Experiments were conducted in the growth chamber and greenhouse to determine the influence of humidity, temperature, simulated rainfall, and oil additives with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide] upon redroot pigweed (Amaranthus retroflexusL.) control. Generally, bentazon gave increased redroot pigweed control with high rather than low humidity. However, the increased weed control with high humidity was greater at 10 C than at 20 or 30 C. A simulated rainfall within 24 hr after bentazon application reduced redroot pigweed control. A simulated rainfall of 650 L/ha within 1.5 hr after bentazon application increased control of redroot pigweed, while more than 1300 L/ha simulated rainfall decreased redroot pigweed control. Emulsifiable linseed oil and petroleum oil additives to the spray reduced the detrimental effect of low humidity and simulated rainfall upon redroot pigweed control with bentazon. Emulsifiable linseed oil was more effective than petroleum oil in reducing the detrimental effect of low humidity and of simulated rainfall. However, emulsifiable linseed oil reduced the redroot pigweed control with bentazon with high humidity at 30 C compared to bentazon applied alone or with petroleum oil.
Postemergence difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) for wild oat(Avena fatuaL.) control in spring wheat(Triticum aestivumL.), durum wheat(Triticum durumDesf.), and barley(Hordeum vulgareL.) was evaluated in the field, greenhouse, and controlled environmental chamber. Wild oat control with difenzoquat was greater at the five- that at the three and one-half or two-leaf stages of growth. Barley tolerance to difenzoquat was excellent; however, spring wheat tolerance was influenced by cultivar. Durum wheat generally was more tolerant of difenzoquat than spring wheat. Tank mix combinations of broadleaf herbicides with difenzoquat had no effect on crop injury or wild oat control. Wild oat control with difenzoquat was greatest with adequate soil moisture, adequate fertility, warm air temperatures and high relative humidity. A simulated rainfall of 0.25 mm within ½ h or 1 mm within 4 h of application reduced wild oat control with difenzoquat.
Lowery, 1985). However, frequent soil movement in conventional tillage (CT) may increase the N mineral- Tillage and N fertilization influence cotton (Gosspium hirsutum L.)ization process (Grace et al., 1993). Azam et al. (1988) growth and yield. The objective of the study was to evaluate the influence of two tillage systems (conventional tillage [CT] and strip-till and Grace et al. (1993) noted that N fertilization not [ST]) and four N rates (0, 67, 134, and 202 kg N ha Ϫ1 ) on growth, de-only increases ammonium N, but also N mineralization velopment, and yield of 'DP 5409' cotton following wheat (Triticum in the soil. aestivum L.). The experiment was conducted at the University of Flo-Previous crop residues, partly due to the residue qualrida's North Florida Research and Education Center in Quincy, FL, ity, affect the optimum N rate for the following cotton in 1995-1997. Lint yields, plant height, boll no. plant Ϫ1 , and boll no. crop (Touchton et al., 1995). Brown et al. (1985) and m Ϫ2 varied across years. With every 1 kg N ha Ϫ1 applied to cotton, Touchton and Reeves (1988) noted that greater N rates, lint yields increased by 1.74 and 1.53 kg ha Ϫ1 in 1996, and 2.76 and due to N immobilization, are required for cotton grown 1.76 kg ha Ϫ1 in 1997 for CT and ST, respectively. In 1995, maximum after wheat than fallow to obtain the same yields. The lint yields were estimated with 105 kg N ha Ϫ1 for CT. Averaged across use of crop rotation and winter crops may also reduce years, cotton lint yield increase with N application greater than 67 kg ha Ϫ1 was not significant and tillage did not influence lint yields. Plant N leaching potential and degradation of ground water height, boll no. plant Ϫ1 , and boll no. m Ϫ2 generally increased with (Touchton et al., 1995). Wood et al. (1991) observed increasing N rates, except for boll no. m Ϫ2 in the ST system in 1995. that soil N concentration at the 0-to 40-cm depth was Greatest boll weight and lint weight boll Ϫ1 were obtained with the reduced with the establishment of conservation tillage. application of 134 kg N ha Ϫ1 . Compared with CT, ST reduced boll Many experiments have shown that cotton yields from no. plant Ϫ1 and increased boll no. m Ϫ2 . Tillage did not influence plant conservation tillage systems are lower or similar to height, boll weight, and lint weight boll Ϫ1 . These results indicate that yields from CT (Brown et al., 1985;Stevens et al., 1992; cotton can be grown successfully in ST and that yields may not increase Burmester et al., 1993;Hutchinson, 1993), or even greater significantly with rates Ͼ67 kg N ha Ϫ1 .for conservation than CT (Bradley, 1995; Delaney et al., 1996; Boquet et al., 1997). Strip-till (ST) is the most common conservation tillage system in the southeastern USA, N ha Ϫ1 ) in the form of ammonium nitrate (34-0-0 of N-P-K). The CT and ST sections in cotton were imposed following the Published in Agron. J. 97:288-293 (2005).
The phytotoxicity of barban (4-chloro-2-butynylm-chlorocarbanilate) applied 14 days after emergence to wheat(Triticum aestivumL. ‘Waldron’) and wild oat(Avena fatuaL.), at constant, fluctuating or alternating day-night temperatures was determined in controlled environmental chambers. Wheat and wild oat susceptibility to barban increased as post-treatment temperature decreased. Maximum barban selectivity for wild oat in wheat occurred with a constant 18 C or an alternating 18 C day and 10 C night post-treatment temperature. At least three days of 10 C immediately following barban application were necessary to cause wheat injury. However, two days at 29 C immediately after barban application in an otherwise 10 C post-treatment regime reduced wheat injury. Further, a night temperature lower than the day temperature after barban application increased wild oat control but did not correspondingly increase wheat injury compared to the constant temperature treatments.
Wild oat(Avena fatuaL.) control and wheat(Triticum aestivumL.) injury with barban (4-chloro-2-butynylm-chlorocarbanilate)-aqueous nitrogen combinations were evaluated in the field and greenhouse. The addition of aqueous nitrogen at volumes as low as 5 L/ha increased wild oat control with barban. The greatest increase in wild oat control with barban-aqueous nitrogen combinations was obtained on soil low in nitrogen. Wild oat control with barban-aqueous nitrogen combinations was not influenced by spray volume or nitrogen source. Aqueous nitrogen applications several days prior to barban were more effective than when the two were applied together. Wheat was generally quite tolerant of barban-aqueous nitrogen combinations; however, some injury was observed in 1974.
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