Soil acidity and poor nutrient use efficiency are major limiting factors as regards output potential on heavy soils, soils which are dominated by high proportions of clay and organic matter, with impeded drainage, high buffering capacity and located in high rainfall areas. Lime is applied in order to counteract these limiting factors and in turn improve agricultural output and productivity. The current study investigates the effects of two commonly used lime products at three comparable treatment rates, ground lime (7.5, 5 and 2.5 tonne/ha) and granulated lime (7.5, 2.5 and 1.5 tonne/ha), applied across three distinct sites. The ability of each lime product and treatment rate to counteract soil acidity, increase nutrient availability and influence soil physical structure was assessed over time. On average across sites, 1 tonne/ha of each lime product increased soil pH by 0.15 and 0.21 pH units between ground and granulated lime, respectively. Site 3 experienced the greatest increase change in soil pH in comparison to the other two sites, largely due to lower clay content and cation exchange capacity. Granulated lime was 5.7 times more expensive than ground lime in its ability to reduce soil acidity. The high treatment rate showed the greatest reduction in soil acidity, aluminium and iron concentration as a mean across all sites. Morgan's soil test phosphorus concentration increased across all sites, with treatment rates having no effect on the rate of increase. There was evidence of reduced soil compaction and lime application showed no negative implication on soil physical structure.

Soil alkalinity imposes important limitations to lupin productivity; however, little attention has been paid to investigate the effects of soil alkalinity on plant growth and development. Many lupins are sensitive to alkaline soils, but Lupinus albus material from Egypt was found to have tolerance to limed soils. The aim of this study was to compare the growth response of two cultivars of L.albus L. – an Egyptian cultivar, P27734, and an Australian cultivar, Kiev Mutant, to different soil pH levels and to understand the physiological mechanisms underlying agronomic alkalinity tolerance of P27734. Plants were grown under three pH levels (5.1, 6.7, and 7.8) in a temperature-controlled glasshouse. For both cultivars, the greatest dry mass production and carboxylate exudation from roots were observed at alkaline pH. The better performance of the Egyptian cultivar at high pH was entirely accounted for by its greater seed weight. From a physiological perspective, the Australian cultivar was as alkaline-tolerant as the Egyptian cultivar. These findings highlight the agronomic importance of seed weight for sowing, and both cultivars can be used in alkaline soils.

The northern New England region includes the states of Vermont, New Hampshire, and Maine and encompasses a large degree of climate and edaphic variation across a relatively small spatial area, making it ideal for studying climate change impacts on agricultural weed communities. We sampled weed seedbanks and measured soil physical and chemical characteristics on 77 organic farms across the region and analyzed the relationships between weed community parameters and select geographic, climatic, and edaphic variables using multivariate procedures. Temperature-related variables (latitude, longitude, mean maximum and minimum temperature) were the strongest and most consistent correlates with weed seedbank composition. Edaphic variables were, for the most part, relatively weaker and inconsistent correlates with weed seedbanks. Our analyses also indicate that a number of agriculturally important weed species are associated with specific U.S. Department of Agriculture plant hardiness zones, implying that future changes in climate factors that result in geographic shifts in these zones will likely be accompanied by changes in the composition of weed communities and therefore new management challenges for farmers.

Field experiments were conducted on a Moody silty clay loam (pH 6.5) and a Crofton silt loam (pH 7.9) to evaluate the influence of soil texture and pH on metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] toxicity to soybeans [Glycine max (L.) Merr. ‘Amsoy 71’] as influenced by trifluralin [α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine]. One Crofton silt loam site contained atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] residue. Soybean growth and yield was not significantly affected by metribuzin and trifluralin applications on the Moody silty clay loam. On the Crofton silt loam without atrazine residue, substantial early season soybean injury from metribuzin did not result in significantly reduced soybean yield. Atrazine residue from previous row banding on corn (Zea mays L.) on the Crofton silt loam reduced soybean tolerance to metribuzin but normal use rates of 0.4 kg/ha metribuzin did not significantly reduce soybean yield. Trifluralin reduced early season soybean injury from metribuzin but this effect was not reflected in soybean yield. Metribuzin injury to soybeans was greater in years when more rainfall and cooler temperatures occurred following herbicide application. Metribuzin applied either preplant incorporated with or as an overlay on trifluralin resulted in equal soybean injury and yield.

Laboratory studies were conducted to evaluate flumetsulam adsorption and mobility in seven Mississippi soils of different organic matter content, pH, and texture. Adsorption isotherms were determined for all soils using a 1:1 (soil: water) technique. In six of seven soils, Freundlich n constants were close to unity, suggesting a partitioning-like adsorption mechanism for flumetsulam. Mobility was examined using packed soil columns. 14C-flumetsulam recoveries in leachate ranged from 1 to 70% and were influenced by both organic matter content and soil pH. However, the effects of organic matter content and soil pH were not independent. Consequently, clear relationships between flumetsulam mobility and either organic matter content or soil pH were not established across all soils. However, among soils of similar pH (7.5 ± 0.3), mobility decreased linearly (R 2 = 0.75) as organic matter content increased from 0.7 to 3.6%. Across soils with similar organic matter content (3.9 ± 0.3%), mobility increased linearly (R 2 = 0.98) as soil pH increased from 5.3 to 7.2. Net adsorption constants (K d ) provided a more accurate assessment of flumetsulam mobility across all soils than K oc .

Chlorsulfuron was applied to wheat at rates of 0, 10, 20, and 40 g ai ha-1 in three locations at Lethbridge and Brooks between 1980 and 1984. The soil pH and organic matter contents at Lethbridge and Brooks were 8.0 and 2.1% and 7.4 and 3.0%, respectively. Rotational crops were seeded for up to 7 yr after chlorsulfuron application. The criteria used to indicate when susceptible crops will grow safely were no significant yield loss at the 40 g ha-1 rate and the magnitude of the upper confidence limit for this difference. The following times after application before crop yields were not affected were required at Lethbridge: barley, 2 yr; canola, 3 yr; peas, beans, 4 yr; flax and potatoes, 5 yr; alfalfa and sugarbeets, 6 yr; and lentils at least 7 yr. The effect of chlorsulfuron residues in the soil on rotational crops appeared to be similar at Brooks and at Lethbridge. Estimated chlorsulfuron concentrations were related to the tolerance of rotational crops.

Degradation of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-yl)amino] carbonyl] benzenesulfonamide} in acidic and alkaline soils was evaluated using plant bioassay and high-performance liquid chromatography (HPLC) radiotracer techniques. Soil sterilization with either ethylene oxide (Et0) or gamma irradiation significantly reduced breakdown of chlorsulfuron; the ability for degradation was restored by reinoculation with indigenous soil microorganisms. Streptomyces griseolus (a soil actinomycete), Aspergillus niger, and Penicillium sp. (soil fungi) were demonstrated to degrade 14C-chlorsulfuron in pure culture. In addition to microbial breakdown, chemical hydrolysis was an important factor in the disappearance of chlorsulfuron from soil. The contribution of chemical hydrolysis to total degradation was a function of soil pH, with hydrolysis occurring most rapidly in acidic soils. Both dissipation processes slowed markedly at low temperatures.

The phytotoxicity of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] benzenesulfonamide} was compared in six soils, and the relationship of activity to soil physical and chemical properties was evaluated. The influence of soil pH (4.2 to 7.8) on phytotoxicity and adsorption of chlorsulfuron incorporated into high-organic-matter soil was also studied. For the phytotoxicity studies, corn (Zea mays L. ‘Pioneer 3320’) was used as the bioassay plant. Organic matter was the soil variable most highly correlated with chlorsulfuron phytotoxicity. There was an inverse relationship between phytotoxicity and organic matter. No significant relationship between clay content and chlorsulfuron toxicity was observed. The adsorption of chlorsulfuron decreased with increasing soil pH while desorption was greater at alkaline pH. Phytotoxicity of chlorsulfuron increased with increasing soil pH and reached a maximum at pH 6.9.

The adsorption of picloram (4-amino-3,5,6-trichloropicolinic acid) was determined on an Aiken silt loam, on three cation exchange resins and on a single anion exchange resin. Adsorption data were evaluated using parameters in the Freundlich equation and their dependance upon cationic composition of the exchange complex, the ionic composition of the equilibrium solution, and the equilibrium solution pH. For the Aiken soil saturated with metallic cations the order of decreasing picloram adsorptive capacity was Fe+3 = Cu+2 > Al+3 > Zn+2 > Ca+2 > native soil. Increases in adsorption compared to the native Aiken soil could be explained on the basis of decreases in the equilibrium solution pH except for Fe+3, Zn+2, and especially the Cu+2 treatments. The adsorptive capacity of the Aiken soil was altered by the addition of several salts simulating addition of fertilizer salts. The Cu+2 and Zn+2 salts were the only treatments showing increased adsorption which could not be explained readily by pH changes. KH2PO4 and NH2CONH2 (urea) reduced picloram adsorption. Dowex 50-1 × 4, a strongly acidic cation exchange resin, showed increased picloram adsorptive capacity in the order Cu+2 > Al+3 > Ca+2 > Zn+2 = H+. Cellex CM, a weakly acidic cellulose exchanger had increased adsorptive capacities in the order of Cu+2 > Ca+2 > Al+3 > Na+ > Fe+3 > Zn+2. Picloram adsorption by an anion exchange resin at pH 6.1 was nearly 100%. These results suggest that complex formation of picloram with polyvalent cations on the exchange complex is likely especially for Cu+2 and to a lesser extent Fe+3 and Zn+2. In soils such complex reactions would most probably involve organic matter, polyvalent cations, and picloram. The formation of chelate ring species is proposed.

The response of corn (Zea mays L. ‘Sokota TS 46’), flax (Linum usitatissimum L. ‘Culbert 79’), grain sorghum [Sorghum bicolor (L.) Merr. ‘Sokota 466’), soybeans [Glycine max (L.) Merr. ‘Corsoy 79’], and sunflowers (Helianthus annuus L. ‘Sokata 4000’) to soil residues 12 and 24 months after application of 17, 34, and 68 g ai/ha chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl] benzenesulfonamide} was determined at two locations, Redfield and Watertown, in eastern South Dakota. All crops at Redfield were injured significantly at 17 g/ha, 12 months after application as determined by plant dry weight and visual evaluations. Corn and sorghum were the most susceptible while flax was the least susceptible. Injury at Watertown was significantly less than at Redfield. Differences in carryover were related to a lower soil pH at Watertown.

Response of flax, canola, field pea, sunflower, field corn, lentils, and common buckwheat to soil residues of CGA-131036 and chlorsulfuron applied at 22 g ai ha–1 was determined on two soil types at Morden, Manitoba. on a fine sandy loam with a pH of 7.4 and 4.5% organic matter, the length of time required before crops showed no phytotoxicity from CGA-131036 residues was: sunflower 4 yr; canola and common buckwheat 3 yr; flax 2 yr; field pea and field corn 1 yr. on a clay loam with a pH of 6.5 and 5.3% organic matter, the corresponding duration was: lentil, canola, and sunflower 3 yr; flax and field pea 1 yr. Chlorsulfuron residues persisted somewhat longer than CGA-131036 residues on the sandy loam but not on the clay loam.

Field studies were conducted to determine the effect of soil surface (upper 5 cm) pH and tillage on weed control and corn (Zea mays L.) yield using simazine [2-chloro-4,6-bis-(ethylamino)-s-triazine] as the herbicide for weed control. Soil pH, weed control, and corn yield were examined under no-tillage and conventional tillage systems with and without added lime and different rates of nitrogen. Increased soil pH significantly increased weed control as compared with added lime vs. no added lime, where the surface soil pH influenced the effectiveness of the applied simazine. Soil pH had a greater effect on weed control under no-tillage than under conventional tillage. Conventional tillage significantly (P<.01) increased weed control, yield, and soil pH over no-tillage. Additions of lime as compared to unlimed treatments resulted in significantly increased weed control (83% vs. 63%), yield (5,930 vs. 5,290 kg/ha) and soil pH (5.91 vs. 5.22). The poorest weed control was observed with no-tillage on unlimed plots. A significant tillage by linear effect of nitrogen interaction for all variables resulted from a greater decrease (P<.01) in weed control and soil pH and a greater increase in yield with increased nitrogen under no-tillage than with conventional tillage.

The effect of soil residues of flumetsulam plus clopyralid on several vegetable crops grown in rotation with field corn was investigated over 2 yr. The effect of soil residues of flumetsulam plus clopyralid on sweet corn cultivars of varying sensitivity to acetolactate synthase (ALS)-inhibiting herbicide was also investigated. Flumetsulam plus clopyralid was applied preemergence (PRE) to field corn at 0, 50 + 135, and 100 + 270 g ai/ha, respectively, in 1993 and 1994. Cucumber, tomato, cabbage, potato, pepper, pea, and sweet corn were planted each spring, both 1 and 2 yr following the herbicide application. Cabbage was very sensitive and showed visible injury symptoms and yield reductions both years following flumetsulam plus clopyralid application. Pepper showed a yield reduction only in 1995. All other crops showed no injury or yield reductions. Flumetsulam plus clopyralid was applied PRE and postemergence (POST) to six sweet corn cultivars in 1995. These six sweet corn cultivars were replanted into the same site 1 yr later. Flumetsulam plus clopyralid severely injured three of six sweet corn cultivars in 1995, the year of application. Soil residues 1 yr later, however, did not injure or reduce yield of any sweet corn cultivars, including cultivars sensitive to ALS-inhibiting herbicides.

Growth chamber studies were conducted to examine the soil residual properties of DPX-A7881, a new sulfonylurea herbicide. The phytotoxic residue levels in the soil were determined by a lentil radicle bioassay. The duration of activity was prolonged in soil adjusted to pH 7.6 and 8.1 relative to more acidic levels. The rate of breakdown in the soil was enhanced with increased temperature and soil moisture content; a significant temperature by moisture interaction was noted over the duration of the incubation period. The dissipation of DPX-A7881 in soil obeyed first-order kinetics in both studies. An accelerated rate of breakdown in unsterilized versus sterilized soil (pH 7.6) indicated that microbial degradation was an important factor affecting the persistence in alkaline soils. Herbicide residues in the soil caused a reduction in taproot length and number of primary lateral roots of canola seedlings 15 days after planting but there were no other morphological effects observed on the root. The secondary laterals, however, had generally recovered by this time.

Field research was conducted in 1994 and 1995 to monitor the dissipation of flumetsulam in five Mississippi soils for a period of 16 wk. These soils allowed evaluation of flumetsulam persistence across three soil series with a relatively constant soil pH of 6.0, as well as across three soils of varied pH from 6.0 to 7.6 within a constant soil series. Bioavailability was determined with a rice root length bioassay. Predicted half-lives ranged from 20 to 26 d in 1994 and from 23 to 46 d in 1995. Persistence decreased with increasing cumulative rainfall and decreasing organic matter content (within a range of 1.2 to 3.5%). Soil pH had no measurable effect on flumetsulam persistence.

Field studies were conducted in Mississippi on a Marietta loam during 1988, 1989, and 1990, and in Tennessee on a Statler loam during 1988 and 1989, to determine effect of tillage on chlorimuron persistence. A corn shoot bioassay was conducted to determine bioavailable chlorimuron in the soil. Tillage system affected chlorimuron persistence only in 1989 at Tennessee. Chlorimuron half-life was 10 to 31 d longer in both tillage systems in Mississippi in 1988 compared to 1989 and 1990, probably due to low soil moisture immediately after application in 1988. In Tennessee, chlorimuron half-life was 71 d shorter in the no-till system in 1988 compared to 1989. Differences did not occur between locations in the conventional tillage system in 1989. Differences in chlorimuron persistence between years and locations were most often attributed to soil water and temperature. Soil pH differences between the two locations did not consistently affect chlorimuron persistence.

Soil thin-layer chromatography and a soil solution technique were used to evaluate chlorimuron adsorption and mobility in five Alabama soils. The order of adsorption was atrazine > metribuzin > chlorimuron; mobility was chlorimuron > metribuzin > atrazine. The order of adsorption of chlorimuron in the five soils was Sumter clay > Eutaw clay > Lucedale fine sandy loam > Decatur silt loam > Dothan sandy loam, and Rf values were 0.63, 0.73, 0.69, 0.76, and 0.80, respectively. Chlorimuron mobility and adsorption were not highly correlated to any one soil type. Adsorption of all herbicides was inversely related to soil pH. Maximum chlorimuron adsorption in the Hiwassee loam was attributed to the high hematite and gibbsite content of the soil.

Field studies and laboratory analyses were conducted to examine factors affecting degradation of 14C-atrazine [2-chloro-4-(ethylamine)-6-(isopropylamino)-s-triazine] under field conditions. The effects of these factors on weed control under no-tillage and conventional tillage systems were also examined. The amount of radioactivity which was unextractable in 90% methanol increased with time following treatment with 14C-atrazine. The rate of formation of unextractable 14C compounds was greater under no-tillage and increased with decreasing pH. After 14 to 18 days, a greater amount of extractable atrazine was present in areas receiving lime. The degradation of atrazine occurred more rapidly when surface pH was less than 5.0 compared with a pH greater than 6.5. The effect of lime on the amount of parent atrazine present in the soil was directly correlated to its effect on soil pH. Extractable atrazine in the soil 45 days after treatment was significantly correlated with weed control with the greatest effect under no-tillage.

Adsorption of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl] benzenesulfonamide} on four soils having different pH values (6.2 to 8.1) was low. Log/log Freundlich isotherms for all soils at 8 and 30 C were linear, the extent of adsorption being greater at 8 than at 30 C. There was an inverse relationship between pH and degradation rate with a half-life of 88.5 days at pH 6.2 and 144 days at pH 8.1 at 20 C. Rapid disappearance was noted during the first 15 days after application. With decreasing moisture and temperature, chlorsulfuron degraded more slowly. The half-life ranged from 229 days at 10 C and moisture content of 75% field capacity to 62.5 days at 40 C and 75% field capacity at pH 7.7.

Persistence of chlorsulfuron and other sulfonylurea herbicides, measured by sorghum injury, was determined on a Pullman clay loam (fine, mixed, thermic family of Torrertic Paleustolls) with soil pH varying from 6.5 to 8.1 in a 3-yr winter wheat-sorghum-fallow crop rotation. As pH increased from 6.5 to 8.0, chlorsulfuron persistence increased greatly. With soil pH of 6.5, chlorsulfuron at 34 g ai/ha used on growing wheat did not injure sorghum planted 16 months later. If pH was 7.5 or above, chlorsulfuron persisted and injured sorghum planted within 25 months after herbicide application. Persistence of sulfometuron and metsulfuron was about the same as chlorsulfuron, all of which persisted longer than metribuzin applied at normal use rates. Four annual applications of chlorsulfuron at 71 g/ha did not accumulate when soil pH was 6.5.