• Authors:
    • Hulugalle, N. R.
  • Source: Communications in Soil Science and Plant Analysis
  • Volume: 31
  • Issue: 5-6
  • Year: 2000
  • Authors:
    • Rhoton, F. E.
  • Source: Soil Science Society of America Journal
  • Volume: 64
  • Issue: 2
  • Year: 2000
  • Summary: The number of growing seasons required for no-till practices to improve soil properties should be considered before changing management systems. To evaluate this time factor, an 8-yr tillage study was conducted on a Grenada silt loam (fine-silty, mixed, active, thermic Glossic Fragiudalfs) using cotton (Gossypium hirsutum L.), grain sorghum [Sorghum bicolor (L.) Moench]-corn (Zea mays L.), and soybean [Glycine max (L.) Merr.]-wheat (Triticum aestivum L.) as test crops. Soil samples were characterized for soil organic matter (SOM), pH, exchangeable Ca and Mg, extractable P, K, Fe, Mn, Cu, and Zn, aggregate stability (AS), water dispersible clay (WDC), total clay (TC), and modulus of rupture (MR) at time 0, 4, and 8 yr. Within 4 yr, no-till (NT) resulted in statistically significant (P less than or equal to 0.05) differences compared to conventional tillage (CT). The surface 2.5 cm of the NT treatments had higher levels of SOM, exchangeable Ca, and extractable P, Mn, and Zn, but lower extractable K, Fe, and Cu. Tillage had no effect on exchangeable Mg and pH. No-till also resulted in higher AS, and lower MR, WDC, and TC in the top 2.5 cm, relative to CT. The differences in soil properties between tillage treatments were essentially independent of crop. Instead, the results are controlled by relative amounts of SOM and clay, and the extent to which these properties change with time. Undoubtedly, NT practices ran improve several fertility and erodibility-related properties of this soil within 4 yr, and-enhance its sustainability.
  • Authors:
    • Samu, F.
    • Sunderland, K.
  • Source: Entomologia Experimentalis Et Applicata
  • Volume: 95
  • Issue: 1
  • Year: 2000
  • Summary: A review of the literature showed that spider abundance was increased by diversification in 63% of studies. A comparison of diversification modes showed that spider abundance in the crop was increased in 33% of studies by `aggregated diversification' (e.g. intercropping and non-crop strips) and in 80% of studies by `interspersed diversification' (e.g., undersowing, partial weediness, mulching and reduced tillage). It is suggested that spiders tend to remain in diversified patches and that extending the diversification throughout the whole crop (as in interspersed diversification) offers the best prospects for improving pest control. There is little evidence that spiders walk in significant numbers into fields from uncultivated field edges, but diversification at the landscape level serves to foster large multi-species regional populations of spiders which are valuable as a source of aerial immigrants into newly planted crops. There are very few manipulative field studies where the impact of spiders on pests has been measured in diversified crops compared with undiversified controls. It is encouraging, however, that in those few studies an increased spider density resulted in improved pest control. Future work needs are identified.
  • Authors:
    • Peters, M.
    • House, R.
    • Lewandrowski, J.
    • McDowell, H.
  • Source: Agricultural Outlook
  • Year: 1999
  • Authors:
    • Bluhm, G.
    • Smith, J. L.
    • Mummey, D. L.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 70
  • Issue: 1
  • Year: 1998
  • Summary: Although agricultural soil management is the predominant anthropogenic source of nitrous oxide (N2O) to the atmosphere, little is known about the effects of alternative soil management practices on N2O emissions. In this study the NGAS model of Parton et al. (1996), coupled with a N and C cycling model, was used to simulate annual N2O emissions from 2639 cropland sites in the US using both no-till and conventional tillage management scenarios. The N2O mitigation potential of returning marginal cropland to perennial grass was also evaluated by comparing simulated N2O emissions from 306 Conservation Reserve Program (CRP) grassland sites with emissions from nearby cropland sites. Extensive soil and land use data for each site was obtained from the Natural Resource Inventory (NRI) database and weather data was obtained from NASA. The initial conversion of agricultural land to no-till showed greater N2O emissions per hectare than conventional tillage. Differences between the two tillage scenarios were strongly regional and suggest that conversion of conventionally tilled soil to no-till may have a greater effect on N2O emissions in drier regions. About 80% of the total emissions were from the Great plains and central regions mainly due to their large cultivated area. Croplands producing soy, wheat, and corn were responsible for about 68% of the total emissions with rice, cotton, and vegetable croplands having the greatest N2O flux (6.5-8.4 kg N2O-N ha-1 yr-1) under either scenario. Model simulations estimate that the agricultural lands in the US produce 448 Gg N2O-N y-1 under a conventional tillage scenario and 478 Gg N2O-N yr-1 under a no-till scenario. Model estimates also suggest that the conversion of 10.5 million hectares of cropland to grassland has a N2O mitigation potential of 31 Gg N2O-N yr-1, (8.4 Tg carbon equivalents yr-1). This value is similar in magnitude to many of the major greenhouse gas (GHG) emission-reduction strategies currently being considered to help meet US GHG reduction goals. Thus the GHG mitigation potential of this conversion is substantial and may be a viable strategy to help meet GHG reduction goals.
  • Authors:
    • Camp, C. R.
  • Source: Transactions of the ASAE
  • Volume: 41
  • Issue: 5
  • Year: 1998
  • Summary: A comprehensive review of published information on subsurface drip irrigation was performed to determine the state of the art on the subject. Subsurface drip irrigation has been a part of drip irrigation development in the USA since its beginning about 1960, but interest has escalated since the early 1980s. Yield response for over 30 crops indicated that crop yield for subsurface drip was greater than or equal to that for other irrigation methods, including surface drip, and required less water in most cases. Lateral depths ranged from 0.02 to 0.70 m and lateral spacings ranged from 0.25 to 5.0 m. Several irrigation scheduling techniques, management strategies, crop water requirements, and water use efficiencies were discussed. Injection of nutrients, pesticides, and other chemicals to modify water and soil conditions is an important component of subsurface drip irrigation. Some mathematical models that simulate water movement in subsurface drip systems were included Uniformity measurements and methods, a limited assessment of root intrusion into emitters, and estimates of overall system longevity were also discussed. Sufficient information exists to provide general guidance with regard to design, installation, and management of subsurface drip irrigation systems. A significant body of information is available to assist in determining relative advantages and disadvantages of this technology in comparison with other irrigation types. Subsurface drip provides a more efficient delivery system if water and nutrient applications are managed properly. Waste water application, especially for turf and landscape plants, offers great potential Profitability and economic aspects have not been determined conclusively and will depend greatly on local conditions and constraints, especially availability and cost of water.
  • Authors:
    • Mitchell, C. C.,Jr.
    • Reeves, D. W.
    • Hubbs, M. D.
  • Source: Proceedings 21st Annual Southern Conservation Tillage Conference for Sustainable Agriculture/Arkansas Agricultural Experiment Station Special Report 186
  • Issue: 186
  • Year: 1998
  • Summary: Investigations were conducted on a Typic Hapludult in USA, to assess the effects of a 3 year rotation (cotton-grain crops plus a winter legume cover crop), a 2 year rotation (cotton-grain crops-winter legume), and 3 continuous cropping systems on soil quality after 100 years. Soil quality was better in the 3 year rotation plus legume cover crop. This was attributed to higher soil C, cation exchange capacity, water retention and water stable aggregates, and reduced surface soil strength. Under continuous cotton, soil strength was increased down to 5 in depth. N fertilizer and/or legume cover crop within continuous cotton increased soil C over the past 100 years. Because of continuous tillage over the 100 years the rotation treatments had little effect on soil extractable nutrients. The semi-quantitative assessment of the USDA-Soil Quality Kit gave higher variability of parameters relative to standard procedures. The Kit should therefore be used only to evaluate trends and comparisons.
  • Authors:
    • Bauer, P. J.
    • Hunt, P. G.
    • Matheny, T. A.
  • Source: Journal of Production Agriculture
  • Volume: 10
  • Issue: 3
  • Year: 1997
  • Summary: Cotton (Gossypium hirsutum L.) production has dramatically increased in the Southeast, but the role of conservation tillage in doublecropped cotton systems has not been clearly defined. Therefore, from 1988 to 1994, we investigated doublecropped wheat (Triticum aestivum L.) and cotton on plots that had been in continuous conservation vs. conventional tillage since 1979. The experimental site wits located near Florence, SC, on a Norfolk loamy sand (fine-loamy, siliceous, thermic Typic Kandiudult). Conventional tillage consisted of multiple diskings and cultivations; surface tillage was eliminated for conservation tillage. Wheat yields were not significantly affected by tillage, but cotton yields were significantly higher for conservation tillage (P less than or equal to 0.01). Cotton planting dates ranged from 7 to 18 June, and 5 of the 7 yr had more than 145 frost-free days. Two years had crop failure because of early freezes, and a June drought prevented the planting of cotton in 1 yr. In the 4 yr with harvestable yields, seed cotton yields among the eight cultivars ranged from about 500 to 2200 and 300 to 1850 lb/acre for conservation and conventional tillage, respectively. The early maturing cultivar, 'Deltapine (DP) 20,' had the highest seed cotton yields with means of 1442 and 1123 lb/acre for conservation and conventional tillage, respectively Development of earlier maturing cotton and wheat cultivars will be important for this cropping system in the northern Coastal Plain portion of the Cotton Belt.
  • Authors:
    • Harriss, R. C.
    • Narayanan, V.
    • Li, C.
  • Source: Global Biogeochemical Cycles
  • Volume: 10
  • Issue: 2
  • Year: 1996
  • Summary: The Denitrification-Decomposition (DNDC) model was used to elucidate the role of climate, soil properties, and farming practices in determining spatial and temporal variations in the production and emission of nitrous oxide (N[2]O) from agriculture in the United States. Sensitivity studies documented possible causes of annual variability in N[2]O flux for a simulated Iowa corn-growing soil. The 37 scenarios tested indicated that soil tillage and nitrate pollution in rainfall may be especially significant anthropogenic factors which have increased N[2]O emissions from soils in the United States. Feedbacks to climate change and biogeochemical manipulation of agricultural soil reflect complex interactions between the nitrogen and carbon cycles. A 20% increase in annual average temperature in °C produced a 33% increase in N[2]O emissions. Manure applications to Iowa corn crops enhanced carbon storage in soils, but also increased N[2]O emissions. A DNDC simulation of annual N[2]O emissions from all crop and pasture lands in the United States indicated that the value lies in the range 0.9 - 1.2 TgN. Soil tillage and fertilizer use were the most important farming practices contributing to enhanced N[2]O emissions at the national scale. Soil organic matter and climate variables were the primary determinants of spatial variability in N[2]O emissions. Our results suggest that the United States Government, and possibly the Intergovernmental Panel on Climatic Change (IPCC), have underestimated the importance of agriculture as a national and global source of atmospheric N[2]O. The coupled nature of the nitrogen and carbon cycles in soils results in complex feedbacks which complicate the formulation of strategies to reduce the global warming potential of greenhouse gas emissions from agriculture.
  • Authors:
    • Li, C.
  • Source: Soil Management and Greenhouse Effect
  • Year: 1995