Interferência alelopática de extratos de plantas de cobertura sobre a germinação de plantas daninhas

Abstract

The rampant and incorrect utilization of herbicides has been causing problems such as the resistance of weeds and environmental pollution. In order to reduce the damage caused by the excessive use of agrochemicals, the scientific community is in search of alternative ways of control which will cause less environmental impact. The adoption of practices such as crop rotation has been proving to be an efficient technique for the control of plagues, diseases and weeds, among other benefits. The use of cover crops not only enables the cultivation system through the maintenance of the soil, nutrient cycling and the use of green manuring but it can also be an alternative for controlling invasive plants. While on the vegetative phase, cover crops compete with weeds which may often hinders their stabilization. The dead vegetation cover offers a layer of straw to the soil which prevents or hampers the gemination of weeds, be it by creating a physical barrier of straw or by the allelophaty caused by the chemical substances released by the cover crops. Thus, the objective of the present paper was to evaluate which is the allelophatic interference of aqueous vegetable extracts of the following cover crops: Avena strigosa Schreb, Cichorium intybus L, Chenopodium quinoa Willd and Fagopyrum esculentum Moench, which where used over the following weeds: Amaranthus spp, Bidens pilosa, Raphanus raphanistrum e Digitaria insularis. The seeds were sown in germination boxes, each box was layered with three germitest (special tissues for seed germination) and posteriorly moistened with the extracts at the concentration of 10% (100g/1 liter of distilled H20), the witnesses were moistened with distilled water. The boxes were stored in BOD a +25 °C, with a 12-hour photoperiod of light/darkness and the evaluation was conducted every 24 hours for seven days from the beginning of germination. The analysed variables were the percentage of plants which germinated (G), the speed index of germination (IVG), the length of the seedlings (CP), green matter (MV) and dry matter (MS). The results obtained led to the conclusion that all extracts do cause interference in the germination and the development of the weeds studied. Digitaria insularis showed great susceptibility to all extracts. Raphanus raphanistrum was the weed that had less interference from the extracts, but it differed statistically from the control. Treatment with Cichorium intybus L extract completely inhibited the germination of Amaranthus spp and Bidens pilosa, and treatment with Chenopodium quinoa Willd completely inhibited the germination of Amaranthus spp, Bidens pilosa and Digitaria insularis.