Masters Theses

Date of Award

5-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Robert M. Hayes

Committee Members

Gilbert N. Rhodes Jr, Elmer Ashburn, P.E. Hoskinson

Abstract

Field experiments were conducted at Jackson and Grand Junction, Tennessee, to determine if tillage influenced the interference of five weed species in cotton (Gossypium hirsutum L.). Common cocklebur (Xanthium strumarium L.), johnsongrass [Sorghum halepense (L.) Pers.], and Palmer amaranth (Amaranthus palmeri S. Wats.) at 1 plant per 1 m of row, and morningglory (Ipomoea hederacea spp.) at 1 plant per 0.5 m of row were examined at both locations in 1987 and 1988. Velvetleaf (Abutilon theophrasti Medic.) at 1 plant per 1 m row was included at Jackson in 1988. Tillage extremes were no-tillage and conventional tillage. All other weeds were controlled with selective herbicides or hand-hoeing. The soils at Jackson and Grand Junction were of the Lexington and Grenada series, respectively. Cotton was harvested with a spindle picker. Treatments were replicated four times in a split-plot randomized complete block design. Data were statistically analyzed by analysis of variance and means were separated by the F test or Duncan's multiple range test.

Cotton lint losses from common cocklebur, johnsongrass, morningglory, and Palmer amaranth in conventional tillage were 35, 40, 33, and 39%, respectively. In no-tillage cotton lint yield losses were 23, 27, 29, and 28%, respectively. Velvetleaf reduced cotton lint yields by 41% but there was no difference between tillage systems. These losses were at cotton lint yield levels of 900 to 1200 kg ha-1 Densities of morningglories twice that of the other weeds were required to give similar yield losses.

With all five weeds, yield losses were higher with conventional tillage, yet there was no difference between tillage systems in the absence of weeds. Palmer amaranth caused yield losses in adjacent rows, indicating an area of influence greater than that of common cocklebur, johnsongrass, or morningglory. Cocklebur, johnsongrass, morningglory. Palmer amaranth, and velvetleaf caused revenue losses of $189, $181, $204, $211, and $238 ha-1 respectively, as a result of reduced cotton yields. Losses of $9, $2, $18, $8, and $18 ha-1 respectively, resulted from lowered grades and fiber properties compared to weed free checks.

With weed interference, cotton revenue was consistently higher in no-tillage plots compared with conventional tillage. Revenue from no-tillage was greater than conventional tillage by $48, $30, $8, $8, and $7 ha-1 with cocklebur, johnsongrass, morningglory. Palmer amaranth, and velvetleaf interference, respectively.

Cotton was earlier maturing in 1987 as evidenced by a higher percentage of open bolls and greater first harvest yields. Cotton stands were greater in conventional tillage. Weed interference with cotton not only reduced yields but also reduced cotton plant populations.

Johnsongrass and Palmer amaranth produced more vegetative growth in no-tillage, while cocklebur and morningglory produced more growth in conventional tillage in 1988. Growth of velvetleaf was not influenced by either tillage method. In 1987, cotton height and canopy width were greater in conventional tillage. Cotton produced more vegetative growth in conventional tillage compared with no-tillage, but cotton growth in some instances was greater in no-tillage with weed interference.

Cocklebur, johnsongrass. Palmer amaranth, and velvetleaf, having a more erect growth habit, reduced the level of photosynthetically active radiation (PAR) at the top of the cotton canopy; while morningglory, with its vining growth habit, did not influence PAR at the top of the cotton canopy.

Weeds interfered more in conventional tillage than in no-tillage. This may be related to competition for available soil water, especially when the moisture conserving advantage of no-tillage is expressed.

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