• 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:
    • Rice, C. W.
    • Claassen, M. M.
    • Nelson, R. G.
    • Williams, J. R.
  • Source: Environmental Management
  • Volume: 33
  • Issue: 1
  • Year: 2004
  • Summary: An economic analysis of wheat and grain sorghum production systems that affect carbon dioxide (CO2) emissions and sequester soil carbon (C) in metric tons (MT) is conducted. Expected net returns, changes in net C sequestered, and the value of C credits necessary to equate net returns from systems that sequester more C with those that sequester less is determined with and without adjustments for CO2 emissions from production inputs. Experiment station cropping practices, yield data, and soil C data for continuously cropped and rotated wheat and grain sorghum produced with conventional tillage and no-tillage are used. No-till has lower net returns because of somewhat lower yields and higher overall costs. Both crops produced under no-till have higher annual soil C gains than under conventional tillage. However, no-till systems have somewhat higher total atmospheric emissions of C from production inputs. The C credit values estimated in this study will equate net returns of no-tillage to conventional tillage range from $8.62 to $64.65/MT/yr when C emissions from production inputs are subtracted from soil C sequestered, and $8.59 to $60.54/MT/yr when atmospheric emissions are not considered. This indicates accounting for CO2 emissions from production inputs may not be necessary in the process to issue C credits.
  • Authors:
    • Tiefenthaler, A. E.
    • Goldman, I. L.
    • Tracy, W. F.
    • Schaber, M. A.
  • Source: Plant Breeding Reviews: Long-term Selection: Crops, Animals, and Bacteria
  • Volume: 24
  • Issue: 2
  • Year: 2004
  • Summary: This review covers some long-term trends of the Illinois Long-term Selection Experiment and offers some perspectives on the impact of long-term selection on productivity of crops (lucerne, oats, rye, barley, winter wheat, spring wheat, soyabeans, groundnuts, sweetcorn, sweet potato, cotton, green peas, sorghum, maize, rice and potato) in the USA. Discussions on the crop productivity, variability of crop productivity and causes of increased productivity, are provided.
  • Authors:
    • Varlev, I.
  • Source: Bulgarian Journal of Agricultural Science
  • Volume: 10
  • Issue: 1
  • Year: 2004
  • Summary: Long-term data (13-18 years) from 15 experimental farms were used to evaluate quantitatively the risk of maize cultivation on drylands in different regions of Bulgaria. Results established that the risk of maize cultivation on drylands in north Bulgaria seldom surpasses 10% of the years. Losses in south Bulgaria cover 20-70% of the years. Only on soils of high water-holding capacity is the risk close to 20%.
  • Authors:
    • Owen, M. D. K.
    • Felix, J.
  • Source: Weed Technology
  • Volume: 18
  • Issue: 1
  • Year: 2004
  • Summary: In 1998, 1,260 soil samples were collected from 63 of 99 Iowa counties to characterize the weed seedbanks in fields under the conservation reserve program (CRP) and adjacent fields under continuous cultivation. Five annual grass and 13 broadleaf weed species were identified in both the CRP and adjacent cultivated fields. Seedbank differences between CRP and adjacent cultivated fields were evident only for foxtails, common lambsquarters, pigweeds, and sweetclover, with the average of 3.288, 10,681, 38, and 1,709 seeds/m(2), respectively; the corresponding seed population in adjacent CRP fields was 59, 57, 1,924, and 74%, respectively. However, weed species diversity was not significantly different between fields in CRP and continuous cultivation. Only CRP fields in the northwest Iowa crop-reporting district had a higher foxtail species seed population (4,915 seeds/m2) than the adjacent cultivated fields (1,782 seeds/m2). Land under CRP in northern (N), eastern, and southern (S) districts had 58% (4,158 seeds/m(2)), 6% (312 seeds/m(2)), and 18% (594 seeds/m(2)) of the continuously cultivated foxtail species seedbank. Common lambsquarters seed populations were 4,128 and 3,801 seeds/m2 in the cultivated fields of the N and central (C) districts, compared with 772 and 252 seeds/m2 in adjacent CRP fields, respectively. Pigweed species seeds were more numerous in the cultivated fields than in adjacent CRP fields in the northeast, C, and S Iowa districts. Sweetclover seed population was consistently higher in CRP land because it was included as part of the CRP covers seeding. Overall, broadleaf weed seeds comprised 90% of the seedbanks in both CRP and adjacent cultivated land. A competitive cover crop canopy in CRP probably reduced weed seedbanks by suppression of weeds and seed production. Also, annual seed production, differences in weed biology, and differential herbicide performance in cultivated fields may have contributed to higher seed populations.
  • Authors:
    • Paustian, K.
    • Eve, M.
    • Sperow, M.
  • Source: Climatic Change
  • Volume: 57
  • Issue: 3
  • Year: 2003
  • Summary: Soil carbon sequestration has been suggested as a means to help mitigate atmospheric CO2 increases, however there is limited knowledge aboutthe magnitude of the mitigation potential. Field studies across the U.S. provide information on soil C stock changes that result from changes in agricultural management. However, data from such studies are not readily extrapolated to changes at a national scale because soils, climate, and management regimes vary locally and regionally. We used a modified version of the Intergovernmental Panel on Climate Change (IPCC) soil organic C inventory method, together with the National Resources Inventory (NRI) and other data, to estimate agricultural soil C sequestration potential in the conterminous U.S. The IPCC method estimates soil C stock changes associated with changes in land use and/or land management practices. In the U.S., the NRI provides a detailed record of land use and management activities on agricultural land that can be used to implement the IPCC method. We analyzed potential soil C storage from increased adoption of no-till, decreased fallow operations, conversion of highly erodible land to grassland, and increased use of cover crops in annual cropping systems. The results represent potentials that do not explicitly consider the economic feasibility of proposed agricultural production changes, but provide an indication of the biophysical potential of soil C sequestration as a guide to policy makers. Our analysis suggests that U.S. cropland soils have the potential to increase sequestered soil C by an additional 60–70 Tg (1012g) C yr-1, over present rates of 17 Tg C yr-1 (estimated using the IPCC method), with widespread adoption of soil C sequestering management practices. Adoption of no-till on all currently annually cropped area (129 Mha) would increase soil C sequestration by 47 Tg C yr-1. Alternatively, use of no-till on 50% of annual cropland, with reduced tillage practices on the other 50%, would sequester less – about 37 Tg C yr-1. Elimination of summer fallow practices and conversion of highly erodible cropland to perennial grass cover could sequester around 20 and 28 Tg C yr-1, respectively. The soil C sequestration potential from including a winter cover crop on annual cropping systems was estimated at 40 Tg C yr-1. All rates were estimated for a fifteen-year projection period, and annual rates of soil C accumulations would be expected to decrease substantially over longer time periods. The total sequestration potential we have estimated for the projection period (83 Tg C yr-1) represents about 5% of 1999 total U.S. CO2 emissions or nearly double estimated CO2 emissions from agricultural production (43 Tg C yr-1). For purposes of stabilizing or reducing CO2 emissions, e.g., by 7% of 1990 levels asoriginally called for in the Kyoto Protocol, total potential soil C sequestration would represent 15% of that reduction level from projected 2008 emissions (2008 total greenhouse gas emissions less 93% of 1990 greenhouse gasemissions). Thus, our analysis suggests that agricultural soil C sequestration could play a meaningful, but not predominant, role in helping mitigate greenhouse gas increases.
  • Authors:
    • Hibbard, B. E.
    • McMullen, M. D.
    • Darrah, L. L.
    • Flint-Garcia, S. A.
  • Source: Theoretical and Applied Genetics
  • Volume: 107
  • Issue: 7
  • Year: 2003
  • Summary: Maize (Zea mays L.) stalk lodging is breakage of the stalk at or below the ear, which may result in loss of the ear at harvest. Stalk lodging is often intensified by the stalk tunneling action of the second-generation of the European corn borer (2-ECB) [Ostrinia nubilalis (Hübner)]. Rind penetrometer resistance (RPR) has been used to measure stalk strength and improve stalk lodging resistance, and quantitative trait loci (QTL) have been identified for both RPR and 2-ECB damage. Phenotypic recurrent selection (PS) increases the frequency of favorable alleles over cycles of selection. Several studies have indicated that marker-assisted selection (MAS) is also a potentially valuable selection tool. The objective of this study was to compare the efficiency of PS versus MAS for RPR and 2-ECB. Marker-assisted selection for high and low RPR was effective in the three populations studied. Phenotypic selection for both high and low RPR was more effective than MAS in two of the populations. However, in a third population, MAS for high RPR using QTL effects from the same population was more effective than PS, and using QTL effects from a separate population was just as effective as PS. Marker-assisted selection for resistance and susceptibility to 2-ECB using QTL effects from the same population was effective in increasing susceptibility, but not in increasing resistance. Marker-assisted selection using QTL effects from a separate population was effective in both directions of selection. Thus, MAS was effective in selecting for both resistance and susceptibility to 2-ECB. These results demonstrated that MAS can be an effective selection tool for both RPR and 2-ECB resistance. These results also validate the locations and effects of QTL for RPR and 2-ECB resistance identified in earlier studies.
  • 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:
    • Laird, D. A.
    • Drummond, P.
    • Christy, C. D.
  • Source: 2003 ASAE Annual Meeting
  • Year: 2003
  • Summary: Laboratory based near infrared spectroscopy (NIRS) has demonstrated good predictive capability for many important soil constituents. Less is known about the feasibility of performing the spectroscopic measurements in a field setting. This paper presents some results of an initial field test of a mobilized in-situ NIRS device. The results demonstrate good pass-to-pass repeatability and meaningful qualitative images. Locally weighted principal component regression was used to develop calibration models relating the reflectance data to levels of soil organic carbon, nitrogen, moisture and pH. The calibrations were used to create constituent maps for a field in central Iowa and compared to images derived from intensive sampling and laboratory analysis.
  • Authors:
    • Zhou, X.
    • Massman, W. J.
    • Litvina, I. V.
    • Garcia, R.
    • Schmidt, R. A.
    • Brandle, J. R.
    • Takle, E. S.
    • Doyle, G.
    • Rice, C. W.
  • Source: Agricultural and Forest Meteorology
  • Volume: 114
  • Issue: 3-4
  • Year: 2003
  • Summary: We report measurements of 2 Hz pressure fluctuations at and below the soil surface in the vicinity of a surface-based CO2 flux chamber. These measurements were part of a field experiment to examine the possible role of pressure pumping due to atmospheric pressure fluctuations on measurements of surface fluxes of CO2. Under the moderate wind speeds, warm temperatures, and dry soil conditions present at the time of our observations, the chamber had no effect on the pressure field in its near vicinity that could be detected above the level of natural pressure fluctuations in the vicinity. At frequencies at or <2 Hz, pressure fluctuations easily penetrated the soil to depths of several cm with little attenuation. We conclude that the presence of the chamber does not introduce pressure perturbations that lead to biases in measurements of surface fluxes of CO2.