Abstract
Soil is normally the final destination of pesticides applied to cultures. After a series of applications, various pesticides reach the soil due to direct application or leaf washing. However, some amount of the pesticides, particularly foliar pesticides, are intercepted and absorbed by the leaves of the weeds or by the culture itself. Plants contaminated with pesticides may return to the soil during the culture cycle (leaf senescence) or after harvesting (as crop residues). The destination of the pesticide residues in the soil from plant material is both generally ignored and unknown. The pesticide and its degradation products can be released into the soil during the decomposition of the plant, leading to an additional risk of environmental contamination. The greatest consideration when using pesticides (herbicides, insecticides, etc.) is the sensitivity and danger to other non-target species and organisms in the area of application. The adverse effects caused by the indiscriminate use of pesticides, especially herbicides, receive substantial attention because they account for 45% of the world's total pesticide market. In this work, Tukey’s test was used (with a 5% level of probability) to compare soil responses to successive applications of aqueous extracts containing bioherbicides. In general, the existence of bioherbicide residues in soil did not change its properties relative to a control soil. The nutrients evaluated herein did not show a tendency to decrease or increase in concentration during successive applications of the extracts onto the weeds, including possible contact with the soil. The use of bioherbicide did not interfere with the availability of the nutrients or affect the soil fertility characteristics, and it consequently promoted the development of plants throughout the experiment. The persistence of the bioherbicide or its byproducts in soil should not be considered an environmental risk.
Highlights
Jack-bean (Canavalia ensiformis) is a fast-growing plant used as a green cover; it is considered a rustic plant due to its great tolerance to a wide range of soil pH, as well as to other environmental problems
It is important to emphasize that the application of the extracts onto the weeds causes the immediate contact of the bioherbicide with the soil
The influence of aqueous extracts containing the prospective bioherbicide on the soil was verified by ANOVA
Summary
Jack-bean (Canavalia ensiformis) is a fast-growing plant used as a green cover; it is considered a rustic plant due to its great tolerance to a wide range of soil pH, as well as to other environmental problems. Jack-bean is able to associate with nitrogen-fixing bacteria and mycorrhizal fungi and, ameliorate the soil by improving its fertility. Herbicides represent the most marketed class of pesticides in the world. In Brazil, sales of herbicides represent approximately 45% of the whole market for pesticides (EMBRAPA, 2009). The use of herbicides is the most employed strategy to combat infestation by weeds; in Brazil, their continuous and intensive use raises concerns about the sustainability of soil fertility. The contact of herbicides with soil changes the effectiveness of an herbicide against weed growth and affects the cycle of various nutrients, resulting in the variation of the enzymatic activity of the soil (Singh and Ghoshal, 2013)
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