• Authors:
    • Greenhalgh, S.
    • Faeth, P.
  • Source: World Resources Climate Notes
  • Year: 2000
  • Authors:
    • Hill, J. E.
    • Scow, K. M.
    • Fitzgerald, G. J.
  • Source: Global Biogeochemical Cycles
  • Volume: 14
  • Issue: 3
  • Year: 2000
  • Summary: In response to legislative mandate to reduce postharvest straw burning and environmental concerns to restore wetland habitat for Pacific fly-way waterfowl, California rice growers are incorporating straw into soil and flooding rice fields in winter. These changes were hypothesized to alter soil carbon cycling pathways across the region. The principal objective of this study was to determine how various winter fallowed straw and water management changes would affect year-round methane emissions. Main plots were winter flood and nonflood, and subplots had straw treatments: burned, soil incorporated, or rolled (partially soil incorporated). Results showed the principal factor controlling methane emissions was the interaction of flooding and straw amendments. The presence of either water or straw alone led to low emissions. Winter emissions accounted for 50% of annual totals in straw-amended treatments despite lower temperatures and the presence of plants in summer. Summer emissions were significantly influenced by winter straw amendments but not by winter flood. Postdrain peaks after winter drain accounted for 10-13% of annual emissions in treatments with amended straw. Although rolled and incorporated treatments had similar straw inputs, methane fluxes from rolled treatments were higher than from incorporated treatments. Measurements of methane should be conducted year-round to capture fallow and postdrain fluxes and improve global emission estimates. Regional emission estimates showed that 2.6 times more methane was emitted after flooding plus incorporation was implemented than before the legislative mandate was enacted.
  • Authors:
    • Wilkinson, S. R.
    • Schomberg, H. H.
    • Stuedemann, J. A.
    • Franzluebbers, A. J.
  • Source: Soil Biology and Biochemistry
  • Volume: 32
  • Issue: 4
  • Year: 2000
  • Summary: Soil organic matter pools under contrasting long-term management systems provide insight into potentials for sequestering oil C, sustaining soil fertility and functioning of the soil±atmospheric interface. We compared soil C and N pools (total, articulate and microbial) under pastures (1) varying due to harvest technique (grazing or haying), species composition (cool- or arm-season), stand age and previous land use and (2) in comparison with other land uses. Grazed tall fescue-common ermudagrass pasture (20 yr old) had greater soil organic C (31%), total N (34%), particulate organic C (66%), articulate organic N (2.4 fold) and soil microbial biomass C (28%) at a depth of 0±200 mm than adjacent land in conservation-tillage cropland (24 yr old). Soil organic C and total N at a depth of 0±200 mm averaged 3800 and 294 g m-2 , respectively, under grazed bermudagrass and 3112 and 219 g m-2, respectively, under hayed bermudagrass. A chronosequence of grazed tall fescue suggested soil organic N sequestration rates of 7.3, 4.4 and 0.6 g m-2 yr-1 to a depth of 200 mm during 0±10, 10±30 and 30±50 yr, respectively. Soil C storage under long-term grazed tall fescue was 85 to 88% of that under forest, whereas soil N storage was 77 to 90% greater under grazed tall fescue than under forest. Properly grazed pastures in the Southern Piedmont USA have great potential to restore natural soil fertility, sequester soil organic C and N and increase soil biological activity.
  • Authors:
    • Stuedemann, J. A.
    • Wright, S. F.
    • Franzluebbers, A. J.
  • Source: Soil Science Society of America Journal
  • Volume: 64
  • Issue: 3
  • Year: 2000
  • Authors:
    • Risse, L. M.
    • Gilley, J. E.
  • Source: Transactions of the ASAE
  • Volume: 43
  • Issue: 6
  • Year: 2000
  • Summary: Manure has been used effectively to improve crop production and soil properties because it contains nutrients and organic matter. While it is generally accepted that the improved soil properties associated with manure application lead to changes in runoff and soil erosion, few studies have quantified these impacts. Water quality models used to assess watershed management and estimate total maximum daily load must accurately predict loading rates from fields where manure has been applied. This study was conducted to assemble and summarize information quantifying the effects of manure application on runoff and soil loss resulting from natural precipitation events, and to develop regression equations relating runoff and soil loss to annual manure application rates. For selected locations at which manure was added annually, runoff was reduced from 2 to 62%, and soil loss decreased from 15 to 65% compared to non-manured sites. Measured runoff and soil loss values were reduced substantially as manure application rates increased. Regression equations were developed relating runoff and soil loss to manure application for rates ranging from 11 to 45 Mg ha–1, and slope lengths varying from 21 to 24 m. The equations can be used in estimating environmental impacts or to account for manure applications in water quality modeling efforts.
  • Authors:
    • Adkins, W.
    • West, L. T.
    • Kissel, D. E.
    • Chen, F.
  • Source: Soil Science Society of America Journal
  • Volume: 64
  • Issue: 2
  • Year: 2000
  • Summary: The surface soil organic C (SOC) concentration is a useful soil property to map soils, interpret soil properties, and guide fertilizer and agricultural chemical applications. The objective of this study was to determine whether surface SOC concentrations could be predicted from remotely sensed imagery (an aerial photograph of bare surface soil) of a 115-ha field located in Crisp County, Georgia. The surface SOC concentrations were determined for soil samples taken at 28 field locations. The statistical relationship between surface SOC concentrations and image intensity values in the red, green, and blue bands was fit to a to a logarithm linear equation (R2 = 0.93). The distribution of the surface SOC concentrations was predicted with two approaches. The first approach was to apply the relationship to individual pixels and then determine the distribution; the second approach was to classify the image and then apply the relationship to determine the class boundaries and means. Eight levels of surface SOC concentrations were classified in both approaches, and there was good agreement between the two approaches with a probability value near one using a paired t-test. The predicted and measured surface SOC concentrations, based on additional soil samples from 31 field locations, were compared using linear regression (r 2 = 0.97 and r 2=0.98 for the two approaches). The surface SOC concentrations were correctly classified in 77.4 and 74.2% of cases for the two approaches. The procedures tested were accurate enough to be used for precision farming applications in agricultural fields.
  • Authors:
    • Dowdy, R. H.
    • Linden, D. R.
    • Layese, M. F.
    • Allmaras, R. R.
    • Clapp, C. E.
  • Source: Soil & Tillage Research
  • Volume: 55
  • Issue: 3-4
  • Year: 2000
  • Summary: Long-term field experiments are among the best means to predict soil management impacts on soil carbon storage. Soil organic carbon (SOC) and natural abundance 13C ([delta]13C) were sensitive to tillage, stover harvest, and nitrogen (N) management during 13 years of continuous corn (Zea mays L.), grown on a Haplic Chernozem soil in Minnesota. Contents of SOC in the 0-15 cm layer in the annually-tilled [moldboard (MB) and chisel (CH)] plots decreased slightly with years of corn after a low input mixture of alfalfa (Medicago sativum L.) and oat (Avena sativa L.) for pasture; stover harvest had no effect. Storage of SOC in no-till (NT) plots with stover harvested remained nearly unchanged at 55 Mg ha-1 with time, while that with stover returned increased about 14%. The measured [delta]13C increased steadily with years of corn cropping in all treatments; the NT with stover return had the highest increase. The N fertilization effects on SOC and [delta]13C were most evident when stover was returned to NT plots. In the 15-30 cm depth, SOC storage decreased and [delta]13C values increased with years of corn cropping under NT, especially when stover was harvested. There was no consistent temporal trend in SOC storage and [delta]13C values in the 15-30 cm depth when plots received annual MB or CH tillage. The amount of available corn residue that was retained in SOC storage was influenced by all three management factors. Corn-derived SOC in the 0-15 cm and the 15-30 cm layers of the NT system combined was largest with 200 kg N ha-1 and no stover harvest. The MB and CH tillage systems did not influence soil storage of corn-derived SOC in either the 0-15 or 15-30 cm layers. The corn-derived SOC as a fraction of SOC after 13 years fell into three ranges: 0.05 for the NT with stover harvested, 0.15 for the NT with no stover harvest, and 0.09-0.10 for treatments with annual tillage; N rate had no effect on this fraction. Corn-derived SOC expressed as a fraction of C returned was positively biased when C returned in the roots was estimated from recovery of root biomass. The half-life for decomposition of the original or relic SOC was longer when stover was returned, shortened when stover was harvested and N applied, and sharply lengthened when stover was not harvested and N was partially mixed with the stover. Separating SOC storage into relic and current crop sources has significantly improved our understanding of the main and interacting effects of tillage, crop residue, and N fertilization for managing SOC accumulation in soil.
  • Authors:
    • Dao, T. H.
    • Douglas, C. L.,Jr.
    • Schomberg, H. H.
    • Allmaras, R. R.
  • Source: Journal of Soil and Water Conservation
  • Volume: 55
  • Issue: 3
  • Year: 2000
  • Summary: Soil organic carbon (SOC) makes up about two-thirds of the C pool in the terrestrial biosphere; annual C deposition and decomposition to release carbon dioxide (CO2) into the atmospheric constitutes about 4% of this SOC pool. Cropland is an important, highly managed component of the biosphere. Among the many managed components of cropland are the production of crop residue, use of tillage systems to control crop residue placement/disturbance, and residue decomposition. An accumulation of SOC is a C sink (a net gain from atmospheric CO2) whereas a net loss of SOC is a C source to atmospheric CO2. A simple three components model was developed to determine whether or not conservation tillage systems were changing cropland from a C source to a C sink. Grain/oil seed yields and harvest indices have indicated a steadily increasing supply of crop residue since 1940, and long term field experiments indicate SOC storage in no-tillage > non moldboard tillage > moldboard tillage systems. According to adoption surveys, moldboard tillage dominated until about 1970, but non moldboard systems are now used nationally on at least 92% of planted wheat, corn, soybean, and sorghum. Consequently, since about 1980, cropland agriculture has become a C sink. Moldboard plow systems had prevented a C sink response to increases in crop residue production that had occurred between 1940 and 1970. The model has not only facilitated a qualitative conclusion about SOC but it has also been used to project production, as well as soil and water conservation benefits, when a C credit or payment to farmers is associated with the C sink in cropland agriculture.
  • Authors:
    • Birdsey,Richard
    • Alig,Ralph J.
    • Adams,Darius M.
  • Source: USDA Forest Service General Technical Report
  • Year: 2000
  • Authors:
    • Rhinhart, K.
    • Walenta, D.
    • Harris, G.
    • Patterson, L.
    • Wysocki, D.
    • Ball, D.
    • Smiley, R.
    • Merrifield, K.
  • Source: Biological and Cultural Tests for Control of Plant Diseases
  • Volume: 15
  • Year: 2000
  • Summary: Root lesion nematode numbers in soil and wheat roots were evaluated on the sixth year of a crop rotation and tillage management study in Oregon, USA. Seven treatments were established in 1993 and culminated with all plots planted with winter wheat in 1999. Treatments comprised: (1) two-year rotation of winter wheat and high-residue fallow, using a disc in autumn following harvest and a chisel plough to prepare fallow in spring; (2) two-year rotation of winter wheat and high-residue fallow, using a chemical fallow in autumn following harvest and chisel plough in standing stubble; (3) three-year rotation of winter wheat, spring barley and fallow with tillage as in treatment 1; (4) three-year rotation of winter wheat, spring barley and fallow with chemical fallow as in treatment 2; (5) three-year rotation of rape, winter wheat and fallow with tillage as in treatment 1; (6) two-year rotation of winter wheat and low-residue fallow using a mouldboard plough during spring (current conventional practice with wheat stubble standing through winter following harvest); and (7) continuous no-till spring wheat for five years and winter wheat during 1998-99. Pratylenchus neglectus was the dominant soil lesion nematode and the only species obtained from the roots. P. thornei occurred in soil of some treatments but its ratios were not determined. The highest numbers of lesion nematodes and lowest grain yields occurred in treatments where wheat followed another crop rather than fallow (e.g. annual wheat and the 3-year rotation of rape, winter wheat and fallow). Yield was inversely associated with lesion nematode numbers in roots and soil. There were no relationships among stunt or nonparasitic nematodes and crop history or wheat grain yield.