of diseases.

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Cite this article:

  • Silva, Karen, and Jairo Castaño-Zapata. "Ethnophytopathology: Rice Fields Free of Diseases, from the Culture of Producers in a Nuquí, Chocó-Colombia´s Community." Research in Plant Sciences 2.1 (2014): 16-21.
  • Silva, K. , & Castaño-Zapata, J. (2014). Ethnophytopathology: Rice Fields Free of Diseases, from the Culture of Producers in a Nuquí, Chocó-Colombia´s Community. Research in Plant Sciences, 2(1), 16-21.
  • Silva, Karen, and Jairo Castaño-Zapata. "Ethnophytopathology: Rice Fields Free of Diseases, from the Culture of Producers in a Nuquí, Chocó-Colombia´s Community." Research in Plant Sciences 2, no. 1 (2014): 16-21.

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1. Introduction

The incidence of diseases such as the “Sheath blight” and “Blast”, has limited rice farming in Colombia, causing the withdrawal of about nine commercial varieties, and endangering other varieties, depending on the region [1]. Since 1995 the sheath blight is considered one of the most threatening diseases of rice fields, especially in the departments of Tolima, Huila and Valle. In consequence, two applications of fungicides must be performed during the development of the crop; the decrease in the yield per hectare caused by sheath blight is estimated between 35% and 40% [2], particularly in the variety Oryzica 1, which reduces producers’ income by 50%. In 1991 the cost of chemical control of the disease in Saldaña, Tolima, reached 425,532 dollars [3]. It is imperative to implement methodological designs not commonly used by the biological sciences, as the ones offered by ethnophytopathology, which takes into consideration the relationship between plant pathology and agricultural communities.

Formal research may be more open to informal experiments conducted by farmers, and attempt to implement less inefficient results generated by agronomic research [4]; often, plant pathologists do not take into account the traditions or customs of the producers, nor are they familiar with their terminology and concepts [5]. An example of this is the culture of the Panguinense community, whose members still preserve the traditions of their ancestors. Agricultural calendars, native seeds, and native varieties have gradually been lost. Also, traditional production and autochthonous feeding systems have been replaced by new models [6]. Peasant knowledge differs from scientific knowledge in that it is not written; it must be documented so that it does not continue to disappear. Therefore, the objective of this research, apart from investigating the culture of Panguí producers in the landscape that they have preserved by traditional methods, was to verify that healthy rice fields that are established in the Nuquí landscape (Chocó) are different from the landscape where the fields are managed by fungicides such as in Lerida (Tolima).

Figure 1. Western region, department of Chocó, Colombia [7]

2. Methodology

2.1. Setting

The research was conducted in the town of Panguí, Nuquí, Chocó, Colombia (Figure 1), which is located in the northern Pacific coast, on the gulf of Tribugá, and georeferenced: 5° 39'21.48'' N and 77° 17'58.80'' W.

2.2. Field Design
2.2.1. Landscape Composition

Observations were performed in the field in order to verify the existence of different and repeated plant species. Further, inventories of plant species of the zone were consulted, in order to record the species (trees, weeds and shrubs) that prevail in Nuquí.


2.2.2. Landscape Structure Determination

It was necessary to verify if there were patches and corridors within the landscape. Thus, the researchers performed displacements toward rice fields in the zone, among forests, jungle, rivers and mountains, and with the help of participant observation [8], the shape of landscape was studied.

2.3. Definition of Study Variables
2.3.1. Categorical Variables

A. Density:

This is the description of landscape conditions with respect to the relationship between species and the ground, with the following categories:

Dense: ground completely covered by vegetation. Medium dense: species sparsely spread on the ground. Uncovered soil: absence of vegetation.

B. Forest thickness:

Determination of the penetrability across the landscape, with the following categories: Very bushy: impenetrable areas due to the amount of overlapping species and their proximity. Bushy: forest with large amounts of contiguous, non-overlapping vegetable species, which can be differentiated. Medium bushy: there is abundant vegetation, but it is not bushy. Separate species: areas where there is a considerable distance between trees and shrubs.


2.3.2. Numeric Variables

A. Number of different species recorded by taking photographs of the landscape.

B. Distance between the camera and vegetal species in the pictures.

The photographs were taken at different distances; this difference in distance affected the study variables, so it was necessary to create an index, dividing the number of species by the distance at which the photographs were taken. The study was conducted taking into account this new variable.

2.4. Photographic Records

The photographs were taken randomly in the morning in order to take advantage of natural daylight and to obtain more intense colors of the plants. This helped to count the vegetal species more accurately.

2.5. Statistical design

The population was divided into two subpopulations: Nuquí and Lerida. The sampling took place in two stages: initially by clusters (Nuquí and Lérida), and later random samples were taken in each cluster.


2.5.1. Sample Size Estimate

Aided by a pilot sample, it was determined that sample sizes were 28 for Nuquí, and 7 for Lérida. However, more photographs were taken in both cases.

2.6. Statistical Methods

Descriptive univariate and multivariate methods were used, as well as cluster analysis. The statistical software Infostat was used.

3. Results

3.1. Field Design
3.1.1. Biotic Composition of the Landscape

The structure of the Panguí landscape is formed by different trees, crops, shrubs and weeds species; being present in different shapes and sizes, the configuration of these species is not uniform, and their quantity varies according to the species. We identified the following forest species:

Carob tree (Hymeneae courbaril L.), Anime (Protium nervosum Cuatrec.), Tree Santa María (Calophyllum brasiliense Camb.), Myrtle (Psidium caudatum Mc Vauh.), Balso (Ochroma lagopus Sw.), Chickadee (Licania sp.), Soutache (Piper sp.), Chachajo (Aníba perutii L.), Umbrella plant (Cheflera sp.), Black Jigua (Ocotea cernua (Nees) Mez), Gualanday (Jacaranda sp.), Guasco (Eschweilera sp.), Guásimo (Guazuma ulmifolia Lam.), Wink (Carapa guianensis Aubl.), Laurel (Nectandra sp.), Otobo (Otoba sp.), Salt (Lecythis ampla Miers.), Sande (Brosimum utile Kunth.), Suelda consuelda (Pseudelephantopus spicatus Aubl.), Tachuelo (Zanthoxylum sp.) and Yarumo (Cecropia peltata L.).

Although the tropics hold the greatest concentration of the planet’s biodiversity, it has been observed that most rice farmers have traditionally sought to eradicate all tree species that surround their rice fields. Further, the plants that remain are usually burnt by herbicides (glyphosate), and are ultimately eliminated (Figure 2); this can be seen in the rice fields in Lerida-Tolima.

Figure 2. Shrub species burnt by herbicides, in the municipality of Lérida-Tolima

For Panguí producers, rotating crops every year or every two years is very important. This practice fosters appropriate nutritional balance, which improves disease resistance [9]. On the other hand, crop diversity and crop rotation is not so important for producers in Lérida.

The following are some of the species found in Nuquí, which illustrates the great diversity in the area: Achín* (Colocasi esculenta L.), Achiote (Bixa Orellana L.), Avocado* (Persea americana L.), Ají (Capsocunn annuum L.), Almirajo* (Patinoaalmirajo Cuart.), Anón (Annona muricata L.), Bread tree*(Artocarpus altilis Park.), Arracacha (Arracacia xanthorrhiza Bancr.), Rice*(Oryza sativa L.), Bacao* (Gadusnorhua L.), Badea (Passiflora cuadrangulares L.), Banana tree* (Musa sapientum L.), Sweet potato (Ipomoea batatas L.), Borojó (Borojo apatinoi Cuatrec.), Cocoa* (Theobroma cacao L.), Caimito* (Chrysophyllum caimito L.), Camote (Ipomovea batatas L.), Cane Brava* (Gynerium sagittatum Aubl.), Sugarcane* (Saccharum officinarum L.), Green onion (Allien fistulosum L.), Custard* (Annona cherimola Mill.), Coriander* (Coriandrumsativum L.), Plum (Spndias purpurea L), Chontaduro* (Bactris gassipaes Kunth), Coconut* (Coccus nucifera L.), Passionflower (Passiflora mollisima Kunth.), Soursop* (Anonna muricata L.), Guava* (Psidium guajaba L), Ginger (Zingiber officinale Roscoe), Lemon lime* (Citrus limón L.), Lulo* (Solanumquitoense Lam.), Corn (Zea mays L.), Mamey* (Mammea americana L.), Mandarin* (Citrus reticulata Blanco.), Mango (Manguifera indica L.), Cashew* (Anacardium occidentale L.), Melón* (Cucumis melo L.), Orange* (Citrus sinensis L.), Yam* (Dioscorea sp.), Papachina (Colocasia esculenta L.), Papayo* (Carica papaya L.), Paprika (Capsicum annum L.), Pineapple* (Ananascomosus L.), Banana* (Musa paradisiaca L.), Watermelon (Citrullus lanatus Thunb.), Tomato (Lycopersicon esculentum Mill.), Yucca* (Manihot esculenta Cranz.), and Sapodilla* (Maticia cordata Bonpl.).

By rotating crops, farmers preserve a heterogeneous microflora. This prevents the development of populations of fungi as Magnaporthe grisea (T.T. Hebert) M.E. Barr., Anamorph Pyricularia grisea (Cooke) Sacc, and particularly those that survive in the soil for up to 20 years such as Thanatephorus cucumeris (Frank) Donk, anamorph Rhizoctonia solani Kuhn [10, 11]. Crops rotation is crucial for controlling plant diseases by interrupting the life cycle, decreasing the primary inoculum.


3.1.2. Landscape Structure: (Productive Biota)

The Panguí landscape is represented by the form of grouping and heterogeneity in a matrix, which consists of forest species, shrubs, weeds, creepers and crops (Figure 3).

The landscapes lack a defined matrix [12]; however, these species occupy 90% of the matrix, while the rivers and dwelling sites comprise 10%.

More than 10 corridors, formed by narrow surfaces, were identified (Figure 3), creating a fringe of Johnnson grass (Sorghum halepense L.) and shrubs such as Matarratón (Gliciridia sepium Jacq.) that separates the rice from the vegetable forest species.

Figure 3. Panguí landscape. A) Forest species. B) Corridors that separate the patch (rice plants) from forest species. C) Rice patch

Within landscape there are nonlinear areas of variable sizes, which differ physiognomically from the adjacent areas; the clustered rice plants have a degree of internal homogeneity, and are immersed within the matrix with contrasting characteristics respect to their composition and physiognomy. The size varies according the amount of seeds that farmers irrigate and distribute; in conclusion this landscape is the result of anthropogenic meddling.

For Panguí producers, neither the amount of different elements that make up the landscape nor their size represents an obstacle. In fact, farmers maintain different plants within their rice fields or in the surrounding area in order to avoid the flow of pathogenic vectors. Insects are important vectors of diseases and the Hemiptera play a crucial role as vectors of viruses [13]. However, in the Panguí rice production system, Sogata (Tagosodes oryzicolus Muir.) the Hoja blanca virus vector [14], has not been recorded yet.

Apart from analyzing the Nuquí landscape, a secondary source was used, and the Lerida (Tolima) landscape was taken into account. It was observed that the number of different species index in Nuquí-Chocó is higher than that of Lerida-Tolima, with an average of 9.55, and 2.93, respectively. It was also observed that the smallest number of different species per field in Nuquí was five, while the maximum was 17.

On the other hand, the smallest number of different species per field in Lerida was one and the maximum was eight (Table 1).

Table 1. Index species number for Nuquí and Lerida

Furthermore, the results showed that in Nuquí, for the forest thickness variable, there were 20 cases in the “very bushy” category and nine cases in the “bushy” category (Table 2). In contrast, 31 cases fell into the “separate species” category in Lerida, while there were eight cases in the "medium bushy" category.

Table 2. Absolute frequencies, forest thickness variable for Nuquí and Lérida

After analyzing the forest thickness variable for Nuquí and Lerida, it was found that Nuquí had the highest index of different vegetable species with characteristics “very bushy”. In contrast, no cases were observed in Lerida under this category (Figure 4).

Figure 4. Different species Index Vs forest thickness and municipality. Forest thickness: very bushy (4), bushy (3), medium bushy (2) and separate species (1). Municipality: Nuquí (nq) and Lérida (le)

Regarding the density variable in the areas studied, Nuquí had the highest number of species under the “dense” category 27 cases, while no case fell under the “uncovered soil” category (Table 3).

Table 3. Absolute frequencies, density variable for Nuquí and Lérida

Figure 5. Index of different species Vs density and municipality. Density: dense (d), medium dense (m), and uncovered soil (s). Municipality: Nuquí (nq) and Lérida (le)

When compared to Lerida, it was found that Nuquí had a higher number of different species under the categories “dense” and “medium dense” (Figure 5). Unlike Nuquí, Lerida had “uncovered soils” around rice fields 18 out of the 40 cases observed, and there were 19 cases under the “medium dense” category.

3.2. Cluster Analysis

The dendrogram indicates that there are two clusters, Lerida (L) and Nuquí (N), with a distance of approximately 2.09 units (Figure 6). It is also shown that in the other two variables (density and forest thickness), the categories cross respectively.

Thus, it is apparent that the landscape conditions in the Nuquí rice fields are a group, while the landscape conditions in the Lerida rice fields represent another group.

Figure 6. Cluster analysis. Cluster 1, Lerida (L), density variable; categories: dense (d), medium dense (m), uncovered soil (s). Cluster 2, Nuquí (N), density variable; categories: dense (d) and medium dense (m). Cluster 1, Lerida (L), forest thickness variable; categories: separate species (1), medium bushy (2), bushy (3). Cluster 2, Nuquí (N); categories: very bushy (4), bushy (3)

4. Discussion

Given their convictions, rice producers seldom see the concept of forest as being separate from agriculture; they consider the forest as a critical element for their subsistence, not precisely for the commercial value of the wood, but because the forest is an important element in meeting their food needs. The colombian agrarian system does not take into account that food production can be strengthened among forests. On the other hand, the Panguí community preserves this model as the basis of their subsistence, which results in disease-free rice plants; farmers are also aware of other benefits such as soil and water conservation, the presence of vegetable cover, and natural fertilization. The conservation of this tropical forest depends on the subsistence of this community’s culture, which does not minimize the complex and dynamic relationship that exists between forests and healthy rice plants.

Often, the diversity of natural forests is viewed as chaotic, because it is not uniform. Even so, this seemingly disorganized mosaic of vegetable species satisfies the food needs of this community by fostering healthy rice fields. The strength of the production systems and of life itself is based on the conservation of diversity [15]; the members of the Panguí community are familiar with this idea, given that they actively maintain a high diversity of vegetal species surrounding their rice fields. As this study has shown, it has been observed that the higher the diversity in the areas surrounding rice fields, the healthier rice plants appear to be.

The commercial varieties of rice monocultures grown in the country’s central area have a narrow genetic base [16] when compared with the numerous varieties of domesticated and wild rice species that Nuquí producers handle; of these, the native “Tumba casas” is the most produced variety by Panguí farmers[17]. In Colombia, the diversity of native rice is being lost, and new varieties are being introduced, along with more sophisticated production systems; this trend seems to be irreversible [18]. Agricultural biodiversity can be affected by large-scale monoculture production, and by the introduction of genetically modified materials [19].

In Bangladesh, for example, the promotion of Green Revolution rice led to the loss of diversity, including around 7,000 varieties [20]. Moreover, the destruction of biodiversity leads to the creation of uniformity, which makes farmers increasingly dependent on external inputs suppliers, cooperatives or companies [21]. Currently, this community sustains agricultural systems without questioning the important role of nature, developing and preserving the genetic diversity that confers at least partial resistance to diseases that are specific to certain cultured varieties [20].

Despite the fact that little research has been done on pest interactions within agroforestry systems, agroforestry has been recommended in order to reduce pest outbreaks generally associated with monocultures [20]. Such is the case in the coffee production system, where agroforestry techniques have been used to reduce borer beetle (Hypothenemus hampei Ferrari.) outbreaks; it is suggested to establish biological barriers in the coffee plantation using plantain, fruit trees or timber trees [22]. The results of this study showed that rice plants remain healthy within the agroforestry arrangements proposed by the Panguí community.

Biodiversity is used by farmers in rainy areas to control diseases and to reduce dependence on scarce and expensive agrochemicals [23]. Rice producers in Lerida often leave uncovered soils around their rice fields, as it has been noted in this article. The forests, seeds, and sacred species are some of the best examples of conservation of the natural landscape, and they illustrate how culture and traditional practices can be beneficial to the protection of biodiversity [15]. Therefore, the recognition that this Panguinense community gives to biodiversity should be considered by the scientific community as a futuristic knowledge and not as a primitive one.

Figure 7. Landscape of rice crops in Lérida-Tolima. a) Separate species. b) Uncovered soil

Lerida farmers have the habit of cutting the trees that exist naturally around their rice plots (Figure 7). Therefore, the forest in this region is characterized for being medium bushy and for having species that are separated from each other.

Nuquí producers establish their rice fields among soils completely covered by different species (dense), as Soutache (Piper auritum Kunth.), Andrea Mata (Hedychium Koenig Coronarium.), Besito Antioqueño (Impatiens balsamina L.), among others.

In this municipality there were nine cases out of the 29 sampled units for this category. Furthermore, these producers do not usually cut the forests (socolar) and neither do they prune them. This landscape is characterized by a high forest thickness, and some of the species that can be found there are Yarumo (Cecropia peltata L.), Gualanday (Jacaranda sp.), Vismia (Vismia baccifera L.), among others (Figure 8).

Figure 8. Landscape of rice plots in Nuquí-Chocó. a) Bushy forest. b) Dense forest

The landscape cannot be viewed as a mere sustainable topographic configuration or a particular combination of ecosystems; moreover, it cannot be stated that the landscape analysis depends exclusively on social processes [24]. Systems of scientific knowledge and producers’ culture provide two different approaches on how to management and use natural resources, so it is desirable to consider both the social and ecological contexts. Despite efforts to try to control diseases in rice plantations, in departments such as Cesar, Meta and Tolima a new symptomatology in the rice panicle has been identified, which causes empty grain, whose causal agent is Burkholderia glumae Kurita and Tabei. [25]. Also, since 2006, it has been reported that rice plants are being affected by crown sheath rot, caused by the fungus Gaeumannomyces graminis var. tritici; these reports come from the departments of Tolima and Huila, where varieties as Impro, Fedearroz 216, Fedearroz 174 and Fedearroz 733 are cultivated. Thus, it is essential to design and implement new methods in phytopathology, in order to explore new management techniques for plant diseases, as indicated by ethnophytopathology.

References

[1]  Fondo Nacional Del Arroz, Reconocimiento y manejo de las principales enfermedades del arroz, Fedearroz Press, Colombia, 2000.
In article      
 
[2]  Guzmán, P, “Manejo integrado del añublo de la vaina (Rhizoctonia solani)”, Revista Arroz, 50 (435). 10-15. 2001.
In article      
 
[3]  Guzmán, P., and Boschell, J, “Estudio agrometeorológico del añublo de la vaina (Rhizoctonia solani) en el cultivo del arroz”, Revista Arroz, 43 (393). 10-16. 1994.
In article      
 
[4]  Hoffmann, V., Probst, K., and Christinck., A, “Farmers and researchers: How can collaborative advantages be creates in participatory research and technology development?”, Agriculture and Human Values, 3 (24). 355-368. Sep, 2007.
In article      CrossRef
 
[5]  Bentley, J.D., Boa, E.R., Kelly, P., Harun-Ar-Rashid., Rahman, A.K.., Kabeere, F. and Herbas, J, “Ethnopatology: local knowledge of plant health problems in Bangladesh, Uganda and Bolivia”, Plant Pathology, 4 (58). 773-781. Agu. 2009.
In article      
 
[6]  Ospina, A, “Aproximación al estudio de las tecnologías agroforestales ecológicas del sur de Colombia”, Agroforesteríaecológica, February, 2008. [Online]. Available: http://biblioteca.ihatuey.cu/links/sistemas_agroforestales/aproximacion_al_estudio.pdf. [Accessed Aug. 7, 2012].
In article      
 
[7]  Mesa, C. A, Tradiciones elaboradas y modernizaciones vividas por pueblos afrochocoanos en la vía al mar, Colección antropología en la modernidad, Icanh Press, Bogotá, 2010.
In article      
 
[8]  Silva, K., Castaño, J., Arocha, J., and Muñoz, G, “Propuesta metodológica para un estudio etnofitopatológico”, in 2th Conferencia Iberoamericana de Complejidad, Informática y Cibernética, International Institute of Informatics and Systemics Publishers, 55-60.
In article      
 
[9]  Cano, E., and Carballo, M. Control biologico de insectos mediante depredadores. In: Carballo, M., and Guaharay, F. Eds., Control biológico de plagas agrícolas, Manuel técnico No 53, CATIE Press, Turrialba, Costa Rica, 2004, 113-276.
In article      
 
[10]  Jacas, J., Caballero, P., and Ávila, J, El control biológico de plagas y enfermedades, Universitat Jaume Press, Castellón de la Plana, 2005.
In article      
 
[11]  Degiovanni, V. B., Martínez, C. R., and Motta, F. O, Producción ecoeficiente de arroz en América Latina, CIAT Press, Cali, 2010.
In article      
 
[12]  Etter, A, Caracterización ecológica general y de la intervención humana en la Amazonia colombiana. In: Andrade, G.I., Hurtado, A and Torres, R. Eds, Amazonia colombiana diversidad y conflicto, Agora Press, Bogotá, 1992, 27-67.
In article      
 
[13]  Caranta, C., Arand, M., Tepfer, M., and Lopez, J, Recent Advances in Plant Virology, Caister Academica Press, Great Britain, 2011.
In article      
 
[14]  Hooksa, C., and Fereres, A, “Protecting crops from non-persistently aphid-transmitted viruses: A review on the use of barrier plants as a management tool”, Virus Research, (120). 1-16. Jun. 2006.
In article      
 
[15]  Shiva, V, Monocultures of the mind, Penang, Zed Books Press, Malaysia, 1993.
In article      
 
[16]  Martínez, C, “Arroz y sus parientes”, Centro Internacional de Agricultura Tropical (CIAT), 2001. [Online]. http://webapp.ciat.cgiar.org/riceweb/esp/resultados.htm. [Accessed Oct. 10, 2012].
In article      
 
[17]  Guerra, J.M, “Valores culturales: una opción para el desarrollo de productos ecoturísticos en el Pacifico Chocoano”, Revista Bioetnia, 2 (8). 117-220. Dec. 2011.
In article      
 
[18]  Laing, D. R, “Análisis de actividades agrícolas potenciales para incrementar los ingresos de los afrocolombianos, con énfasis en la región pacífica”, Revista Agricultura Tropical, 34 (3,4).18-50. Dec. 2011.
In article      
 
[19]  Centro de prensa, “Las perspectivas de la FAO sobre la bioenergía”, FAO, Mar 2012. [Online]. Available: http://www.fao.org/news/story/es/item/124067/icode/. [Nov. 09, 2012].
In article      
 
[20]  Altieri, M.A., and Nocholls, C. I, Biodiversidad y manejo de plagas en agroecosistemas, Icara Press, Barcelona, 2007.
In article      
 
[21]  Rosset, P., and Altieri, M. A, “Agroecology versus input substitution: a fundamental contradiction of sustainable agriculture”, Society and Natural Resources, 10 (3). 283–95. 1997.
In article      CrossRef
 
[22]  Fischersworring, B., and Robkamp, R, Guía para la caficultura Ecológica, Editorial López Press, América Latina, 2001.
In article      
 
[23]  Altieri, M. A, Agroecology: the scientific basis of alternative agriculture. Westview Press, Boulder, 1987.
In article      
 
[24]  Vaccaro. I., and Norman, K, “Social Sciences and landscape analysis: Opportunities for the improvement of conservation policy design”, Journal of Environmental Management, (88). 360-371. Mar. 2007.
In article      
 
[25]  Pérez, C., Saavedra, E., López, P., and Cárdenas, G, “Medidas de prevención sobre la bacteria Burkholderia glume en el cultivo de arroz”, Revista de Arroz, 56 (476). 125-128. 2008.
In article      
 
[26]  Ospina, J. (2009), “Alternativas de control de la mancha naranja (Gaeumannomyces graminis var. graminis)”, Revista de Arroz, 57(479). 129-134. 2009.
In article      
 
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