Limited observations
Another factor to be considered is that farmers in this study generally only take the topsoil or the plough layer into account. So their perceptions rely on soil indicators that they can see and/or experience directly. Farmers’ interpretations then are not necessarily based on sufficient information because of their limited observations. For example, although the majority of farmers (97%) identified earthworms as an indicator of soil quality, the presence or absence of earthworms in the soil was not important in their decision-making. A possible explanation is that they hardly see earthworms in their own fields because of the effects of management systems, particularly tillage, water management and pesticide use. Farmers said: “Our lands are under the water most of the time, so there is no time for the earthworm to appear … besides, the earthworm does not like inundated soil … they cannot survive in that.” (Orzeli Reinard) or “Because of the herbicides the soil is dead!” (Antônio Kila Neto).
Earthworm species that may occur in deeper layers or semi-aquatic earthworms did not concern the regional farmers. In a recent publication, Lima and Rodriguez [50] highlighted the presence of a number of earthworm species in irrigated rice fields in the region of this study.
The fact that farmers recognize that the presence of earthworms is an indicator of soil quality is remarkable, but their incapability of using this in their decision-making is not surprising. Farmers have experience with cropping dry soils (most of farmers still have their own vegetable gardens and orchards around their houses, where earthworms are easily visible) and therefore promptly associate earthworms with good soils. But as it is more difficult to observe earthworms in flooded rice fields, they become doubtful about their utility when assessing soil quality. From the scientist's point of view, therefore, the farmers do not use an indicator that they consider important to its full potential. On the other hand, scientists often underestimate the importance of socio-economic factors in farmers’ management decisions, as shown above when the farmers have to decide about some specific practices (e.g., rice–soya bean rotation).