When we talk about biodiversity we refer to all the species of plants, animals and existing microorganisms that interact within an ecosystem, according to Altieri (200), in agroecosystems, pollinators, natural enemies, worms and soil microorganisms, are all key components of biodiversity that play important ecological roles in processes such as natural pest control, nutrient cycling, decomposition, among others.
Some studies have shown that it is possible to stabilize insect populations in agroecosystems by designing and building plant architectures that maintain populations of natural enemies or that have direct deterrent effects on pest herbivores. By replacing simple systems with diverse ones or adding variety to existing systems, it is possible to exert changes in the habitat that favor the abundance of natural enemies.
On the other hand, the main cause of the appearance of pests is the loss of biodiversity, agriculture is a human activity that implicitly leads to a decrease in it, and this leads to the loss of the characteristics of natural communities; in a natural community there are mechanisms that disappear as said community is simplified, for this reason the increase of a functional biodiversity that offers ecological services similar to those of nature and that promotes preventive pest management under the conditions that predominate locally for agricultural exploitation is sought.
In natural ecosystems, the vegetation cover of a forest or a natural meadow prevents soil erosion, replenishes water in the soil and controls floods by improving infiltration and reducing water runoff. In agricultural systems, biodiversity performs ecosystem services beyond the production of food, fiber and income. Examples include the control of microclimates, the regulation of local hydrological processes, the regulation of the abundance of undesirable organisms and the detoxification of harmful chemicals. These processes of renewal of ecosystem services are mostly biological, therefore, their persistence depends on the maintenance of biodiversity.
One way in which soil fertility management can directly reduce the susceptibility of plants to pests, is through its influence on the health of those, many researchers and farmers have observed, that fertility practices that increase and maintain high organic matter contents and levels of diversity of the macro and microfauna of the soil improves the characteristics of these.
The relationship that exists between plant nutrition and pest incidence has been given by comparing the effects of organic and conventional agricultural practices on specific pest populations; practices to improve soil fertility can directly impact the physiological susceptibility of the crop to pest insects, either by resistance or by altering the acceptability of some plants to certain herbivores. According to Altieri and Nicholls (2007), some studies have shown how the change from organic soil management to the use of chemical fertilizers has increased the potential of certain pest insects and diseases.
The above mentioned by Altieri and Nicholls, may be based on the theory of trophobiosis exposed by Chaboussou who considers that a plant will only be attacked by a pathogen when its sap contains the right food for these pathogens, basically free amino acids, which have not come to form proteins due to a deficit of enzymes, soluble sugars and nitrates. This situation is generated when a nutritional deficiency occurs in the plant, when the metabolism and biochemical balance of crops are altered by pesticides, fungicides and herbicides and when soluble nitrogen fertilizers are used in excess.
On the other hand, some researchers mention that two distinct components of biodiversity can be distinguished in agroecosystems. The first component, the planned biodiversity, which is associated with crops and livestock intentionally included in the agroecosystem by the farmer and which can vary depending on the management and spatial and temporal arrangements of crops. The second component, associated biodiversity, includes all the flora and fauna of the soil, herbivores, carnivores, decomposing microorganisms among others, that colonize the agroecosystems from surrounding environments and that remain in the agroecosystems depending on the type of management.
Dear readers, as mentioned in the previous paragraph, planned biodiversity has a direct function, the associated biodiversity also has a function, but it is mediated through planned biodiversity, which also has an indirect function. For example, trees in an agroforestry system create shade, which makes it possible to grow crops that tolerate little sun. Therefore, the direct function of trees is to create shade. Along with the trees can come small wasps that use the nectar of the flowers of the same, these wasps can also be natural parasites of pests that normally attack crops.
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| Bibliographic references |
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Altieri, M. and Nicholls, C. 2007. Agroecological conversion of conventional production systems: theories, strategies and evaluation. Ecosystems Magazine. Vol. 16 (1) p 3-12.
Altieri, M. and Nicholls, C. 2000. Agroecology. Theory and practice for sustainable agriculture. Mexico. First edition. 169 p.
Altieri, M. and Nicholls, C. 2000. Agroecology. Theory and practice for sustainable agriculture. Mexico. First edition. 169 p.
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