1661. Soil organic matter in temperate agroecosystems: Long-term Experiments in North America

• Authors:
  • Cole, C. V.
  • Elliott, E. T.
  • Paustian, K.
  • Paul, E. A.
• Year: 1997

1662. Crop rotation and tillage effects on organic carbon sequestration in the semiarid southern Great Plains

• Authors:
  • Unger, P. W.
  • Torbert, H. A.
  • Jones, O. R.
  • Potter, . N.
• Source: Soil Science
• Volume: 162
• Issue: 2
• Year: 1997
• Summary: Limited information is available regarding soil organic carbon (SOC) distribution and the total amounts that occur in dryland cropping situations in semiarid regions. We determined crop rotation, tillage, and fertilizer effects on SOC distribution and mass in the semiarid southern Great Plains. A cropping system study was conducted for 10-years at Bushland, TX, to compare no-till and stubblemulch management on four dryland cropping systems: continuous wheat (CW) (Triticum aestivum L.); continuous grain sorghum (CS) (Sorghum bicolor [L.] Moench.); wheat/fallow/sorghum/fallow (WSF); and wheat/fallow (WF). Fertilizer (45 kg N ha-1) was added at crop planting to main plots. Subplots within each tillage and cropping treatment combination received no fertilizer. Ten years after treatment initiation, soil cores were taken incrementally to a 65-cm depth and subdivided for bulk density and SOC determination. The no-till treatments resulted in significant differences in SOC distribution in the soil profile compared with stubblemulch tillage in all four crop rotations, although differences were largest in the continuous cropping systems. Continuous wheat averaged 1.71% SOC in the surface 2 cm of soil compared with 1.02% SOC with stubblemulch tillage. Continuous sorghum averaged 1.54% SOC in the surface 2 cm of soil in no-till compared with 0.97% SOC with stubblemulch tillage. Total SOC content in the surface 20 cm was increased 5.6 t C ha-1 in the CW no-till treatment and 2.8 t C ha-1 in the CS no-till treatment compared with the stubblemulch treatment. Differences were not significantly different between tillage treatments in the WF and WSF systems. No-till management with continuous crops sequestered carbon in comparison to stubblemulch management on the southern Great Plains. Fallow limits carbon accumulation., (C) Williams & Wilkins 1997. All Rights Reserved.

1663. A comparison of the performance of nine soil organic matter models using datasets from seven long-term experiments

• Authors:
  • Parton, W. J.
  • Mueller, T.
  • Molina, J. A. E.
  • Li, C.
  • Komarov, A. S.
  • Klein-Gunnewiek, H.
  • Kelly, R. H.
  • Jensen, L. S.
  • Jenkinson, D. S.
  • Frolking, S.
  • Franko, U.
  • Coleman, K.
  • Chertov, O. G.
  • Arah, J. R. M.
  • McGill, W. B.
  • Powlson, D. S.
  • Smith, J. U.
  • Smith, P.
  • Thornley, J. H. M.
  • Whitmore, A. P.
• Source: Geoderma
• Volume: 81
• Issue: 1-2
• Year: 1997
• Summary: Nine soil organic models were evaluated using twelve datasets from seven long-term experiments. Datasets represented three different land-uses (grassland, arable cropping and woodland) and a range of climatic conditions within the temperate region. Different treatments (inorganic fertilizer, organic manures and different rotations) at the same site allowed the effects of differing land management to be explored. Model simulations were evaluated against the measured data and the performance of the models was compared both qualitatively and quantitatively. Not all models were able to simulate all datasets; only four attempted all. No one model performed better than all others across all datasets. The performance of each model in simulating each dataset is discussed. A comparison of the overall performance of models across all datasets reveals that the model errors of one group of models (RothC, CANDY, DNDC, CENTURY, DAISY and NCSOIL) did not differ significantly from each other. Another group (SOMM, ITE and Verberne) did not differ significantly from each other but showed significantly larger model errors than did models in the first group. Possible reasons for differences in model performance are discussed in detail.

1664. Soil management and nitrous oxide emissions from cultivated fields in southern Ohio

• Authors:
  • Dick, W. A.
  • Jacinthe P. -A.
• Source: Soil & Tillage Research
• Volume: 41
• Issue: 3-4
• Year: 1997
• Summary: Nitrous oxide (N2O) is an important atmospheric trace gas due to its involvement in the postulated global warming phenomenon and in the depletion of the ozone layer. Widespread concern has been triggered by recent reports of increased atmospheric N2O concentration. Since agriculture has been implicated as one contributor to that increase, a monitoring program was undertaken during the 1993 and 1994 cropping season (May-October) to evaluate the effect of several soil management practices on N2O emission from soil. Our results show that rates of N2O emission were generally near baseline levels during most sampling occasions. Major, but short-lived, fluxes of N2O were observed after rainfall events and during the days immediately following fertilizer application. It was during these times that most of the seasonal N2O loss occurred. An excellent relationship was found between seasonal N2O loss (y) and the maximum daily flux of N2O (x) during a season (y = -0.4x2 + 43.1x + 338, r2 = 0.89, P < 0.0001). The N2O emission data were log normally distributed for both years. Average daily emissions of N2O were 6.9 ± 6.3 g (range, 0.3 - 74.7 g) N2O---N ha-1 day-1 and 17.6 ± 10.5 g (range, 0.1-326 g) N2O---N ha-1 day-1 during the 1993 and 1994 seasons, respectively. Seasonal N2O---N losses were, in general, highest in the continuous corn (CC) (Zea mays L.) plots and lowest in the soybean (Glycine max L.) plots of the corn/soybean/wheat (Triticum aestivum L.)-hairy vetch (Vicia villosa Roth) rotation (CSW-V). Average N loss as N2O during a cropping season was between 0.6 kg (for the soybean crop of the CSWV rotation and ridge till treatment) and 3.7 kg N2O---N ha-1 year-1, (for the CC rotation and the chisel till treatment). Approximately 0.5-3% of the inorganic N fertilizer added was lost as N2O. Our data show that seasonal N2O---N loss from chisel-till plots were generally significantly higher than from no-till or ridge till plots.

1665. Residue management, conservation tillage and soil restoration for mitigating greenhouse effect by CO2 enrichment

• Authors:
  • Lal, R.
• Source: Soil & Tillage Research
• Volume: 43
• Issue: 1-2
• Year: 1997
• Summary: This manuscript reviews the potential impact of residue management, conservation tillage and soil restoration on carbon sequestration in world soils. The greenhouse effect is among four principal ecological issues of global concern that include: (i) adequacy of land resources to meet needs of present and future generations; (ii) role of world soils and agricultural practices in the "greenhouse" effect; (iii) potential of crop residue management, restoration of degraded soils, and conservation tillage in carbon sequestration in soil; and (iv) minimizing risks of soil degradation by enhancing soil resilience and soil quality. Annual increase in CO, concentration in the atmosphere is 3.2 X 1015 g, and there exists a potential to mitigate this effect through C sequestration in soils. Just as world soils are an important active pool of organic carbon and play a major role in the global carbon cycle, crop residue is a major renewable resource which also has an important impact on the global carbon cycle. I have estimated the annual production of crop residue to be about 3.4 billion Mg in the world. If 15% of C contained in the residue can be converted to passive soil organic carbon (SOC) fraction, it may lead to C sequestration at the rate of 0.2 X 1015 g/yr. Similarly restoring presently degraded soils, estimated at about 2.0 billion ha, and increasing SOC content by 0.01%/yr may lead C sequestration at the rate of 3.0 Pg C/yr. Conservation tillage is an important tool for crop residue management, restoration of degraded soil, and for enhancing C sequestration in soil. Conservation tillage, any tillage system that maintains at least 30% of the soil surface covered by residue, was practised in 1995 on about 40 X 106 ha or 35.5% of planted area in USA. It is projected that by the year 2020, conservation tillage may be adopted on 75% of cropland in USA (140 X 106 ha), 50% in other developed countries (225 X 106 ha), and 25% in developing countries (172 X 106 ha). The projected conversion of conventional to conservation tillage may lead to a global C sequestration by 2020 at a low estimate of 1.5 X 1015 g, and at a high estimate of 4.9 X 1015 g of C. These potentials of C sequestration can be realized through adoption of regional, national and global soil policy that stipulate appropriate use of world soil resources.

1666. Vegetation, cattle, and economic responses to grazing strategies and pressures

• Authors:
  • Manley, J. T.
  • Waggoner, J. W.,Jr.
  • Smith, M. A.
  • Samuel, M. J.
  • Hart, R. H.
  • Manley, W. A.
• Source: Journal of Range Management
• Volume: 50
• Issue: 6
• Year: 1997
• Summary: Rotation grazing strategies have been proposed to increase stocking capacity, improve animal gains, and improve forage production and range condition. We compared continuous or season-long, 4-pasture rotationally deferred, and 8-paddock time-controlled rotation grazing on mixed-grass rangeland near Cheyenne, Wyo. from 1982 through 1994. Stocking rates under light, moderate and heavy grazing averaged 21.6, 47.0, and 62.7 steer-day ha(-1); grazing pressures were 11.0 to 90.1 steer-day Mg-1 of forage dry matter produced. We estimated above-and below-ground biomass, botanical composition and basal cover. Bare ground and cover of warm-season grasses, forbs, and lichens were greater under heavy stocking; cover of litter, western wheatgrass, and total cool-season graminoids were greater under light stocking. Stocking rate and grazing strategy had no effect on above-ground biomass and little effect on below-ground biomass. Under heavy stocking, percent of above-ground biomass contributed by forbs increased, especially under time-controlled rotation grazing, and that of western wheatgrass decreased. Otherwise, effects of grazing strategy, level vs. slope, and north vs. south slope on vegetation were insignificant. Steer average daily gain decreased linearly as grazing pressure increased (r(2) = 0.44); grazing strategies had no significant effect. When cattle prices are favorable, the stocking rates that are most profitable in the short run may be high enough to reduce range condition.

1667. Does grazing mediate soil carbon and nitrogen accumulation beneath C4, perennial grasses along an environmental gradient?

• Authors:
  • Boutton, T. W.
  • Briske, D. D.
  • Derner, J. D.
• Source: Plant and Soil
• Volume: 191
• Issue: 2
• Year: 1997
• Summary: An experiment was conducted to evaluate the influence of long-term (>25 yrs) grazing on soil organic carbon (SOC) and total soil nitrogen (N) accumulation beneath individual plants of three perennial grasses along an environmental gradient in the North American Great Plains. The zone of maximum SOC and N accumulation was restricted vertically to the upper soil depth (0-5 cm) and horizontally within the basal area occupied by individual caespitose grasses, which contributed to fine-scale patterning of soil heterogeneity. Long-term grazing mediated SOC and N accumulation in the tall-, mid- and shortgrass communities, but the responses were community specific. SOC and N were lower beneath Schizachyrium scoparium plants in long-term grazed sites of the tall- and midgrass communities, but higher beneath Bouteloua gracilis plants in the long-term grazed site of the shortgrass community. SOC, but not N, was greater in soils beneath compared to between S. scoparium plants in an abandoned field seeded in 1941, indicating that this caespitose grass accumulated SOC more rapidly than N. SOC and N were greater in the 0-5 cm soil depth beneath a caespitose grass (S. scoparium) compared to a rhizomatous grass (Panicum virgatum) in the tallgrass community, with no significant accumulation of either SOC or N beneath P. virgatum plants. Grazing appears to indirectly mediate nutrient accumulation beneath caespitose grasses along the environmental gradient by modifying the size class distribution of plants. Populations with a greater proportion of large plants have a greater potential for biomass incorporation into soils and may more effectively capture redistributed organic matter from between plant locations. Contrasting plant responses to grazing at various locations along the environmental gradient conform to the predictions of the generalized grazing model, as the selection pressures of grazing and aridity may have also influenced the ability of caespitose grasses to accumulate nutrients in soils beneath them by mediating grazing resistance, competitive ability and population structure.

1668. Carbon isotope ratios of Great Plains soils and in wheat-fallow systems

• Authors:
  • Peterson, G. A.
  • Lyon, D. J.
  • Halvorson, A. D.
  • Leavitt, S. W.
  • Paul, E. A.
  • Follett, R. F.
• Source: Soil Science Society of America Journal
• Volume: 61
• Issue: 4
• Year: 1997
• Summary: The purposes of this study were to improve knowledge of regional vegetation patterns of C-3 and C-4 plants in the North American Great Plains and to use delta(13)C methodology and long-term research sites to determine contributions of small-grain crops to total soil organic carbon (SOC) now present, Archived and recent soil samples were used, Detailed soil sampling was in 1993 at long-term sites near Akron, CO, and Sidney, NE, After soil sieving, drying, and deliming, SOC and delta(13)C were determined using an automated C/N analyzer interfaced to an isotope-ratio mass spectrometer, Yield records from long-term experimental sites were used to estimate the amount of C-3 plant residue C returned to the soil, Results from delta(13)C analyses of soils from near Waldheim, Saskatchewan, to Big Springs, TX, showed a strong north to south decrease in SOC derived from C-3 plants and a corresponding increase from C-4 plants. The delta(13)C analyses gave evidence that C-3 plant residue C (possibly from shrubs) is increasing at the Big Springs, TX, and Lawton, OK, sites, Also, delta(13)C analyses of subsoil and topsoil layers shows evidence of a regional shift to more C-3 species, possibly because of a cooler climate during the past few hundreds to thousands of years, Data from long-term research sites indicate that the efficiency of incorporation of small-grain crop residue C was about 5.4% during 84 Jr at Akron, CO, and about 10.5% : during 20 yr at Sidney, NE, The C-14 age of the SOC at 0- to IO-tm depth was 193 yr and at 30 to 45 cm was 4000 yr; C-14 age of nonhydrolyzable C was 2000 and 7000 yr for these same two respective depths, Natural partitioning of the C-13 isotope by the photosynthetic pathways of C-3 and C-4 plants provides a potentially powerful tool to study SOC dynamics at both regional and local scales.

1669. Organic versus conventional grain production in the mid-Atlantic: An economic and farming system

• Authors:
  • Lichtenberg, E.
  • Hanson, J. C.
  • Peters, S. E.
• Source: American Journal of Alternative Agriculture
• Volume: 12
• Issue: 1
• Year: 1997
• Summary: Compares the profitability of the organic and conventional cash grain rotations since 1982. Dependence of sustainable farming on the generated income from farmers; Conduct of a Farming Systems Trial; Analysis of two FST systems; Advantage of the organic rotation; Tabulation of net returns for three different periods; Net returns and labor requirements.

1670. Management effects on soil organic carbon and nitrogen in the east-central Great Plains of Kansas

• Authors:
  • Kissel, D. E.
  • Havlin, J. L.
• Source: Soil Organic Matter in Temperate Agroecosystems: Long-Term Experiments in North America
• Volume: 1
• Year: 1997