8 results
Seed bank characterization and emergence of a weed community in a moldboard plow system
- Dawit Mulugeta, David E. Stoltenberg
-
- Journal:
- Weed Science / Volume 45 / Issue 1 / February 1997
- Published online by Cambridge University Press:
- 12 June 2017, pp. 54-60
-
- Article
- Export citation
-
Field experiments were conducted in 1992 and 1993 to characterize the weed seed bank, to determine the influence of moldboard plowing and secondary soil disturbance on the emergence pattern of weeds, and to measure weed seed bank depletion by emergence in a long-term moldboard plow corn cropping system. Viable seeds of common lambsquarters, redroot pigweed, and each of 10 other species accounted for about 85, about 9, and less than 1%, respectively, of the total weed species in the seed bank. A negative binomial distribution described the spatial distribution of viable seeds of 10 species, but not of common lambsquarters or of redroot pigweed. Decreased density of seeds among species was associated with increased aggregation. Secondary soil disturbance increased the rate and magnitude of common lambs quarters emergence in 1992 but did not influence emergence in 1993. Secondary soil disturbance did not influence the magnitude and rate of emergence of redroot pigweed or velvetleaf. Whereas cumulative growing degree days from April through July were similar between years, the amount of rainfall was about 50% less in 1992 than in 1993. Secondary soil disturbance may have increased common lambsquarters emergence by increasing the availability of soil moisture and improving conditions for seed germination during the dry year. Even though seed bank depletion by seedling emergence was relatively low for all species, secondary soil disturbance in creased seed bank depletion of common lambsquarters and redroot pigweed about 7- and 3-fold, respectively, in 1992. Seasonal variation in the amount of rainfall may have influenced the effect of soil disturbance on emergence and seed bank depletion of common lambsquarters, which is the most abundant species in the weed community.
Increased weed emergence and seed bank depletion by soil disturbance in a no-tillage system
- Dawit Mulugeta, David E. Stoltenberg
-
- Journal:
- Weed Science / Volume 45 / Issue 2 / April 1997
- Published online by Cambridge University Press:
- 12 June 2017, pp. 234-241
-
- Article
- Export citation
-
The influence of secondary soil disturbance on the emergence pattern and seed bank depletion of an annual weed community in a long-term, no-tillage corn cropping system was determined in 1992 and 1993. As a component of this research, the seed bank was characterized prior to implementation of soil disturbance treatments. The seed bank was initially composed of common lambsquarters, redroot pigweed, and giant foxtail, with approximately 55, 36, and 8% of the total viable seeds, respectively. The remaining 1% was comprised of five other species in 1992 and eight in 1993. The spatial distribution of viable seeds of each species, except common lambsquarters and redroot pigweed, was described by a negative binomial distribution. Three dispersion indices indicated that seeds of individual and total weed species were aggregated and that the level of aggregation of viable seeds of a species was associated with seed density; at lower seed densities, the level of aggregation was greater. Soil disturbance increased common lambsquarters emergence 6-fold in 1992 relative to nondisturbed soil, but did not influence emergence in 1993. Rainfall was about 50% less in 1993. In contrast, soil disturbance increased giant foxtail and redroot pigweed emergence approximately 6- and 3-fold in 1992 and 1993, respectively. Seedling emergence associated with soil disturbance, relative to nondisturbed soil, increased seed bank depletion of common lambsquarters 16-fold in 1992, and giant foxtail and redroot pigweed and average of 6- and 3-fold in 1992 and 1993, respectively. These results indicated that soil disturbance increased seedling emergence and seed bank depletion of the predominant species in the weed community of a long-term, no-tillage system, but that this response was dependent on rainfall for common lambsquarters.
Influence of cohorts on Chenopodium album demography
- Dawit Mulugeta, David E. Stoltenberg
-
- Journal:
- Weed Science / Volume 46 / Issue 1 / February 1998
- Published online by Cambridge University Press:
- 12 June 2017, pp. 65-70
-
- Article
- Export citation
-
Peak germination and emergence of common lambsquarters usually occur in early to mid-spring, but both processes can occur during summer and fall. Seeds produced by different common lambsquarters cohorts (seedlings that emerge at nearly the same time) may vary in dormancy status, response to environmental conditions, and response to management factors. Therefore, experiments were conducted to determine the influence of different cohorts on common lambsquarters demography. Field experiments determined plant density, biomass, and seed production of different common lambsquarters cohorts within a crop-free community of annual weed species that included redroot pigweed, giant foxtail, and velvetleaf. Common lambsquarters plant density and aboveground biomass were greater for a mid-May cohort than for early June, late June, mid-July, or early August cohorts, but seed production of the mid-May and early June cohorts did not differ (about 192,000 seeds m−2) and was greater than that of other cohorts (111,500 seeds m−2 or less). In the laboratory, percent germination prior to stratification (exposure of seeds to low temperatures) was less for seeds harvested from early May and late May cohorts (≥ 9%) than those of mid-June or early July cohorts (≤ 75%). After stratification in the field, percent emergence (seedlings per number of planted seeds) and mean emergence time were similar among early May, late May, mid-June, and early July cohort seed sources, and were not influenced by shallow burial in soil. These results suggest that recruitment from seeds produced by different common lambsquarters cohorts is similar, but proportional to the number of seeds produced by each cohort.
Seasonal abundance and spatial pattern of Setaria faberi, Chenopodium album, and Abutilon theophrasti in reduced-tillage soybeans
- Dawit Mulugeta, Chris M. Boerboom
-
- Journal:
- Weed Science / Volume 47 / Issue 1 / February 1999
- Published online by Cambridge University Press:
- 12 June 2017, pp. 95-106
-
- Article
- Export citation
-
A better understanding of the influence of various crop and weed management practices on spatiotemporal dynamics of weeds could improve the design of integrated weed management systems. We examined the influence of 18- and 76-cm soybean row spacings on emergence pattern and spatial aggregation of giant foxtail, common lambsquarters, and velvetleaf seedling cohorts. In addition, we characterized the soil seedbank and determined the quantitative and spatial relationship between the seedbank and seedling populations. Viable seeds of about 10 weed species and twice as many species of seedlings were identified in the weed community. Giant foxtail and common lambsquarters were the predominant species in the seedling and seedbank population, respectively, each accounting for 60 to 70% of the total weed species density. Emergence of giant foxtail, common lambsquarters, and velvetleaf depleted 12 to 33%, < 2% and 12 to 49% of the seedbank in the upper 10 cm of the soil profile. Peak time and periodicity of weed emergence was not influenced by soybean row spacing, and peak time of emergence of giant foxtail, common lambsquarters, and velvetleaf occurred 3 to 4, 3 to 6, and 3 to 9 weeks after soybean planting (WAP), respectively. Magnitude of giant foxtail emergence 5, 6, and 9 WAP was 98, 96, and 76% greater in 76- than in 18-cm row soybeans only when the population of 76-cm row soybeans was 57% lower than the 18-cm soybeans in 1997. Giant foxtail and common lambsquarters seeds in the seedbank were aggregated in 1996 and 1997 according to the Taylor power law (TPL) and the negative binomial distribution (NBD). The TPL and the NBD were similar in describing the spatial aggregation of giant foxtail and common lambsquarters but not some velvetleaf seedling cohorts. The spatial aggregation of seedlings varied among cohorts for different weed species and was likely due to species-specific biological characteristics that influence seed dispersal, germination, and seedling emergence. Within a 1.5-ha area, aggregation declined with decreasing density. Within a 24-m2 area, the level of aggregation of all weed species decreased as seedling densities increased. These results indicated that soybean row spacing influenced neither weed emergence pattern nor weed spatial aggregation; thus, several management decisions can be similar in 18- and 76-cm row soybeans.
Kochia (Kochia scoparia) Pollen Dispersion, Viability and Germination
- Dawit Mulugeta, Bruce D. Maxwell, Peter K. Fay, William E. Dyer
-
- Journal:
- Weed Science / Volume 42 / Issue 4 / December 1994
- Published online by Cambridge University Press:
- 12 June 2017, pp. 548-552
-
- Article
- Export citation
-
Kochia pollen dispersion was measured during 24 and 48 h periods from a kochia population in an 8- by 10-m area in the center of a 1.6 ha fallow field. Pollen counts from traps at 50- and 100-cm heights declined rapidly with increasing distance from the pollen source. Pollen deposition was highest along the prevailing wind direction: up to 23 pollen grains cm–2 were recovered 50 m from the pollen source along the southeast (SE) vector. Nonlinear regression analysis of pollen deposition along the SE vector was used to estimate that 99.9% of shed pollen would be deposited within 154.4 m of the source. Viability of pollen from greenhouse- and field-grown plants was measured using staining and germination assays. of four pollen stains tested, only 1,2,3-triphenyl tetrazolium chloride gave consistent results and did not stain heat-killed pollen. Depending on environmental conditions, kochia pollen remained viable from less than 1 d to 12 d. Length of kochia pollen viability was shortest under high temperatures (22 and 28 C) and low relative humidity (7 and 32%). Less than 0.5% germination was observed in 1.1% agar media with various additions; however, up to 17.8% germination was observed after incubation at 28 C in 100% relative humidity.
Weed and seedbank management with integrated methods as influenced by tillage
- Dawit Mulugeta, David E. Stoltenberg
-
- Journal:
- Weed Science / Volume 45 / Issue 5 / October 1997
- Published online by Cambridge University Press:
- 12 June 2017, pp. 706-715
-
- Article
- Export citation
-
Many growers perceive that reduced herbicide inputs and greater reliance on mechanical methods will result in increased weed management problems over time. Previous research has shown short-term benefits of integrated weed management strategies, but information concerning the long-term implications of these strategies is lacking. Therefore, research was conducted from 1992 through 1995 to determine the influence of full-rate preemergence broadcast, half-rate preemergence broadcast plus cultivation, and full-rate preemergence band plus cultivation treatments on weed population and seedbank dynamics in no-tillage (NT), chisel plow (CP), and moldboard plow (MP) systems in both continuous corn (CC) and corn—soybean (CS) rotation. Seventeen weed species were identified in the plant population and seedbank across all treatments, but common lambsquarters, giant foxtail, and redroot pigweed dominanted. Vertical distribution of weed seeds in soil was influenced by tillage, with 74, 59, and 43% of the total viable seed of these species less than 10 cm deep in NT, CP, and MP, respectively. In contrast, seed dormancy in the spring was not influenced greatly by tillage and averaged 79, 10, and 42% for common lambsquarters, giant foxtail, and redroot pigweed, respectively, across tillage methods. Crop rotation was not a major factor influencing weed population and seedbank dynamics. From 1992 to 1995, reduction of shoot biomass and seed production of the predominant weed species were similar among weed management treatments in most tillage and crop rotation systems. The influence of weed management treatments on the seedbank was also similar, with up to 50, 95, and 92% less seed of common lambsquarters, giant foxtail, and redroot pigweed, respectively, in the seedbank in 1995 than in 1992. Corn and soybean grain yields were similar among weed management treatments and were greater than the nontreated check in each tillage and crop rotation treatment. These results indicate that reduced herbicide inputs plus interrow cultivation were as effective as full-rate herbicide inputs for the management of several annual weed species in both conventional- and conservation-tillage systems over 4 yr.
Weed species–area relationships as influenced by tillage
- Dawit Mulugeta, David E. Stoltenberg, Chris M. Boerboom
-
- Journal:
- Weed Science / Volume 49 / Issue 2 / April 2001
- Published online by Cambridge University Press:
- 20 January 2017, pp. 217-223
-
- Article
- Export citation
-
The relationship between species richness and sample area has been characterized in many natural communities but has rarely been examined in crop–weed communities. We determined the species–area relationship in short-term (≤4 yr) and long-term (>15 yr) moldboard-plowed (MP), chisel-plowed (CP), and no-tillage (NT) fields cropped to corn and in short-term MP, CP, and NT fields cropped to soybean. A total of 10 corn fields and 10 soybean fields were sampled for species richness in 14 nested sample areas that ranged from 0.0625 to 512 m2. The influence of sample area on frequency of species occurrence was also determined. Species richness was greater in long-term NT fields than in tilled or short-term NT fields. The species–area relationship in tilled and short-term NT fields was best described by an exponential function. In contrast, a power function was the best fit for the species–area relationship in long-term NT fields. The functional minimum area required to represent 75% of the total weed species in tilled and short-term NT fields was 32 m2. A functional minimum area could not be determined in long-term NT fields because species richness continued to increase over the range of sample areas. Regression functions predicted that sample areas of 1 m2 would contain less than 50% of the observed maximum species richness in these fields. Sample areas of 36 m2 in tilled and short-term NT fields and 185 m2 in long-term NT fields were predicted to measure 75% of observed maximum species richness in these fields. Pigweed species and common lambsquarters occurred at high frequencies and were detected in most sample areas. This information could be used to better define sample area requirements and improve sampling procedures for species richness of weed communities.
Critical time of weed removal in glyphosate-resistant Glycine max
- Dawit Mulugeta, Chris M. Boerboom
-
- Journal:
- Weed Science / Volume 48 / Issue 1 / February 2000
- Published online by Cambridge University Press:
- 20 January 2017, pp. 35-42
-
- Article
- Export citation
-
Field experiments were conducted in 1996 and 1997 to determine the effect of the rate and time of glyphosate application on weed emergence, survival, biomass, and Glycine max yield in reduced-tillage (RT) and no-tillage (NT) glyphosate-resistant G. max planted in rows spaced 18 (narrow-row) and 76 cm (wide-row). Glyphosate was applied at 0.42, 0.63, and 0.84 kg ae ha−1 at V2, V4, R1, and R4 growth stages. On separate plots, 0.84 kg ha−1 glyphosate was applied at each growth stage with hand weeding. A weed-free check was maintained with preemergence imazethapyr plus metolachlor supplemented with hand weeding, and a nontreated check was included. Weed population density before glyphosate application ranged from 239 to 606 plants m−2 in RT and 33 to 500 plants m−2 in NT systems. Setaria faberi and Chenopodium album were the predominant species. Weed control efficacy and crop yield were influenced more by application time than by glyphosate rate. Glyphosate applied at V2, V4, and R1 gave season-long control of weeds in 18-cm rows. In 76-cm rows, glyphosate applied at V2, V4, and R1 gave almost complete control of weeds, but broadleaf weeds emerged after application at V2. The critical time of weed removal, the time beyond which weed competition reduced G. max yield by 3% or more compared to the weed-free check, was at R1 and V4 in 18-cm RT G. max in 1996 and 1997, respectively, and at V2 in 76-cm RT G. max in both years. The predicted critical time of weed removal in 18- and 76-cm NT G. max was R1 and V4, respectively, in 1996 and R1 in 1997. This research showed that there was variation in the onset of the critical time of weed removal between tillage systems, as well as within tillage systems across years. The results indicate a single glyphosate application can prevent yield loss in narrow-row, glyphosate-resistant G. max under favorable conditions, but application timing becomes more critical in wide rows because the critical period of weed removal occurs earlier. Late-emerging weeds may warrant a second glyphosate application in wide-row G. max.