Levantamento Fitossociológico e Florístico de Plantas Daninhas em Áreas Agrícolas da Região Sudoeste de Goiás - Plantas Daninhas (2024)

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Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201665Weed phytosociological and floristic survey in agricultural ...1 Recebido para publicação em 13.8.2015 e aprovado em 26.8.2015.2 Universidade de Rio Verde/Programa de Pós-graduação em Produção Vegetal/Faculdade de Agronomia, Rio Verde-GO, Brasil,<santoswf1@gmail.com>; 3 Embrapa Tabuleiros Costeiros, Aracaju-SE, Brasil.WEED PHYTOSOCIOLOGICAL AND FLORISTIC SURVEY IN AGRICULTURALAREAS OF SOUTHWESTERN GOIÁS REGION1Levantamento Fitossociológico e Florístico de Plantas Daninhas em Áreas Agrícolas da RegiãoSudoeste de GoiásSANTOS, W.F.2, PROCÓPIO, S.O.3, SILVA, A.G.2, FERNANDES, M.F.3, and BARROSO, A.L.L.2ABSTRACT - The use of the Roundup Ready® technology and the cultivation of a second cropinfluence the floristic composition of weed communities in Brazilian Central-West regioncropping systems. This study has aimed to diagnose the dominant weed species insouthwestern Goiás in areas of genetically-modified and conventional soybeans, usingphytosociological and floristic surveys. Weed sampling was obtained by collecting all theplants present within a 0.5 m hollow frame, randomly thrown 20 times in each of thirty-fiveagricultural areas in the 2012/2013 harvest. Field survey was carried out in three periods:before desiccation for soybean sowing, before postemergence herbicide in soybean firstapplication and before postemergence herbicide application in late harvest. A total of 525 m2was inventoried and 3,219 weeds were collected, which included 79 species, 58 genera and28 families. Families Poaceae, Asteraceae, Euphorbiaceae, Fabaceae, Amaranthaceae, werethe most representative in the survey. Species Cenchrus echinatus, Glycine max, Chamaesycehirta, Commelina benghalensis, and Alternanthera tenella stood out in importance. The RR+milletsoybean treatment had the highest number of species (44), while the conventional soybean+ sorghum treatment had the lowest number of species (18). The highest number of specieswas recorded in first sampling period. Treatments conventional soybean + maize andconventional soybean + millet showed higher similarity (70%), while treatments RR soybean+ millet and conventional soybean + sorghum showed the least (51%). Species of difficultcontrol were recorded in all cultivation systems analyzed.Keywords: phytosociology, floristic, soybean, late harvest, importance value.RESUMO - A utilização da tecnologia Roundup Ready® e o cultivo de segunda safra influenciam acomposição florística das comunidades infestantes dos sistemas de cultivo do Centro-Oeste. Esteestudo objetivou diagnosticar as espécies de plantas daninhas predominantes na região sudoestede Goiás, em áreas de soja geneticamente modificada e soja convencional, por meio de levantamentofitossociológico e florístico. Para amostragem das plantas daninhas foi utilizado um quadrado vazadode 0,5 m, lançado aleatoriamente 20 vezes em cada uma das 35 áreas agrícolas na safra 2012/2013. O levantamento de campo foi realizado em três épocas: antes da dessecação para o plantio dasoja, previamente à primeira aplicação de herbicida em pós-emergência da soja e anteriormente àaplicação de pós-emergência da safrinha. Foram inventariados 525 m2 no total, sendo coletadas3.219 plantas daninhas, distribuídas em 79 espécies, 58 gêneros e 28 famílias. As famílias Poaceae,Asteraceae, Euphorbiaceae, Fabaceae e Amaranthaceae, foram as mais representativas. As espéciesCenchrus echinatus, Glycine max, Chamaesyce hirta, Commelina benghalensis eAlternanthera tenella destacaram-se em valor de importância. O tratamento soja RR + milhetoapresentou o maior número de espécies (44), e o tratamento soja convencional+sorgo, o menor (18).Registrou-se o maior número de espécies na primeira época de avaliação. Os tratamentos sojaconvencional+milho e soja convencional + milheto mostraram maior similaridade (70%), enquanto ostratamentos soja RR+milheto e soja convencional + sorgo apresentaram a menor (51%). Espécies dedifícil controle foram registradas em todos os sistemas cultivo de analisados.Palavras-chave: fitossociologia, florística, soja, safrinha, valor de importância.Gisele HigaTexto digitadodoi: 10.1590/S0100-83582016340100007SANTOS, W.F. et al.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201666INTRODUCTIONThe cultivation of glyphosate-tolerantsoybeans significantly alters the chemicalcontrol mechanisms in Brazil. In recentdecades, this has been the main weed controltool in Brazilian agroecosystems (Balbinot Jr.& Veiga, 2014).The expansion of the areas that useRoundup Ready® (RR) soybeans associated withsecond crop cultivation are notably the mainchanges diagnosed in agricultural systemsfocused on grain production. These changeshave a direct influence on the weeds populationdynamics in different crop rotation/successionsystems.After the release of the RR soybean in the2003/04 harvest, there was a rapid growth ofthe cultivated area with such materials,increasing the use of glyphosate across thecountry (Fialho et al., 2011). Several reasonsare given to justify the rapid adoption of thistechnology: 1) broad spectrum of action;2) action in both early and late postemergence;3) simplification of the process of choosingherbicides; 4) decrease in the occurrence ofvisual symptoms in soybean plants; 5) nocarryover problems; and 6) control of perennialor annual species (Barros et al., 2014).Prior identification of weeds is the firststep in planning the best control methods incropping systems. The highest populationdensities and the most harmful species inagricultural areas must be observed, fromconducting floristic and phytosociologicalstudies (Pitelli, 2000; Cruz et al., 2009).The presence of weeds in agriculturalareas can cause losses in grain yield, mainlydue to competition for water, light andnutrients. Most often, these growth factors areinsufficient even for the development of themain culture (Radosevich et al., 1997).Southwestern Goiás has become oneof the main responsible areas for thedomestic growth of grain production. Soybeanscultivation in the harvest and maize, sorghumand millet in the late harvest have includedthis region in the economic dynamics ofthe country. Conducting research that supportthese production systems is critical toincreased agricultural expansion, makingthe agroecosystems more efficient andbalanced.The expansion of direct seeding andincreased use of RR soybeans have modifiedthe management mechanisms and chemicalcontrol in southwestern Goiás. These changesinfluence the floristic composition andpopulation dynamics of weeds. However, fewstudies have been conducted about the weedcommunities in this region.Considering the changes in southwesternGoiás cropping systems, this study has aimedto diagnose and compare the predominantweed species in agricultural areas which growglyphosate-tolerant soybeans and conventionalsoybeans in the first season with different cropsin late harvest.MATERIAL AND METHODSThe areas of this study are located insouthwestern Goiás farms. Field surveys havecovered Brazilian municipalities Rio Verde,Santa Helena de Goiás, Santo Antônioda Barra, and Montividiu, in the 2012/2013harvest between the months of June 2012 andJuly 2013.Regarding the Köppen-Geigerclassification, the studied municipalities havean Aw climate, with average temperatures of23.0 to 24.3 oC and average annual rainfall of1510-1663 mm, with the highest concentrationin the summer. Winter are dry, with mildtemperatures and no rain between the monthsof May and September. The soils of the regionare types dystrophic red latosol and dystrophicred latosol (Santos et al., 2011).Field surveys took place in sevenproduction systems (treatments), withfive replications in different properties thathad at least three consecutive years ofimplementation, totaling 35 agricultural areas(Table 1). In these properties, soybeans in theharvestand maize, sorghum and millet orfallow after the main harvest (succession orlate harvest) predominate.Field survey was conducted in threeevaluation periods: before desiccation forsoybean crop implementation; prior to the firstapplication of postemergence herbicides in thesoybean crop, at 20 days after sowing; andPlanta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201667Weed phytosociological and floristic survey in agricultural ...Table 1 - Location of properties conducting a weeds survey in southwestern GoiásRR soybeans (glyphosate-tolerant soybeans) CV soybeans (conventional soybeans).prior to the application of postemergenceherbicide, at 20 days after the implementationof late harvest, or in a fallow area. Weedswere inventoried from the random releaseof hollow frames in sample areas, andphytosociological analysis was based on themethod by Braun-Blanquet (1979). The hollowframes were made of 0.5 m PVC, which actedas sample units.Considering the three seasons of thefield survey in each agricultural area of20 ha with five replications, 20 sampleunits (5 m2/season or 15 m2 in total) werestandardized, amounting to 100 units pertreatment (25 m2/season or 75 m2 in total)and 700 sampling units in each stage of thesurvey (175 m2/season or 525 m2 in total), in2,100 sampled frames-inventories.Treatment Location No Soybeans/ summer Late harvest Areas (Replications) Coordinates (Universal Transversa de Mercator (UTM)) Height (m) Municipalities/Goiás 1 RR Soybean RR Maize 1 22 k 482613.93/8100304.26 862 Montividiu 1 RR Soybean RR Maize 2 22 k 540809.09/8008785.91 639 Rio Verde 1 RR Soybean RR Maize 3 22 k 524462.03/8019154.20 635 Rio Verde 1 RR Soybean RR Maize 4 22 k 560434.78/8044516.10 557 Santa Helena 1 RR Soybean RR Maize 5 22 k 528012.52/8021719.00 627 Rio Verde 2 RR Soybean Millet 1 22 k 503225.37/8077848.74 828 Rio Verde 2 RR Soybean Millet 2 22 k 505769.78/8079871.48 799 Montividiu 2 RR Soybean Millet 3 22 k 506350.89/8079876.84 768 Montividiu 2 RR Soybean Millet 4 22 k 524439.59/8016860.74 626 Rio Verde 2 RR Soybean Millet 5 22 k 482278.90/8083495.89 874 Montividiu 3 RR Soybean Sorghum 1 22 k 532499.20/8030623.97 685 Santa Helena 3 RR Soybean Sorghum 2 22 k 525340.12/8020605.52 629 Rio Verde 3 RR Soybean Sorghum 3 22 k 480231.77/8099772.54 847 Montividiu 3 RR Soybean Sorghum 4 22 k 503766.73/8078668.74 792 Montividiu 3 RR Soybean Sorghum 5 22 k 560464.02/8042437.67 530 Santa Helena 4 RR Soybean Fallow 1 22 k 502135.51/8079836.23 756 Rio Verde 4 RR Soybean Fallow 2 22 k 503231.39/8080329.71 768 Rio Verde 4 RR Soybean Fallow 3 22 k 481486.73/8099463.40 858 Montividiu 4 RR Soybean Fallow 4 22 k 480977.40/8099669.14 863 Montividiu 4 RR Soybean Fallow 5 22 k 506231.98/8044023.95 832 Rio Verde 5 CV Soybean RR Maize 1 22 k 500502.47/8079165.26 753 Montividiu 5 CV Soybean RR Maize 2 22 k 500701.46/8079859.67 750 Montividiu 5 CV Soybean RR Maize 3 22 k 526129.0/8018108.76 666 Rio Verde 5 CV Soybean RR Maize 4 22 k 525957.64/8018272.84 660 Rio Verde 5 CV Soybean RR Maize 5 22 k 518887.66/8019237.99 650 Rio Verde 6 CV Soybean Millet 1 22 k 525933.31/8018614.52 654 Rio Verde 6 CV Soybean Millet 2 22 k 526285.71/8018965.53 653 Rio Verde 6 CV Soybean Millet 3 22 k 540987.37/8057939.34 569 St. Antônio da Barra 6 CV Soybean Millet 4 22 k 541670.84/8058093.42 574 St. Antônio da Barra 6 CV Soybean Millet 5 22 k 541911.35/8057517.36 584 St. Antônio da Barra 7 CV Soybean Sorghum 1 22 k 525763.47/8018402.43 651 Rio Verde 7 CV Soybean Sorghum 2 22 k 540645.54/8073577.33 608 St. Antônio da Barra 7 CV Soybean Sorghum 3 22 k 540331.35/8073928.66 617 St. Antônio da Barra 7 CV Soybean Sorghum 4 22 k 507115.76/8044911.38 779 Rio Verde 7 CV Soybean Sorghum 5 22 k 506929.16/8044116.21 819 Rio Verde SANTOS, W.F. et al.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201668Weeds present in the frames were cutclose to the ground and taken to a laboratoryfor identification and accounting of the numberof individuals per species. After botanicalidentification, they were placed in paperbags to determine the shoot dry matterby drying in a forced ventilation oven at65 oC for 72 hours and weighed on a precisionscale.Descriptive analysis of the species foundin the areas was conducted through groupingthe structural data to calculate the generalphytosociological parameters of the study. Theimportance value index was considered as themain parameter for discussions about severityand species occurrence.From the quantification of weeds byspecies and determination of dry biomass,one proceeded to the descriptive analysis,calculating the absolute and relative valuesof density (D and RDe), frequency (F, RF),dominance (ADo and RDo), and importancevalue index (IVI), following the same methodsused by Adegas et al. (2010) and Corrêia et al.(2011), according to the formulas proposed byMueller-Dombois and Ellenberg (1974),represented in the expressions below:D = total number of individuals of thespecies/total area (m2) sampled;RDe = species density/density of allspecies x 100;F = number of frames where the specieswas found/total number of frames of thesampling;RF = species frequency/frequency of allspecies x 100;ADo = accumulated dry biomass of thespecies/total of dry biomass of the sample;RDo = dominance of the species/dominance of all species x 100; andIVI = RF + RDe + RDo.In the results were presented only therelative values of these indexes. Thedetermination of the floristic composition wasdone from the phytosociological survey. TheShannon-Wiener (H’) diversity indexes,Simpson (D) diversity and equitability (E’) fornumber of individuals were calculated withsoftware PC-ORD 6.1 (McCune & Mefford,2011), according to the expressions below:S = richness,E = H/ln (S),H = - Σ (Pi*ln(Pi),D = 1 – Σ (Pi*Pi),where: Pi = probability of importance of the ispecies (i species relativized by the total ofspecies in the sample).Floristic comparison of the relevantspecies was also held among the differenttreatments by using the Sorensen (1972)coefficient of similarity, according to thefollowing expression:SDI = 2C/(A+B)where: SDI= Sørensen-Dice similarity index;A = no. of species of area 1; B = no. of species ofarea 2; and C = no. of species common to areas1 and 2.RESULTS AND DISCUSSIONPhytosociological surveyIn the phytosociological survey, thefamilies that had the highest number ofcollected weeds, in descending order,were: Poaceae, Asteraceae, Euphorbiaceae,Fabaceae, Commelinaceae, Amaranthaceae,Convolvulaceae, Malvaceae, Cyperaceae andCaesalpiniaceae (Table 2). These ten familiescorresponded to 96% of the number ofindividuals. These same families, exceptfor Caesalpiniaceae, were also the mostrepresentative in importance value. Regardingthe weight in shoot dry matter, whichexpresses the dominance of each family orspecies within the community, the highlights,in descending order, were families Poaceae,Asteraceae, Amaranthaceae, Malvaceae,Euphorbiaceae, Commelinaceae, Fabaceae,Smilacaceae, Menispermaceae, andCyperaceae.As for the species, Cenchrus echinatushad the greatest number of individuals,dominance and importance value, followed byvoluntary or harvested soybeans (Table 3).Because of the importance of the second cropPlanta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201669Weed phytosociological and floristic survey in agricultural ...Table 2 - Families phytosociological parameters: dry matter (DM), number of individuals (NI), number of frames (NF), relativefrequency (RF), relative density (RDe), relative dominance (RDo), and importance value index (IVI) in southwestern GoiásFamilie DM (g) NI NF RF RDe RDo IVI IVI (%) Poaceae 2,336.81 1001 950 31.64 31.10 40.18 102.92 34.31 Asteraceae 1,495.01 560 504 16.78 17.40 25.71 59.89 19.96 Euphorbiaceae 197.66 377 338 11.26 11.71 3.40 26.37 8.79 Fabaceae 169.70 310 308 10.26 9.63 2.92 22.81 7.60Amaranthaceae 401.20 257 230 7.66 7.99 6.90 22.54 7.51 Commelinaceae 193.92 261 250 8.33 8.11 3.33 19.77 6.59 Malvaceae 311.98 103 98 3.26 3.20 5.36 11.83 3.94 Convolvulaceae 75.49 111 110 3.66 3.45 1.30 8.41 2.80 Cyperaceae 80.26 86 85 2.83 2.67 1.38 6.88 2.29 Smilacaceae 152.36 18 14 0.47 0.56 2.62 3.65 1.22 Menispermaceae 104.09 27 24 0.80 0.84 1.79 3.43 1.14 Caesalpiniaceae 73.55 34 29 0.97 1.06 1.26 3.29 1.10 Rubiaceae 49.13 24 23 0.77 0.75 0.84 2.36 0.79 Polygonaceae 31.84 8 8 0.27 0.25 0.55 1.06 0.35 Lamiaceae 16.16 12 10 0.33 0.37 0.28 0.98 0.33 Mimosaceae 35.11 5 5 0.17 0.16 0.60 0.93 0.31 Myrtaceae 22.93 5 5 0.17 0.16 0.39 0.72 0.24 Solanaceae 19.42 5 5 0.17 0.16 0.33 0.66 0.22 Boraginaceae 16.51 1 1 0.03 0.03 0.28 0.35 0.12 Malpighiaceae 7.29 3 2 0.07 0.09 0.13 0.29 0.10 Chrysobalanaceae 7.63 1 1 0.03 0.03 0.13 0.20 0.07 Nyctagynaceae 3.83 2 2 0.07 0.06 0.07 0.19 0.06 Simaroubaceae 6.72 1 1 0.03 0.03 0.12 0.18 0.06 Phyllanthaceae 0.93 2 2 0.07 0.06 0.02 0.14 0.05 Anacardiaceae 0.90 2 2 0.07 0.06 0.02 0.14 0.05 Moraceae 4.03 1 1 0.03 0.03 0.07 0.13 0.04 Connaraceae 0.85 1 1 0.03 0.03 0.01 0.08 0.03 Vochysiaceae 0.45 1 1 0.03 0.03 0.01 0.07 0.02 Total 5,815.74 3,219 2,100 100 100 100 300 100 in this region, resurgent soybeans, known asharvested, were classified as invasive of lateharvest. The harvested ones were recordedwith high frequency in crop rotation. Thissituation was observed in all the studied areas,demonstrating grain losses in mechanizedharvesting and competition with the secondharvest crops. Furthermore, the presence ofsoybeans in agricultural areas throughout theperiod of fallowing favors the development ofphytosanitary problems. Other eight species(Chamaesyce hirta, Commelina benghalensis,Alternanthera tenella, Bidens subalternans,Sida glaziovii, Eleusine indica, Euphorbiaheterophylla, and Cyperus difformis) wereamong the ten most significant in importancevalues.As far dominance as is concerned, afterC. echinatus, stood out: Conyza bonariensis,A. tenella, S. glaziovii, Praxelis pauciflora,C. benghalensis, Malvastrum coromandelianum,Conyza canadensis, C. hirta and E. indica.In areas of rotated crops in the cerrado ofRoraima, 23 species were recorded (Cruz et al.,2009), of which nine (E. heterophylla, Urochloadecumbens, C. benghalensis, A. tenella,S. glaziovii, S. obtusifolia, E. indica, C. hyrta andPortulaca oleraceae) were common to thissurvey. Of these species, six are amongSANTOS, W.F. et al.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201670Table 3 - Species phytosociological parameters: dry matter (DM), number of individuals (NI), number of frames (NF), relativefrequency (RF), relative density (RDe), relative dominance (RDo), and importance value index (IVI) in southwestern GoiásSpecies DM (g) NI NF RF RDe RDo IVI IVI (%) Cenchrus echinatus 1,589.75 680 640 21.312 21.125 27.34 69.77 23.257 Alternanthera tenella 367.41 244 217 7.211 7.580 6.32 21.11 7.036 Commelina benghalensis 193.92 261 250 8.308 8.108 3.33 19.75 6.583 Glycine max 85.89 284 283 9.404 8.823 1.48 19.70 6.568 Chamaesyce hirta 146.70 276 247 8.208 8.574 2.52 19.30 6.435 Sida glaziovii 366.72 134 122 4.054 4.163 6.31 14.52 4.841 Bidens subalternans 111.68 176 156 5.184 5.468 1.92 12.57 4.191 Eleusine indica 143.46 112 117 3.888 3.479 2.47 9.83 3.278 Conyza bonariensis 398.78 44 44 1.462 1.367 6.86 9.69 3.229 Praxelis pauciflora 198.82 60 48 1.595 1.864 3.42 6.88 2.293 Cyperus difformis 79.21 85 84 2.791 2.641 1.36 6.79 2.265 Euphorbia heterophyla 35.82 100 90 2.991 3.107 0.62 6.71 2.238 Conyza canadensis 151.66 48 45 1.495 1.491 2.61 5.59 1.865 Sida rhombifolia 136.92 48 48 1.595 1.491 2.35 5.44 1.814 Tridax procumbens 103.21 56 51 1.695 1.740 1.77 5.21 1.736 Malvastrum coromandelianum 152.24 39 34 1.130 1.212 2.62 4.96 1.653 Ipomoea grandifolia 42.00 65 65 2.160 2.019 0.72 4.90 1.634 Digitaria horizontalis 94.55 44 35 1.163 1.367 1.63 4.16 1.385 Pennisetum setosum 74.39 45 40 1.329 1.398 1.28 4.01 1.335 Ipomoea cordifolia 33.49 46 45 1.495 1.429 0.58 3.50 1.167 Panicum maximum 138.99 13 13 0.432 0.404 2.39 3.23 1.075 Senna obtusifolia 73.24 33 28 0.930 1.025 1.26 3.21 1.072 Setaria parviflora 91.71 22 21 0.698 0.683 1.58 2.96 0.986 Gnaphalium coarctatum 43.29 22 20 0.665 0.683 0.74 2.09 0.697 Smilax polyantha 86.61 9 7 0.233 0.280 1.49 2.00 0.667 Rhinchelytrum repens 49.93 15 15 0.498 0.466 0.86 1.82 0.608 Digitaria insularis 26.81 21 21 0.698 0.652 0.46 1.81 0.604 Crotalaria spectabilis 40.78 15 14 0.465 0.466 0.70 1.63 0.544 Cissampelos sp2. 60.95 10 8 0.266 0.311 1.05 1.62 0.541 Richardia brasiliense 37.15 14 13 0.432 0.435 0.64 1.51 0.502 Zea mays 24.07 16 16 0.532 0.497 0.41 1.44 0.481 Amaranthus viridis 33.79 13 13 0.432 0.404 0.58 1.42 0.472 Brachiaria sp. 35.19 11 11 0.366 0.342 0.61 1.31 0.437 Emilia fosbergii 47.97 6 6 0.199 0.186 0.82 1.21 0.404 Pennisetum americanum 10.44 16 16 0.532 0.497 0.18 1.21 0.403 Cissampelos ovolifolia 28.41 8 8 0.266 0.249 0.49 1.00 0.334 Leonotis nepetaefolia 15.00 12 10 0.332 0.373 0.26 0.96 0.321 Smilax brasiliensis 39.41 5 3 0.100 0.155 0.68 0.93 0.311 Mimosa hirsutissima 35.11 5 5 0.166 0.155 0.60 0.93 0.308 Cissampelos sp1. 14.73 9 8 0.266 0.280 0.25 0.80 0.266 Andira vermifuga 30.74 4 4 0.133 0.124 0.53 0.79 0.262 Sorghum halepense 38.00 1 1 0.033 0.031 0.65 0.72 0.239 Solanum americanum 19.42 5 5 0.166 0.155 0.33 0.66 0.218 To be continued...Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201671Weed phytosociological and floristic survey in agricultural ...Tabela 3, cont.Species DM (g) NI NF RF RDe RDo IVI IVI (%) Digitaria ciliares 19.51 5 4 0.133 0.155 0.34 0.62 0.208 Vernonia ferruginea 28.20 2 2 0.066 0.062 0.48 0.61 0.204 Spermacoce latifolia 7.19 7 7 0.233 0.217 0.12 0.57 0.191 Smilax campestris 21.65 3 3 0.100 0.093 0.37 0.57 0.188 Rumex acetoselha 9.38 6 6 0.199 0.186 0.16 0.55 0.182 Sida cordifolia 12.45 5 5 0.166 0.155 0.21 0.54 0.178 Rumex obtusifolius L. 22.46 2 2 0.066 0.062 0.39 0.51 0.172 Bidens pilosa 11.04 6 4 0.133 0.186 0.19 0.51 0.170 Indigofera hirsuta 5.61 6 6 0.199 0.186 0.10 0.48 0.161 Eugenia sp. 15.03 3 3 0.100 0.093 0.26 0.45 0.150 Acanthospermum hispidum 18.65 2 2 0.066 0.062 0.32 0.45 0.150 Synedrellopsis grisebachii 12.41 3 3 0.100 0.093 0.21 0.41 0.135 Heliotropium indicum 16.51 1 1 0.033 0.031 0.28 0.35 0.116 Cnidoscolus urens 15.13 1 1 0.033 0.031 0.26 0.32 0.108 Sida urens 7.19 3 3 0.100 0.093 0.12 0.32 0.106 Heteropterys sp. 7.29 3 2 0.066 0.093 0.13 0.29 0.095 Spermacoce verticilata 4.79 3 3 0.100 0.093 0.08 0.28 0.092 Myrcia guianensis 7.90 2 2 0.066 0.062 0.14 0.26 0.088 Pavonia rosa-campestris 1.24 3 3 0.100 0.093 0.02 0.21 0.071 Gossypum hirsutum 0.19 3 3 0.100 0.093 0.00 0.20 0.065 Couepia grandiflora 7.63 1 1 0.033 0.031 0.13 0.20 0.065 Neea theifera 3.83 2 2 0.066 0.062 0.07 0.19 0.065 Simaba sp. 6.72 1 1 0.033 0.031 0.12 0.18 0.060 Crotalaria incana 6.68 1 1 0.033 0.031 0.11 0.18 0.060 Smilax ovolifolia 4.69 1 1 0.033 0.031 0.08 0.14 0.048 Phyllanthus tenellus 0.93 2 2 0.066 0.062 0.02 0.14 0.048 Brosimum gaudichaudii 4.03 1 1 0.033 0.031 0.07 0.13 0.045 Sida spinosa 1.75 1 1 0.033 0.031 0.03 0.09 0.031 Ageratum conyzoides 1.40 1 1 0.033 0.031 0.02 0.09 0.029 Cresta sphaerocephala 1.20 1 1 0.033 0.031 0.02 0.08 0.028 Hyptis lophanta 1.16 1 1 0.033 0.031 0.02 0.08 0.028 Cyperus odoratus 1.05 1 1 0.033 0.031 0.02 0.08 0.027 Lithraea molleoides 0.90 1 1 0.033 0.031 0.02 0.08 0.027 Connarus suberosus 0.85 1 1 0.033 0.031 0.01 0.08 0.026 Qualea parviflora 0.45 1 1 0.033 0.031 0.01 0.07 0.024 Bauhinia sp. 0.31 1 1 0.033 0.031 0.01 0.07 0.023 TOTAL 5,815.74 3,219 2,100 100 100 100 300 100 sp1: species 1 of genus Cissampelos; sp2: species 2 of genus Cissampelos.the greatest number of individuals andimportance value in this study, excluding onlyS. obtusifolia and P. oleracea. Foltran et al.(2010), by means of a phytosociological survey incrop rotationin the Brazilian city of Botucatu,SP, have recorded the occurrence of speciesA. tenella and C. benghalensis in the crop-fallowsystem and green manure crop even with lowdensity. Both species are among the ten oneswith the highest importance value for thisstudy. Adegas et al. (2010), in sunflowercultivation, have found that C. hirta,E. heterophyla, C. benghalensis, C. echinatus, andA. tenella had higher levels of importance forBrazilian states of Goiás and Mato Grosso do Sul– data similar to the ones in the present study.SANTOS, W.F. et al.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201672In qualitative and quantitativeassessments in soybean production areas ofconventional direct seeding, Pereira et al.(2000) have recorded in Botucatu, SP,eight species similar to this ones inthis survey, as follows: Sida rhombifolia,C. benghalensis, E. heterophylla, Amaranthusviridis, Acanthospermum hispidum, Digitariahorizontalis, C. echinatus and Bidens pilosa.These floristic similarities in relation to theimportance values for different regions of thecountry demonstrate predominance of somespecies of weeds in soybeans crops. This maybe associated with tolerance or resistance tothe main herbicides used on this crop.Floristic compositionAs for the floristic composition, 79 specieswere recorded, belonging to 28 families and58 botanical genera (Tables 4 and 5). Thedistribution by classes consisted of 59 species,Table 4 - Floristic listing of magnoliopsida weed species recorded in southwestern GoiásTreatment Families/class: Magnoliopsida Species Common name RR soybean + maize RR soybean + millet RR soybean + sorghum RR soybean + fallow CV soybean + maize CV soybean + millet CV soybean + sorghum Alternanthera tenella Colla Joyweeds X X X X X X X 1. Amaranthaceae Amaranthus viridis L. Large-fruit amaranth, low amaranth, or Argentina amaranth. X X X X X 2. Anacardiaceae Lithraea molleoides (Vell.) Engl. Aroeira-branca X Acanthospermum hispidum DC. Bristly starbur, goat's head, hispid starburr, or starbur X Ageratum conyzoides L. Billygoat-weed, chick weed, goatweed, whiteweed X Bidens subalternans DC. Beggarticks, black jack, burr marigolds, cobbler's pegs, Spanish needles, stickseeds, tickseeds, or tickseed sunflowers X X X X X X X Bidens pilosa L. Black-jack, beggarticks, cobbler's pegs, or Spanish needle. X X Conyza bonariensis (L.) Cronquist Horseweed X X X X X X Conyza canadensis (L.) Cronquist Canadian horseweed X X X X X Cresta sphaerocephala DC. João-bobo X Emilia fosbergii Nicolson Florida tasselflower. X X Gnaphalium coarctatum Willd. Cudweed X X X X X Praxelis pauciflora (Kunth) R. M. King e H. Rob. Anil X X X X X X Synedrellopsis grisebachii Hieron & Kuntze Straggler daisy X X Tridax procumbens L. Coat buttons or tridax daisy X X X X X X X 3. Asteraceae Vernonia ferruginea Less. Ironweed X To be continued...Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201673Weed phytosociological and floristic survey in agricultural ...Tabela 4, cont.Treatment Families/class: Magnoliopsida Species Common name RR soybean + maize RR soybean + millet RR soybean + sorghum RR soybean + fallow CV soybean + maize CV soybean + millet CV soybean + sorghum 4. Boraginaceae Heliotropium indicum L. Indian heliotrope X Senna obtusifolia (L.) H. S. Irwin e Barneby Chinese Senna or Sicklepod. X X X X X X X 5. Caesalpiniaceae Bauhinia sp. Orchid tree X 6. Chrysobalanaceae Couepia grandiflora Benth. Oiti X 7. Connaraceae Connarus suberosus L. Pau-de-brinco X Ipomoea cordifolia L. (triloba) Heart-leaved morning glory X X X X X 8. Convolvulaceae Ipomoea grandifolia L. Morning glory, sweet potato, bindweed, moonflower, etc. X X X X X X X Chamaesyce hirta (L.) Millsp. Asthma plant, asthma weed, asthmaplant, cat's hair, flowery headed spurge, garden spurge, hairy spurge, Jean Roberts, old blood, pill bearing spurge, pill-bearing spurge, pillpod sandmat, pillpod spurge, Queensland asthma weed, red euphorbia, red milkweed, snake weed, snakeweed, sneeze weed, or spurge X X X X X X X Cnidoscolus urens (L.) Arthur 'Bull nettle', 'spurge nettle', or 'mala mujer' (evil woman). X 9. Euphorbiaceae Euphorbia heterophyla L. (Mexican) fireplant, painted euphorbia, Japanese poinsettia, desert poinsettia, wild poinsettia, fire on the mountain, paintedleaf, painted spurge, milkweed, and kaliko plant X X X X X X X Andira vermifuga Mart. Ex Benth. Angelim-do-cerrado X X X Crotalaria incana L. Woolly rattlepod X Crotalaria spectabilis Roth Rattlepod or rattlebox X Glycine max L. Soybean X X X X X X X 10. Fabaceae Indigofera hirsuta L. Hairy indigo, rough hairy indigo X Leonotis nepetifolia (L.) R. Br. Klip dagga, Christmas candlestick, or lion's ear X X X X Hyptis lophantha Mart. Ex Benth Bushmint X Mimosa hirsutissima Mart. Malícia X X X 11. Lamiaceae Heteropterys sp. ------- X X To be continued...SANTOS, W.F. et al.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 20167424 families and 45 genera belonging to theMagnoliopsidas (eudicotyledonous), and20 species, 4 families and 13 genera belongingto the Liliopsidas (monocotyledonous).Families which showed the greatestnumber of species were: Asteraceae,Poaceae, Malvaceae, Fabaceae, Smilacaceae,Euphorbiaceae, Menispermaceae andTabela 4, cont.RR soybeans (glyphosate-tolerant soybeans); CV soybeans (conventional soybeans).Treatment Families/class: Magnoliopsida Species Common name RR soybean + maize RR soybean + millet RR soybean + sorghum RR soybean + fallow CV soybean + maize CV soybean + millet CV soybean + sorghum Gossypum hirsutum L. Upland cotton or Mexican cotton X Malvastrum coromandelianum (L.) Garcke False mallow, broom weed, Clock plant, or prickly malvastrum X X X X X Pavonia rosa-campestris A. St. Hill Rosa-vermelha X X Sida cordifolia L. Country-mallow, flannel sida X X Sida glaziovii K. Schum Malva X X X X X X X Sida spinosa L. Prickly fanpetals X Sida rhombifolia L. Paddy’s lucerne, jelly leaf X X X X X X 14. Malvaceae Sida urens L. Tropical fanpetals, balai-zortie X X X Cissampelos ovolifolia DC. Orelha-de-onça X X X Cissampelos sp2. Orelha-de-onça X X X 15. Menispermaceae Cissampelos sp1. Orelha-de-onça X X X 16. Moraceae Brosimum gaudichaudii Trécul Mama cadela X Eugenia sp. Cagaíta X X 17. Myrtaceae Myrcia guianensis (Aubl.) DC. Birch, bois de fer, bois de Ste. Lucie, bois petite feuille, guava berry X X 18. Nyctagynaceae Neea theifera Oerst. Nia, neea, or saltwood. X 19. Phyllanthaceae Phyllanthus tenellus Roxb. Leafflower X X Rumex acetoselha L. Sheep's sorrel, red sorrel, sour weed, or field sorrel X X X 20. Polygonaceae Rumex obtusifolius L. Bitter dock, broad-leaved dock, bluntleaf dock, dock leaf, or butter dock X Richardia brasiliensis Gomes Tropical Mexican clover, Brazilian calla-lily, white-eye, for Brazil pusley X X X X Spermacoce latifolia Aubl. Buttonweed X X X 21. Rubiaceae Spermacoce verticilata L. Shrubby false buttonweed X 22. Simaroubaceae Simaba sp. ------- X 23. Solanaceae Solanum americanum Mill. American nightshade or glossy nightshade X X 24. Vochysiaceae Qualea parviflora Mart. Pau-terra X Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201675Weed phytosociologicaland floristic survey in agricultural ...Table 5 - Floristic listing of liliopsida weeds species in alphabetical order of families recorded in southwester GoiásTreatment Families/class: Liliopsida Species Common name RR soybean + maize RR soybean + millet RR soybean + sorghum RR soybean + fallow CV soybean + maize CV soybean + millet CV soybean + sorghum 1. Commelinaceae Commelina benghalensis L. Benghal dayflower X X X X X X X Cyperus difformis L. Variable flatsedge or smallflower umbrella-sedge X X X X X X X 2. Cyperaceae Cyperus odoratus L. Cyperus odoratus is a species of sedge known by Fragrant flatsedge or rusty flatsedge X Brachiaria decumbens Stapf. Signalgrass X X X Cenchrus echinatus L. Southern sandspur or southern sandbur X X X X X X X Digitaria ciliares (Retz) Koeler Southern crabgrass, tropical crabgrass, or summer grass. X Digitaria horizontalis Willd. Jamaican crabgrass X X X X X X Digitaria insularis (L.) Fedde Sourgrass X X X X X Eleusine indica (L.) Gaertn. Indian goosegrass, wiregrass, or crowfootgrass X X X X X X X Panicum maximum Jacq. Guinea grass X X X X X Pennisetum americanum (L.) Leeke Millet X X Pennisetum setosum (Sw). Rich. Fountain grass X X X X X Rhynchelytrum repens (Willd.) C. E. Hubb Red Natal grass X X Setaria parviflora (Poir.) Kerguélen Marsh bristlegrass, bristly foxtail, knotroot bristlegrass, or yellow bristlegrass X X X X X X Sorghum halepense (L.) Pers. Sorghum X 3. Poaceae Zea mays L. Maize X X Smilax brasiliensis Spreng. Catbriers, greenbriers, prickly-ivys, or smilaxes. X Smilax campestris Griseb. Common names include catbriers, greenbriers, prickly-ivys, and smilaxes X X X Smilax ovolifolia Roxb. Common names include catbriers, greenbriers, prickly-ivys, and smilaxes X 4. Smilacaceae Smilax polyantha Griseb. Common names include catbriers, greenbriers, prickly-ivys, and smilaxes X RR soybeans (glyphosate-tolerant soybeans); CV soybeans (conventional soybeans).SANTOS, W.F. et al.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201676Rubiaceae. Families Amaranthaceae,Convolvulaceae, Cyperaceae, Lamiaceae,Caesalpiniaceae, Myrtaceae and Polygonaceaepresented two species each. The otherfamilies (13 of the total) contributed with asingle species. In sunflower cultivation inGoiás, Adegas et al. (2010) have recorded41 species distributed in 13 botanical families.Of this total, 24 species were equal to the onesin the present study. For the same crop grownin Brazilian state Rio Grande do Sul, theseauthors have cataloged 37 species and15 families, of which 14 species were similarto those of this survey.Families Asteraceae, Poaceae andEuphorbiaceae were the ones that contributedthe largest number of species in sunflowercrops in Brazilian municipalities Chapadão doCéu, Jataí and Montividiu, in Goiás (Brighentiet al., 2003, Adegas et al., 2010). Thesefamilies were also representative in thesoybeans rotated with maize and rice inBrazilian state Roraima (Cruz et al., 2009).These latter authors state that Asteraceaeand Poaceae are the two main families ofexisting weeds in the cerrado, being presentin different grain production systems,sugarcane, floodplain fields exploitation andpastures.Regarding the distribution of speciesper genera, those which have contributed ingreater diversity were: Sida, Smilax,Cissampelos, Digitaria, Bidens, Conyza,Ipomoea, Cyperus, Crotalaria, Pennisetum,Rumex and Spermacoce. The other genera, 48of the total, had only a single species. As forthe aforementioned genera, it should behighlighted that there was no mention aboutthe Smilax genus incidence in areas ofa*gricultural crops in the cerrado.As for the distribution of the number ofspecies per treatment, the combinationRR soybean + millet presented the highestnumber (44 species), followed by RR soybean +maize (43), RR soybean + sorghum (40),conventional soybean + maize (38), RR soybean+ fallow (35), conventional soybean + millet (30)and conventional soybean + sorghum (18)(Figure 1).It was observed that for glyphosate-tolerantsoybeans, regardless of the succession culture,the highest diversity of species was recordedin relation to conventional soybean fields.These data contradict some studies that showthat successive applications of glyphosatereduce the diversity of the weed community.However, it is known that, in conventionalsoybeans, herbicides used are repeated yearafter year and primarily consist of anassociated application of ALS inhibitors withProtox inhibitors, followed by an application ofACCase inhibitor. That is, the characteristicsof the species selection factor are onlychanged.As for the distribution of species byseasons, the RR soybeans + millet treatmenthad the highest number of species (39) in thefirst evaluation (pre-planting desiccation),followed by RR soybean + maize (38),conventional soybean + maize (36), RR soybean+ sorghum (34), RR soybean + fallow (31),conventional soybean + millet (27), andconventional soybean + sorghum (16)(Figure 2). In the second evaluation (periodprior to the postemergence herbicideapplication), the RR soybean + maize treatmentshowed the greatest number of species(16 of the total). Regarding the third evaluation(late harvest), for treatments RR soybean +millet, RR soybean + sorghum and conventionalsoybean + millet, 14 species were recorded,followed by conventional soybean + maize (13),RR soybean + maize (12), RR soybean + fallow,and conventional soybean + sorghum (11).Figure 1 - Number of species (richness) of weeds found inagricultural areas in southwestern Goiás under differentproduction systems.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201677Weed phytosociological and floristic survey in agricultural ...It is noteworthy that in sorghum,regardless of the type of soybeans andevaluation time, there was less diversity ofspecies. In these areas, the predominance ofthe C. echinatus species was noted in the periodprior to desiccation for soybean seeding. Soilcover by the species in question, along withsorghum stover on the surface, may causeallelopathy (Vidal & Trezzi, 2004) and hasinfluenced the smaller number of species inthe study area. Additionally, sorghum presentslimitation of grass herbicides for use inpostemergence (Archangelo et al., 2002; Danet al., 2010), which favors the simultaneousdevelopment of the C. echinatus species withthe culture, and its spread in the growing area.Greater diversity of weeds was noted in thefirst evaluation, which is justified by the longerperiod without herbicide application. Insouthwestern Goiás agricultural areas, theabsence of cultivation from June/July toOctober/November because of low rainfall isobserved. Furthermore, the stover on thesurface from the late harvest cultures inmany cases is not sufficient to suppress theemergence of weeds at this time. The specieswith the highest importance values in the firstevaluation were A. tenella, B. subalternans,C. echinatus, C. hirta, C. benghalensis,C. canadensis, E. heterophyla, P. pauciflora,S. glaziovii, and S. rhombifolia.Although the number of species hasdecreased in the second evaluation period(main crop), some remained as predominantFigure 2 - Number of species (richness) of weeds in agriculturalareas in southwestern Goiás under different productionsystems and different survey seasons.in the areas analyzed, which stood out inimportance: A. tenella, B. subalternans,C. echinatus, C. hirta, C. benghalensis,C. bonariensis, C. difformis, E. indica,E. heterophyla and I. grandifolia.Other species persisted in the thirdevaluation (late harvest), behaving as mostimportant: C. echinatus, G. max (voluntary),C. benghalensis,E. indica, D. horizontalis,A. tenella, E. heterophyla, B. subalternans,I. cordifolia, and S. obtusifolia, regardless ofthe late harvest.Floristic similarityIn floristic comparison, it was foundthat treatments conventional soybean + maizeand conventional soybeans and millet hada higher similarity index, with 70% ofthe species common to these productionsystems (Table 6). Twenty-five species weresimilar in these treatments, as follows:A. tenella, B. subalternans, C. canadensis,G. coarctatum, P. pauciflora, T. procumbens,C. benghalensis, I. cordifolia, I. grandifolia,C. dif formis, C. hirta, E. heterophylla,L. nepetifol ia, S. obtusifol ia, G . max,S. glaziovii, S. rhombifolia, Cissampelos sp2.,C. echinatus, D. insularis, E. indica,P. maximum, P. setosum, S. parviflora andR. brasiliensis. Treatments RR soybean +millet and conventional soybeans + sorghumwere those that showed less similarity (51%of common species). The similarity amongtreatments was greater than 50%, which forthat index is considered a high percentage(Felfili & Venturoli, 2000).It is worth noting that in the floristiccomparison, C. benghalensis and C. echinatushad wide distribution, as they were presentin all treatments in the three evaluationperiods. Species A. tenella, B. subalternans,T. procumbens, I. grandifolia, C. difformis,C. hirta, E. heterophylla, S. obtusifolia, G. max,S. glaziovii, and E. indica have also hadwidespread occurrence, being observed in alltreatments in at least one of the evaluationtimes.It is noteworthy that, from thesespecies common to the seven treatments,B. subalternans and C. hirta were present insix treatments in all evaluation periods.SANTOS, W.F. et al.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201678Species A. tenella was found in five treatments(RR soybean + maize, RR soybean + millet, RRsoybean + sorghum, RR soybean + fallow, andconventional soybean + millet). On the otherhand, Euphorbia heterophylla was observed infour treatments (RR soybean + maize, RRsoybean + sorghum, conventional soybean +maize and conventional soybean + sorghum).Other five species (C. bonariensis,P. pauciflora, S. rhombifolia, D. horizontalis,and S. parviflora) were recorded in six of theseven treatments, and A. viridis, C. canadensis,G. coarctatum, I. cordifolia, M. coromandelianum,D. insularis, P. maximum, and P. setosum in fivetreatments, regardless of the evaluationperiod. Twenty-eight species were endemic toonly one treatment, with changes inevaluation periods.Of the species recorded in this study, itwas observed that Benghal dayflower(C. benghalensis), asthma plant, asthma weed,asthmaplant, cat’s hair, flowery headedspurge, garden spurge, hairy spurge, JeanRoberts, old blood, pill bearing spurge, pill-bearing spurge, pillpod sandmat, pillpod spurge,Queensland asthma weed, red euphorbia, redmilkweed, snake weed, snakeweed, sneezeweed, or spurge (Chamaesyce hirta), joyweeds(Alternanthera tenella), Indian goosegrass,wiregrass, or crowfootgrass (E. indica),(Mexican) fireplant, painted euphorbia,Japanese poinsettia, desert poinsettia, wildpoinsettia, fire on the mountain, paintedleaf,painted spurge, milkweed, and kaliko plant(E. heterophylla), morning glory, sweet potato,bindweed, moonflower, etc. (Ipomoea spp.),coat buttons or tridax daisy (T. procumbens),horseweed (Conyza spp.), sourgrass(D. insularis), tropical Mexican clover,Brazilian calla-lily, white-eye, for Brazil pusley(R. brasiliensis), buttonweed (S. latifolia),shrubby false buttonweed (S. verticilata),straggler daisy (S. grisebachii), and beggarticks,black jack, burr marigolds, cobbler’s pegs,Spanish needles, stickseeds, tickseeds, ortickseed sunflowers (Bidens spp.) are oftenoccurring in soybean cropping systems. It isnoteworthy that in Brazil and other countriessuch as Argentina and the United States,these species have been reported as tolerantor glyphosate resistant (Papa et al., 2002;Culpepper, 2006; Heap, 2015).Regarding diversity and equitability(Table 6), these indexes are used to analyzeeach area or treatment due to the variety ofspecies and for comparison of similarityamong treatments. This information providesTable 6 - Sørensen-Dice similarity index (SDI) and diversity – number of species (NSP), Shannon-Wiener index (H’), Simpsondiversity index (D’) and equitability (E´) – for RR soybeans (glyphosate-tolerant soybeans) and CV soybeans (conventionalsoybeans) in southwestern GoiásDiversity Similarity (IS) NSP E' H' D Treatment RR soybean + RR maize RR soybean + RR maize RR soybean + RR maize RR soybean + RR maize RR soybean + RR maize RR soybean + RR maize RR soybean + RR maize 43 0.85 1.86 0.79 RR soybean + maize - 0.6206 0.6265 0.6153 0.6419 0.6849 0.5573 44 0.83 1.71 0.76 RR soybean + millet - 0 0.6428 0.5569 0.5609 0.6486 0.5161 40 0.76 1.5 0.67 RR soybean + sorghum - - 0 0.5866 0.6666 0.6571 0.5517 35 0.81 1.64 0.73 RR soybean + fallow - - - 0 0.6575 0.6769 0.6792 38 0.78 1.49 0.68 CV soybean + maize - - - - 0 0.7058 0.5357 30 0.79 1.59 0.71 CV soybean + millet - - - - - 0 0.625 18 0.71 1.11 0.57 CV soybean + sorghum - - - - - - 0 Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201679Weed phytosociological and floristic survey in agricultural ...important elements for the understanding ofthe occurrence of species interactionsaccording to the selection of the managementsystem and the practices in the areas(Concenço et al., 2013).In this study, soybeans RR + maizetreatment had higher equitability (0.85), whichdepicts a lower number of dominant speciesor with high relative abundance, showinggreater species variability. Also in thistreatment higher values of the Shannon-Wiener and Simpson diversity indexes werefound: 1.86 and 0.79, respectively.The cultivation system involvingconventional soybean + sorghum had thelowest average values of equitability anddifferences, showing that a small number ofspecies predominates in these areas. Itwas expected that fallow sites in the lateharvest period presented the highest diversity,which was not observed. This treatmentwas positioned as intermediate regardingequitability (0,81), Shannon-Wiener (1,64)diversity and Simpson (0,73) for number ofindividuals. In fallow areas, predominanceof species such as southern sandspur orsouthern sandbur (Cenchrus echinatus) andjoyweeds (Alternanthera tenella), covering thesoil surface has also been observed.Assessing five treatments in the Braziliancity of Dourados, MS, Concenço et al. (2013)have found Shannon-Wiener and Simpsonindexes in the areas of maize succeedingsoybeans of 3.11 and 0.83, respectively. Thediversity data for the maize + signalgrasstreatment recorded by these authors and theRR soybean + maize treatment of this studyshowed similar values for Simpson index(0.79).Areas with RR soybean crops had greaterspecies diversity in relation to areas withconventional soybeans. Sites with geneticallymodified soybean in succession with maizehad fewer dominant species, i.e., greaterdiversity. As for sites with conventionalsoybeans + sorghum in succession, there waslow variability, and a few dominant speciesoccurring.Species C. echinatus and C. benghalensiswere the ones of higher incidence. Other11 species (A. tenella, B. subalternans,T. procumbens, I. grandifolia, C. difformis,C. hirta, E. heterophylla, S. obtusifolia, G. max,S. glaziovii, and E. indica) have also shownwidespread occurrence, since they wererecorded in RR soybean fields and inconventional soybean sites, irrespective of thetype of second crop culture.Field surveys allowed to verify thequalitative and quantitative differences inthe weed communities analyzed. In theglyphosate-tolerant soybeans cultivation sites,a higher number of species was recorded. Inthe areas of late harvest sorghum, dominanceof a small number of species was evident.Unwieldy species wererecorded in all farmingsystems analyzed. These species must beobserved prior to chemical, mechanical orcultural management decisions in the studyarea.LITERATURE CITEDADEGAS, F. S. et al. Levantamento fitossociológico deplantas daninhas na cultura do girassol. Planta Daninha,v. 28, n. 4, p. 705-716, 2010.ARCHANGELO, E. R. et al. Tolerância do sorgo forrageiroao herbicida Primestra SC. R. Bras. Milho Sorgo, v. 1, n. 2,p. 59-66, 2010.BALBINOT JR., A. A.; VEIGA, M. Densidade de plantasdaninhas afetada por sistemas de manejo do solo e deadubação. R. Ci. Agrovet., v. 13, n. 1, p. 47-55, 2014.BARROS, M. P. C.; MENDONÇA, C. G.; TROPALDI, L.Controle de plantas daninhas com herbicida glyphosateutilizando diferentes pontas de pulverização. Sci. Agr., v. 15,n. 1, p. 15-21, 2014.BRAUN-BLANQUET, J. Fitossociologia: bases para elestudio de lãs comunidades vegetales. Madri: H. Blume, 1979.820 p.BRIGHENTI, A. M. et al. Cadastramento fitossociológico deplantas daninhas na cultura de girassol. Pesq. Agropec. Bras.,v. 38, n. 5, p. 651-657, 2003.CONCENÇO, G. et al. Phytosociological surveys: tools forweed science. Planta Daninha, v. 31, n. 2, p. 469-482, 2013.CORRÊA M. L. P. et al. Dinâmica populacional de plantasdaninhas na cultura do milho em função de adubação e manejo.R. Ci. Agron., v. 42, n. 2, p. 354-363, 2011.SANTOS, W.F. et al.Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 65-80, 201680CRUZ, D. L. S. et al. Levantamento de plantas daninhas emárea rotacionada com as culturas da soja, milho e arroz irrigadono cerrado de Roraima. R. Bras. Agroamb, v. 3, n. 1,p. 58-63, 2009.CULPEPPER, A. S. Glyphosate induced weed shifts. WeedTechnol., v. 20, n. 2, p. 277-281, 2006.DAN, H. A. et al. Tolerância do sorgo granífero ao herbicidatembotrione. Planta Daninha, v. 28, n. 3, p. 615-620, 2010.FELFILI, J. M.; VENTUROLI, F. Tópicos em análise devegetação. Comunicações Técn. Flor., v. 2, n. 2, p. 1-25,2000.FIALHO, C. M. T. et al. Fitossociologia da comunidade deplantas daninhas na cultura da soja transgênica sob doissistemas de preparo do solo. Sci. Agr., v. 12, n. 1, p. 9-17,2011.FOLTRAN, R. et al. Levantamento fitossociológico dascomunidades de plantas infestantes em diferentes sistemas derotação de culturas. In: CONGRESSO BRASILEIRO DACIÊNCIA DAS PLANTAS DANINHAS, 2010, RibeirãoPreto. Anais... Ribeirão Preto: SBCPD, 2010.HEAP, I. The international survey of herbicide resistantweeds. Disponível em: <http://www.weedscience.com/summary/MOA. aspx>. Acesso em: 25 ago. 2015.MCCUNE, B. J.; MEFFORD, M. J. Multivariate analysisof ecological data. PC-ORD Version 6.0, 2011.MUELLER-DOMBOIS, D.; ELLEMBERG, H. A. Aims andmethods of vegetation ecology. New York: John Wiley,1974. 574 p.PAPA, J. C. M.; FELÍZIA, J. C.; ESTÉBAN, A. J. Cambiosem la flora de malezas como consecuencia del cambiotecnologico em Argentina: malezas nove dosas quepiedenafectar al cultivo de soja. In: CONGRESSOBRASILEIRO DE SOJA/MERCOSOJA, Londrina, 2002.Anais... Londrina: Embrapa Soja; 2002. p. 346-354.(Documentos, 180),PEREIRA, E. S. et al. Avaliações qualitativas e quantitativasde plantas daninhas na cultura da soja submetida aos sistemasde plantio direto e convencional. Planta Daninha, v. 18, n. 2,p. 207-216, 2000.PITELLI, R. A. Estudos fitossociológicos em comunidadesinfestantes de agroecossistemas. J. Consherb, v. 1, n. 2,p. 1-7, 2000.RADOSEVICH, S. R.; HOLT, J.; GHERSA, C. Weedecology: implications for management. 2. ed. New York: JohnWiley & Sons, 1997. 589 p.SANTOS, H. G. et al. O novo mapa de solos do Brasil.Rio de Janeiro: Embrapa Solos, 2011. 67 p.(Documentos, 130)SORENSEN, T. A. Method of establishing groups of equalamplitude in plant society based on similarity of speciescontent. In: ODUM, E. P. Ecologia. 3. ed. México:Interamericana, 1972. p. 341-405.VIDAL, R. A.; TREZZI, M. M. Potencial da utilização decoberturas vegetais de sorgo e milheto na supressão deplantas daninhas em condição de campo: I-plantas emdesenvolvimento vegetativo. Planta Daninha, v. 22, n. 2,p. 217-233, 2004.