• Authors:
    • Lewis, D. T.
    • Reedy, T. E.
    • Martens, D. A.
  • Source: Global Change Biology
  • Volume: 10
  • Issue: 1
  • Year: 2004
  • Summary: Conversion of former agricultural land to grassland and forest ecosystems is a suggested option for mitigation of increased atmospheric CO2. A Sharpsburg prairie loess soil (fine, smectitic, mesic Typic Argiudoll) provided treatments to study the impact of long-term land use on soil organic carbon (SOC) content and composition for a 130-year-old cropped, pasture and forest comparison. The forest and pasture land use significantly retained more SOC, 46% and 25%, respectively, compared with cropped land use, and forest land use increased soil C content by 29% compared with the pasture. Organic C retained in the soils was a function of the soil N content (r=0.98, P<0.001) and the soil carbohydrate (CH) concentration (r=0.96, P<0.001). Statistical analyses found that soil aggregation processes increased as organic C content increased in the forest and pasture soils, but not in the cropped soil. SOC was composed of similar percentages of CHs (49%, 42% and 51%), amino acids (22%, 15% and 18%), lipids (2.3%, 2.3% and 2.9%) and unidentified C (21%, 29% and 27%), but differed for phenolic acids (PAs) (5.7%, 11.6% and 1.0%) for the pasture, forest and cropped soils, respectively. The results suggested that the majority of the surface soil C sequestered in the long-term pasture and forest soils was identified as C of plant origin through the use of CH and PA biomarkers, although the increase in amino sugar concentration of microbial origin indicates a greater increase in microbial inputs in the three subsoils. The practice of permanent pastures and afforestation of agricultural land showed long-term potential for potential mitigation of atmospheric CO2.
  • Authors:
    • Perfect, E.
    • Herbeck, J.
    • Murdock, L.
    • Grove, J. H.
    • Dí­az-Zorita, M.
  • Source: Agronomy Journal
  • Volume: 96
  • Issue: 6
  • Year: 2004
  • Summary: The development of well-structured soils is a goal for achieving sustainable and productive agricultural systems. Nevertheless, the maintenance of soil structure in continuous no-till (NT) soils has sometimes been thought to induce soil conditions that are detrimental to crop yields. The objectives of this research were to characterize the effects of periodic tillage disruption in otherwise NT systems on soil properties and the yields of winter wheat (Triticum aestivum L.), double-cropped soybean [Glycine max (L.) Merr.], and maize (Zea mays L.) in rotation and to determine if soil structural changes occurring in tilled soils are independent of changes in other soil properties. A field experiment was established in 1992 on a Huntington silt loam soil (Fluventic Hapludoll) at the University of Kentucky Research and Education Center in Princeton (KY) under a NT crop sequence with two seedbed preparation methods for winter wheat, (a) NT or (b) chisel plus disk tillage (Till). In fall 2000, similar soil chemical properties were observed between disrupted and continuous NT systems over the 0- to 20-cm layer. The geometric mean diameter of dry fragments and the soil water content retained between 0.0003 and 0.03 MPa water potential was greater in NT soils than in soils tilled for winter wheat. Tillage for winter wheat enhanced winter wheat yields (4.2% increase), mostly under low-yielding conditions, but it resulted in a reduction of subsequent summer crop yields (i.e., 3.7% for soybean and 7.0% for maize). The yields obtained in our study translate to an economic benefit for the continuous NT system. Net returns per hectare were estimated to be $73 higher for the winter wheat/double-crop soybean-maize rotation under NT than under Till treatments. The differences in maize yields between NT and tilled treatments were attributed to a better water supply in NT soil due to the maintenance of a larger number of mesopores and a great hydraulic conductivity. In the absence of significant changes in other physicochemical properties, periodic tillage appears to disrupt soil structure, which negatively affects crop productivity.
  • Authors:
    • Spurlock, S.
    • Heatherly, L.
    • Reddy, K.
  • Source: Agronomy Journal
  • Volume: 96
  • Issue: 3
  • Year: 2004
  • Summary: Management inputs that maximize economic return from the early plantings of soyabean ( Glycine max) in the midsouthern USA have not been evaluated fully. The objective was to compare perennial weed control in and yields and economic returns from plantings of maturity group (MG) IV and V soyabean cultivars grown in the field (Mississippi, USA) under different weed management systems (WMS) following shallow (ST) and deep (DT) fall tillage. Adjacent experiments were conducted near Stoneville, Mississippi. Weed management systems were (i) glyphosate ( N-(phosphonomethyl)glycine)-resistant (GR) cultivars with preemergent (PRE) nonglyphosate herbicides followed by postemergent (POST) glyphosate; (ii) GR cultivars with POST glyphosate; (iii) non-GR cultivars with PRE plus POST nonglyphosate herbicides; and (iv) non-GR cultivars with POST nonglyphosate herbicides. Control of perennial redvine ( Brunnichia ovata) declined in the ST environment when non-GR cultivars were used, but this did not result in a yield decline. Control of perennial johnsongrass ( Sorghum halepense) at the end of the study period averaged 93% when GR cultivars were used regardless of tillage treatment, and this was associated with lower yield. Use of PRE+POST vs. POST-only weed management sometimes resulted in lower profits regardless of fall tillage treatment. The fall tillage treatment * WMS interaction was not significant for yield or net return, which indicates that use of DT for perennial weed management is not economical.
  • Authors:
    • Everts, K.
    • Sardanelli, S.
    • Kratochvil, R.
    • Gallagher, E.
  • Source: Agronomy Journal
  • Volume: 96
  • Issue: 5
  • Year: 2004
  • Summary: Root-knot ( Meloidogyne incognita) and lesion ( Pratylenchus penetrans) nematodes are important pathogens that cause yield and quality losses for most vegetable and field crops in Maryland, USA when they exceed certain threshold levels and if control measures are not applied. Chemical nematicides are the primary control tactic, but their use is both costly and raises environmental concerns. This study was conducted from 2000 to 2002 to evaluate the efficacy of crop rotation and other cultural practices for management of southern root-knot nematodes (RKNs) and lesion nematodes. Three nonhost crops, a RKN-resistant soyabean ( Glycine max) cultivar, and poultry litter/tillage (Year 1) and fallow (Year 2) were used as summer rotation crops/management options following production of nematode-susceptible crops on 2 sites in Dorchester County, Maryland, on Downer and Hammonton sandy loam soils (coarse-loamy, siliceous, mesic Typic and Aquic Hapludults), respectively. Sorghum sudangrass ( Sorghum bicolor * Sorghum arundinaceum var. sudanense), grown annually as a green manure crop following a nematode-susceptible crop, potato ( Solanum tuberosum) or cucumber ( Cucumis sativus), reduced the RKN population as effectively as the control treatment (soyabean cultivar with no known RKN resistance and one nematicide application). Sorghum sudangrass and poultry litter/tillage/fallow were equally effective in managing the lesion nematode population. Annual inclusion of these practices was necessary to maintain the reduced population levels that were attained for these 2 nematode species. Finally, either summer or early-autumn sampling dates were determined to be more effective than a midspring sampling date for identifying threshold levels of these 2 pests.
  • Authors:
    • Rogers, H.
    • Runion, G.
    • Torbert, H.
    • Prior, S.
  • Source: Environmental Management
  • Volume: 33
  • Issue: Supplement 1
  • Year: 2004
  • Summary: Elevated atmospheric CO 2 concentration can increase biomass production and alter tissue composition. Shifts in both quantity and quality of crop residue may alter carbon (C) and nitrogen (N) dynamics and management considerations in future CO 2-enriched agroecosystems. This study was conducted to determine decomposition rates of the legume soybean [ Glycine max (L.) Merr.] and nonlegume grain sorghum [ Sorghum bicolor (L.) Moench.] residue produced under two levels of atmospheric CO 2 (ambient and twice ambient) on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults) in Auburn, Alabama, USA, managed using no-till practices. At maturity, harvested plants were separated into component parts for dry weight determination and tissue analysis. Mass, C, and N losses from residues were determined using the mesh bag method. Biomass production was significantly greater for soybean compared to sorghum and for elevated versus ambient CO 2-grown plants. The CO 2 level had little affect on the C/N ratio of residue (probably because the tissue used was senesced). Elevated CO 2 concentration did not affect percent residue recovery; however, greater biomass production observed under elevated CO 2 resulted in more residue and C remaining after overwintering. The higher total N content of soybean residue, particularly when grown under elevated CO 2, indicated more N may be available to a following crop with lower N inputs required. Results suggest that in a high CO 2 environment, greater amounts of residue may increase soil C and ground cover, which may enhance soil water storage, improve soil physical properties, and reduce erosion losses.
  • Authors:
    • Richardson, J.
    • Hons, F.
    • Ribera, L.
  • Source: Agronomy Journal
  • Volume: 96
  • Issue: 2
  • Year: 2004
  • Summary: Tillage systems that reduce the number of cultivation steps can, according to soil scientists, save soil moisture, fuel, labour, and machinery costs, as well as reduce wind and water erosion. However, many producers in south Texas, USA, are reluctant to adopt these practices. The objective of this study was to compare the economics of conventional tillage (CT) and no-tillage (NT) systems on three commercial crops produced in south Texas: grain sorghum ( Sorghum bicolor), wheat ( Triticum aestivum), and soyabean ( Glycine max). When considering the economics of both tillage systems, three areas affecting profit were addressed: changes in cost per hectare, changes in yield per hectare, and the impact on net income risk. Empirical distributions of net income for different tillage systems under risk were estimated using a Monte Carlo simulation model of net income per hectare. Certainty equivalents were used to rank the tillage systems because they can be used to rank risky alternatives for risk-averse decision makers. The risk premium for risk-averse decision makers who prefer NT over CT ranges between $12.60 and $34.25 per hectare for all five crop rotations. Risk-neutral decision makers would prefer continuous sorghum and sorghum-wheat-soyabean rotation over all other rotations under CT and NT, respectively. However, risk-averse decision makers would prefer continuous sorghum over all other rotations either under CT or NT. The results suggest that under risk-neutral rankings, NT would be preferred over CT in three out of the five crop rotations tested. However, assuming a risk-averse decision maker, NT would be preferred over CT in all five crop rotations.
  • Authors:
    • Carmo, C.
    • Lhamby, J.
    • Ambrosi, I.
    • Santos, H.
  • Source: Ciencia Rural
  • Volume: 34
  • Issue: 1
  • Year: 2004
  • Summary: Soil tillage and crop rotation and succession systems were assessed in Passo Fundo, Rio Grande do Sul, Brazil, from 1994/95 to 1997/98. Four soil tillage systems, i.e. no-tillage, minimum tillage, conventional tillage using a disc plough, and conventional tillage using a mouldboard plough, and three crop rotation and succession systems, i.e. system I (wheat/soyabean), system II (wheat/soyabean and common vetch [ Vicia sativa]/sorghum or maize) and system III (wheat/soyabean, common vetch/sorghum or maize, and white oats/soyabean), were compared. An experimental design of randomized blocks with split-plots and three replications was used. The main plot was formed by the soil tillage systems, while the split-plots consisted of the crop rotation and succession systems. Two types of analysis were applied to the net return of soil tillage and crop rotation and succession systems: mean-variance and risk analysis. By the mean-variance analysis, no-tillage and minimum tillage, which presented higher net returns, were the best alternatives to be offered to the farmer. By the stochastic dominance analysis, no-tillage and crop rotation with two winters without wheat showed the highest profit and the lowest risk.
  • Authors:
    • Rice, CW
    • Doyle, G.
    • Garcia, R.
    • Litvina, IV
    • Zhou, XH
    • Schmidt, RA
    • Brandle, JR
    • Massman, WJ
    • Takle, ES
  • Source: Agricultural and Forest Meteorology
  • Volume: 124
  • Issue: 3-4
  • Year: 2004
  • Summary: We report measurements at 2 Hz of pressure fluctuations at and beneath the soil in an agricultural field with dry soil and no vegetation. The objective of our study was to examine the possible role of pressure fluctuations produced by fluctuations in ambient wind on the efflux of M at the soil surface. We observed that pressure fluctuations penetrate to 50 cm in the soil with little attenuation, thereby providing a mechanism for bulk transport of trace gases throughout the porous medium. Concurrent measurements of CO2 fluxes from the soil surface produced systematically larger values for larger values of root-mean-square pressure, pumping rate, and mean wind speed. Soil CO2 fluxes measured under conditions conducive to pressure pumping exceeded the diffusional fluxes, estimated from use of Fick's Law and concurrent vertical profiles of soil CO2, by a factor of 5-10. Extrapolation of measured fluxes to conditions uninfluenced by pressure pumping revealed that other mechanisms, such as thermal expansion of soil air caused by soil heating or flushing by evaporating water deep in the soil, may be contributing up to 60% to measured fluxes. Ambient meteorological conditions leading to flux enhancement may change on scales of hours to months, so these results underscore the need to report concurrent meteorological conditions when surface CO2 efflux measurements are made. They further suggest that fluctuations in the static pressure fields introduced by wind interactions with terrain and vegetation may lead to pressure pumping at the surface and hence large spatial inhomogeneities in soil fluxes of trace gases. Although our measurements were made at an agricultural field site and focused on CO2 efflux, the pressure pumping mechanism will be active on other sites, including forest environments, snow-covered surfaces, and fractured rocky surfaces. Furthermore, the physical processes examined apply to movement of other trace gases such as oxygen, water vapor, and methane. (C) 2004 Elsevier B.V. All rights reserved.
  • Authors:
    • Skinner, D. Z.
    • Liang, G. H.
  • Year: 2004
  • Summary: This book contains chapters on: genetic transformation; mechanisms of transgene locus formation; gene stacking through site-specific integration; transgenics of plant hormones and their potential application in horticultural crops; avidin in transgenic maize; genetic engineering protocols and use to enhance stress tolerance in wheat; development and utilization of transformation in Medicago spp.; sorghum transformation for resistance to fungal pathogens and drought; current progress and future prospects in rice transformation; successes and challenges in cotton transformation; progress in transforming the recalcitrant soyabean; progress in vegetable crop transformation and future prospects and challenges; genetic transformation of turfgrass; and risks associated with genetically engineered crops.
  • Authors:
    • Reddy, G. B.
    • Brock, B.
    • Naderman, G.
    • Raczkowski, C. W.
  • Source: Proceedings of the 26th Southern Conservation Tillage Conference for Sustainable Agriculture 8-9 June, 2004, Raleigh, North Carolina
  • Year: 2004
  • Summary: This study reports the results of sampling soil within a field experiment at CEFS, the Cherry Farm, Goldsboro, North Carolina. The experiment tested effects of six years of conservation tillage with cover crops, contrasted with chisel plow/disk tillage without cover crops, under three crop rotations. In April, 2003 two sets of undisturbed core samples were collected from six mapped soil areas, at depth increments of 0-2 and 2-5 inches, replicated four times. One set was used for soil bulk density; the other provided soil carbon and total nitrogen contents. The study found strong and consistent inverse correlations between soil carbon content and bulk density. Under conservation tillage the surface two inches generally sustained suitable density for root activities. However, at 2-5 inches density approached or exceeded 1.6 g cm-3. Given the textures involved, this density likely would affect root growth, especially under non-ideal, wet/cool or dry/hard conditions. This would be especially important for crop establishment within this prime rooting zone. This low carbon/high-density problem was less likely for soils containing the influences of more silt with less sand. It was greater when corn, peanut and cotton were grown compared to producing soyabean or wheat/soybean with corn. This study revealed increased carbon sequestration from the conservation tillage systems used, along with increased total N content in the surface five inches of soil. Conservation tillage as practiced helped to reduce the "greenhouse effect" and lessened N leaching losses, holding more of these elements within the topsoil.