Herbicides Effect on Nitrogen Cycling in Agroecossystems

Abstract

With the widespread use of post-emergent herbicides and their increased use in areas under conservation management systems (no-till and minimum tillage), concerns about environmental and public health problems due to herbicidal molecules has been growing. The use of herbicides has been justified by the resultant reduction in production costs because expenses regarding application and product price are lower with these treatments compared with existing alternatives. However, studies in the literature have demonstrated that there can be an increasing need for greater doses of nitrogen (N) fertilizers and pesticides after herbicides have been applied (Cakmak, 2007; Damin et al., 2008, 2009). The use of nitrogen fertilizers in doses that are enough to supply the demand of crops is one of the main practices associated with high productivity. However, these fertilizers are expensive, and their indiscriminate use can cause the emission of green-house gases (Sherlock et al., 1989), the contamination of superficial waters with nitrate and the destruction of ozone in the stratosphere, with N2O as an intermediary (Groffman, 2000). In addition, fossil fuels, which are non-renewable resource, are consumed in the manufacture of N fertilizers. Recent research has shown that about 15 to 20% of the N introduced by fertilization can be lost after plants have been desiccated by herbicides. This losses can be even greater when the N that was already in the system is considered. Moreover, some laboratory studies have shown an increase in the emission of N2O, a gas that has a global heating potential 298 times greater than that of CO2, in areas using desiccants. Despite the importance of awareness about the effects of herbicides in the nitrogen cycle, this subject has been seldom discussed and studied in the literature. Within this context, this chapter will discuss the effects of herbicides in the nitrogen cycle processes that determine its availability to plants in agricultural systems.