• Authors:
    • Santos, H. P. dos
    • Roman, E. S.
  • Source: Pesquisa Agropecuária Gaúcha
  • Volume: 7
  • Issue: 1
  • Year: 2001
  • Summary: Field experiments were conducted in Passo Fundo (1984-89) and in Coxilha (1996-97), Rio Grande do Sul, and in Guarapuava (1984-90 and 1990-94), Parana, Brazil, to study the effects of winter crop residues on soyabean grown in succession, under no-till system. Winter crops were white oats knife rolled for mulching purposes, white oats, barley, rapeseed, flax, and wheat for grain yield. In these cropping systems, soyabean was grown in the summer in monoculture and in rotation with maize and pearl millet. Soyabean grown after flax and rape showed lower yield and plant height than soyabean after barley and wheat. Yields of soyabean grown in monoculture were moderate compared with yields of soyabean grown in crop rotation and soyabean grown after rape or flax. Soyabean grown after barley and wheat may be included in the different systems studied without yield losses. Volunteer white oat seeds may reduce soyabean yield and plant height.
  • Authors:
    • Christoffoleti, P. J.
    • Shiratsuchi, L. S.
  • Source: The BCPC Conference: Weeds, 2001, Volume 1 and Volume 2. Proceedings of an international conference held at the Brighton Hilton Metropole Hotel, Brighton, UK, 12-15 November 2001
  • Year: 2001
  • Summary: Weed control represents a high percentage of the production costs in no-till systems in Brazil, and chemical control using herbicides is by far the most important method used. However, the weeds are not uniformly or randomly distributed but have a patchy distribution such that the broadcast application of herbicides can spray post-emergence herbicides in areas where there are no weeds. Therefore, this work had the objective of demonstrating the potential of saving of herbicides in the no-till production system of the Brazilian agriculture, based on weed seed bank and weed seedling maps. The density of several weeds was mapped using a backpack DGPS and laptop computer. Experiments were conducted in Sao Paulo [date not given] in a 17.7-ha field of no-till maize under centre pivot irrigation. Seed bank data was determined from soil cores collected from a depth of 0.05 m in the centre of a 20*20 m grid and emergence assessments in a greenhouse. On the same grid size, weed seedlings were counted in 0.25 m 2 quadrats. Resultant maps showed a high weed density in the seed bank over just 4.67 ha, which was only 26% of the field area. The seedling maps demonstrated that grasses and broadleaf weeds had different distributions with broadleaf weeds occupying 12.6% of the field and grasses 87.4%. The targeting of herbicide to weed patches using pre- and postemergent herbicides has the potential to reduce herbicide use compared to broadcast application giving both environmental and economic advantages.
  • Authors:
    • Jackson, R. B.
    • Jobbágy, E. G.
  • Source: Ecological Applications
  • Volume: 10
  • Issue: 2
  • Year: 2000
  • Summary: As the largest pool of terrestrial organic carbon, soils interact strongly with atmospheric composition, climate, and land cover change. Our capacity to predict and ameliorate the consequences of global change depends in part on a better understanding of the distributions and controls of soil organic carbon (SOC) and how vegetation change may affect SOC distributions with depth. The goals of this paper are (1) to examine the association of SOC content with climate and soil texture at different soil depths; (2) to test the hypothesis that vegetation type, through patterns of allocation, is a dominant control on the vertical distribution of SOC; and (3) to estimate global SOC storage to 3 m, including an analysis of the potential effects of vegetation change on soil carbon storage. We based our analysis on >2700 soil profiles in three global databases supplemented with data for climate, vegetation, and land use. The analysis focused on mineral soil layers. Plant functional types significantly affected the vertical distribution of SOC. The percentage of SOC in the top 20 cm (relative to the first meter) averaged 33%, 42%, and 50% for shrublands, grasslands, and forests, respectively. In shrublands, the amount of SOC in the second and third meters was 77% of that in the first meter; in forests and grasslands, the totals were 56% and 43%, respectively. Globally, the relative distribution of SOC with depth had a slightly stronger association with vegetation than with climate, but the opposite was true for the absolute amount of SOC. Total SOC content increased with precipitation and clay content and decreased with temperature. The importance of these controls switched with depth, climate dominating in shallow layers and clay content dominating in deeper layers, possibly due to increasing percentages of slowly cycling SOC fractions at depth. To control for the effects of climate on vegetation, we grouped soils within climatic ranges and compared distributions for vegetation types within each range. The percentage of SOC in the top 20 cm relative to the first meter varied from 29% in cold arid shrublands to 57% in cold humid forests and, for a given climate, was always deepest in shrublands, intermediate in grasslands, and shallowest in forests (P < 0.05 in all cases). The effect of vegetation type was more important than the direct effect of precipitation in this analysis. These data suggest that shoot/root allocations combined with vertical root distributions, affect the distribution of SOC with depth. Global SOC storage in the top 3 m of soil was 2344 Pg C, or 56% more than the 1502 Pg estimated for the first meter (which is similar to the total SOC estimates of 1500-1600 Pg made by other researchers). Global totals for the second and third meters were 491 and 351 Pg C, and the biomes with the most SOC at 1-3 m depth were tropical evergreen forests (158 Pg C) and tropical grasslands/savannas (146 Pg C). Our work suggests that plant functional types, through differences in allocation, help to control SOC distributions with depth in the soil. Our analysis also highlights the potential importance of vegetation change and SOC pools for carbon sequestration strategies.
  • Authors:
    • Mielniczuk, J.
    • Martin-Neto, L.
    • Bayer, C.
    • Ceretta, C. A.
  • Source: Soil & Tillage Research
  • Volume: 53
  • Issue: 2
  • Year: 2000
  • Summary: In weathered tropical and subtropical soils organic matter is crucial for soil productivity and its quantity depends heavily on soil management systems. This study evaluated the effect of no-till cropping systems on organic matter content and quality in a sandy clay loam Acrisol soil (Paleudult in US taxonomy) from Southern Brazil. Ten cropping systems with varying additions of C and N were conducted for 12 years (from 1983 to 1994), The addition of crop residues increased total organic carbon (TOC) and total nitrogen (TN) in the soil at 0-17.5 cm depth, and this increase was directly related with C and N added or recycled by the systems. The crop residues added to the soil were associated with reduced semiquinone free radical concentration, detected by electron spin resonance (ESR), in the organo-mineral aggregates <53 mu m and humic acid (HA) samples, in the soil at 0-2.5 cm depth. This showed that stable organic matter originating from crop residues was less humidified than the original soil organic matter. Results obtained from organo-mineral aggregates showed a higher amplitude (highest and lowest values were 5.47 and 2.09 x 10(17) spins g(-1) of TOC, respectively) of semiquinone free radical concentration than HA samples (highest and lowest values were 2.68 and 1.77 x 10(17) spins g(-1) of HA, respectively). These data showed that alterations due to tillage in soil organic matter characteristics, e.g,, humification degree can be better identified through a combination of soil physical fractionation and spectroscopic analysis. Semiquinone content in the HA samples, detected by ESR, related significantly to aromaticity, as measured by nuclear magnetic resonance (NMR) of C-13. Management systems including no-till and cropping systems with high C and N additions to the soil improved its quality in Southern Brazil. (C) 2000 Elsevier Science B,V. All rights reserved.
  • Authors:
    • Fernandes, S. V.
    • Martin-Neto, L.
    • Amado, T. J. C.
    • Mielniczuk, J.
    • Bayer, C.
  • Source: Soil & Tillage Research
  • Volume: 54
  • Issue: 1-2
  • Year: 2000
  • Summary: Soil organic matter decline and associated degradation of soil and environmental conditions under conventional tillage in tropical and subtropical regions underline the need to develop sustainable soil management systems. This study aimed first to evaluate the long-term effect (9 years) of two soil-tillage systems (conventional tillage: CT, and no-tillage: NT) and two cropping systems (oat (Avena strigosa Schreb)/maize (Zea mays L.): O/M; and oat+common vetch (Vicia sativa L.)/ maize+cowpea (Vigna unguiculata (L.) Walp): O+V/M+C without N fertilization on total organic carbon (TOC) and total nitrogen (TN) concentrations in a sandy clay loam Acrisol in southern Brazil. The second objective was to assess soil potential for acting as an atmospheric CO2 sink. Under NT an increase of soil TOC and TN concentrations occurred, in both cropping systems, when compared with CT. However, this increase was restricted to soil surface layers and it was higher for O+V/M+C than for O/M, The O+V/M+C under NT, which probably results in the lowest soil organic matter losses (due to erosion and oxidation) and highest addition of crop residues, had 12 Mg ha(-1) more TOC and 0.9 Mg ha(-1) more TN in the 0-30.0 cm depth soil layer, compared with O/M under CT which exhibits highest soil organic matter losses and lowest crop residue additions to the soil. These increments represent TOC and TN accumulation rates of 1.33 and 0.10 Mg ha(-1) per year, respectively. Compared with CT and O/M, this TOC increase under NT and O+V/M+C means a net carbon dioxide removal of about 44 Mg ha(-1) from the atmosphere in 9 years. NT can therefore be considered, as it is in temperate climates, an important management strategy for increasing soil organic matter. In the tropicals and subtropicals, where climatic conditions cause intense biological activity, in order to maintain or increase soil organic matter, improve soil quality and contribute to mitigation of CO2 emissions, NT should be associated with cropping systems resulting in high annual crop residue additions to soil surface. (C) 2000 Elsevier Science B.V. All rights reserved.
  • Authors:
    • Ulbrich, A. V.
    • Yada, I. F. U.
    • Lima, J. de
    • Rodrigues, B. N.
    • Fornarolli, D. A.
  • Source: Planta Daninha
  • Volume: 18
  • Issue: 2
  • Year: 2000
  • Summary: Field experiments, conducted during 1997/98 in Londrina, Parana, Brazil, bioassays and chromatographic analyses were conducted to investigate the effect of mulch (oat residues) on crop-weed competition and retention of imazaquin in no-till soyabean crop. Imazaquin was applied at 0, 75, 150 and 300 g/ha on 7000 and 14 000 kg/ha of oat residues and on soil without mulch. Twenty-four hours after imazaquin application, the field was irrigated and more samples were collected for bioassays and chromatographic analyses. The weed population consisted of Brachiaria plantaginea, Euphorbia heterophylla and Bidens pilosa. Oat residues intercepted 90% of the imazaquin before irrigation, indicating the potential of this herbicide in no-till system.
  • Authors:
    • Van Noordwijk, M.
    • Sitompul, S. M.
    • Rodrigues, V.
    • Ricse, A.
    • Parton, W. J.
    • Njomgang, R.
    • Murdiyarso, D.
    • Moukam, A.
    • Mendes, A.
    • Kotto-Same, J.
    • Hairiah, K.
    • Feigl, B.
    • Cordeiro, D. G.
    • Castilla, C.
    • Arevalo, L.
    • Alegre, J.
    • Woomer, P. L.
    • Palm, C. A.
  • Source: ASB Climate Change Working Group Final Report, Phase II
  • Year: 1999
  • Summary: The overall objectives of the Climate Change Working Group during Phase II of the Alternatives to Slash-and-Burn Programme (ASB) were to determine those land-use systems that sequester more carbon and reduce trace gas emissions. The research consisted of three activities: 1 Collect strategic information on changes in carbon stocks and land use, 2 Develop a database on trace gas fluxes from different land-use systems, and 3 Assess land rehabilitation techniques for increasing carbon sequestration.
  • Authors:
    • Hall, D. O.
    • Scurlock, J. M. O.
  • Source: Global Change Biology
  • Volume: 4
  • Issue: 2
  • Year: 1998
  • Summary: The challenge to identify the biospheric sinks for about half the total carbon emissions from fossil fuels must include a consideration of below-ground ecosystem processes as well as those more easily measured above-ground. Recent studies suggest that tropical grasslands and savannas may contribute more to the 'missing sink' than was previously appreciated, perhaps as much as 0.5 Pg (= 0.5 Gt) carbon per annum. The rapid increase in availability of productivity data facilitated by the Internet will be important for future scaling-up of global change responses, to establish independent lines of evidence about the location and size of carbon sinks.
  • Authors:
    • Lindwall, C. W.
    • Roman, E. S.
    • Moyer, J. R.
    • Blackshaw, R. E.
  • Source: Crop Protection
  • Volume: 13
  • Issue: 4
  • Year: 1994
  • Summary: Soil erosion by wind or water is a serious problem in North and South America. When no-till or reduced tillage is used to control erosion, the density of certain annual and perennial weeds can increase and new weed control techniques are usually required. The effects of conservation tillage on annual and perennial weeds, weeds that are spread by wind, plants from rangelands and pasture as weeds and volunteer plants as weeds arc reviewed. Current weed control methods with minimum tillage, herbicides, cover crops and other cultural practices in conservation tillage systems in North and South America are described. Some producers are successfully controlling weeds in continuous summer cropping systems in North America and in double cropping systems that include wheat in the winter and soybean or corn in the summer in Brazil, Argentina and southeastern United States. Successful conservation tillage systems usually involve cropping sequences of three or more crop types and several herbicides. In these cropping sequences, the ground is covered with a crop during most of the period in which the climate is favourable for weed growth. Perennial weeds are a problem in all tillage systems and there is a general dependence on glyphosate for perennial weed control. In successful conservation tillage systems, the amount and cost of herbicides used is similar to that for herbicides used in conventional tillage systems.