• Authors:
    • Samu, F.
    • Sunderland, K.
  • Source: Entomologia Experimentalis Et Applicata
  • Volume: 95
  • Issue: 1
  • Year: 2000
  • Summary: A review of the literature showed that spider abundance was increased by diversification in 63% of studies. A comparison of diversification modes showed that spider abundance in the crop was increased in 33% of studies by `aggregated diversification' (e.g. intercropping and non-crop strips) and in 80% of studies by `interspersed diversification' (e.g., undersowing, partial weediness, mulching and reduced tillage). It is suggested that spiders tend to remain in diversified patches and that extending the diversification throughout the whole crop (as in interspersed diversification) offers the best prospects for improving pest control. There is little evidence that spiders walk in significant numbers into fields from uncultivated field edges, but diversification at the landscape level serves to foster large multi-species regional populations of spiders which are valuable as a source of aerial immigrants into newly planted crops. There are very few manipulative field studies where the impact of spiders on pests has been measured in diversified crops compared with undiversified controls. It is encouraging, however, that in those few studies an increased spider density resulted in improved pest control. Future work needs are identified.
  • Authors:
    • TCG
    • Teasdale,John R.
    • Rosecrance,R. C.
    • Coffman,Charles B.
    • Starr,J. L.
    • Paltineanu,I. C.
    • Lu,Y. C.
    • Watkins,B. K.
  • Source: American Journal of Alternative Agriculture
  • Volume: 15
  • Issue: 2
  • Year: 2000
  • Summary: Sustainable production systems are needed to maintain soil resources and reduce environmental contamination on erodible lands that are incompatible with tillage-intensive operation. A long-term cropping systems comparison was established at Beltsville, Maryland, on a site with 2 to 15% slope to evaluate the efficacy of sustainable strategies compatible with reduced-tillage systems. All systems followed a 2-year rotation of corn the first year and winter wheat followed by soybean the second year. Treatments included (1) no-tillage system with recomended fertilizer and herbicide inputs, (2) crownvetch living mulch system with similar inputs to the no-tillages system, (3) cover crop system including a hairy vetch cover crop before corn and a wheat cover crop before soybean with reduced fertilizer and herbicide inputs, (4) manure systemd including crimson clover green manure plus cow manure for nutrient sources, chisel plow/disk for incorporatin manure and rotary hoe plus cultication for weed control. Results from the initial 4 years demonstrated the relative productivity of these systems. Corn yields were similar in the no-tillage and cover crop systems in each year. both systems average 7.8 Mg ha-1 compared to 5.7 Mg ha-1 in both the croen vetch and manure systems. Wheat yields were highest in the manure system in the first 2 years and in the crown vetch system in the last 2 years. Soybean yields were highest in the cover crop system in all years. The manure system usually had lower yields than the highest yielding system, partly because of competitions from uncontrolled weeds. Several measures of the efficience of grain production were evaluated. The no-tillage system produced the most grain per total vegetative biomass throughout the rotation. The cover crop system produced the most grain per unit of external N input and, along with the no-tillage system, had the highest corn water-use efficiency. The cover crop system also recycled the most vegetative residues and nutrients of all systems. No single system perfomed best according to all measures of comparison, suggesting that trade-offs will be required when choosing production systems.
  • Authors:
    • Jackson, R. B.
    • Jobbágy, E. G.
  • Source: Ecological Applications
  • Volume: 10
  • Issue: 2
  • Year: 2000
  • Summary: As the largest pool of terrestrial organic carbon, soils interact strongly with atmospheric composition, climate, and land cover change. Our capacity to predict and ameliorate the consequences of global change depends in part on a better understanding of the distributions and controls of soil organic carbon (SOC) and how vegetation change may affect SOC distributions with depth. The goals of this paper are (1) to examine the association of SOC content with climate and soil texture at different soil depths; (2) to test the hypothesis that vegetation type, through patterns of allocation, is a dominant control on the vertical distribution of SOC; and (3) to estimate global SOC storage to 3 m, including an analysis of the potential effects of vegetation change on soil carbon storage. We based our analysis on >2700 soil profiles in three global databases supplemented with data for climate, vegetation, and land use. The analysis focused on mineral soil layers. Plant functional types significantly affected the vertical distribution of SOC. The percentage of SOC in the top 20 cm (relative to the first meter) averaged 33%, 42%, and 50% for shrublands, grasslands, and forests, respectively. In shrublands, the amount of SOC in the second and third meters was 77% of that in the first meter; in forests and grasslands, the totals were 56% and 43%, respectively. Globally, the relative distribution of SOC with depth had a slightly stronger association with vegetation than with climate, but the opposite was true for the absolute amount of SOC. Total SOC content increased with precipitation and clay content and decreased with temperature. The importance of these controls switched with depth, climate dominating in shallow layers and clay content dominating in deeper layers, possibly due to increasing percentages of slowly cycling SOC fractions at depth. To control for the effects of climate on vegetation, we grouped soils within climatic ranges and compared distributions for vegetation types within each range. The percentage of SOC in the top 20 cm relative to the first meter varied from 29% in cold arid shrublands to 57% in cold humid forests and, for a given climate, was always deepest in shrublands, intermediate in grasslands, and shallowest in forests (P < 0.05 in all cases). The effect of vegetation type was more important than the direct effect of precipitation in this analysis. These data suggest that shoot/root allocations combined with vertical root distributions, affect the distribution of SOC with depth. Global SOC storage in the top 3 m of soil was 2344 Pg C, or 56% more than the 1502 Pg estimated for the first meter (which is similar to the total SOC estimates of 1500-1600 Pg made by other researchers). Global totals for the second and third meters were 491 and 351 Pg C, and the biomes with the most SOC at 1-3 m depth were tropical evergreen forests (158 Pg C) and tropical grasslands/savannas (146 Pg C). Our work suggests that plant functional types, through differences in allocation, help to control SOC distributions with depth in the soil. Our analysis also highlights the potential importance of vegetation change and SOC pools for carbon sequestration strategies.
  • Authors:
    • Lal, R.
  • Source: The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect
  • Year: 2000
  • Authors:
    • Hart, R. H.
    • Reeder, J. D.
    • Schuman, G. E.
    • Morgan, J. A.
    • LeCain, D. R.
  • Source: Journal of Range Management
  • Volume: 53
  • Issue: 2
  • Year: 2000
  • Summary: The influence of cattle grazing on carbon cycling in the mixed grass prairie was investigated by measuring the CO2 exchange rate in pastures with a 13 year history of heavy or light grazing and an ungrazed exclosure at the High Plains Grasslands Research Station near Cheyenne, Wyo. In 1995, 1996 and 1997 a closed system chamber, which covered 1 m(2) of ground, was used every 3 weeks from April to October to measure midday CO2 exchange rate. Green vegetation index (similar to leaf area index), soil respiration rate, species composition, soil mater content, soil temperature, and air temperature were also measured to relate to CO2 exchange rates of the 3 grazing treatments. Treatment differences varied among gears, but overall early season (mid April to mid June) CO2 exchange rates in the grazed pastures were higher (up to 2.5 X) than in the exclosure. Higher early season CO2 exchange rates were associated with earlier spring green-up in grazed pastures, measured as higher green vegetation index. As the growing season progressed, green vegetation index increased in all pastures, but more so in the ungrazed exclosure, resulting in occasionally higher (up to 2 X) CO2 exchange rate compared with grazed pastures late in the season. Seasonal treatment differences mere not associated with soil temperature, soil respiration rate, or air temperature, nor was there a substantial change in species composition due to grazing. We hypothesize that early spring green-up and higher early season CO2 exchange rate in grazed pastures may be due to better light penetration and a warmer microclimate near the soil surface because of less litter and standing dead compared to the ungrazed pastures. When all the measurements mere averaged over the entire season, there mas no difference in CO2 exchange rate between heavily grazed, lightly prated and ungrazed pastures in this ecosystem.
  • Authors:
    • Dowdy, R. H.
    • Clapp, C. E.
    • Linden, D. R.
  • Source: Soil & Tillage Research
  • Volume: 56
  • Issue: 3-4
  • Year: 2000
  • Summary: Because the adoption of conservation tillage requires long-term evaluation, the effect of tillage and residue management on corn (Zea mays L.) grain and stover yields was studied for 13 seasons in east central Minnesota. Three primary tillage methods (no-till (NT), fall chisel plow (CH), fall moldboard plow (MB)) and two residue management schemes (residue removal versus residue returned) were combined in a factorial design experiment on a Haplic Chernozem silt loam soil in Minnesota. No significant effects on grain yield were seen due to tillage treatments in 9 out of 13 years. The NT treatment resulted in lower yields than CH and MB treatments in years 6 and 7, and lower than the MB in year 8, indicating a gradual decrease in yield over time with continuous use of NT. There were differences due to residue management in 8 out of 13 years. The residue-returned treatments contributed about 1 Mg ha-1 greater yields in intermediate level dry years such as years 3 and 6, which had cumulative growing season precipitation 20 and 30% below the 9-year average, respectively. In excessively dry or long-term-average years, residues resulted in little yield difference between treatments. The most pronounced effects of residues were with the CH treatment for which yields were greater in 8 out of 13 years. The ratio of grain to total dry matter yield averaged 0.56 and did not vary with time or between treatments. These results apply primarily to soils wherein the total water storage capacity and accumulated rainfall are insufficient to supply optimum available water to the crop throughout the growing season. Under conditions with deeper soils or in either wetter or drier climates, the results may differ considerably.
  • Authors:
    • Carlson, G. R.
    • Engel, R. E.
    • Long, D. S.
  • Source: Precision Agriculture
  • Volume: 2
  • Year: 2000
  • Summary: By accounting for spatial variation in soil N levels, variable-rate fertilizer application may improve crop yield and quality, and N use efficiency within fields. The main purpose of this study was to demonstrate how site-specific wheat yield and protein data, and a geographic information system may be used in developing precision N-recommendations for spring wheat. The three steps in the procedure include: (1) estimate the amount of N-removed in wheat in the year in which the crop is harvested, (2) estimate the N-deficit, defined as the amount of additional N needed for raising protein concentration in a future crop to a specified target level, and (3) estimate the total N-recommendation by summing the mapped values of the N-removed and the N-deficit. A map for variable-rate application of fertilizer is derived by specifying cutoff values to divide the range in the total N-recommendation into classes representing N management zones. A field experiment was conducted within an annually cropped wheat field 101 ha in northern Montana to determine whether the proposed method could improve grain yields and protein levels. The N-removal and N-deficit were estimated from site-specific wheat yield and protein data that were acquired during harvest of 1996. In 1997, which was a dry year, an experiment was conducted in the same field that consisted of a randomized complete block design arranged as pairs of strip plots. Variable- or uniform-rate N treatments were randomly assigned to each pair of strips. Both treatments received nearly the same amount of fertilizer, however, N in the variable treatment was varied to match patterns in grain yield and protein levels that previously existed in 1996. Yields were not significantly different between management systems, but proteins were significantly enhanced by spatially variable N application. In addition, variability in protein levels was reduced within the whole field. Field areas deficient in N fertility could be identified without having to sample for soil profile N.
  • Authors:
    • Wooley, R.
    • Ibsen, K.
    • Yee, W.
    • Taylor, F.
    • McAloon, A.
  • Year: 2000
  • Summary: The mature corn-to-ethanol industry has many similarities to the emerging lignocelluloseto-ethanol industry. It is certainly possible that some of the early practitioners of this new technology will be the current corn ethanol producers. In order to begin to explore synergies between the two industries, a joint project between two agencies responsible for aiding these technologies in the Federal government was established. This joint project of the U.S. Department of Agriculture's Agricultural Research Service (USDAARS)and the U.S. Department of Energy (DOE) with the National Renewable Energy Laboratory (NREL) looked at the two processes on a similar process design and engineering basis, and will eventually explore ways to combine them. This report describes the comparison of the processes, each producing 25 million annual gallons of fuel ethanol. This paper attempts to compare the two processes as mature technologies, which requires assuming that the technology improvements needed to make the lignocellulosic process commercializable are achieved, and enough plants have been built to make the design well-understood.
  • Authors:
    • Schneider, U. A.
    • McCarl, B. A.
  • Source: Applied Economic Perspectives and Policy
  • Volume: 22
  • Issue: 1
  • Year: 2000
  • Summary: International agreements are likely to stimulate greenhouse gas mitigation efforts. Agriculture can participate either as a source of emission reductions or as a sink for gas emission storage. Emission trading markets are likely to emerge where agriculture could sell emission offsets. Several agricultural opportunities are available at a cost of $10-25 per ton carbon dioxide. Abatement costs for non-agricultural industries have been estimated to be as much as $200-250 per ton carbon dioxide. In the longer run, agriculture's role may diminish because many agricultural strategies offer only one-time gains and non-agricultural emitters may lower costs through technical change.
  • Authors:
    • Rossoni-Longnecker, L.
    • Janke, R. R.
    • Drinkwater, L. E.
  • Source: Plant and Soil
  • Volume: 227
  • Issue: 1
  • Year: 2000
  • Summary: Abstract In 1988 an experiment was established at the Rodale Institute Experimental Farm to study weed control and nitrogen (N) management in rotations with grain crops and N-fixing green manures under reduced tillage without the use of herbicides. Tillage intensities ranging from moldboard plow (MP) to continuous no-till (NT) were compared. We present results for maize production in 1994, the seventh year of the experiment. Our goal was to further investigate reduced tillage regimes that alternated no-till with different forms of primary tillage in legume-based systems. In the chisel-disc (CD) and MP treatments comparable yields were achieved under so-called organic (weeds controlled with cultivation and green manure N source) and conventional management (weeds controlled with herbicides and mineral N fertilizer applied). Weed competition in these treatments was minimal and the N status of maize plants was essentially the same regardless of the N source (fertilizer or green manure). Of the four organic no-till maize treatments, only the mixed-tillage system with cultivation for weed control (CD-NTc) produced yields comparable to conventional NT maize. The fate of vetch N as well as temporal N dynamics were largely determined by tillage intensity and the handling of the vetch residues at maize planting. Treatments with primary tillage (CD and MP) had extremely high levels of mineral N early in the season and had greater average net N-mineralization, even though N content of hairy vetch in these treatments was equal to or lower than that in treatments with mow-killed vetch. In terms of soil mineral N concentrations, the CD-NTc treatment was similar to the other mow-killed vetch/no-till maize treatments. However, N availability in this treatment was greater, probably due to more complete decomposition of green manure residues. Cultivation for weeds not only helped control weeds but also increased mineralization of the vetch residues, which in turn increased the N supply during the period of maximum N demand by the maize. Carefully designed rotations combining tillage reductions with the use of leguminous N sources can have multiple benefits, including improved timing of N availability, reduced herbicide applications, and improved soil quality in the long term.