• Authors:
    • Ali, M. K.
    • Paustian, K.
    • Capalbo, S. M.
    • Antle, J. M.
  • Source: Climatic Change
  • Volume: 80
  • Issue: 1-2
  • Year: 2007
  • Summary: The purpose of this paper is to develop and apply a new method to assess economic potential for agricultural greenhouse gas mitigation. This method uses secondary economic data and conventional econometric production models, combined with estimates of soil carbon stocks derived from biophysical simulation models such as Century, to construct economic simulation models that estimate economic potential for carbon sequestration. Using this method, simulations for the central United States show that reduction in fallow and conservation tillage adoption in the wheat-pasture system could generate up to about 1.7 million MgC/yr, whereas increased adoption of conservation tillage in the corn-soy-feed system could generate up to about 6.2 million MgC/yr at a price of $200/MgC. About half of this potential could be achieved at relatively low carbon prices (in the range of $50 per ton). The model used in this analysis produced estimates of economic potential for soil carbon sequestration potential similar to results produced by much more data-intensive, field-scale models, suggesting that this simpler, aggregate modeling approach can produce credible estimates of soil carbon sequestration potential. Carbon rates were found to vary substantially over the region. Using average carbon rates for the region, the model produced carbon sequestration estimates within about 10% of those based on county-specific carbon rates, suggesting that effects of spatial heterogeneity in carbon rates may average out over a large region such as the central United States. However, the average carbon rates produced large prediction errors for individual counties, showing that estimates of carbon rates do need to be matched to the spatial scale of analysis. Transaction costs were found to have a potentially important impact on soil carbon supply at low carbon prices, particularly when carbon rates are low, but this effect diminishes as carbon prices increase.
  • Authors:
    • Griffis, T. J.
    • Venterea, R. T.
    • Ochsner, T. E.
    • Baker, J. M.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 118
  • Issue: 1-4
  • Year: 2007
  • Summary: It is widely believed that soil disturbance by tillage was a primary cause of the historical loss of soil organic carbon (SOC) in North America, and that substantial SOC sequestration can be accomplished by changing from conventional plowing to less intensive methods known as conservation tillage. This is based on experiments where changes in carbon storage have been estimated through soil sampling of tillage trials. However, sampling protocol may have biased the results. In essentially all cases where conservation tillage was found to sequester C, soils were only sampled to a depth of 30 cm or less, even though crop roots often extend much deeper. In the few studies where sampling extended deeper than 30 cm, conservation tillage has shown no consistent accrual of SOC, instead showing a difference in the distribution of SOC, with higher concentrations near the surface in conservation tillage and higher concentrations in deeper layers under conventional tillage. These contrasting results may be due to tillage-induced differences in thermal and physical conditions that affect root growth and distribution. Long-term, continuous gas exchange measurements have also been unable to detect C gain due to reduced tillage. Though there are other good reasons to use conservation tillage, evidence that it promotes C sequestration is not compelling.
  • Authors:
    • Myers, L.
    • Sherwood, J.
    • Edelson, J.
    • Damicone, J.
    • Motes, J.
  • Source: Plant Disease
  • Volume: 91
  • Issue: 5
  • Year: 2007
  • Summary: In five field trials over 3 years, control of aphid-transmitted, nonpersistent virus diseases on pumpkin, caused mostly by the potyviruses Watermelon mosaic virus (WMV) and Papaya ringspot virus type-W (PRSV-W), was achieved by intercropping with grain sorghum, as opposed to clean tillage. Reductions in disease incidence ranged from 43 to 96% ( P≤0.05). Surrounding pumpkin plots with borders of peanut, soybean, or corn was not effective. Borders of grain sorghum were effective, but disease control was generally less than for the intercrop treatment. Intercropping soybean and peanut with pumpkin reduced disease incidence by 27 to 60% ( P≤0.05), but disease control generally was less than for grain sorghum. Peak periods of alate aphid immigration generally preceded virus disease outbreaks by 7 to 14 days. However, alate landing rates, as measured in green tile traps, did not differ among treatments. Marketable yield was not increased by the intercrop treatments, and yield was reduced by up to 50% for the intercrop treatment with grain sorghum in two trials. The use of grass-selective herbicide applied along pumpkin rows, reduced seeding rates of the intercrops, or mowing did not alleviate the adverse effects of competition between pumpkin and the grain sorghum intercrop on yield.
  • Authors:
    • Hons, F.
    • Wright, A.
    • Dou, F.
  • Source: Soil & Tillage Research
  • Volume: 94
  • Issue: 2
  • Year: 2007
  • Summary: Crop management practices have potential to enhance subsoil C and N sequestration in the southern U.S., but effects may vary with tillage regime and cropping sequence. The objective of this study was to determine the impacts of tillage and soyabean cropping sequence on the depth distribution of soil organic C (SOC), dissolved organic C (DOC), and total N after 20 years of treatment imposition for a silty clay loam soil in central Texas. A continuous soyabean monoculture, a wheat-soybean doublecrop, and a sorghum-wheat-soybean rotation were established under both conventional (CT) and no tillage (NT). Soil was sampled after soyabean harvest and sectioned into 0-5, 5-15, 15-30, 30-55, 55-80, and 80-105 cm depth intervals. Both tillage and cropping intensity influenced C and N dynamics in surface and subsurface soils. No tillage increased SOC, DOC, and total N compared to CT to a 30 cm depth for continuous soyabean, but to 55 cm depths for the more intensive sorghum-wheat-soybean rotation and wheat-soybean doublecrop. Averaged from 0 to 105 cm, NT increased SOC, DOC, and total N by 32, 22, and 34%, respectively, compared to CT. Intensive cropping increased SOC and total N at depths to 55 cm compared to continuous soyabean, regardless of tillage regime. Continuous soyabean had significantly lower SOC (5.3 g kg -1) than sorghum-wheat-soybean (6.4 g kg -1) and wheat-soybean (6.1 g kg -1), and 19% lower total N than other cropping sequences. Dissolved organic C was also significantly higher for sorghum-wheat-soybean (139 mg C kg -1) than wheat-soybean (92 mg C kg -1) and continuous soyabean (100 mg C kg -1). The depth distribution of SOC, DOC, and total N indicated treatment effects below the maximum tillage depth (25 cm), suggesting that roots, or translocation of dissolved organic matter from surface soils, contributed to higher soil organic matter levels under NT than CT in subsurface soils. High-intensity cropping sequences, coupled with NT, resulted in the highest soil organic matter levels, demonstrating potential for C and N sequestration for subsurface soils in the southern U.S.
  • Authors:
    • Drijber, R.
    • Mamo, M.
    • Wortmann, C.
    • Garcia, J.
    • Tarkalson, D.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 4
  • Year: 2007
  • Summary: Stratification of nutrient availability, especially of P, that develops with continuous no-till (NT) can affect runoff nutrient concentration and possibly nutrient uptake. The effects of composted manure application and one-time tillage of NT on the distribution of soil chemical properties, root colonization by arbuscular mycorrhizae (AM), and plant P uptake were determined. Research was conducted on Typic Argiudoll and Mollic Hapludalf soils under rainfed corn ( Zea mays L.) or sorghum [ Sorghum bicolor (L.) Moench.] rotated with soybean [ Glycine max (L.) Merr.] in eastern Nebraska. Tillage treatments included NT, disk, chisel, moldboard plow (MP), and mini-moldboard plow (MMP). Subplots had either 0 or 87.4 kg P ha -1 applied in compost before tillage. Bray-P1 was five to 21 times as high for the 0- to 5-cm as compared with the 10- to 20-cm soil depth. Greater redistribution of nutrients and incorporation of compost P resulted from MP tillage than from other tillage treatments. One-time chisel or disk tillage did not effectively redistribute nutrients while MMP tillage had an intermediate effect. Compost application reduced AM colonization of roots at R6 for all crops. Tillage reduced AM colonization with reductions at R6 due to MP tillage of 58 to 87%. The tillage effect on colonization persisted through the second year with no indication of AM recovery. Root P concentration was increased by MP and was negatively correlated to colonization. Decreased colonization did not result in decreased plant P uptake. Infrequent MP tillage can reduce surface soil P and the potential for P loss in runoff, but may reduce AM colonization of the roots, possibly reducing P uptake with some low P soils. The results do not indicate any advantage to one-time tillage of NT if runoff P loss is not a concern.
  • Authors:
    • Lamond, R.
    • Mengel, D.
    • Pierzynski, G.
    • Godsey, C.
  • Source: Soil Science Society of America Journal
  • Volume: 71
  • Issue: 3
  • Year: 2007
  • Summary: Recent attention has focused on management of soil acidity in no-till (NT) soils due to the limited movement of surface-applied lime in these systems. Interactions of exchangeable Al and organic matter have been recognized for many years, but limited data exist investigating how these interactions should affect management decisions for NT soils. This study was conducted to identify effects of rotation and tillage on soil pH and soil organic carbon (OC) content and to determine the influence of soil pH and OC on KCl and CuCl 2 extractable-Al (Al KCl and Al CuCl2, respectively). Soil samples were collected to a depth of 15 cm, in 2.5-cm increments, from a long-term rotation and tillage study near Manhattan, KS. Soil pH and OC concentrations were influenced by rotation and tillage, especially in the surface 2.5 cm. Organic C concentrations were on average 2.3 g kg -1 greater with NT than with conventional tillage in the surface 15 cm of soil. Aluminum extracted with KCl and Al CuCl2 increased exponentially with decreasing soil pH. Copper chloride extractable-Al values were on average 8% greater than Al KCl values. When using a regression model to predict the difference between Al CuCl2 and Al KCl, inclusion of OC explained only 4% more variability compared with inclusion of only soil pH in the model. A change in OC concentrations of 2.3 g kg -1, as observed in this study, after reducing tillage would likely not alleviate Al toxicity if pH became very acidic (pH
  • Authors:
    • Sweeney, D.W.
    • Kelley, K.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 4
  • Year: 2007
  • Summary: Because of improved equipment technology, many producers in the eastern Great Plains are planting winter wheat ( Triticum aestivum L.) no-till (NT) into previous crop residues, but management of fertilizer N and P remains critical. This field study was conducted from 1998 through 2003 in southeastern Kansas on a Parsons silt loam soil (fine, mixed, thermic, Mollic Albaqualf). The objectives were to determine effects and interactions of previous crop [corn, Zea mays L.; grain sorghum, Sorghum bicolor (L.); and soybean, Glycine max (L.) Merr.], preplant placement method of liquid N-P fertilizer [subsurface-knife (KN), surface-band (SB), and surface-broadcast (BC)], and fertilizer N rate (22, 45, 90, and 134 kg N ha -1) on NT winter wheat yield, yield components, and nutrient uptake in a 2-yr cropping rotation. Wheat yields averaged 3.73, 3.56, and 2.97 Mg ha -1 following soybean, corn, and grain sorghum, respectively. However, as fertilizer N rate increased, yield differences between previous crops decreased. Grain yields also were influenced by placement of N-P fertilizer, averaging 3.68 Mg ha -1 for KN, 3.40 Mg ha -1 for SB, and 3.19 Mg ha -1 for BC. Plant and grain N responses indicated that grain yield differences were primarily related to greater immobilization of both fertilizer and soil N following grain sorghum, compared with soybean and corn, and to better utilization of KN N-P than surface-applied. Fertilizing with greater N rates applied as a subsurface band, especially if following grain sorghum, may be necessary to maximize NT wheat yield potential in the eastern Great Plains.
  • Authors:
    • Paustian, K.
    • Capalbo, S.
    • Antle, J.
    • Gerow, K.
    • Mooney, S.
  • Source: Climatic Change
  • Volume: 80
  • Issue: 1/2
  • Year: 2007
  • Summary: Several studies have suggested that geostatistical techniques could be employed to reduce overall transactions costs associated with contracting for soil C credits by increasing the efficacy of sampling protocols used to measure C-credits. In this paper, we show how information about the range of spatial autocorrelation can be used in a measurement scheme to reduce the size of the confidence intervals that bound estimates of the mean number of C-credits generated per hectare. A tighter confidence interval around the mean number of C-credits sequestered could increase producer payments for each hectare enrolled in a contract to supply C-credits. An empirical application to dry land cropping systems in three regions of Montana shows that information about the spatial autocorrelation exhibited by soil C could be extremely valuable for reducing transactions costs associated with contracts for C-credits but the benefits are not uniform across all regions or cropping systems. Accounting for spatial autocorrelation greatly reduced the standard errors and narrowed the confidence intervals associated with sample estimates of the mean number of C-credits produced per hectare. For the payment mechanism considered in this paper, tighter confidence intervals around the mean number of C-credits created per hectare enrolled could increase producer payments by more than 100 percent under a C-contract.
  • Authors:
    • Schumacher, R.
    • Schroeder, K.
    • Li, C.
    • Okubara, P.
    • Lawrence, N.
  • Source: Canadian Journal of Plant Pathology
  • Volume: 29
  • Issue: 3
  • Year: 2007
  • Summary: Soilborne pathogens are important biotic factors in yield reduction in the dryland cereal production region of the Pacific Northwest. Rhizoctonia solani AG-8, Rhizoctonia oryzae, and Pythium spp. are causal agents of root rot, bare patch, and damping-off of wheat ( Triticum aestivum) and barley ( Hordeum vulgare). Although these pathogens can be rapidly and specifically quantified using quantitative real-time PCR, the extraction of Rhizoctonia DNA from agricultural samples is often inconsistent, especially at low pathogen population densities. Using a novel extraction system that uses pressure cycling technology (PCT), we improved the extraction of R. solani AG-8 DNA up to 16-fold and of P. abappressorium DNA up to 2-fold from three types of agricultural soils compared with a bead beating extraction method. PCT also yielded quantifiable amounts of R. solani AG-8 and R. oryzae DNA from lyophilized wheat roots that were otherwise recalcitrant to homogenization. Furthermore, the extractions were so consistent that pathogen quantification generally could be derived from two rather than three or four replicated extracts. Because PCT is performed in a closed system and minimizes sample shearing and heating, it confers a substantial advantage over conventional extraction systems. Here, we report for the first time the application of PCT in a laboratory setting for the improved extraction and quantification of three types of soilborne pathogens in soil samples. The effectiveness of PCT for three soils suggests that it will be beneficial for other hard-to-extract pathogen samples.
  • Authors:
    • Franti, T.
    • Mamo, M.
    • Wortmann, C.
    • Quincke, J.
    • Drijber, R.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 4
  • Year: 2007
  • Summary: Soil organic carbon (SOC) accumulation occurs mostly in the top 5 cm of soil with continuous no-till (NT) while SOC losses often occur at deeper depths. We hypothesize that one-time tillage conducted once in >10 yr to mix the high SOC surface layer with deeper soil will not result in large SOC losses following tillage with a net positive gain in SOC eventually. Two experiments in long-term NT fields were installed under rainfed corn ( Zea mays L.) or sorghum [ Sorghum bicolor (L.) Moench.] rotated with soybean [ Glycine max (L.) Merr.] in eastern Nebraska. Tillage treatments were applied in the spring or fall and included: NT, disk, chisel with 10-cm wide twisted shanks, moldboard plow (MP), and mini-moldboard plow (miniMP). A portable infrared gas analyzer was used to monitor CO 2 flux immediately following tillage. Effect of tillage on profile distribution of total and labile (particulate and oxidizable) SOC was determined. At 24 to 32 mo following tillage, SOC mass was determined for depths of 0 to 5, 5 to 20, and 20 to 30 cm. Some tillage operations effectively redistributed total and labile SOC with little increase in CO 2 flux compared with NT. Total and labile SOC concentrations were reduced by 24 to 88% in the 0- to 2.5-cm depth and increased by 13 to 381% for the 5- to 10-cm depth for the various tillage operations. Moldboard plowing caused the greatest redistribution of SOC. On an equivalent soil mass basis, tillage did not cause significant losses of total or labile SOC between tillage and planting of the next crop or by 24 to 32 mo after tillage. Stratification of SOC in long-term NT soil could be reduced most effectively by means of one-time MP tillage without increased loss of labile SOC.