- Authors:
- de Sousa, R. O.
- Leitzke, V. W.
- Pinto, L. F. S.
- Sousa, R. O. de
- Pauletto, E. A.
- Borges, J. R.
- Source: Revista Brasileira de Agrociencia
- Volume: 10
- Issue: 1
- Year: 2004
- Summary: Soil compaction is a problem that affects most crops and influences both plant growth and productivity, as well as soil and water conservation. A 3-year experiment was conducted in Centro Agropecuaho da Raima, Federal University of Pelotas (Rio Grande do Sul, Brazil) to evaluate the compaction of a Typical Endoaqualf involving continuous rice systems (conventional, minimum tillage and no tillage) and crop rotation systems with different cover crops under no-tillage, using a penetrometer. The results show that the largest resistance of the soil to the penetrometer in the 0-20 cm layer occurred in the conventional and minimum tillage continuous rice systems. Results for the continuous rice and crop rotation under no-tillage were similar to the non-cultivated soil. All treatments presented increased resistance to penetration below 40 cm depth.
- Authors:
- Silva, E. M. da
- Rauber, J. C.
- Azevedo, J. A. de
- Reatto, A.
- Source: Boletim de Pesquisa e Desenvolvimento - Embrapa Cerrados
- Issue: 101
- Year: 2003
- Summary: The no-till system have positive impacts in soil and water conservation. This work aims to evaluate the main modifications on the soil physical properties caused by no-till system, carried out during 3, 6, and 12 years under rainfed conditions. The cases of direct drilling for five years under irrigated condition, a conventional tillage system, and a soil condition under natural Biome Cerrado were also evaluated in the Ampessan farm, Cabeceiras, Goias, Brazil. The soil physical characteristics were evaluated by samples taken from the following layers: 0-5, 2.5-7.5, 5-10, 10-15, 20-25, 42.5-47.5 and 72.5-77.5 cm. The infiltration characteristics were evaluated at 12 and 80 cm soil depth, using the Guelph permeameter to determine the field saturated hydraulic conductivity. The results showed that the intense soil mechanization on irrigated condition favoured a significant decrease in the field saturated hydraulic conductivity in the layers near to the soil surface. There was a tendency for higher water availability in the cultivated soils, in relation to that under natural soil environment, up to 22.5 cm soil depth.
- Authors:
- Nunes, R. P.
- Pinho, J. L. N.
- Silva, J. B. F.
- Pitombeira, J. B.
- Cavalcante Junior, A. T.
- Source: Planta Daninha
- Volume: 21
- Issue: 1
- Year: 2003
- Summary: A study was conducted from September to December 1997, in Pentecoste, Ceara, Brazil, to determine the effectiveness of the herbicides glyphosate (1800 g ha -1) and paraquat (800 g ha -1), applied as desiccants before sowing, and fenoxaprop-P-ethyl [fenoxaprop-P] (0, 40, 80 and 120 g ha -1) and imazamox (0, 21, 42 and 63 g ha -1), applied in post-emergence conditions, in controlling the weeds and to evaluate the phytotoxicity of the herbicides to cowpea plants ( Vigna unguiculata cv. Epace 10) under a no-tillage system with furrow irrigation. The treatments with glyphosate associated with imazamox or fenoxaprop-P-ethyl was more efficient in controlling the weeds, showing reduced weed shoot dry biomass production, when compared to paraquat combined with the post-emergence herbicides. Fenoxaprop-P-ethyl and imazamox did not cause visual phytotoxicity symptoms to the cowpea plants. The best post-emergence weed control was provided by fenoxaprop-P-ethyl at the rate of 80 g ha -1, associated with glyphosate (1800 g ha 1). Fenoxaprop-P-ethyl was effective against the grass weeds, but not against Cenchrus echinatus and Digitaria horizontalis. Imazamox was not effective in controlling the broadleaf weeds Chamaesyce hirta and Euphorbia heterophylla at the studied rates.
- Authors:
- Source: Critical Reviews in Plant Sciences
- Volume: 22
- Issue: 2
- Year: 2003
- Summary: An increase in atmospheric concentration of CO2 from 280 ppmv in 1750 to 367 ppmv in 1999 is attributed to emissions from fossil fuel combustion estimated at 270 +/- 30 Pg C and land use change at 136 +/- 55 Pg. Of the emissions from land use change, 78 +/- 12 Pg is estimated from depletion of soil organic carbon (SOC) pool. Most agricultural soils have lost 50 to 70% of their original SOC pool, and the depletion is exacerbated by further soil degradation and desertification. The restoration of degraded soils, conversion of agriculturally marginal lands to appropriate land use, and the adoption of recommended management practices on agricultural soils can reverse degradative trends and lead to SOC sequestration. Technological options for SOC sequestration on agricultural soils include adoption of conservation tillage, use of manures, and compost as per integrated nutrient management and precision fanning strategies, conversion of monoculture to complex diverse cropping systems, meadow-based rotations and winter cover crops, and establishing perennial vegetation on contours and steep slopes. The global potential of SOC sequestration and restoration of degraded/desertified soils is estimated at 0.6 to 1.2 Pg C/y for about 50 years with a cumulative sink capacity of 30 to 60 Pg. The SOC sequestration is a cost-effective strategy of mitigating the climate change during the first 2 to 3 decades of the 21(st) century. While improving soil quality, biomass productivity and enhanced environment quality, the strategy of SOC sequestration also buys us time during which the non-carbon fuel alternatives can take effect.
- Authors:
- Glaser, B.
- Zech, W.
- Nehls, T.
- Steiner, C.
- Pereira da Silva, J.
- Lehmann, J.
- Source: Plant and Soil
- Volume: 249
- Issue: 2
- Year: 2003
- Authors:
- Yang, H.
- Walters, D. T.
- Dobermann, A.
- Cassman, K. G.
- Source: Annual Review of Environment and Resources
- Volume: 28
- Issue: 1
- Year: 2003
- Summary: Agriculture is a resource-intensive enterprise. The manner in which food production systems utilize resources has a large influence on environmental quality. To evaluate prospects for conserving natural resources while meeting increased demand for cereals, we interpret recent trends and future trajectories in crop yields, land and nitrogen fertilizer use, carbon sequestration, and greenhouse gas emissions to identify key issues and challenges. Based on this assessment, we conclude that avoiding expansion of cultivation into natural ecosystems, increased nitrogen use efficiency, and improved soil quality are pivotal components of a sustainable agriculture that meets human needs and protects natural resources. To achieve this outcome will depend on raising the yield potential and closing existing yield gaps of the major cereal crops to avoid yield stagnation in some of the world's most productive systems. Recent trends suggest, however, that increasing crop yield potential is a formidable scientific challenge that has proven to be an elusive goal.
- Authors:
- Cerri, C. C.
- Victoria, R.
- Bernoux, M.
- Jenkinson, D. S.
- Coleman, K.
- Cerri, C. E. P.
- Source: Soil Science Society of America Journal
- Volume: 67
- Issue: 6
- Year: 2003
- Summary: Conversion of tropical forest to agricultural management has important implications for C storage in soils and global climate change. The Nova Vida Ranch in the Western Brazilian Amazon basin provided a unique opportunity to study the conversion of tropical forests to pastures established in 1989, 1987, 1983, 1979, 1972, 1951, and 1911, in comparison with uncleared forest. Soils were analyzed for organic C, bulk density, total N, pH, clay content, and biomass C. The forest soil contained 34 Mg C ha(-1) in the 0- to 30-cm layer: modeling clearance and conversion to pasture caused an initial fall in the C stock, followed by a slow rise. After 88 yr, the pasture soil contained 53% more C than the forest soil. The increase in total N on conversion to pasture was less marked, which led to C/N ratios in the pasture soils being higher than in the forest soil. The Rothamsted C turnover model (RothC-26.3) was used to simulate changes in the 0- to 10- and 0- to 30-cm layer of soils when forest was converted to pasture. The model predicted that conversion to pasture would cause a 54% increase in the stock of organic C in the top 30 cm of soil in 100 yr. The modeled input of plant C to the 0- to 30-cm layer of soil under pasture was assumed to be 8.28 Mg C ha(-1) yr(-1). The model provided a reasonable estimate of the microbial biomass (BIO) C in the 0- to 10-cm soil layer. This was an independent test of model performance, because no adjustments were made to the model to generate output.
- Authors:
- Source: Soil Science Society of America Journal
- Volume: 66
- Issue: 6
- Year: 2002
- Summary: Changes agricultural management can potentially increase the accumulation rate of soil organic C (SOC), thereby sequestering CO2 from the atmosphere. This study was conducted to quantify potential soil C sequestration rates for different crops in response to decreasing tillage intensity or enhancing rotation complexity, and to estimate the duration of time over which sequestration may occur. Analyses of C sequestration rates were completed using a global database of 67 long-term agricultural experiments, consisting of 276 paired treatments. Results indicate, on average, that a change from conventional tillage (CT) to no-till (NT) can sequester 57 +/- 14 g C m(-2) yr(-1), excluding wheat (Triticum aestivum L.)-fallow systems which may not result in SOC accumulation with a change from CT to NT. Enhancing rotation complexity can sequester an average 20 +/- 12 g C m(-2) yr(-1), excluding a change from continuous corn (Zea mays L.) to corn-soybean (Glycine mar L.) which may not result in a significant accumulation of SOC. Carbon sequestration rates, with a change from CT to NT, can be expected to peak in 5 to 10 yr with SOC reaching a new equilibrium in 15 to 20 yr. Following initiation of an enhancement in rotation complexity, SOC may reach a new equilibrium in approximately 40 to 60 yr. Carbon sequestration rates, estimated for a number of individual crops and crop rotations in this study, can be used in spatial modeling analyses to more accurately predict regional, national, and global C sequestration potentials.
- Authors:
- Albrecht, A.
- Sa, J. C. D.
- Ogle, S. M.
- Denef, K.
- Feller, C.
- Six, J.
- Source: Agronomie
- Volume: 22
- Issue: 7
- Year: 2002
- Summary: The long-term stabilization of soil organic matter (SOM) in tropical and temperate regions is mediated by soil biota (e. g. fungi, bacteria, roots and earthworms), soil structure (e. g. aggregation) and their interactions. On average, soil C turnover was twice as fast in tropical compared with temperate regions, but no major differences were observed in SOM quality between the two regions. Probably due to the soil mineralogy dominated by 1:1 clay minerals and oxides in tropical regions, we found a higher aggregate stability, but a lower correlation between C contents and aggregate stability in tropical soils. In addition, a smaller amount of C associated with clay and silt particles was observed in tropical versus temperate soils. In both tropical and temperate soils, a general increase in C levels (approximate to 325 +/- 113 kg C.ha(-1).yr(-1)) was observed under no-tillage compared with conventional tillage. On average, in temperate soils under no-tillage, compared with conventional tillage, CH4 uptake (approximate to0.42 +/- 0.10 kg C-CH4.ha(-1) yr(-1)) increased and N2O emissions increased (approximate to 1.95 +/- 0.45 kg N-N2O.ha(-1).yr(-1)). These increased N2O emissions lead to a negative global warming potential when expressed on a CO2 equivalent basis.
