No abstract

The effectiveness of a grassed waterway in decreasing 2,4‐D [(2,4‐dichlorophenoxy) acetic acid] content in surface runoff was investigated. Corn (Zea mays L.) plots were treated with 2,4‐D (0.56 kg/ha) and runoff produced by applying simulated rain was directed through a 24.4‐m‐long grassed waterway. The 2,4‐D concentrations were measured under wet and dry antecedent waterway and plot conditions. Reduction in 2,4‐D load in waterways results from water loss by infiltration, sediment loss, and by attachment‐absorption on vegetative and organic matter. Of the simulated rainfall applied 1 day after application of 2,4‐D, 50% of the water ran off the plots under dry antecedent soil conditions, and 78% ran off under wet conditions. Infiltration reduced runoff flowing down the waterway an additional 25% under dry conditions and 2% under wet conditions. Suspended sediment reduction in the waterway was 98 and 94% of the total amount moving from the plot for the dry and wet waterway conditions, respectively. The total loss (on sediment and in solution) of the applied 2,4‐D from the plot in the dry and wet states was 2.5 and 10.3%, respectively. Of the 2,4‐D lost from the plots and entering the 24.4‐m waterway, approximately 30% reached the end of the waterway, regardless of antecedent soil moisture.

Little trifluralin (α,α,α‐trifluoro‐2,6.dinitro‐N,N‐dipropyl‐p‐toluidine) moved in the surface flow from a small agricultural watershed located in the Southeastern Coastal Plain. Movement of trifluralin in 1974 and 1975 in surface water was 0.17 and 0.03%, respectively, of the total amount applied (1.12 kg/ha). Trifluralin movement in the shallow subsurface flow (above the 214 cm depth) was recorded only in 1974 and was negligible. Trifluralin was detectable in the soil from the 1974 application before the 1975 application. Soil concentration of trifluralin in 1974 was 320 ng/g (immediately after application) in the 0‐ to 10‐cm depth and after 114 days the concentration decreased to 73 ng/g. However, no trifluralin was detected in the 30‐ to 60‐cm depth 60 days after application. Simulated surface runoff from subplots on the watershed produced measurable concentrations of trifluralin 38 days after application, but it could not be detected after 71 days. Trifluralin movement was greater in runoff caused by simulated rainfall than that from natural rainfall due to the high application rate of water (19.1 cm/hour) and the lack of a vegetational buffer. Trifluralin loss in the simulated rainfall runoff water from a small plot directed through a 24.4‐m waterway was reduced 96% under dry and 86% under wet conditions. Hence, trifluralin movement can be significantly reduced and possibly managed by buffer strips or vegetated waterways adjoining cropped areas. Appropriate use of these buffer areas should reduce to acceptable levels the chemical concentration in the runoff before the runoff reaches the surrounding streams.

Peanut (Arachis hypogaeaL. ‘Tifspan’ or ‘Florunner’) yields were not reduced when the crop was maintained free of Florida beggarweed [Desmodium tortuosum(Sw.) DC.] or sicklepod (Cassia obtusifoliaL.) for 4 weeks after crop emergence and when vigorous crop growth was maintained for the remainder of the season. Sometimes weed-free maintenance for only 2 weeks resulted in near-normal yields, which indicated that the canopy of peanut leaves effectively suppressed the weeds. Conversely, these weeds had to compete with peanuts for more than 10 weeks before crop yield was reduced. Weeds that overtopped the peanuts at harvest emerged during the first 6 weeks after planting.

No abstract

Peanuts (Arachis hypogaea L. ‘Florunner’), infested with sicklepod (Cassia obtusifolia L.) were grown during 1977 and 1978 in 20.3-, 40.6- and 81.2-cm row widths (on Dothan sandy loam and on Greenville sandy clay loam). The crop was maintained weed-free for 0, 2, or 5 weeks or for the entire growing season. Three herbicidal systems with various intensities were utilized. In 1978, reduced and regular rates of in-row crop seeding were compared. Weed-free maintenance for 5 weeks generally produced yields of peanuts equivalent to those obtained with continuous weeding. Sicklepod green weights were reduced by 28 and 53% in peanuts with row spacings of 40.6 and 20.3 cm, respectively, as compared to standard 81.2 cm spaced rows. Peanuts in close-row patterns yielded about 14% higher than the conventional 81.2 cm row spacing when averaged for all studies. Adjustments of the in-row seeding rate to produce a more normal seed-drop per hectare reduced the yield of peanuts only 1 to 3% and, therefore, did not negate the increased yields produced with close-row spacings.

In a 3 year herbicide-crop rotation involving corn (Zea maysL. ‘Coker 811A’), cotton (Gossypium hirsutumL. ‘Carolina Queen’), and peanuts (Arachis hypogaeaL. ‘Argentine’), uncontrolled yellow nutsedge (Cyperus esculentusL.) and annual weeds drastically reduced all crop yields. By the end of the rotation sequences, intensive cultivation throughout the rotation killed 97 to 99% of the nutsedge tubers, but this level of control depended on hand-weeding the cotton. Moderate application of herbicides killed from 78 to over 99% of the yellow nutsedge tubers, while intensive treatment with herbicides produced at least 99% kill. In addition, all annual weeds present when the experiment was initiated were controlled satisfactorily by intensive herbicide applications except Florida beggarweed [Desmodium tortuosum(Sw.) DC.] in peanuts. The major change in composition of the weed population was a reduction in yellow nutsedge and in the total number of weeds; however, certain other population shifts also seemed affected by the weed control treatments. Compared to intensive cultivation, the investment in intensive herbicide treatment produced maximum yields and highest gross profit per acre. None of the treatments affected the market grade or organoleptic characteristics of peanuts. The fatty acid content of corn and cotton changed significantly only in 1967.

Peanuts [Arachis hypogaea(L.) ‘Florunner’], infested with sicklepod (Cassia obtusifoliaL.) and Florida beggarweed [Desmodium tortuosum(Sw.) DC.] were grown in 20.3-, 40.6-, and 81.2-cm rows on Dothan sandy loam at Headland, Alabama, and on Greenville sandy clay loam at Plains, Georgia. In-row seeding rates were equal, regardless of row width. Peanuts were maintained free of sicklepod and Florida beggarweed for 0, 2, and 5 weeks after emergence or throughout the season. In either the absence or presence of weeds, peanut yields generally increased with decreasing row width. Quality of peanuts was not adversely affected; in fact, desirable attributes such as percent sound mature kernels (SMK's) were sometimes increased as the row width decreased. Weed growth with close rows was much less than with standard 81.2-cm rows. Although yields of peanuts were lower with increasing time of weed competition, the influence of row spacing on competitiveness of the peanut canopy remained relatively constant on both soil types. Generally, weeds from either seeded or natural stands produced equivalent competitive results.