Development of bean plants in soil contaminated with trifloxysulfuron-sodium after Stizolobium aterrimum and Canavalia ensiformis cultivation

Phytoremediation, the use of plants to decontaminate soils and water resources from organic pollutants such as herbicides, is economically and environmentally a promising technique applied in many areas, including agriculture. The objective of this work was to evaluate the development of bean plants cultivated in the field, in soil with different levels of trifloxysulfuron-sodium contamination, following cultivation of two green manure species, as well as to evaluate the possibility of recontamination of the area by such herbicide with the straw permanence on the soil. The experiment was carried out in Coimbra, MG, Brazil, on a sandy clayey Red - Yellow Argisol from March to November 2003. Four levels of soil contamination with trifloxysulfuron-sodium (0.00; 3.75; 7.50; and 15.00 g ha-1) were used as well as the following five types of cultivation prior to bean sowing in the area after herbicide application: black velvet beans (Stizolobium aterrimum) followed by removal of straw; S. aterrimum, followed by permanence of straw; jack bean (Canavalia ensiformis), followed by removal of straw; C. ensiformis followed by permanence of straw; and without prior cultivation, weed-free (weeded control). The leguminous plants were kept in the area for 65 days, cut close to the soil, and with its aerial part left or not on the surface of the experimental plot, depending on the treatment. Fifteen days after the species were cut, bean was sown in the area. At 45 days after emergence (DAE) of the bean plants, plant height and dry mass of the aerial part were evaluated. Grain productivity was determined during harvest. Height, dry matter of the aerial part and grain productivity of the bean plants, cultivated in an area previously contaminated with trifloxysulfuron-sodium at any of the levels tested, were higher with prior cultivation of S. aterrimum or C. ensiformis. At the lowest level of herbicide contamination, prior cultivation of C. ensiformis was found to be more efficient than that of S. aterrimum in mitigating the harmful effects of trifloxysulfuron-sodium on bean grain production. The permanence of the straw of the green manure species during the bean cycle did not harm the development of the plants or caused culture productivity losses, indicating that straw permanence in the area does not promote recontamination of the area.

Water use efficiency of cassava plants under competition conditions

The objective of this work was to evaluate characteristics associated with the photosynthetic activity of cassava plants in competition with weeds or not. The trial was performed on open environment conditions, with experimental units consisting of fiber glass vases with 150 dm³ filled with Red Yellow Latosol, previously fertilized. Treatments consisted in the cultivation of cassava plants isolated and associated to three weed species (Bidens pilosa, Commelina benghalensis and Brachiaria plantaginea). After cassava shooting, 15 days after planting, a removal of the weeds excess was performed, sown at the time of cassava planting, leaving six plants m-2 of B. pilosa and four plants m-2 of C. benghalensis and B. plantaginea. At 60 days after emergence (DAE), stomatal conductance (Gs), vapor pressure in the substomatal cavity (Ean), temperature gradient between leaf and air (ΔT), transpiration rate (E) and water use efficiency (WUE) were evaluated. B. pilosa showed greater capacity to affect growth of cassava plants. B. plantaginea is very efficient in using water, especially by presenting C4 metabolism, and remains competitive with cassava even under temporarily low water status. C. benghalensis, in turn, is not a good competitor for light and apparently is not the primary cause of water depletion in the soil. The effects of weeds, in this case, were more associated with the competition. However, they were found between moderate to low. This implies that the competition established at experimental level was low.

Use of herbicides on turfgrass

In crop production, weeds must be controlled so as not to adversely affect crop yield and crop quality. Thus, a low level of weeds infesting a field, in most instances, is not a problem. Except in sod or seed production, turfgrass does not have a yield component. The value of turfgrass is its inherent aesthetic quality and usability. Aesthetic quality is the beauty and value that turfgrass adds to a managed landscape. Usability can be the durability of a sport field, trueness of golf putting green roll, or reduction in soil loss from water runoff or wind. Any weed presence in turfgrass can decrease the aesthetic quality and usability of turfgrass. Utilizing herbicides is the only way to completely control weeds in a turfgrass stand. While it is possible to reduce weed populations using cultural or mechanical management practices, it is impossible to completely eliminate weeds as can be accomplished with herbicides. This manuscript will review the major herbicides used in turfgrass in the United States with respect to their modes of action, herbicide family, and primary use in turfgrass.

Effect of period of sugarcane cultivation on the abundance and distribution of weed seeds in the soil profile

An experiment was laid down in a screen house to determine the distribution of weed seeds at different soil depths and periods of cultivation of sugarcane in Ilorin, Nigeria. Soil samples from different depth levels (0-10 cm, 11-20 cm and 21-30 cm) were collected after harvesting of canes from three different land use fields (continuous sugarcane cultivation for > 20 years, continuous sugarcane cultivation for < 10 years after long fallow period and continuous sugarcane cultivation for < 5 years after long fallow period) in November, 2012. One kilogram of the sieved composite soil samples was arranged in the screen house and watered at alternate days. Germinating weed seedlings were identified, counted and then pulled out for the period of 8 months. Land use and soil depth had a highly significant (p £ 0.05) effect on the total number of weeds that emerged from the soil samples. The 010 cm of the soil depth had the highest weed seedlings that emerged. There was an equal weed seed distribution at the 11-20 cm and 21-30 cm depths of the soil. Sugarcane fields which have been continuously cultivated for a long period of time with highly disturbing soil tillage practices tend to have larger seed banks in deeper soil layers (11-20 cm and 21-30 cm) while recently opened fields had significantly larger seed banks at the 0-10 cm soil sampling depth.

Population density and weed infestation in organic no-tillage corn cropping system under different soil covers

Currently, one of the biggest challenges faced by organic no-tillage farming is weed control. Thus, the use of cropping practices that help in the control of weeds is extremely important. The objective of this study was to evaluate population density and level of weed infestation in an organic no-tillage corn cropping system under different soil covers. The experiment was conducted in a randomized block design with six repetitions and five treatments, consisting of three soil covers in an organic no-tillage system, and an organic and a conventional system, both without soil cover. The treatments with soil cover used a grass species represented by the black oat, a leguminous species represented by the white lupine, and intercropping between both species. Corn was sown with spacing of 1.0 m between rows and 0.20 m between plants, using the commercial hybrid AG 1051. Infestation in corn was evaluated at stages V5 and V10, and weed density was evaluated at stage V5. The use of black oat straw alone or intercropped with white lupine, in the organic no-tillage corn cropping system, reduced the percentage of weed infestation and absolute weed density. Management-intensive systems and systems without soil cover showed higher relative densities for species Oxalis spp., Galinsoga quadriradiata and Stachys arvensis. The species Cyperus rotundus showed the highest relative density on organic no-tillage corn cropping systems. Black oat straw in the organic no-tillage cropping system limited the productive potential of corn.

Soil microorganisms and their role in the interactions between weeds and crops

The competition between weeds and crops is a topic of great interest, since this interaction can cause heavy losses in agriculture. Despite the existence of some studies on this subject, little is known about the importance of soil microorganisms in the modulation of weed-crop interactions. Plants compete for water and nutrients in the soil and the ability of a given species to use the available resources may be directly affected by the presence of some microbial groups commonly found in the soil. Arbuscular mycorrhizal fungi (AMF) are able to associate with plant roots and affect the ability of different species to absorb water and nutrients from the soil, promoting changes in plant growth. Other groups may promote positive or negative changes in plant growth, depending on the identity of the microbial and plant partners involved in the different interactions, changing the competitive ability of a given species. Recent studies have shown that weeds are able to associate with mycorrhizal fungi in agricultural environments, and root colonization by these fungi is affected by the presence of other weeds or crops species. In addition, weeds tend to have positive interactions with soil microorganisms while cultures may have neutral or negative interactions. Competition between weeds and crops promotes changes in the soil microbial community, which becomes different from that observed in monocultures, thus affecting the competitive ability of plants. When grown in competition, weeds and crops have different behaviors related to soil microorganisms, and the weeds seem to show greater dependence on associations with members of the soil microbiota to increase growth. These data demonstrate the importance of soil microorganisms in the modulation of the interactions between weeds and crops in agricultural environments. New perspectives and hypotheses are presented to guide future research in this area.

SELECTION OF HERBICIDES TARGETING THE USE IN CROP SYSTEMS CULTIVATED WITH SHOWY CROTALARIA

ABSTRACT The increase in the area planted with Crotalaria spectabilishas occurred by several factors, highlighting the potential to reduce the nematodes, nitrogen fixation and the high production of biomass. By becoming a species sown as a crop, it is necessary to control the weeds that coexist with showy crotalaria. This change in the use of this crop creates the possibility of this specie becoming a weed. The aim of this study was to assess the potential use of herbicides applied in preemergence and postemergence of C.spectabilisfor different purposes (control of volunteer and selectivity plants). Three experiments were installed in a greenhouse (two with herbicides applied in preemergence - in soils with distinct textural categories; and one experiment with herbicides applied in postemergence). The results of the experiments with herbicides applied in preemergence showed that: amicarbazone, atrazine, diuron, metribuzin, prometryn, fomesafen and sulfentrazone showed effectiveness for control of C.spectabilis in clayey soil. Besides these, flumioxazin and isoxaflutole also showed potential to be used in the control of showy crotalaria in soils with loam texture. In relation to the postemergence herbicides, atrazine, diuron, prometryn, flumioxazin, fomesafen, lactofen, saflufenacil, amonio-glufosinate and glyphosate can be used aiming the chemical control of C.spectabilis. Herbicides chlorimuron-ethyl, diclosulan, imazethapyr, pyrithiobac-sodium, trifloxysulfuron-sodium, clomazone, pendimethalin, S-metolachlor and trifluralin applied in preemergence, and imazethapyr, pyrithiobac-sodium, flumiclorac, bentazon and clethodim applied in postemergence caused low levels of injury to C.spectabilis plants, making necessary the development of new searches to ensure the selectivity of these products.

Weed Community in a Raw Sugarcane Renovation Area Submitted to Different Soil Managements

The objective of this study was to evaluate the weed community in a raw sugarcane renovation area with three soil managements and peanut sowing in succession. The experiment was conducted during the 2007/08 season on a raw sugarcane area harvested without prior burning in the last five cuts. A randomized block design with treatments arranged in a split plot and arranged in four replications was used. The main treatments consisted of three cropping systems: conventional tillage, minimum tillage and direct planting, and subplots consisted in the absence (resting) or presence of crop rotation with peanuts. After 135 days from planting peanuts and 180 days of sugarcane harvest, the number of weeds m-2 was counted and the shoot dry biomass of the weeds collected was determined. The data were interpreted by analysis of variance and the means were compared by Tukey's test at 5% probability so that phytosociological indices a, b, c e d were calculated. The use of soil conservation tillage and peanut in rotation with sugarcane in the renovation areas is effective in controlling weeds and suppression of weed species difficult to control like Cyperus rotundus, Commelina bengalensis, Urochloa plantaginea, and Digitaria nuda.