• Authors:
    • Sweeney, D. W.
    • Moyer, J. L.
  • Source: Soil Science Society of America Journal
  • Volume: 58
  • Issue: 5
  • Year: 1994
  • Summary: With increased emphasis on conservation tillage, information is needed on the use of spring- or fall-seeded legumes as green manures for eastern Great Plains grain sorghum [Sorghum bicolor (L.) Moench] production. This study was conducted to determine whether legumes can be beneficial to subsequent grain sorghum crops grown in conservation tillage systems on prairie soil. Comparisons included the effects of (i) red clover (Trifolium pratense L.) and hairy vetch (Vicia villosa Roth) before grain sorghum vs. continuous grain sorghum, (ii) reduced or no-tillage, and (iii) fertilizer N rates on grain sorghum grown on two sites of a Parsons silt loam (fine, mixed, thermic Mollic Albaqualf). Surface soil at Site 1 was higher in pH (7.2 vs. 6.2), P (12 vs. 4 mg kg(-1)), and K (80 vs. 60 mg kg(-1)) than at Site 2. Yield of the first sorghum crop after legume kill-down in 1987 ranged from 79 to 131% more than for continuous grain sorghum. At the higher fertility Site 1, red clover residual increased yields to 3.7 from 2.7 Mg ha(-1) with continuous grain sorghum in the third year; at the lower fertility Site 2, the legume residual did not influence yield after the first year. First-year grain sorghum yielded 1.1 to 1.6 Mg ha(-1) more with reduced tillage than with no-tillage, but the difference was less in subsequent years. In 1987, yield was not affected by fertilizer N even following grain sorghum, but the response was significant in subsequent years. Low N response on this high organic matter prairie soil contributed to uncertain fertilizer N equivalencies and suggested other non-N benefits from the legumes.
  • Authors:
    • Grisso, R. D.
    • Jasa, P. J.
    • Dickey, E. C.
  • Source: Journal of Production Agriculture
  • Volume: 7
  • Issue: 4
  • Year: 1994
  • Summary: In Nebraska, early adopters of conservation tillage, especially those using no-till planting, had some concerns regarding planter performance, early season weed control, and possible yield reductions. Selected tillage and planting systems were used long term to evaluate effects on soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] yield, soil properties, and residue cover in a nonirrigated rotation. The six tillage and planting systems selected for evaluation were: no-till, no-till with row-crop cultivation, disk, double disk, chisel, and plow. In 1981, two sets of field plots were established near Lincoln, NE, on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls) so that both crops could be evaluated each year. Measurements were not taken until completion of one crop rotation cycle. After this cycle, for the first 3 yr of yield measurements, no differences occurred in grain yield among the tillage and planting systems. After five additional years, differences in yield were measured, with no-till tending to have the greatest yield for both crops. Row-crop cultivation of no-till soybean did not result in any measurable yield differences, but for grain sorghum, row-crop cultivation resulted in an average yield decrease of 6 bu/acre. Soil organic matter tended to be greatest for the continuous no-till system and lowest for the plow system. The plow system had slightly less penetration resistance within the 4- to 8-in. depth than the other treatments, whereas, the double-disk system was slightly greater within the 2- to 6-in. depth. Draft and power requirements for planting in the selected tillage and planting systems were not different. The major difference among the tillage and planting systems was residue cover remaining after planting. No-till had the most residue cover, but there was no appreciable accumulation of residue over the 10 yr of continuous use of the tillage and planting systems. For the last 5 yr, no-till tended to have the greatest yield for both crops. Thus, for the soil and conditions evaluated, no-till yields were as good as the other systems during early years, and were better after 5 yr of continuous use. Thus, producers adopting no-till and other residue management practices have the opportunity to enhance profitability because of the same or greater yields and reduced production costs by eliminating tillage operations.
  • Authors:
    • Hughes, E. E.
    • Wright, L. L.
  • Source: Water, Air, & Soil Pollution
  • Volume: 70
  • Issue: 1-4
  • Year: 1993
  • Summary: A previous analysis had assumed that about 20% of 1990 U.S. C emissions could be avoided by the substitution of biomass energy technologies for fossil energy technologies at some point in the future. Short-rotation woody crop (SRWC) plantations were found to be the dedicated feedstock supply system (DFSS) offering the greatest C emission reduction potential. High efficiency biomass to electricity systems were found to be the conversion technology offering the greatest C emission reduction potential. This paper evaluates what would be required in terms of rate of technology implementation and time period to reach the 20% reduction goal. On the feedstock supply side, new plantings would have to installed at an average a rate of 1 x 106 ha yr -I while average yields would have to increase by 1.5% annually over the 35-year period. Such yield increases have been observed for high value agricultural crops with large government research support. On the generation side, it requires immediate adoption of available technologies with a net efficiency of 33% or higher (such as the Whole Tree Energy TM technology), installation of approximately 5000 MWe of new capacity each year, and rapid development and deployment of much higher efficiency technologies to result in an average of 42% efficiency by 2030. If these technology changes could be achieved at a linear rate, U.S. C emission reduction could progress at a rate of about 0.6 % yr a over the next 35 years.
  • Authors:
    • Lindstrom, M. J.
    • Reicosky, D. C.
  • Source: Agronomy Journal
  • Volume: 85
  • Issue: 6
  • Year: 1993
  • Summary: The increasing concern for rising CO2 concentrations from agricultural activities has prompted the need to better understand the flux of greenhouse gases to the atmosphere. This work determines the effect of four fall tillage methods on short-term CO2 flux from a Hamerly clay loam (fine-loamy, frigid Aerie Calciaquoll) in the northern Corn Belt. Moldboard plow only, moldboard plow plus disk harrow twice, disk harrow once, and chisel plow once using standard tillage equipment following a wheat (Triticum aestivum L.) crop were compared with no-tillage. The CO2 flux was measured with a large portable system commonly used to measure canopy gas exchange of field crops. Measurements of CO2 flux were initiated within 5 min after tillage completion for each tillage treatment and continued intermittently for 19 d. Moldboard plow had the roughest soil surface and the highest initial CO, flux (29 g m-2 h-1) and maintained the highest flux throughout the study. Moldboard plow plus disking twice and chisel plow had similar initial rates (7 and 6 g m-2 h-1, respectively) that were greater than disk harrow and no-tillage. The high initial CO2 fluxes were more related to depth of soil disturbance that resulted in a rougher surface and larger voids than to residue incorporation. The differences in CO2 flux between tillage treatments were small but consistent 19 d after initial tillage and 64 mm rain. Lower CO2 flux rates caused by tillage were associated with low soil disturbance and/or small voids. Tillage methods affected the initial CO2 flux differently and suggest improved soil management can minimize agriculture's impact on global CO2 increase.
  • Authors:
    • Deverel, S. J.
    • Rojstaczer, S.
  • Source: Geophysical Research Letters
  • Volume: 20
  • Issue: 13
  • Year: 1993
  • Summary: Historical and contemporary subsidence in the San Joaquin-Sacramento Delta, California indicates that subsidence rates associated with drainage of organic soils have declined over time. Contemporary measurements of carbon flux into the atmosphere can be used to predict contemporary rates of permanent subsidence. This correspondence indicates that most subsidence is caused by carbon oxidation. The current contribution of atmospheric carbon from the Delta is 2 x 10(12) gm C/yr. This estimate is a factor of 3-4 less than previous estimates and reflects the declining rate of CO2 production in the Delta over the last several decades. Estimates of current production of CO2 from other drained agricultural lands that are based upon time-averaged historical rates of subsidence are also likely to be too large.
  • Authors:
    • Killorn, R.
  • Source: Solutions
  • Volume: 37
  • Issue: 2
  • Year: 1993
  • Authors:
    • Liu, R.
    • Phillips, D. L.
    • Lee, J. J.
  • Source: Water, Air, & Soil Pollution
  • Volume: 70
  • Issue: 1
  • Year: 1993
  • Summary: The EPIC model was used to simulate soil erosion and soil C content at 100 randomly selected sites in the US corn belt. Four management scenarios were run for 100 years: (1) current mix of tillage practices maintained; (2) current trend of conversion to mulch-till and no-till maintained; (3) trend to increased no-till; (4) trend to increased no-till with addition of winter wheat cover crop. As expected, the three alternative scenarios resulted in substantial decreases in soil erosion compared to the current mix of tillage practices. C content of the top 15 cm of soil increased for the alternative scenarios, while remaining approximately constant for the current tillage mix. However, total soil C to a depth of 1 m from the original surface decreased for all scenarios except for the no-till plus winter wheat cover crop scenario. Extrapolated to the entire US corn belt, the model results suggest that, under the current mix of tillage practices, soils used for corn and/or soybean production will lose 3.2 x 10^6 tons of C per year for the next 100 years. About 21% of this loss will be C transported off-site by soil erosion; an unknown fraction of this C will be released to the atmosphere. For the base trend and increased no-till trend, these soils are projected to lose 2.2 x 10^6 t-C yr-1 and 1.0 x 10^6 t-C yr-1, respectively. Under the increased no-till plus cover crop scenario, these soils become a small sink of 0.1 x 10^6 t-C yr-1. Thus, a shift from current tillage practices to widespread use of no-till plus winter cover could conserve and sequester a total of 3.3 x 10^6 t-C yr-1 in the soil for the next 100 years.
  • Authors:
    • Smith, J. L.
    • Johnstone, D. L.
    • Geyer, D. J.
    • Keller, C. K.
  • Source: Journal of Contaminant Hydrology
  • Volume: 11
  • Issue: 1-2
  • Year: 1992
  • Summary: Increased nitrate concentrations in groundwater associated with the application of nitrogen fertilizers have led to inquiries concerning the fate of nitrate beneath agricultural fields. This study was conducted to identify the processes affecting the distribution of nitrate in the unsaturated and saturated zones beneath an agricultural field and to assess how each process is influenced by factors associated with slope position. Nested piezometers were installed at two slope positions at the study site in southeastern Washington, U.S.A. Unsaturated- and saturated-zone sediment cores were analyzed for water content, pH, total and soluble organic carbon, ammonium, nitrate, and denitrification potential. Waters from the piezometers showed decreasing nitrate concentrations with depth below the water table. Trends in measured parameters indicated depth intervals where the distribution of nitrate could be attributed either solely to transport or to a combination of transport and biological denitrification. Denitrification explained the distribution of nitrate in the root zone while transport explained the interval between the root zone and the water table. There was a higher potential for denitrification below the water table at the bottom slope than at the top slope. Factors associated with slope position, such as a shallow water table and impeding stratigraphic layers, may explain this higher potential. Regardless of slope position, comparing nitrous oxide and carbon dioxide production from nitrate- and carbon-amended or -unamended samples indicated that denitrifier populations present in high-potential zones arc nitrate-limited. Results from spherical microsite modelling suggest that anoxic conditions are possible in the bulk sediment despite the presence of oxygenated groundwaters beneath both slope positions. Advective-dispersive transport will continue to transport nitrate through the unsaturated and saturated zones. The data from this study suggest that there is greater potential for nitrate attenuation by denitrification beneath the bottom slope than the top slope. The data also show that large masses of nitrate reside in deep subsoil vadose zones. These regions must therefore be monitored to detect threats to future groundwater quality.
  • Authors:
    • Luna, J. M.
    • Laub, C. A.
    • Pimentel, D.
  • Source: Environmental Entomology
  • Volume: 21
  • Issue: 1
  • Year: 1992
  • Summary: Rye, Secale cereale L., used as a winter cover crop was killed by the herbicide paraquat or by mowing with a rotary mower. In subsequent no-ill corn, Glyptapanteles militaris (Walsh) (Hymenoptera: Braconidae) and Periscepsia laevigata (Wulp) (Diptera: Tachinidae) were the most abundant of twelve species of parasitoids that emerged from field-collected larvae of the armyworm, Pseudaletia unipuncta (Haworth). No effects of cover crop suppression practices were detected for parasitism rates for any individual species or for total armyworm parasitism. Seasonal parasitism rates ranged from 32 to 45%. HIgher numbers of Pterostichus spp. and Scarites spp. (Coleoptera: Carabidae), and wolf spiders (Araneae: Lycosidae) occurred early in the corn season in the mowed cover crop treatment compared with the herbicide killed cover crop treatment. Subsequent reduction oflarval densities of armyworm in mowed plots following higher predator densities suggests the role of these generalist predators in biological control of armyworm.
  • Authors:
    • Turhollow, A. F.
    • Wright, L. L.
    • Graham, R. L.
  • Source: Climatic Change
  • Volume: 22
  • Issue: 3
  • Year: 1992
  • Summary: Short-rotation woody crops (SRWC) could potentially displace fossil fuels and thus mitigate CO 2 buildup in the atmosphere. To determine how much fossil fuel SRWC might displace in the United States and what the associated fossil carbon savings might be, a series of assumptions must be made. These assumptions concern the net SRWC biomass yields per hectare (after losses); the amount of suitable land dedicated to SRWC production; wood conversion efficiencies to electricity or liquid fuels; the energy substitution properties of various fuels; and the amount of fossil fuel used in growing, harvesting, transporting, and converting SRWC biomass. Assuming the current climate, present production, and conversion technologies and considering a conservative estimate of the U.S. land base available for SRWC (14 x 106 ha), we calculate that SRWC energy could displace 33.2 to 73.1 x 106 Mg of fossil carbon releases, 3-6% of the current annual U.S. emissions. The carbon mitigation potential per unit of land is larger with the substitution of SRWC for coal-based electricity production than for the substitution of SRWC-derived ethanol for gasoline. Assuming current climate, predicted conversion technology advancements, an optimistic estimate of the U.S. land base available for SRWC (28 x 106 ha), and an optimistic average estimate of net SRWC yields (22.4 dry Mg/ha), we calculate that SRWC energy could displace 148 to 242 x 106 Mg of annual fossil fuel carbon releases. Under this scenario, the carbon mitigation potential of SRWC-based electricity production would be equivalent to about 4.4% of current global fossil fuel emissions and 20% of current U.S. fossil fuel emissions.