• Authors:
    • Barfoot, P.
    • Brookes, G.
  • Year: 2008
  • Authors:
    • Coble, H. D.
    • Pedersen, M. K.
    • Burton, J. D.
  • Source: Journal of Plant Growth Regulation
  • Volume: 27
  • Issue: 4
  • Year: 2008
  • Summary: Cyclanilide is a plant growth regulator that is registered for use in cotton at different stages of growth, to either suppress vegetative growth (in combination with mepiquat chloride) or accelerate senescence (enhance defoliation and boll opening, used in combination with ethephon). This research was conducted to study the mechanism of action of cyclanilide: its potential interaction with auxin (IAA) transport and signaling in plants. The activity of cyclanilide was compared with the activity of the auxin transport inhibitors NPA and TIBA. Movement of [3H]IAA was inhibited in etiolated corn coleoptiles by 10 mu M cyclanilide, NPA, and TIBA, which demonstrated that cyclanilide affected polar auxin transport. Although NPA inhibited [3H]IAA efflux from cells in etiolated zucchini hypocotyls, cyclanilide had no effect. NPA did not inhibit the influx of IAA into cells in etiolated zucchini hypocotyls, whereas cyclanilide inhibited uptake 25 and 31% at 10 and 100 mu M, respectively. Also, NPA inhibited the gravitropic response in tomato roots (85% at 1 mu M) more than cyclanilide (30% at 1 mu M). Although NPA inhibited tomato root growth (30% at 1 mu M), cyclanilide stimulated root growth (165% of control at 5 mu M). To further characterize cyclanilide action, plasma membrane fractions from etiolated zucchini hypocotyls were obtained and the binding of NPA, IAA, and cyclanilide studied. Cyclanilide inhibited the binding of [3H]NPA and [3H]IAA with an IC50 of 50 mu M for both. NPA did not affect the binding of IAA, nor did IAA affect the binding of NPA. Kinetic analysis indicated that cyclanilide is a noncompetitive inhibitor of both NPA and IAA binding, with inhibition constants (K (i)) of 40 and 2.3 mu M, respectively. These data demonstrated that cyclanilide interacts with auxin-regulated processes via a mechanism that is distinct from other auxin transport inhibitors. This research identifies a possible mechanism of action for cyclanilide when used as a plant growth regulator.
  • Authors:
    • D'Ordine, R.
    • Navarro, S.
    • Back, S.
    • Fernandes, M.
    • Targolli, J.
    • Dasgupta, S.
    • Bonin, C.
    • Luethy, M. H.
    • Heard, J. E.
    • Salvador, S.
    • Kumar, G.
    • Abad, M.
    • Stoecker, M.
    • Harrison, J.
    • Anstrom, D. C.
    • Bensen, R. J.
    • Warner, D.
    • Castiglioni, P.
    • Carpenter, J. E.
  • Source: Plant Physiology
  • Volume: 147
  • Issue: 2
  • Year: 2008
  • Summary: An article about bacterial RNA chaperones conferring abiotic stress tolerance in plants and improved grain yield in maize under water-limited conditions.
  • Authors:
    • Raper, R. L.
    • Wood, C. W.
    • Reeves, D. W.
    • Shaw, J. N.
    • Franzluebbers, A. J.
    • Causarano, H. J.
  • Source: Soil Science Society of America Journal
  • Volume: 72
  • Issue: 1
  • Year: 2008
  • Summary: Quantification of the impact of long-term agricultural land use on soil organic C (SOC) is important to farmers and policyrnakers, but few studies have characterized land use and management effects on SOC across physiographic regions. We measured the distribution and total stock of SOC to a depth of 20 cm under conventional tillage (CvT), conservation tillage (CsT), and pasture in 87 production fields from the Southern Piedmont and Coastal Plain Major Land Resource Areas. Across locations, SOC at a depth of 0 to 20 cm was: pasture (38.9 Mg ha(-1)) > CsT (27.9 Mg ha(-1)) > CvT (22.2 Mg ha(-1)) (P <= 0.02). Variation in SOC was explained by management (41.6%), surface horizon clay content (5.2%), and mean annual temperature (1.0%). Higher clay content and cooler temperature contributed to higher SOC. Management affected SOC primarily at the soil surface (0-5 cm). All SOC fractions (i.e., total SOC, particulate organic C, soil microbial biomass C, and potential C mineralization) were strongly correlated across a diversity of soils and management systems (r = 0.85-0.96). The stratification ratio (concentration at the soil surface/concentration at a lower depth) of SOC fractions differed among management systems (P <= 0.0001), and was 4.2 to 6.1 under pastures, 2.6 to 4.7 under CsT and 1.4 to 2.4 under CvT; these results agree with a threshold value of 2 to distinguish historically degraded soils with improved soil conditions from degraded soils. This on-farm survey of SOC complements experimental data and shows that pastures and conservation tillage will lead to significant SOC sequestration throughout the region, resulting in improved soil quality and potential to mitigate CO2 emissions.
  • Authors:
    • Conklin, A. E.
    • Teasdale, J. R.
    • Cavigelli, M. A.
  • Source: Agronomy Journal
  • Volume: 100
  • Issue: 3
  • Year: 2008
  • Summary: Despite increasing interest in organic grain crop production, there is inadequate information regarding the performance of organically-produced grain crops in the United States, especially in Coastal Plain soils of the mid-Atlantic region. We report on corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) yields at the USDA-ARS Beltsville Farming Systems Project (FSP), a long-term cropping systems trial established in Maryland in 1996 to evaluate the sustainability of organic and conventional grain crop production. The five FSP cropping systems include a conventional no-till corn-soybean-wheat/soybean rotation (NT), a conventional chisel-till corn-soybean-wheat/soybean rotation (CT), a 2-yr organic corn-soybean rotation (Org2), a 3-yr organic corn-soybean-wheat rotation (Org3), and a 4- to 6-yr organic corn-soybean-wheat-hay rotation (Org4+). Average corn grain yield during 9 yr was similar in NT and CT (7.88 and 8.03 Mg ha-1, respectively) but yields in Org2, Org3, and Org4+ were, respectively, 41, 31, and 24% less than in CT. Low N availability explained, on average, 73% of yield losses in organic systems relative to CT while weed competition and plant population explained, on average, 23 and 4%, respectively, of these yield losses. The positive relationship between crop rotation length and corn yield among organic systems was related to increasing N availability and decreasing weed abundance with increasing rotation length. Soybean yield averaged 19% lower in the three organic systems (2.88 Mg ha-1) than in the conventional systems (3.57 Mg ha-1) and weed competition alone accounted for this difference. There were no consistent differences in wheat yield among cropping systems. Crop rotation length and complexity had little impact on soybean and wheat yields among organic systems. Results indicate that supplying adequate N for corn and controlling weeds in both corn and soybean are the biggest challenges to achieving equivalent yields between organic and conventional cropping systems.
  • Authors:
    • Mora, G.
    • Helmers, M.
    • Shepherd, G.
    • Asbjornsen, H.
  • Source: Plant and Soil
  • Volume: 308
  • Issue: 1-2
  • Year: 2008
  • Summary: In agricultural landscapes, variation and ecological plasticity in depth of water uptake by annual and perennial plants is an important means by which vegetation controls hydrological balance. However, little is known about how annual and perennial plants growing in agriculturally dominated landscapes in temperate humid regions vary in their water uptake dynamics. The primary objective of this study was to quantify the depth of water uptake by dominant plant species and functional groups growing in contrasting annual and perennial systems in an agricultural landscape in Central Iowa. We used stable oxygen isotope techniques to determine isotopic signatures of soil water and plant tissue to infer depth of water uptake at five sampling times over the course of an entire growing season. Our results suggest that herbaceous species (Zea mays L., Glycine max L. Merr., Carex sp., Andropogon gerardii Vitman.) utilized water predominantly from the upper 20 cm of the soil profile and exhibited a relatively low range of ecological plasticity for depth of water uptake. In contrast, the woody shrub (Symphoricarpos orbiculatus Moench.) and tree (Quercus alba L.) progressively increased their depth of water uptake during the growing season as water became less available, and showed a high degree of responsiveness of water uptake depth to changes in precipitation patterns. Coexisting shrubs and trees in the woodland and savanna sites extracted water from different depths in the soil profile, indicating complementarity in water uptake patterns. We suggest that deep water uptake by perennial plants growing in landscapes dominated by rowcrop agriculture can enhance hydrologic functioning. However, because the high degree of ecological plasticity allows some deep-rooted species to extract water from surface horizons when it is available, positive effects of deep water uptake may vary depending on species' growth patterns and water uptake dynamics. Knowledge about individual species' and plant communities' depth of water uptake patterns in relation to local climate conditions and landscape positions can provide valuable information for strategically incorporating perennial plants into agricultural landscapes to enhance hydrologic regulation.
  • Authors:
    • Van Cleemput, O.
    • Ahmed, H. P.
    • Boeckx, P.
    • Beheydt, D.
  • Source: Biology and Fertility of Soils
  • Volume: 44
  • Issue: 6
  • Year: 2008
  • Summary: In this study, we investigated N2O emissions from two fields under minimum tillage, cropped with maize (MT maize) and summer oats (MT oats), and a conventionally tilled field cropped with maize (CT maize). Nitrous oxide losses from the MT maize and MT oats fields (5.27 and 3.64 kg N2O-N ha(-1), respectively) were significantly higher than those from the CT maize field (0.27 kg N2O-N ha(-1)) over a period of 1 year. The lower moisture content in CT maize (43% water-filled pore space [WFPS] compared to 60 -65%) probably caused the difference in total N2O emissions. Denitrification was found to be the major source of N2O loss. Emission factors calculated from the MT field data were high (0.04) compared to the CT field (0.001). All data were simulated with the denitrification decomposition model (DNDC). For the CT field, N2O and N2O+N-2 emissions were largely overestimated. For the MT fields, there was a better agreement with the total N2O and N2O+N-2 emissions, although the N2O emissions from the MT maize field were underestimated. The simulated N2O emissions were particularly influenced by fertilization, but several other measured N2O emission peaks associated with other management practices at higher WFPS were not captured by the model. Several mismatches between simulated and measured NH4+, NO3-and WFPS for all fields were observed. These mismatches together with the insensitivity of the DNDC model for increased N2O emissions at the management practices different from fertilizer application explain the limited similarity between the simulated and measured N2O emissions pattern from the MT fields.
  • Authors:
    • Lal, R.
    • Blanco-Canqui, H.
  • Source: Geoderma
  • Volume: 145
  • Issue: 3
  • Year: 2008
  • Summary: Crop residues are a potential source for biofuel production. Yet, impacts of removal of corn (Zea mays L.) stover and other residues as biofuel feedstocks on micro-scale soil properties affecting the behavior of the whole soil are not well understood. Data on both macro- and micro-scale soil properties under different scenarios of stover management are needed to define the threshold levels of stover removal. Previous studies on stover removal impacts on soil properties have primarily focused on macroscale properties and little or not on microscale properties. Thus, this study was designed to assess impacts of annual stover removal for 3 consecutive years at rates of 0, 25, 50, 75, and 100% on soil physical properties at the aggregate level under no-tillage (NT) continuous corn systems in a Rayne silt loam (RSL) (fine-loamy, mixed, active, mesic Typic Hapludult) with 10% slope, Celina silt loam (CSL) (fine, mixed, active, mesic Aquic Hapludalfs) with 2% slope, and Hoytville clay loam (HCL) (fine, illitic, mesic Mollic Epiaqualfs) with < 1% slope in Ohio. Aggregates were sensitive to stover removal particularly in the 0- to 10-cm soil depth. Stover removal reduced aggregate stability, tensile strength (TS), water retention (WR), and subcritical water repellency, while it increased water sorptivity but had no effect on pore-size distribution within an aggregate. The interaction of aggregate stability, strength, and subcritical water repellency with aggregate structural properties due to stover removal depended on the variable antecedent soil water conditions. The aggregate stability and strength decreased while water repellency increased with increasing water potential. Impacts of stover removal on the clayey soils were equal to or higher than those on silt loam soils. Removal at rates ≥ 25% reduced the raindrop kinetic energy (KE) required to break aggregates by 13 times at HCL, while removal at rates ≥ 50% reduced the KE by 2 to 3 times at RSL and CSL for air-dry aggregates. The KE and TS decreased with increasing soil water potentials. The TS was reduced by 10% to 30% at all water potentials at RSL, by 20% to 35% between - 0.1 and - 1.5 MPa, and by 2.2 times at - 166 MPa at CSL, and by 2 to 3 times between - 1.5 and - 166 MPa at HCL under complete stover removal. Removal of stover at rates ≥ 50% reduced subcritical water repellency by 2 to 10 times in all soils. Overall, stover removal altered micro-scale soil properties, and complete stover removal had the most detrimental effects. Based on the data from previous studies on macroscale soil properties and this study, stover removal adversely affects both macro- and micro-scale soil properties.
  • Authors:
    • Fabian, E.
    • Pegoraro, R.
    • Bertol, I.
    • Zoldan Junior, W.
    • Zavaschi, E.
    • Vazquez, E.
  • Source: REVISTA BRASILEIRA DE CIENCIA DO SOLO
  • Volume: 32
  • Issue: 1
  • Year: 2008
  • Summary: Surface soil roughness is affected by many factors, such as the residual effect of the soil management, tillage and rainfall erosivity and, together with the soil cover of crop residues, influences water erosion. The objective of this study was to determine the effects of a chiselling operation, together with rainfall erosivity, on soil surface roughness, from June 2005 to March 2006, in an aluminic Typical Hapludox, under the following soil management systems: bare soil under conventional tillage (BCT), cultivated soil under conventional tillage (CCT), no-tillage in a never-tilled soil with burnt plant residues (BNT), and traditional no-tillage (TNT). The crop sequence in the treatments CCT, BNT and TNT was black oat, soyabean, common vetch, maize, black oat, common bean, fodder radish, soyabean, common vetch, maize and black oat. Five simulated rain tests were applied, with a constant intensity of 64 mm h -1 and durations of 20, 30, 40, 50, and 60 min each. Natural rains during the experimental period accounted for 57 mm, between the 2nd and 3rd rainfall test; 21 mm, between the 3rd and 4th test; and, 30 mm, between the 4th and 5th test. The surface roughness was determined immediately before and immediately after the chiseling tillage, and immediately after each test of rain simulation. The original and linear soil surface roughness was not influenced by the management, unlike random roughness, at the end of a six-month fallow period. The original, linear and random roughness in different soil management systems was affected by a six-month fallow period, when the soil was subjected to chiselling. Random roughness was less influenced by soil slope than by tillage marks, which decreased with the increasing rainfall erosivity. The coefficient of decay of this kind of soil roughness was similar in the studied soil management systems under no tillage and conventional tillage.
  • Authors:
    • Kremer, R. J.
    • Sudduth, K. A.
    • Kitchen, N. R.
    • Jung, W. K.
  • Source: Soil Science and Plant Nutrition
  • Volume: 54
  • Issue: 6
  • Year: 2008
  • Summary: Crop management has the potential to either enhance or degrade soil quality, which in turn impacts on crop production and the environment. Few studies have investigated how crop management affects soil quality over different landscape positions. The objective of the present study was to investigate how 12 years of annual cropping system (ACS) and conservation reserve program (CRP) practices impacted soil quality indicators at summit, backslope and footslope landscape positions of a claypan soil in north-central Missouri. Claypan soils are particularly poorly drained because of a restrictive high-clay subsoil layer and are vulnerable to high water erosion. Three replicates of four management systems were established in 1991 in a randomized complete block design, with landscape position as a split-block treatment. The management systems were investigated: (1) annual cropping system 1 (ACS1) was a mulch tillage (typically >= 30% of soil covered with residue after tillage operations) corn (Zea mays L.)-soybean (Glycine max (L.) Merr.) rotation system, (2) annual cropping system 2 (ACS2) was a no-till corn-soybean rotation system, (3) annual cropping system 3 (ACS3) was a no-till corn-soybean-wheat (Triticum aestivum L.) rotation system, with a cover crop following wheat, (4) CRP was a continuous cool-season grass and legume system. In 2002, soil cores (at depths of 0-7.5, 7.5-15 and 15-30 cm) were collected by landscape position and analyzed for physical, chemical and biological soil quality properties. No interactions were observed between landscape and crop management. Relative to management effects, soil organic carbon (SOC) significantly increased with 12 years of CRP management, but not with the other management systems. At the 0-7.5-cm soil depth in the CRP system, SOC increased over this period by 33% and soil total nitrogen storage increased by 34%. Soil aggregate stability was approximately 40% higher in the no-till management systems (ACS2 and ACS3) than in the tilled system (ACS1). Soil aggregation under CRP management was more than double that of the three grain-cropping systems. Soil bulk density at the shallow sampling depth was greater in ACS3 than in ACS1 and ACS2. In contrast to studies on other soil types, these results indicate only minor changes to claypan soil quality after 12 years of no-till management. The landscape had minor effects on the soil properties. Of note, SOC was significantly lower in the 7.5-15-cm soil depth at the footslope compared with the other landscape positions. We attribute this to wetter and more humid conditions at this position and extended periods of high microbial activity and SOC mineralization. We conclude that claypan soils degraded by historical cropping practices will benefit most from the adoption of CRP or CRP-like management.