Sugarcane Mulch Research Articles

Arbuscular mycorrhizal fungi regulate plant mineral nutrient uptake and partitioning in iron ore tailings undergoing eco-engineered pedogenesis

Excess available K and Fe in Fe-ore tailings with organic matter and water-deficiencies may restrain plant colonization and growth, which hinders the formation of eco-engineered soil from these tailings for sustainable and cost-effective mine site rehabilitation. Arbuscular mycorrhizal (AM) fungi are widely demonstrated to assist plant growth under various unfavorable environments. However, it is still unclear whether AM symbiosis in tailings amended with different types of plant biomass, and under different water conditions could overcome the surplus K and Fe stress for plants in Fe ore tailings, and if so, by what mechanisms. Here, host plants (Sorghum spp. Hybrid cv. Silk) either colonized or non-colonized by the AM fungi (Glomus spp.), were cultivated in Lucerne hay- (C: N ratio of 18, LH) or Sugarcane mulch- (C: N ratio of 78, SM) amended Fe-ore tailings under well-watered (55% water holding capacity (WHC) of tailings) or water-deficient (30% WHC of tailings) conditions. Mycorrhizal colonization, plant growth, and mineral elemental uptake and partitioning were examined. The results indicated that AM fungal colonization improved plant growth in tailings amended with plant biomass under water deficient conditions. AM fungal colonization enhanced plant mineral element uptake, especially P, both in the LH- and SM-amended tailings regardless of water condition. Additionally, AM symbiosis development restrained the translocation of excess elements (i.e., K and Fe) from roots to shoots, thereby relieving their phytotoxicity. AM roles in phosphorus uptake, and excess elemental partitioning were greater in tailings with LH amendment than those with SM amendment. Water deficiency weakened AM fungal colonization and functions in terms of mineral element uptake and partitioning. These findings have highlighted the vital role AM fungi played in regulating plant growth and nutrition status in Fe-ore tailings technosols, providing the basis for involvement of AM fungi in the eco-engineered pedogenesis of iron ore tailings.

Plant biomass amendment regulates arbuscular mycorrhizal role in organic carbon and nitrogen sequestration in eco-engineered iron ore tailings

Arbuscular mycorrhizal (AM) symbiosis plays an important role in organic matter (OM) stabilization and aggregate formation in eco-engineered Fe-ore tailings technosol, but their role may be influenced by the properties of tailings technosol with different plant biomass amendment and water supply, which has not been addressed. The present study investigated if different plant biomass amendments-- Lucerne hay (LH) (low C: N ratio) and Sugarcane mulch (SM) (high C: N ratio) -- could influence the AM roles in organic carbon (OC) and nitrogen (N) sequestration in tailings under well-watered or water deficit conditions. Sorghum spp. Hybrid cv. Silk with or without AM fungal inoculation was grown in tailings amended with plant biomass (either LH or SM) for 20 weeks under glasshouse conditions. The OC and N distribution among aggregates of various sizes (based on physical fractionation) were examined in the tailings technosol with different treatments. To uncover the mechanisms of OC sequestration, the mineral composition, OC forms, and the Fe phases in organo-mineral association were determined by means of X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared analysis (ATR-FTIR), quantitative X-ray diffraction (qXRD), and synchrotron-based Fe K edge X-ray absorption fine structure spectroscopy (Fe K edge XAFS) analysis. AM symbiosis stimulated OC and N sequestration in aggregates formed from the amended tailings, which was regulated by the amendment of plant biomass with different C: N ratios. In LH amended tailings, AM symbiosis enhanced OC sequestration in both particulate OM (POM) and mineral-associated OM (MOM) within macroaggregates. In comparison, AM symbiosis enhanced N sequestration in MOM of both macro- and micro- aggregates in the SM amended tailings. Water deficit generally diminished these AM effects. Furthermore, AM symbiosis enriched carboxyl-rich organics in association with Fe/Si-rich minerals within MOM fraction. These results imply that the AM role in OC and N sequestration in Fe ore tailings is regulated by amendment using plant biomass with different C:N ratio, which should be considered in the eco-engineered pedogenesis for sustainable mine site rehabilitation.

Pre-culturing soil microbial inoculum in plant residues enhanced the resilience of tolerant bacteria and bioneutralization efficacy in alkaline bauxite residues

Bioneutralization of alkaline bauxite residues (BR) may be achieved through in situ organic acids produced from fermentative decomposition of carbohydrates-rich organic matters (e.g., plant residues), which are driven by organophilic and heterotrophic prokaryotes tolerant of extremely saline and alkaline conditions. The present study investigated if the resilience of tolerant prokaryotes in soil microbial inoculums could be improved by pre-culturing them in carbohydrate-rich plant residues, leading to enhanced bioneutralization efficacy in strongly alkaline BR. In a 2-week microcosm experiment with BR (pH ~ 10.5), it was found that the resilience of prokaryotic communities and their functional modules and bioneutralization efficacy were significantly boosted in BR admixed with plant residues (i.e., SM: sugarcane mulch, LH: Lucerne hay) pre-cultured with soil microbial inoculum. The results showed that 10–20% of the initially inoculated soil prokaryotic features were recovered in treatments with pre-cultured plant residues. Besides, the enriched diverse prokaryotes formed highly clustered networks in the amended BR. These modules actively drove C and N mineralization and sustained 0.8–2.0 units of pH reduction, despite the buffering effects of alkaline minerals in BR solid phase. In contrast, soil microbial inoculation cultured in the growth medium lost >99% of the original prokaryotic features in soil inoculums, resulting in merely 0.2–0.7 unit pH reduction in the treated BR. Therefore, pre-culturing soil inoculum in plant residues would be preferred as an integral system to treat BR for effective bioneutralization.

Mulching operation favours the suppression of weed seed germination and its growth. Hence, it keeps the weed under control

Field experiment was conducted at Vegetable block of College of Horticulture, Bagalkote, University of Horticultural Sciences, Bagalkote to study the effect of different levels of irrigation and mulches on growth and yield of tomato. The experiment with 12 treatment combinations was laid out in split plot design with three replications. Main plot constitutes four irrigation levels (I1: 100%, I2: 80%, I3: 60% and I4: 40% cumulative pan evapotranspiration) and subplot comprised of three levels of mulches (M1: Without mulch, M2: Sugarcane mulch and M3: Polythene mulch). Irrigation was given based on cumulative pan evapotranspiration following alternate day irrigation schedule using drip irrigation. The treatment combination receiving drip irrigation at 80 per cent CPE along with polythene mulch (I2M3) was recorded with highest fruit yield per plant (2.74 kg), yield per plot (60.90 kg) and yield per hectare (51.83 t/ha). The same treatment combination was noticed with highest benefit cost ratio of 3.23. Whereas, highest water use efficiency was noticed under individual treatments of drip irrigation (I4) provided at 40 per cent CPE (255.44 kg ha-1mm-1) and under polythene mulch (204.03 kg ha-1mm-1). The highest soil moisture content was observed under the treatment combination with drip irrigation at 100 per cent CPE under polythene mulch (I2M3) at 30 and 60 DAT, whereas, at 90 DAT it was highest under I2M3. However, lowest weed density was noticed under all the four irrigation levels in combination with polythene mulch at all the monthly intervals.

Soil fertility and nutrients mediate soil carbon dynamics following residue incorporation

A substantial proportion of soil carbon (C) is commonly lost following cultivation of soil and in the transition of pastures to crops. Incorporation of plant residues with nutrient addition (nitrogen, phosphorus and sulphur) may reduce these losses. We investigated the impact of initial soil fertility and supplementary nutrient addition on breakdown of sugarcane residue and associated changes in soil C following a pasture to crop transition. The legume-based pasture was previously managed with fertilizer to develop soils with high and low C. The soils were cultivated with sugarcane mulch (10 Mg ha−1), a C4 crop residue that enabled isotopic 13C tracking, with or without nutrients and sown to a triticale crop [Triticale (× Triticosecale)]. Higher soil fertility with additional nutrients reduced the decrease in total soil C as a proportion of the initial C (14.9% compared to 21.8% without nutrients) to 100 mm depth. Supplementary nutrient addition also resulted in lower physical recovery of sugarcane mulch after 105 days (38.2% in high fertility with nutrients, compared to 97% recovery in low fertility no-nutrient). A larger decline of 13C from the total soil in the high fertility nutrient treatment was similarly observed, compared to low fertility without nutrients (decreases of 47 and 38 mg 13C kg−1 soil, respectively). More fertile pastures with tactical nutrient addition was an effective means for reducing the loss of C during transition to crop.

Application of N Fertilizer to Sugarcane Mulches: Consequences for the Dynamics of Mulch Decomposition and CO2 and N2O Fluxes

Using organic fertilizers on sugarcane mulches is a potentially interesting substitute for mineral fertilization in terms of economic and environmental impacts. However, no general agreement exists regarding the short-term effect of combining mulching and organic fertilization on greenhouse gas (GHG) emissions. Therefore, we studied different mixtures in the field by combining two amounts of sugarcane mulch (5 and 10 Mg ha−1) with different N fertilizers (urea, pig slurry, and digested sewage sludge). We measured CO2 and N2O emissions shortly after application of the mixtures (0–14 days) and the mulch decomposition dynamics from 0 to 120 days after application. We hypothesized that the relative amount of N to C modifies the decomposition dynamics and GHG fluxes. The emitted N2O-N and CO2-C were measured using static chambers. Mulch-C decomposition was measured using litterbags. Our results showed that the proportion of mulch-C remaining on the soil on day 120 was not altered by either the type of N fertilizer or the mulch amount. On a shorter time scale (0–49 days), the different N treatments affected the mulch-C and mulch-N losses and the C:N ratios, indicating a transient interaction between the dynamics of the mulch and the added N. The intensity of N2O-N emission was ranked as pig slurry > urea > digested sewage sludge, underscoring the effect of the physical form of N fertilizer. This work highlights the need to jointly study carbon and nitrogen dynamics and consider both soil carbon and gas emissions to assess the GHG balances of sugarcane farming practices.

Microbial decomposition of biomass residues mitigated hydrogeochemical dynamics in strongly alkaline bauxite residues

Effective neutralization of strongly alkaline conditions in bauxite residues (BR) is the fundamental step to initiate the process of eco-engineering BR into growth substrate (or soil-like medium) for direct phytostabilization with pioneer plant species. The present study aimed to evaluate the effectiveness of microbial decomposition of organic matter (OM) (i.e., biomass residues) in neutralizing the strong alkalinity of residues under saturated conditions, together with the regulatory role of calcium sulfate (CaSO4) addition. Admixing OM (i.e., sugarcane mulch, Lucerne hay) alone in the BR significantly lowered the porewater pH from 11.4 to around 9.0 by Day 7, which persisted until the end of incubation (Day 28). The pH reduction in the porewater of OM-amended BR coincided with the production of acidic organic compounds (mainly acetic acid). Diverse species of organotrophic bacteria (e.g., Enterobacteriales, Pasteurellales, Lactobacillales, and Streptophyta) were found to have colonized in the OM-amended BR, but which were dominated by haloalkaliphilic bacteria (e.g., Halomonas and Bacillaceae). The CaSO4 addition in the OM-amended BR further lowered pH to 8.3 in the porewater. Besides, the bioneutralization effects resulted in dramatic reduction (>90%) of soluble Al in the porewater, which is a prerequisite to lowering Al toxicity in plants. At the same time, the levels of major cations (i.e., K, Ca, Mg) in the porewater were elevated by the OM + CaSO4 amendment, which would facilitate subsequent leaching of these soluble salts to lower the salinity in the BR, and improve the diversity of organotrophic bacterial communities in the amended BR.

On-farm trials of practical options for hydrogen sulphide removal from piggery biogas

Manure-derived biogas is increasingly used at Australian piggeries to produce heat and generate electricity. However, high concentrations of hydrogen sulphide (H2S) in piggery biogas is discouraging further use, because of a lack of practical, cost-effective H2S removal options. To address this issue, on-farm trials were conducted at two piggeries. One trial tested H2S oxidation; adding small amounts of air to biogas, upstream of a low-cost enhanced surface treatment vessel which was fabricated on-farm with intrinsic safety measures. Covered anaerobic pond (CAP) effluent provided a convenient, low-cost nutrient source for the biofilm of naturally-occurring microorganisms in the packed column. This treatment was effective, removing over 90% of the H2S in a single pass and reducing H2S concentrations from 4000 ppm to <400 ppm. Another trial tested chemisorption performance of natural, iron-rich red soil, mixed with a ground sugar cane mulch bulking agent, in comparison with cg5 commercial media (iron-oxide pellets). The red soil removed H2S, but had a substantially lower capacity (similar to 2 g Sikg red soil) than the cg5 (similar to 200 g Sikg media). Accordingly, red soil is unlikely to be feasible as a primary treatment medium, but may be useful for final polishing after an oxidation step has removed most of the H2S. Crown Copyright (C) 2018 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers. All rights reserved.

Biochar and biomass organic amendments shaped different dominance of lithoautotrophs and organoheterotrophs in microbial communities colonizing neutral copper(Cu)-molybdenum(Mo)-gold(Au) tailings

The present study aimed to characterize effects of organic amendments (i.e., biochar (BC) and sugarcane mulch (SM), respectively) on microbial properties in fresh and neutral Cu-Mo-Au tailings, for the purpose to eco-engineer tailings into technosols in glasshouse microcosms with native plant cover. Organic amendments modified key physicochemical conditions, including water holding capacity, cation exchange capacity, and levels of labile organic carbon and nitrogen. SM elevated available C and N, and microbial diversity, respiration rate and enzymatic activities in the amended tailings, regardless of plant species established. Specifically, SM amendment elevated the abundance of Bacteroidetes, especially the organic matter decomposers (e.g., Algoriphagus, Chitinophagaceae). Although BC addition reduced the Cu availability and uptake by plants, it had little impacts on levels of available nutrients, microbial biomass and enzymatic activities in the treated tailings. The BC amendment enhanced the abundance of Actinobacteria and Gammaproteobacteria, among which Fe- and S-oxidizing bacteria (Acidithiobacillus) appeared to be the most abundant. The improved water-soluble organic carbon and nitrogen status in SM amended tailings were the strongest driving factors in the shift of bacterial communities towards organoheterotrophic dominance. The plant biomass-based option (e.g., SM) together with tolerant pioneer plants as hosts would be preferred for eco-engineering the neutral Cu-Mo-Au tailings into functional technosol.

Sugarcane mulch C and N dynamics during decomposition under different rates of trash removal

Abstract Sugarcane is a worldwide crop that leaves a considerable amount of crop residues (called trash) on the soil surface each year after green cane harvesting. However, the recent industrial valorization of these residues raises the question of how much trash to leave as mulch after harvest. Here, we studied the decomposition of three different trash quantities (4, 8 and 12 Mg ha −1 ) across five experimental sites from a subtropical climate over one year. We quantified the dry matter (DM), carbon (C) and nitrogen (N) contents of the remaining mulch at one-month intervals for one year after trash addition at all sites. The chemical composition of the trash was characterized by proximate analysis at one site. Our results showed that mulch degradation was proportional to the initial amount of trash left on the soil surface, i.e., the degradation rates were similar for the three trash treatments at each site, suggesting no limiting factor to decomposition associated with trash quantity and its contact with the soil. On average, 64% of the trash was degraded after 12 months in all treatments, leading to considerable differences in the mass of C degraded after one year (1.2 ± 0.1, 2.3 ± 0.2 and 3.5 ± 0.3 Mg ha −1 for the 4, 8 and 12 Mg ha −1 treatments, respectively). An interaction between trash quantity and site was observed, which translated into more differences in the C degradation rates between sites for the 4 Mg ha −1 trash treatment. The N content of the remaining mulch was rather stable throughout the year, which indicated the efficient use and recycling of N by the decomposing microflora during trash decomposition. These results will help determine the amount of sugarcane trash that should be left on fields to preserve soil C and soil fertility.

Low-cost filter media for removal of hydrogen sulphide from piggery biogas

The presence of elevated concentrations of hydrogen sulphide (H2S) in piggery biogas is problematic due to its corrosiveness and toxicity. At small scale, the cost of using iron or carbon-based commercial filter media to remove H2S can act as a barrier to the uptake of on-farm biogas technology. To identify cost-effective, alternative options, this study tested and compared H2S removal by the commercial iron-oxide H2S scavenger (cg5) with the alternative solid media: granulated steel furnace slag (GSFS), red soil, compost, composted beef feedlot manure, granular activated carbon (GAC) and biochar. Experiments measured single-pass H2S removal from a pre-humidified standard gas (2000ppm H2S in nitrogen) onto solid media contained in a cylindrical plastic column (DN 25mm, depth 110–147mm). The commercial medium (cg5) performed considerably better than the other media, achieving sulphur removal of 143gS/kg medium at breakthrough (>10ppm outlet H2S). A red soil was the most promising alternative medium (2–12gS/kg medium at breakthrough). The crystalline structure of the iron-oxide minerals appeared to strongly influence the H2S removal capacity of the red soils, and pressure drop was generally high. Bulking with ground sugar cane mulch (SCM) was effective at reducing pressure drop. Interestingly, H2S removal with red soil improved when the soil was regenerated by exposure to air, followed by reuse in the column. Overall, red soil may be a suitable low-cost option, especially for polishing biogas after initial biological H2S removal.

Replenishing Humic Acids in Agricultural Soils

For many decades, it was commonly believed that humic acids were formed in soils by the microbial conversion of plant lignins. However, an experiment to test whether these humic acids were formed prior to plant matter reaching the soil was never reported until the late 1980s (and then only as a side issue), even though humic acids were first isolated and reported in 1786. This was a serious omission, and led to a poor understanding of how the humic acid content of soils could be maintained or increased for optimum fertility. In this study, commercial sugar cane mulch and kelp extracts were extracted with alkali and analyzed for humic acid content. Humic acids in the extracts were positively identified by fluorescence spectrophotometry, and this demonstrated that humic acids are formed in senescent plant and algal matter before they reach the soil, where they are then strongly bound to the soil and are also resistant to microbial metabolism. Humic acids are removed from soils by wind and water erosion, and by water leaching, which means that they must be regularly replenished. This study shows that soils can be replenished or fortified with humic acids simply by recycling plant and algal matter, or by adding outside sources of decomposed plant or algal matter such as composts, mulch, peat, and lignite coals.

Ferric minerals and organic matter change arsenic speciation in copper mine tailings

Arsenic (As) is commonly associated with Cu ore minerals, with the resultant risk that As can be released offsite from mine tailings. We used synchrotron-based fluorescence X-ray absorption near-edge spectroscopy (XANES) imaging to provide in situ, laterally-resolved speciation of As within tailings which differed in magnetite content (5–12%) and organic matter content (0–5%). Although the total As content was lower in tailings with low magnetite (LM), the soluble (pore water) As was actually 7-times higher in LM tailings than in high magnetite (HM) tailings. Additionally, amendment with 5% sugarcane mulch residues (SMR) (for revegetation) further increased soluble As due to the dissolution and oxidation of arsenopyrite or orpiment. Indeed, in HM tailings, arsenopyrite and orpiment initially accounted for 88% of the total As, which decreased to 48% upon the addition of SMR – this being associated with an increase in AsV-ferrihydrite from 12% to 52%. In LM tailings, the pattern of As distribution and speciation was similar, with As as AsV-ferrihydrite increasing from 57% to 75% upon the addition of SMR. These findings indicate that changes in ore processing technology, such as the recovery of magnetite could have significant environmental consequences regarding the As mobilisation and transformation in mine tailings.

The influence of sugarcane mulch on sand dune stabilization in Khuzestan, the southwest of Iran

ABSTRACT- Over the past 50 years, oil mulching has been a common technique for sand dune stabilization in the southwest of Iran (Khuzestan province). However, concerns over the release of heavy metals from oil mulching have led to the search for alternative mulches that are capable of stabilizing sand dunes without environmental hazards. This study investigates the feasibility of using sugarcane residues for producing environment-friendly mulches. Dunder, Press Mud, and clay soil from the surrounding area near the sand dunes were used to make sugarcane mulches for comparison with the traditional oil mulch. A sand dune was selected as a sample bed for applying the mulch. To select the proper ingredients and treatments, Dunder, Press Mud, and clay soil were mixed with water by a trial-and-error method. The selected batch mix was then used to make the desired mulch and sprayed on a sand dune bed. Shear strength of surface soil (SSS), penetration resistance (PR), soil surface shear resistance (SSR), and erodibility of selected treatments were measured by the shear torvane, hand penetrometer, Zhang’s surface shear device, and the wind tunnel. The treatments were arranged in a factorial experiment within a completely random design with the factors including mulch type (seven sugarcane mulches and one traditional oil mulch), thickness (1 or 2 layers), and rainfall (rain and no rain). The results indicate that SSS and PR increased with mulch thickness; the average values of SSS and PR obtained with the two-layer treatments were 1.27‒1.33 and 1.13‒1.15 times as great as the single-layer treatments. Increasing fraction of sugarcane residues significantly increased the SSS and PR. Higher concentrations of organic matter, CaCO3, and electrolyte in the sugarcane mulches may have helped the bonding of soil particles and increased the SSS and PR. However, the oil mulch had the lowest SSS but the highest PR. This might be due to the lower viscosity of oil mulch that allows it to penetrate sand dunes more easily than sugarcane mulches do.

Efecto de diferentes mulches orgánicos sobre el cultivo de brócoli (Brassica olerácea L. var. Itálica) en Ecuador

ABSTRACT In a broccoli (Brassica oleracea L. var. Italica) culture of the ecuadorian Andes (2850 m.s.n.m., 01° 24' S, 78° 35' O), some variables of growth, crop production, weed control and moisture and nitrogen content, were evaluated in response to the application of different types of organic mulch. A randomized experimental block design with five treatments and three replicates was used. The treatments were: M0: without mulch; MM: maize mulch (Zea mays L.); MV: vicia mulch (Vicia sativa L.); MA: oat mulch (Avena sativa L.) and MC: sugarcane mulch (Saccharum officinarum L.). Vegetative growth and crop production were higher (p < 0.05) in vetch mulch treatment (31.8 t/ha) followed by oat mulch (18.6 t/ha). Corn mulch (11.4 t/ha) obtained similar crop production than control without mulch (13.9 t/ha), but sugar cane mulch treatment had lowerproduction (7.9 t/ha) than control without mulch, probably due to some sort of allelopathy. As for weed control, all treatments had a lower fresh weight of weed (p < 0.05) than control without mulch (6.9 kg), however oat mulch (3.4 kg) was less effective than vetch mulch (2.4 kg) and sugar cane mulch (1.9 kg). Moisture and nitrogen concentration were similar in all treatments. The results show that the best option for growing broccoli is vetch mulch as it achieved an increase in production and an efficient weed control.

Retention of Metribuzin by Sugarcane Residue

Assessment of herbicide retention in the soil environment is essential for minimizing their potential contamination of surface and groundwater resources. In this study, metribuzin retention characteristics by sugarcane mulch residue were quantified. Batch methods were used to quantify adsorption and desorption of metribuzin by the residue over a wide range of input concentrations and reaction times. Desorption was carried out after 1- and 21-day adsorption, which was followed by methanol extraction. Metribuzin retention by the residue exhibited linear adsorption where the partitioning coefficient (Kd) increased over time. Adsorption-desorption exhibited strong hysteresis indicative of time-dependent retention. The extent of hysteresis and nonextractable or residual amounts increased as the time for adsorption increased. A multireaction model provided good description of the time-dependent adsorption and desorption behavior for all input concentrations. In addition, based on measured Kd values, we found that metribuzin retention by the residue did not change significantly with the age of the decaying residue. Metribuzin breakthrough results (breakthrough curves) from miscible displacement experiments showed high mobility of metribuzin in residue-amended Sharkey and Commerce soil columns. Metribuzin breakthrough curves exhibited gradual release during leaching as well as significant responses to flow interruption and were well described using the multireaction model.

Efeitos de períodos sem a ocorrência de chuva na eficácia do flumioxazin aplicado no solo e na palha de cana-de-açúcar

The present work aimed to evaluate the efficacy of flumioxazin applied over the soil or in association with sugarcane mulch, followed by different periods without the rain occurrence. The experiment was conducted in vases under greenhouse conditions in Botucatu County, São Paulo, Brazil. Vases were filled with soil and Brachiaria decumbens, Digitaria horizontalis, Ipomoea nil, Ipomoea grandifolia, Bidens pilosa and Sida rhombifolia weeds were sown and then covered or not with sugarcane mulch, depending on the treatment used. The experimental design used was entirely randomized with four replications. Treatments were displaced in 4 x 2 factorial scheme, with factors representing four periods without rain occurrence, 1, 15, 30 and 60 days and two herbicides positioning, over the soil without sugarcane mulch and over sugarcane mulch. Control evaluations were carried out at 14, 28 and 42 days after rain occurrence. In general mode, it was possible to observe that flumioxazin application over the soil or over sugarcane mulch promoted control satisfactory levels of weeds. Reductions on control levels of some weed species were observed when the herbicide was exposed to a period of 60 days without rain occurrence.

Eficácia da associação entre os herbicidas clomazone e hexazinona no controle de plantas daninhas em cana-de-açúcar

The aim of this study was to evaluate the association between the herbicides clomazone + hexazinone applied during a dry period and at different doses, on soil and sugarcane mulch, in the weed control. The experiment was applied in August 22, 2007 in Santa Maria, São Paulo, Brazil. The experimental plots were constituted of five sugarcane lines spaced in 1,5 m, with 6 m of length. In the plots were sown the weeds Brachiaria decumbens, Euphorbia heterophylla, Ipomoea grandifolia, Ipomoea nil, Ipomoea hederifolia, Ipomoea quamoclit e Merremia cissoides. The treatments were the herbicides clomazone + hexazinona at doses 720 + 180; 800 + 200; 880 + 220 e 1000 + 250 g ha-1 and imazapic at 147 g ha-1, applied over the soil and sugarcane mulch. Two herbicide untreated were also used as check, being one with and other without sugarcane mulch. The treatments promoted an efficacy control of weeds species evaluated, especially until 119 days after application (DAA). At 153 DAA were observed good control for M. cissoides, E. heterophylla, I. nil and B. decumbens for the association of clomazone + hexazinone. For I. quamoclit clomazone + hexazinone only at higher doses in the presence and absence of mulch and imazapic applied over the mulch promoted satisfactory levels of control. For I. hederifolia, to the 153 DAA, the combination of clomazone + hexazinone promoted unsatisfactory levels of control and imazapic applied on the straw promoted effective control of this species and I. grandifolia only imazapic and clomazone + hexazinone at the highest dose, both over the mulch promoted good control.

Efeitos de períodos de permanência de clomazone + hexazinona no solo e na palha de cana-de-açúcar antes da ocorrência de chuvas na eficácia de controle de plantas daninhas

O presente trabalho teve por objetivo avaliar a eficácia da mistura formulada de clomazone e hexazinona aplicada sobre o solo e em associação com a palha de cana-de-açúcar, após diferentes períodos de permanência sem a ocorrência de chuvas. O experimento foi conduzido em vasos em casa de vegetação, no município de Botucatu-SP. Os vasos foram preenchidos com solo, e as sementes de plantas daninhas (Brachiaria decumbens, Ipomoea grandifolia, Ipomoea hederifolia e Euphorbia heterophylla) foram semeadas superficialmente e, em seguida, cobertas ou não com palha de cana-de-açúcar, dependendo do tratamento utilizado. O delineamento experimental utilizado foi o inteiramente casualizado, com quatro repetições. Os tratamentos foram dispostos em um esquema fatorial 3 x 6, sendo os fatores seis períodos sem ocorrência de chuvas (0, 3, 7, 15, 30 e 60 dias) e três posicionamentos do produto (sobre o solo sem palha, sobre e sob a palha de cana). Foram realizadas avaliações de controle aos 10, 21, 35 e 42 dias após a ocorrência da chuva. A mistura de clomazone + hexazinona promoveu excelentes resultados de controle para todas as espécies estudadas quando aplicada sobre, sob ou na ausência de palha de cana-de-açúcar. No entanto, observou-se tendência de redução nos níveis de controle para períodos superiores a 60 dias sem ocorrência de chuva.

Girassol: emergência e crescimento inicial de plantas sob resíduos de cana-de-açúcar

O objetivo do trabalho foi avaliar o efeito da palha residual da colheita da cana-de-açúcar e da adição de vinhaça sobre o solo na emergência e no crescimento inicial de cultivares de girassol. Os tratamentos foram dispostos em esquema fatorial (5 x 2 x 3), em blocos ao acaso, com quatro repetições, combinando-se cinco quantidades de palha de cana-de-açúcar (0, 5, 10, 15 e 20t ha-1) com aplicação ou não de 150m³ ha-1 de vinhaça residual da indústria sulcroalcooleira, utilizando-se três cultivares de girassol ("IAC-iarama", "Catissol" e "Helio 358"). Foram determinadas a velocidade e a porcentagem final de emergência de plântulas, além do comprimento e da biomassa seca da parte aérea de plantas aos 30 dias após a semeadura. Verificou-se que a presença da palha de cana-de-açúcar e da vinhaça, em quantidade equivalente a 150m³ ha-1, em ação conjunta ou isolada, reduz a emergência de plântulas e o crescimento inicial de cultivares de girassol. Entretanto, essa redução não compromete drasticamente o desempenho das cultivares ("IAC-iarama", "Catissol" e "Helio-358"), que não diferiram entre si.