• Authors:
    • Johnson, D. W.
    • Moeltner, K.
    • van Kooten, G. C.
    • Manley, J.
  • Source: Climatic Change
  • Volume: 68
  • Issue: 1-2
  • Year: 2005
  • Summary: Carbon terrestrial sinks are often seen as a low-cost alternative to fuel switching and reduced fossil fuel use for lowering atmospheric CO2. To determine whether this is true for agriculture, one meta-regression analysis (52 studies, 536 observations) examines the costs of switching from conventional tillage to no-till, while another (51 studies, 374 observations) compares carbon accumulation under the two practices. Costs per ton of carbon uptake are determined by combining the two results. The viability of agricultural carbon sinks is found to vary by region and crop, with no-till representing a low-cost option in some regions (costs of less than $10 per tC), but a high-cost option in others (costs of $100-$400 per tC). A particularly important finding is that no-till cultivation may store no carbon at all if measurements are taken at sufficient depth. In some circumstances no-till cultivation may yield a triple dividend of carbon storage, increased returns and reduced soil erosion, but in many others creating carbon offset credits in agricultural soils is not cost effective because reduced tillage practices store little or no carbon.
  • Authors:
    • Milbrandt, A.
  • Source: Technical Report
  • Year: 2005
  • Authors:
    • Culpepper, A. S.
    • Young, B. G.
    • Mitchell, P. D.
    • Mueller, T. C.
  • Source: Weed Technology
  • Volume: 19
  • Issue: 4
  • Year: 2005
  • Summary: The value of glyphosate has been compromised in some fields where weed populations have developed resistance or tolerant species increased. Three case studies related to reduced control from glyphosate are: (1) a weed population that has become resistant to glyphosate, with horseweed in Tennessee as an example; (2) a weed population increases due to lack of control in ‘‘glyphosate only’’ systems, with tropical spiderwort in Georgia cotton used as an example; and (3) the hypothetical resistance of common waterhemp to glyphosate in Illinois. For each of these case studies, an economic analysis was performed using a partial budget approach. This economic analysis provides the cost of control to the farmer when glyphosate fails to control these weeds and gives a critical time in years to compare different glyphosate resistance management philosophies (applicable only before resistance has evolved). The cost of glyphosate-resistant horseweed in cotton-soybeancorn rotation in Western Tennessee was calculated to be $30.46/ha per year. The cost of tropical spiderwort in cotton in southern Georgia was calculated to be $35.07/ha per year. The projected cost if common waterhemp were to develop glyphosate resistance in a corn-soybean rotation in southern Illinois was projected to be $44.25/ha per year, and the critical time was determined to be greater than 20 yr, indicating that a resistance management strategy would extend the value of glyphosateresistant crops.
  • Authors:
    • Franzluebbers, A. J.
  • Source: Soil & Tillage Research
  • Volume: 83
  • Issue: 1
  • Year: 2005
  • Summary: Agriculture in the southeastern USA can be highly productive (i.e., high photosynthetic fixation of atmospheric CO2) due to warm-moist climatic conditions. However, its impacts on greenhouse gas emissions and mitigation potential have not been thoroughly characterized. This paper is a review and synthesis of literature pertaining to soil organic C (SOC) sequestration and greenhouse gas emissions from agricultural activities in the southeastern USA. Conservation tillage is an effective strategy to regain some of the SOC lost following decades, and in some areas centuries, of intensive soil tillage and erosion. With conventional tillage (CT) as a baseline, SOC sequestration with no tillage (NT) was 0.42 ± 0.46 Mg ha-1 year-1 (10 ± 5 years). Combining cover cropping with NT enhanced SOC sequestration (0.53 ± 0.45 Mg ha-1 year-1) compared with NT and no cover cropping (0.28 ± 0.44 Mg ha-1 year-1). By increasing cropping system complexity, SOC could be increased by 0.22 Mg ha-1 year-1, irrespective of tillage management. Taking into account an average C cost of producing and transporting N fertilizer, SOC sequestration could be optimized at 0.24 Mg ha-1 year-1 with application of 107 kg N ha-1 year-1 on N-responsive crops, irrespective of tillage management. In longer-term studies (5-21 years), poultry litter application led to SOC sequestration of 0.72 ± 0.67 Mg ha-1 year-1 (17 ± 15% of C applied). Land that was previously cropped and converted to forages sequestered SOC at a rate of 1.03 ± 0.90 Mg ha-1 year-1 (15 ± 17 years). Limited data suggest animal grazing increases SOC sequestration on upland pastures. By expanding research on SOC sequestration into more diverse pasture and manure application systems and gathering much needed data on methane and nitrous oxide fluxes under almost any agricultural operation in the region, a more complete analysis of greenhouse gas emissions and potential mitigation from agricultural management systems would be possible. This information will be necessary for developing appropriate technological and political solutions to increase agricultural sustainability and combat environmental degradation in the southeastern USA.
  • Authors:
    • Strickland, T. C.
    • Bednarz, C. W.
    • Truman, C. C.
    • Potter, T. L.
    • Bosch, D. D.
  • Source: Transactions of the ASAE
  • Volume: 48
  • Issue: 6
  • Year: 2005
  • Summary: Conservation tillage has significant potential as a water management tool for cotton production on sandy, drought-prone soils. Plant residue remaining at the soil surface from prior crops serves as a vapor barrier against water loss, reduces raindrop impact energy, slows surface runoff, and often increases infiltration. By increasing infiltration, the potential for greater plant-available water can be enhanced and irrigation requirements reduced. Five years of data were collected to quantify the hydrologic differences between strip till and conventional till production systems. Surface runoff and lateral subsurface flow were measured on six 0.2 ha plots in South Georgia in order to quantify the water-related effects of conservation tillage. Significant differences in surface and subsurface water losses were observed between the conventional and strip tilled plots. Surface runoff from the conventionally tilled plots exceeded that from the strip tilled plots, while subsurface losses were reversed. Surface runoff losses from the conventionally tilled plots exceeded those from the strip tilled plots by 81% (129 mm/year). Shallow lateral subsurface losses from the strip tilled plots exceeded those from the conventionally tilled plots by 73% (69 mm/year). Overall, a net annual gain of 60 mm of water was observed for the strip tilled plots.
  • Authors:
    • Saggin, A.
    • Santos, D.
    • Gatiboni, L.
    • Brunetto, G.
    • Kaminski, J.
  • Source: REVISTA BRASILEIRA DE CIENCIA DO SOLO
  • Volume: 29
  • Issue: 4
  • Year: 2005
  • Summary: The critical potassium level for fertilizer recommendation for soils in the State of Rio Grande do Sul (RS) and Santa Catarina (SC), Brazil, with cation exchange capacity (CEC) from 5.1 to 15 cmol c dm -3 is 60 mg dm -3. However, until 2002 concentrations of 80 mg dm -3 had been used. Two experiments were carried out on an experimental area of the Department of Soil Science of the Federal University of Santa Maria (RS-Brazil) on a sandy Typic Hapludalf under no-tillage. The objective of the study was to evaluate critical potassium levels for fertilizer recommendations for soyabean, maize and sorghum. The first experiment was set up in 1991 and carried out until 2002. The main plot treatments were the application of 0, 60, 120, and 180 kg ha -1 K 2O every four years, and split-plot treatments were the reapplication of 60 kg of K 2O in 0, 1, 2, or 3 years. The second experiment was carried out from 1995 to 2002 and the treatments were 0, 50, 100, 150, and 200 kg ha -1 year -1 K 2O. Results showed that the critical potassium level extracted with Mehlich-1 solution is 42 mg dm -3. When using the critical potassium level established by the Regional Soil Chemistry and Fertility Commission in these soils it is possible to reach over 95% of the maximum crop yield.
  • Authors:
    • Reeves, D.
    • Torbert, H.
    • Rogers, H.
    • Runion, G.
    • Prior, S.
  • Source: Global Change Biology
  • Volume: 11
  • Issue: 4
  • Year: 2005
  • Summary: Increasing atmospheric CO 2 concentration has led to concerns about potential effects on production agriculture as well as agriculture's role in sequestering C. In the fall of 1997, a study was initiated to compare the response of two crop management systems (conventional and conservation) to elevated CO 2. The study used a split-plot design replicated three times with two management systems as main plots and two CO 2 levels (ambient=375 L L -1 and elevated CO 2=683 L L -1) as split-plots using open-top chambers on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system was a grain sorghum ( Sorghum bicolor (L.) Moench.) and soybean ( Glycine max (L.) Merr.) rotation with winter fallow and spring tillage practices. In the conservation system, sorghum and soybean were rotated and three cover crops were used (crimson clover ( Trifolium incarnatum L.), sunn hemp ( Crotalaria juncea L.), and wheat ( Triticum aestivum L.)) under no-tillage practices. The effect of management on soil C and biomass responses over two cropping cycles (4 years) were evaluated. In the conservation system, cover crop residue (clover, sunn hemp, and wheat) was increased by elevated CO 2, but CO 2 effects on weed residue were variable in the conventional system. Elevated CO 2 had a greater effect on increasing soybean residue as compared with sorghum, and grain yield increases were greater for soybean followed by wheat and sorghum. Differences in sorghum and soybean residue production within the different management systems were small and variable. Cumulative residue inputs were increased by elevated CO 2 and conservation management. Greater inputs resulted in a substantial increase in soil C concentration at the 0-5 cm depth increment in the conservation system under CO 2-enriched conditions. Smaller shifts in soil C were noted at greater depths (5-10 and 15-30 cm) because of management or CO 2 level. Results suggest that with conservation management in an elevated CO 2 environment, greater residue amounts could increase soil C storage as well as increase ground cover.
  • Authors:
    • Norby, R. J.
    • Matamala, R.
    • Miller, R. M.
    • Jastrow, J. D.
    • Boutton, T. W.
    • Rice, C. W.
    • Owensby, C. E.
  • Source: Global Change Biology
  • Volume: 11
  • Issue: 12
  • Year: 2005
  • Summary: The general lack of significant changes in mineral soil C stocks during CO2-enrichment experiments has cast doubt on predictions that increased soil C can partially offset rising atmospheric CO2 concentrations. Here, we show, through meta-analysis techniques, that these experiments collectively exhibited a 5.6% increase in soil C over 2-9 years, at a median rate of 19 g C m(-2) yr(-1). We also measured C accrual in deciduous forest and grassland soils, at rates exceeding 40 g C m(-2) yr(-1) for 5-8 years, because both systems responded to CO2 enrichment with large increases in root production. Even though native C stocks were relatively large, over half of the accrued C at both sites was incorporated into microaggregates, which protect C and increase its longevity. Our data, in combination with the meta-analysis, demonstrate the potential for mineral soils in diverse temperate ecosystems to store additional C in response to CO2 enrichment.
  • Authors:
    • Milliken, GA
    • Rice, CW
    • Mikha, MM
  • Source: Soil Biology and Biochemistry
  • Volume: 37
  • Issue: 2
  • Year: 2005
  • Summary: Drying and rewetting of soil is an important process in soil aggregation, soil organic matter (SOM) decomposition, and nutrient cycling We investigated the source of the C and N flush that occurs upon rewetting of dry soil, and whether it is from microbial death and/or aggregate destruction. A moderately well drained Kennebec silt loam (Fine-silty, mixed, superactive, mesic Cumulic Hapludoll) was sampled to a 10 cm depth. Soil under constant water content (CWC) was compared with soil subjected to a series of four dry-wet (DW) cycles during the experimental period (96 d) and incubated at 25 degreesC. Mineralized C and N were measured during the drying and rewetting periods. Aggregate size distributions were studied by separating the soil into four aggregate size classes (> 2000, 250-2000, 53-250, and 2053 pm) by wet sieving. Repeated DW cycles significantly reduced cumulative N mineralization compared with CWC. The reduction in cumulative mineralized C resulting from DW compared with CWC increased as the DW treatments were subjected to additional cycles. The flush of mineralized C significantly decreased with repeated DW cycles. There was no significant effect on aggregate size distributions resulting from to the DW cycles compared with CWC treatment. Therefore, the flush of mineralized C and N seemed to be mostly microbial in origin in as much as aggregate distribution was unaffected by DW cycles. Published by Elsevier Ltd.
  • Authors:
    • Klepker, D.
    • Yamada, M.
    • Hitsuda, K.
  • Source: Agronomy Journal
  • Volume: 97
  • Issue: 1
  • Year: 2005
  • Summary: Sulfur deficiency symptoms are more often observed in crops at early stages of growth since S can be easily leached from the surface soil. The objectives of this study were to evaluate some of the popular rotation crops grown in Brazil for tolerance to low external S levels and to determine the critical tissue concentration for S deficiency during early stages of growth. Germinated seedlings of soybean [ Glycine max (L.) Merr.], rice ( Oryza sativa L.), maize ( Zea mays L.), field bean ( Phaseolus vulgaris L.), wheat ( Triticum aestivum L.), cotton ( Gossypium spp.), sorghum ( Sorghum bicolor L.), and sunflower ( Helianthus annuus L.) were transferred to water culture with 0.0 to 32.0 mg S L -1 and were grown for 29 d. The minimum S concentration required in nutrient solutions was 2.0 mg L -1 for sunflower; 1.0 mg L -1 for cotton, sorghum, wheat, and soybean; and 0.5 mg L -1 or less for field bean, rice, and maize. All crops achieved optimum growth at 2.0 mg S L -1. Critical shoot S concentration at early stages of growth was 0.8 g kg -1 in maize and soybean; 1.1 to 1.3 g kg -1 in cotton, sorghum, and rice; and 1.4 to 1.6 g kg -1 in wheat, sunflower, and field bean. Our results demonstrate that the tolerance to low external S (