The Piedmont region in the southeastern USA is characterized by sloping, crust-prone soils conducive to runoff losses of agricultural chemicals. Three tillage-residue management systems were compared for their effect on concentrations of atrazine [2-chloro-4-ethylamino-6isopropylamino-l,3,5-triazine], metolachlor [2-chloro-N-(2-ethyl-6methylphenyl)-N-(2-methoxy-l-methylethyi) acetamide], and bromide in surface runoff and in the soil profile of a Pacolet sandy clay loam (clayey, kaolinitic, thermic Typic Kanhapludults). These systems included conventional tillage (CT), no-tillage grain production with corn (Zea mays L.) residue (NTG), and no-tillage silage production without residue (NTS). The first simulated rainfall event consisted of a low (1.27 cm h-~) or high (5.08 cm -z) rainfall r ate a pplied f or 30 min following herbicide and bromide application. One week later, the high rate was simulated on all plots. The CT treatment generally produced less surface runoff, and accompanying lower chemical concentrations, compared with both no-tillage treatments on the first date. Runoff differences due to tillage system were less on the second date because of surface sealing processes under CT. Averaged over 2 yr, the percentage of applied atrazine lost on the first runoff event was 6.2% for NTG, 4.4% for NTS, and 1.5% for CT. Losses of atrazine in runoff on the second date were 1.5, 1.4, and 1.0% of that applied for NTG, NTS, and CT, respectively. The surface 7.5 cm of soil contained the highest concentrations of chemicals for all treatments, with treatment differences occurring primarily in the surface 0 to 15 cm of soil. Lower runoff values under CT generally resulted in higher soil chemical concentrations.
Leguminous cover crops can provide biologically fixed N to a subsequent corn (Zea mays L.) crop as well as erosion control and moisture conserving mulch, but establishment is costly and often unsuccessful. A field experiment was conducted for 3 yr to determine the self-reseeding potential of crimson clover (Trifolium incarnatum L.) and its N contribution in a no-tillage corn production system. Four cover crop management treatments (fallow, annual-seeded, volunteer-reseeded, and volunteer strip-reseeded) were combined factorially with four fertilizer-N rates (0, 50, 100, or ISO kg ha-1 ) applied to the subsequent corn crop. The annual-seeded, volunteerreseeded, and volunteer strip-reseeded clover treatments were desiccated at corn planting. Averaged over 3 yr, crimson clover dry matter was 2.6, 4.2, and 3.5 Mg ha-1 for the annual-seeded, volunteer-reseeded, and strip-reseeded treatments, respectively. In 1988 and 1989, cover crop treatments produced mean corn grain yields of 6.0 and 6.1 Mg ha-1 compared to fallow treatment yields of 3.4 and 4.0 Mg ha-l, respectively. This same pattern was reflected in the silage yields and total corn N uptake. Corn grain yields were unaffected by fertilizer-N rate in two out of 3 yr due to limited rainfall. Both self-reseeding treatments successfully reestablished each year and increased corn yields primarily by a mulching effect. Allowing crimson clover to mature before chemical desiccation or leaving strips between corn rows to produce seed appear to be effective methods of reseeding clover in a no-tillage corn silage production system. Agron. J. 83:985-991 (1991).
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Unusual cone-shaped iron oxide concretions occur in the Late Triassic, lower fluvial sandstone member of the Trujillo Formation at Palo Duro Canyon in the Texas panhandle. In situ concretions are significant because they record both historical information about past processes that occurred within the geologic unit and present-day information about the ability of the unit to conduct fluids. The dominant orientation of the concretions is coneapex up, body radiating down and out, with long axis perpendicular to bedding. Concretion morphologies are associated with the sedimentary texture and primary bedding structure of the host rock and the corresponding hydrologic regime (i.e. advection versus dispersion for iron-transport behavior). Three lithofacies in the lower Trujillo member exhibit different cone forms. Field observations of cone orientation and morphology suggest vadose conditions for diagenetic precipitation of iron oxide cements, with timing potentially represented by the major pre-Miocene unconformity.
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