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Interaction between Sweet Sorghum and weeds

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Paulo Roberto Fidelis Giancotti
Total Authors: 1
Document type: Doctoral Thesis
Press: Jaboticabal. 2016-01-18.
Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agrárias e Veterinárias. Jaboticabal
Defense date:
Advisor: Pedro Luís da Costa Aguiar Alves

Sweet sorghum (Sorghum bicolor) is featured by the high level of fermentable sugars present in its stalk. The crop is currently considered of high potential to compose the national energetic system, by producing alcohol during the sugarcane off season. The weed interference is one of the most important factors during a crop management. Because not too much have been studied about sweet sorghum, studies about the interaction between weeds and sweet sorghum crop are very welcome for the development of the bioenergy nationwide. The aim of this research were: (I) determine the periods of weed interference and the phytosociological indexes of the weed community on the sweet sorghum crop; (II) analyze the initial growth of sweet sorghum under high weed infestation; (III) study the effect of the sweet sorghum root exudate in other plant species and also evaluate the root extract of an potential stimulant plant on the production of sorgoleone by sorghum; (IV) evaluate the suppressive effect of sweet sorghum crop residues on weeds. For the first objective, the treatments were composed by increasing periods of weed presence and weed absence at two crop seasons; when it was evaluated the sweet sorghum biometry and yield, besides the determination of phytosociological indexes of the weed community (the relative indexes of density, dominance and importance, and the weed community indexes of diversity and equitability). In pots, it was carried out an assay in order to evaluate the third aim, in which hybrids of sweet sorghum were submitted to the presence of five weed species in higher density. It was evaluated the morphophysiological features of sweet sorghum and the dry mass of both crop and weeds. The studies about allelopathy were carried out in laboratory, using different methods of analytical chemistry. Bioassays was carried out in order to evaluate the activity of exudates of sweet sorghum hybrids on test plants seed germinability and seedling development. In the study of the suppressor effect of sweet sorghum residues, it was compared at field with other cover crops and it was evaluated the reinfestation of the weed community by phytosociological studies and seed soil bank evaluation. During the sweet sorghum crop, the weed density was the determinant factor for the weed importance in the weed community, once the weed development and dry mass accumulation were suppressed by the competition established by the crop. The sweet sorghum showed an extremely competitive behavior on field and the interference of weeds did not cause yield loss, in two crop seasons. The weed suppression provided by the sweet sorghum crop residues was similar to the one provided by Mucuna pruriens, controlling the weeds on field for at least four months, during the dry season. In pots, four weed species had their dry mass reduced by the presence of sweet sorghum, even in lower density of the crop. Besides that, the sweet sorghum was insensitive to the presence of three weed species that were present in higher density. The bioassays didn’t show the expected result of allelopathic inhibition of sweet sorghum exudate on test plants. Due to the high coefficient of variation, the production of sorgoleone by sorghum subjected to root extract of A. theophrasti, did not show conclusive results. (AU)

FAPESP's process: 12/11464-5 - Study of interaction between sweet sorghum and weeds in sugarcane field reform
Grantee:Paulo Roberto Fidelis Giancotti
Support Opportunities: Scholarships in Brazil - Doctorate