Organic systems in the southeastern USA offer unique challenges and solutions to crop production due to regional soil and climate characterized by highly weathered soil types, high precipitation and the capacity to grow cover crops in the winter. Recently, the interest of producers and researchers in high-residue cover crops and conservation tillage systems has increased. Various designs of the roller-crimper to manage cover crops have been invented and demonstrated to growers in the southeastern region of the USA over the past 17 years. The impacts of high-residue cover crop mulches on the agronomic systems in the region are diverse. Legume cover crops assist with meeting N demand from cash crops though they decompose rapidly and are seldom sufficient for N demanding crops such as corn. Cereal cover crop mulches can have the opposite effect by immobilizing N and have a longer impact on soil moisture and weed dynamics. While undesirable for many crops, N immobilization is one possible mechanism for weed suppression in legume cash crops planted into cereal residues. Other cover crop weed suppression mechanisms include physical impedance, light availability, allelopathy and microclimate effects. Regardless of the cause, successful weed control by mulches is highly dependent on having substantial biomass. The southeastern region is capable of producing cover crop biomass in excess of 9000 kg ha − 1 , which is sufficient for weed control in many cash crops, although supplementary weed control is sometimes necessary. Long-term data are needed to predict when farmers should add supplementary weed control. More work is also needed on how much additional N is required for the cash crops and how best to deliver that N in a high-residue environment using organic sources.

The influence of herbicide placement and plant growth stage on the absorption and translocation patterns of 14C-glyphosate in glyphosate-resistant cotton was investigated. Plants at four growth stages were treated with 14C-glyphosate on a 5-cm2 section of the stem, which simulated a postemergence-directed spray (PDS) application, or on the newest mature leaf, which simulated a postemergence (POST) application. Plants were harvested 3 and 7 d after treatment and divided into the treated leaf or treated stem, mature leaves, immature leaves and buds, stems, roots, fruiting branches (including the foliage on the fruiting branch), squares, and bolls. The PDS versus POST application main effect on absorption was significant. Absorption of 14C-glyphosate applied to stem tissue was higher in PDS applications than in POST applications. Plants receiving PDS applications absorbed 35% of applied 14C-glyphosate, whereas those receiving POST applications absorbed 26%, averaged over growth stages at application. Absorption increased from the four-leaf growth stage to the eight-leaf stage in POST applications but reached a plateau at the eight-leaf stage. Plants with PDS applications showed an increase in absorption from the four- to eight- to twelve-leaf stages and reached a plateau at the 12-leaf stage. Translocation of 14C-glyphosate to roots was greater at all growth stages with PDS treatments than with POST treatments. Herbicide placement did not affect translocation of 14C-glyphosate to squares and bolls. Squares and bolls retained 0.2 to 3.7% of applied 14C-glyphosate, depending on growth stage. Separate studies were conducted to investigate the fate of foliar-applied 14C-glyphosate at the four- or eight-leaf growth stages when harvested at 8- or 10-leaf, 12-leaf, midbloom (8 to 10 nodes above white bloom), and cutout (five nodes above white bloom, physiological maturity) stages. Thirty to 37% of applied 14C-glyphosate remained in the plant at cutout in four- and eight-leaf treatment stages, respectively. The concentration of 14C-glyphosate in tissue (Bq g−1 dry weight basis) was greatest in mature leaves and immature leaves and buds in plants treated at the four-leaf stage. Plants treated at the eight-leaf stage and harvested at all growth stages except cutout showed a higher concentration of 14C-glyphosate in squares than in other plant tissue. Accumulation of 14C-glyphosate in squares reached a maximum of 43 Bq g−1 dry weight at harvest at the 12-leaf stage. This concentration corresponds to 5.7 times greater accumulation of 14C-glyphosate in squares than in roots, which may also be metabolic sinks. These data suggest that reproductive tissues such as bolls and squares can accumulate 14C-glyphosate at higher concentrations than other tissues, especially when the herbicide treatment is applied either POST or PDS during reproductive stages (eight-leaf stage and beyond).

The increased use of conservation tillage in cotton production requires that information be developed on the role of cover crops in weed control. Field experiments were conducted from fall 1994 through fall 1997 in Alabama to evaluate three winter cereal cover crops in a high-residue, conservation-tillage, nontransgenic cotton production system. Black oat, rye, and wheat were evaluated for their weed-suppressive characteristics compared to a winter fallow system. Three herbicide systems were used: no herbicide, preemergence (PRE) herbicides alone, and PRE plus postemergence (POST) herbicides. The PRE system consisted of pendimethalin at 1.12 kg ai/ha plus fluometuron at 1.7 kg ai/ha. The PRE plus POST system contained an additional application of fluometuron at 1.12 kg/ha plus DSMA at 1.7 kg ai/ha early POST directed (PDS) and lactofen at 0.2 kg ai/ha plus cyanazine at 0.84 kg ai/ha late PDS. No cover crop was effective in controlling weeds without a herbicide. However, when black oat or rye was used with PRE herbicides, weed control was similar to the PRE plus POST system. Rye and black oat provided more effective weed control than wheat in conservation-tillage cotton. The winter fallow, PRE plus POST input system yielded significantly less cotton in 2 of 3 yr compared to systems that included a winter cover crop. Use of black oat or rye cover crops has the potential to increase cotton productivity and reduce herbicide inputs for nontransgenic cotton grown in the Southeast.

Information is needed on the role of cover crops as a weed control alternative due to the high adoption of conservation tillage in soybean [Glycine max (L.) Merr.] production. Field experiments were conducted from fall 1994 through fall 1997 in Alabama to evaluate three winter cereal cover crops in a high-residue conservation-tillage, soybean production system. Black oat (Avena strigosa Schreb.), rye (Secale cereale L.), and wheat (Triticum aestivum L.) were evaluated for their weed-suppressive characteristics compared to a winter fallow system. Three herbicide systems were utilized: no herbicide, a mixture of two pre-emergence (PRE) herbicides, or PRE plus post-emergence (POST) herbicides. The PRE system contained pendimethalin plus metribuzin. The PRE plus POST system contained pendimethalin plus a prepackage of metribuzin and chlorimuron ethyl applied PRE, followed by an additional chlorimuron ethyl POST application. No cover crop was effective in controlling weeds without a herbicide. However, when black oat or rye was utilized with only PRE herbicides, weed control was similar to the PRE plus POST input system. Thus, herbicide reductions may be attained by utilizing cover crops that provide weed suppression. Rye and black oat provided more effective weed control in the PRE only herbicide input system than wheat in conservation-tillage soybean. The winter fallow, PRE plus POST herbicide input system yielded significantly less soybean one out of three years when compared to systems that included a winter cover crop.

Rollers crimpers have been used in conservation agriculture to terminate cover crops; however, excessive vibration generated by the original straight-bar roller design has delayed adoption of this technology in the United States. To avoid excessive vibration, producers generally reduce operating speeds that increase the time needed to perform the field operation. The objectives of this research were to identify roller crimper designs that terminated rye cover crops consistently, resulted in soil moisture conservation after use, and minimized vibrations when operated in the field. Six different roller types were developed and tested at 3.2 and 6.4 km h -1 in Alabama field experiments during the 2006, 2007 and 2008 growing seasons. All roller types were used alone and one also in combination with glyphosate. Rye mortalities were evaluated 1, 2 and 3 weeks after rolling and compared with the check (non-rolled standing rye). Soil volumetric moisture content (VMC) was measured at the day of rolling, and then at 1, 2 and 3 weeks after rolling. Vibration was measured on the rollers' and tractor's frames during operation. Mortality for rolled rye 2 weeks after rolling was at least 98% compared with 96% for the check in 2006, 93% for rolling compared with 75% for the check in 2007, and 94% for rolling compared with 60% for the check in 2008 (P < 0.10). There were no consistent differences in rye mortality across roller types (without glyphosate) and speeds. VMC for soil in non-rolled rye plots was consistently lower than in rolled rye plots, averaging 3% compared with 7% 2 weeks after rolling in 2006, and 4% compared with 8% in 2008. During 2007, VMC was affected by severe drought conditions, and differences between roller treatments were detected but minor. The straight-bar roller generated the highest vibration on the tractor's frame at 6.4 km h -1 (0.71 m s -2 , RMS), which exceeded International Standards (International Standard Office (ISO)). At 6.4 km h -1 , new roller designs generated significantly lower acceleration levels from 0.12 to 0.32 m s -2 on the tractor's frame and were below detrimental effects on health 'health limits' classified by ISO. Overall, 2 weeks after rolling, all roller designs effectively terminated rye above 90%, which is the recommended termination level of rye to plant a cash crop into residue mat, while protecting soil surface from water loss. New roller designs generate less vibration than the original design and can be used safely at higher operating speeds.

Field experiments were conducted to evaluate possible interactions of clethodim with imazapic applied as mixtures or sequentially for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. Imazapic at 70 g ai/ha alone controlled grass weeds inconsistently, whereas clethodim at 140 g ai/ha alone controlled the same weeds at least 99%. Imazapic did not affect broadleaf signalgrass control by clethodim. Reduced control of fall panicum, goosegrass, and large crabgrass was observed when clethodim and imazapic were applied in mixture. Antagonism of clethodim occurred when clethodim was applied 1 d before or up to 3 d after application of imazapic (fall panicum and large crabgrass). Antagonism of goosegrass control was noted when imazapic was applied 3 d before or up to 7 d after application of clethodim. In other experiments, large crabgrass and Texas panicum control by clethodim (70 and 140 g/ha) applied alone or with imazapic (70 g/ ha) or bentazon (1.1 kg ai/ha) plus 2,4-DB (0.28 kg ai/ha) either with or without ammonium sulfate (2.8 kg/ha) was evaluated. Texas panicum control by clethodim was reduced by imazapic regardless of the ammonium sulfate rate. However, large crabgrass control by imazapic was not affected in these experiments. Control of both grasses by clethodim was reduced substantially by bentazon plus 2,4-DB, although in some instances ammonium sulfate improved control when in mixture. Ammonium sulfate improved control by clethodim in some instances irrespective of the broadleaf–sedge herbicide treatments.

A study was conducted to quantify volatiles generated from Indian mustard (Brassica juncea L. Czerniak) tissue incorporated into soils under controlled conditions. Mustard residues were incorporated into noncovered and covered soils that varied by texture, temperature, moisture, pH, or sterility (autoclaved or nonautoclaved). Sandy loam soil had 38% more allyl isothiocyanate (AITC) than clay loam soil. AITC concentration in 45 °C soil was 81% higher than in soil at 15 °C, and 56% higher in covered compared to noncovered treatments. The microbial catabolism of AITC was suggested by the result that AITC concentration in autoclaved soils was over three times that measured in nonautoclaved soils. The highest AITC level detected (1.71 μmol·L–1) occurred in the autoclaved covered soil. Several factors also influenced CO2 evolution. At 30 or 45 °C, CO2 concentration was at least 64% higher than at 15°C. The covered soil had over twice the CO2 found in the noncovered soil, and the nonautoclaved soil treatment yielded twice the CO2 measured in the autoclaved soil. There were no main effect differences among soil moisture, soil pH, and soil texture treatments for CO2 concentrations. This information could be helpful in defining ideal soil conditions for field scale experiments. Additionally, this study demonstrates a sampling technique for testing fumigation potential of biofumigation and solarization systems that may have the potential to replace methyl bromide.

Conservation agriculture (CA) practices are threatened by glyphosate-resistant Palmer amaranth. Integrated control practices including PRE herbicides and high-residue CA systems can decreaseAmaranthusemergence. Field experiments were conducted from autumn 2006 through crop harvest in 2009 at two sites in Alabama to evaluate the effect of integrated weed management practices onAmaranthuspopulation density and biomass, cotton yield, and economics in glyphosate-resistant cotton. Horizontal strips included four CA systems with three cereal rye cover crop seeding dates and a winter fallow (WF) CA system compared to a conventional tillage (CT) system. Additionally, vertical strips of four herbicide regimes consisted of: broadcast, banded, or no PRE applications ofS-metolachlor (1.12 kg ai ha−1) followed by (fb) glyphosate (1.12 kg ae ha−1) applied POST fb layby applications of diuron (1.12 kg ai ha−1) plus MSMA (2.24 kg ai ha−1) or the LAYBY application alone. Early-seasonAmaranthusdensity was reduced in high-residue CA in comparison to the CA WF systems in 2 of 3 yr.Amaranthusdensities in herbicide treatments that included a broadcast PRE application were lower at three of five sampling dates compared to banding early-season PRE applications; however, the differences were not significant during the late season and cotton yields were not affected by PRE placement. High-residue conservation tillage yields were 577 to 899 kg ha−1more than CT, except at one site in 1 yr when CT treatment yields were higher. CA utilizing high-residue cover crops increased net returns over CT by $100 ha−1or more 2 out of 3 yr at both locations. High-residue cover crop integration into a CA system reducedAmaranthusdensity and increased yield over WF systems; the inclusion of a broadcast PRE application can increase early-seasonAmaranthuscontrol and might provide additional control when glyphosate-resistantAmaranthuspopulations are present.