Fallow Weed Research Articles

Population dynamics of yellow nutsedge (Cyperus esculentus) in cropping systems in the southeastern coastal plain

Studies were conducted from 1990 through 1994 near Tifton, GA, on the population dynamics of yellow nutsedge and certain annual weeds in peanut—corn and peanut—cotton rotations. Converse rotation sequences were included to eliminate year effects. Continuous fallow plots (noncrop) were included for comparison. Within each crop, including fallow, were 3 levels of weed management: low, moderate, and intensive. Weed densities and numbers of yellow nutsedge tubers were not affected by crop rotations, but they were affected by individual crops and weed management systems in each crop. Fallow plots, including those with intensive fallow weed management using tillage and nonselective herbicides, consistently contained more yellow nutsedge plants and tubers than other plots. Moderate and intensive weed control systems in peanut and cotton reduced yellow nutsedge densities and tubers, but only peanut yields were increased by intensive weed management. Weed management systems did not affect yellow nutsedge densities in corn, although yields were increased by moderate and intensive systems due to improved control of other weeds. Our results suggest that uninterrupted plantings of peanut, corn, or cotton with moderate levels of weed management are generally sufficient to suppress yellow nutsedge and allow for optimum crop yield. If fields are fallow, yellow nutsedge population densities and tubers will increase exponentially, even with intensive fallow weed management.

Root and inorganic nitrogen distributions in sesbania fallow, natural fallow and maize fields

One hypothesis for a benefit of integrating trees with crops is that trees with deep root systems can capture and “pump up” nutrients from below the rooting zone of annual crops. Few studies have compared both root and nutrient distribution for planted trees, crops and grassland vegetation. A field study was conducted on a Kandiudalfic Eutrudox in the highlands of western Kenya to measure rooting characteristics and distribution of inorganic N and water in three land-use systems (LUS): (i) Sesbania sesban (L.) Merr. fallow, (ii) uncultivated natural weed fallow and (iii) unfertilized maize (Zea mays L.) monoculture. The maximum rooting depth was 1.2 m in the maize LUS, 2.25 m in a 13-month-old natural fallow, and > 4 m in a 15-month-old sesbania fallow. Total root length was 1.26 km m-2 for the maize LUS, 5.98 km m-2 for the natural fallow, and 4.56 km m-2 to 4 m for the sesbania fallow. Root length to 1.2 m was greater (p < 0.01) for natural fallow than for maize and sesbania fallow. A considerable portion of the sesbania root length to 4 m was in the subsoil; 47% was at 1.2 to 4 m and 31% was at 2.25 to 4 m. Deep rooting of sesbania coincided with lower soil water below 2 m in the sesbania fallow than the natural fallow. Nitrate-N, but not ammonium-N, to 4 m was affected by LUS. Total nitrate to 4 m was 199 kg N ha-1 for the maize LUS, 42 kg N ha-1 for the natural fallow and 51 kg N ha-1 for the sesbania fallow. Soil nitrate in the maize LUS was highest at 0.3 to 1.5-m depth on this Oxisol with anion sorption capacity. No such accumulation of subsoil nitrate was present under sesbania and natural fallow.

Soil Nitrate and Water Dynamics in Sesbania Fallows, Weed Fallows, and Maize

We hypothesized that the integration of trees into agricultural land-use systems can reduce NO3 leaching and increase subsoil N utilization. A field study was conducted on a Kandiudalfic Eutrudox (Ochinga site) and a Kandic Paleustalf (Muange site) in the subhumid highlands of Kenya to measure changes in soil NO3 and water to 200-cm depth for one rainy season in four land-use systems (LUS): (i) planted tree fallow using Sesbania sesban (L.) Merr., (ii) unfertilized maize (Zea mays L.), (iii) weed fallow, and (iv) bare fallow. Subsoil (50-200 cm) NO3-N at the start of the season ranged from 58 to 87 kg ha-1 for the four LUS and two sites. In maize, subsoil NO3-N differed by <5 kg ha-1 between planting and harvest at both sites. In sesbania, subsoil NO3-N decreased by 22 kg ha-1 at both sites, whereas in weed fallow subsoil NO3-N decreased by 26 and 38 kg ha-1 at Ochinga and Muange, respectively. At both sites, subsoil water contents at the start of the season were similar in the four LUS; but at the end of the season, soil water at 100 to 200 cm was significantly lower for sesbania than for maize. Adsorption of NO3 increased with soil depth. Sorbed NO3 at 100 to 200 cm was about 60% in the Kandiudalfic Eutrudox and about 15% in the Kandic Paleustalf. Rotation of maize with either a sesbania fallow or a weed fallow can result in more effective subsoil NO3 and water utilization than maize monoculture.

Effect of crop rotations on weed control, Bidens cernua and Erigeron canadensis populations, and carrot yields in organic soils

Organic coils in Quebec are prone to infestation by nodding beggarticks ( Bidens cernua L.) and Canada fleabane ( Erigeron canadensis L.), and by the root-knot nematode ( Meloidogyne hapla Chitwood). Yield losses can be very severe in fields where carrots have been grown continuously for several years. Six 3-year crop rotations, including onion ( Allium cepa L.), barley ( Hordeum vulgare L.) or a weed fallow, were compared to continuous carrot production to establish their effect on weed control and carrot yield. Weed populations and above ground dry biomass were monitored four times each season. Total and marketable yields of carrots also were measured each year. Results show that weed populations increase when onions are part of the production cycle, and decrease with barley. Beggarticks and fleabane populations were static when cropping sequences included 2 years of carrots with or without onions. Total carrot yield increased by 35–50% and marketable yield increased 17–25-fold due to a drastic reduction in root-knot nematode populations when barley was included in the rotation. The onion-barley-carrot rotation provided good weed control, including nodding beggarticks and Canada fleabane, and yielded high quality carrots.

Using Crop Rotation to Control Meloidogyne hapla Chitwood and Improve Marketable Carrot Yield

The influence of various crop rotations on population densities of Meloidogyne hapla, the northern root-knot nematode, and subsequent carrot yields was studied in organic soil under field conditions. Seven 3-year sequences with barley (Hordeum vulgare L.), carrot (Daucus carota L.), onion (Allium cepa L.), or weedy fallow, all with carrot as the third-year crop, were replicated six times in a completely randomized block design. Carrot monoculture, two seasons of weedy fallow, or carrot followed by onion resulted in high M. hapla population densities and severe root damage on carrot the third year. Barley followed by onion or onion followed by barley harbored low M. hapla population densities and provided the highest yields, with 56.8 and 47.2 t marketable carrots/ha, respectively, compared to 2.2 t·ha–1 in the carrot monoculture. A single crop of barley reduced nematode population densities and provided 88% and 73% marketable carrot roots in the subsequent years. High M. hapla population densities and the high proportion of culls recorded in plots in weed fallow emphasize the importance of an effective weed management program for successfully using crop rotation against root-knot nematode in muck-grown carrot.

Management systems for conservation fallow on the southern Canadian prairies

Fallow continues to be a common agronomic practice on the southern Canadian prairies, but it has been associated with increased soil erosion and salinity and declining soil fertility. Field experiments were conducted at Lethbridge, Alberta, from 1987 to 1992 to determine the effects of various fallow treatments on weed control, conservation of surface crop residues, accumulation of soil water, and succeeding spring and winter wheat yields. Conventional cultivation during the fallow year with 168-cm sweeps controlled most spring-germinating weeds but did not adequately control overwintered flix-weed or downy brome. Repeated applications of glyphosate and 2,4-D effectively controlled most weeds. Paraquat did not control wild buckwheat or dandelion. Glyphosate alone often did not control wild buckwheat or Russian thistle. Treatments involving a combination of herbicides and tillage gave the best control of all weed species. Although not as effective in conserving surface crop residues as sole use of herbicides, many of the combined herbicide-tillage treatments maintained sufficient crop residue to keep the risk of soil erosion low. Soil water accumulation and succeeding wheat yields with the combined herbicide-tillage treatments were similar to, or greater than, those attained with repeated herbicides or repeated tillage. Management systems combining herbicides and tillage for fallow weed control may reduce costs and prevent or retard the development of herbicide resistance. Key words: Water conservation, herbicides, reduced tillage, soil erosion, stubble retention, weed control, wheat yield, no-till

The development of plant‐parasitic nematode infestations on micro‐propagated banana plants following field control measures in Côte d'Ivoire

SummaryOf the weeds that were found in banana production areas, only Asystasia gangetica was parasitised by Radopholus similis; Helicotylenchus multicinctus and Hoplolaimus pararobustus were able to parasitise all weed species. Field trials were carried out in Cote d'Ivoire to assess the potential for using nematode‐free micro‐propagated banana plants following cultural and chemical methods for nematode control. Banana (Musa acuminata) cv. Poyo was examined for nematodes after weed fallow, flooding and chemical treatment. Before replanting bananas, nematode assays showed that: i) all nematode species declined but were not eliminated after a 1,3‐dichloropropene soil treatment; ii) H. multicinctus, H. pararobustus and Cephalenchus emarginatus were still present after either a 2‐year weed fallow (dominated by Chromolaena odorata or Asystasia gangetica) or a 10‐week flooding; iii) R. similis did not persist after fallowing or flooding. All nematode species were found in plots treated with 1,3‐dichloropropene and that had been planted with bullheads, suckers or nematode‐free micropropagated plants. After both fallow and flooding, R. similis was reintroduced on infested planting materials (bullheads and suckers) even when they were pre‐treated with a nematicide. When fallow and flooded plots were planted with nematode‐free materials (vitro‐plants), R. similis did not appear in the roots for two vegetative cycles. The other species, still present in the soil, invaded the roots and increased slowly in numbers. These results were confirmed in commercial banana plantations.

Tolerance of Safflower (Carthamus tinctorius), Corn (Zea mays), and Proso Millet (Panicum miliaceum) to Clomazone

Clomazone is used in the Central Great Plains for weed control during fallow in a winter wheat-fallow rotation. Improved precipitation storage during non-crop periods has stimulated new crop rotations such as winter wheat-corn or proso millet-fallow. The objective of this study was to determine if clomazone applied in the fall after winter wheat harvest would injure succeeding spring-planted crops. Greenhouse studies indicated crop tolerance to clomazone was in the order of safflower &gt; corn &gt; proso millet &gt; barley &gt; winter wheat. Clomazone did not affect grain yields of safflower, corn, or proso millet grown at two field sites with different soil textures (silt loam and sandy loam), nor germination of seed from treated plants of these crops. A no-till production system with clomazone increased grain yields for all crops compared to the conventional system where tillage replaced clomazone for fallow weed control.

Winter cereal production on the Darling Downs dash a comparison of reduced tillage practices

Five experiments, 1 of which was continued over 3 years on the same site, were established on non-sloping Darling Downs cracking clays to compare conventional, reduced and zero tillage systems of fallowing for annual wheat production. Average values for soil water storage efficiency (percentage of fallow rainfall stored) were 14.0% for stubble burnt and conventional cultivation with tined implements (TI); 19.8% for stubble retained and conventional cultivation with tined implements (T2); 25.3% for stubble retained and zero tillage with chemical control of fallow weed growth (T3); 21.1% for stubble retained with no tillage but chemical weed control until early March, followed by cultivations with tined implements until sowing (T4); and 21.1% for stubble retained and fallow cultivations with a sweep plough (T6). Nitrogen mineralisation during fallow periods was measured over 3 seasons at the final site. No major treatment differences occurred. A small mean grain yield advantage of 4.6% to T3 over T1 was established in those seasons when improved fallow water storage was obtained with T3. The lack of yield improvement by reduced tillage treatments (T4, T5 and T6) over T1 is attributed largely to above-average crop period rainfall in those seasons when the treatments had resulted in improved presowing water.

Effects of cover crops on soil structure and on yield of subsequent arable crops grown under strip tillage on an eroded alfisol

Effects of weed fallow and of three grasses and five leguminous cover crops were investigated on soil structure of an eroded Alfisol. Crop growth and yields of subsequently grown arable crops were assessed under strip-tillage through the mechanically or chemically suppressed sods. Cover crops and fallowing improved soil organic matter content, total N, water retention and transmission properties, and decreased bulk density only in the top 0–10 cm depth. The improvements rendered were, however, slight. Grasses were difficult to suppress with paraquat or mechanical mowing, which resulted in low or negligible yield of maize, cowpea, and cassava. Leguminous covers were easily suppressed with paraquat application, and resulted in good yield of maize and cowpea. Mechanical mowing was as successful as herbicide application for suppressing Stylosanthes guianensis and resulted in satisfactory yield of maize and cowpea. Yield of cassava tubers was extremely low due to shallow surface soil, compacted sub-soil horizons, and competition from weeds and regrown cover crops. Results are discussed in terms of the amelioration of eroded and degraded soil.

Fallow Systems for Winter Wheat in Western Nebraska1

AbstractThe need for conservation of soil and water and the energy situation makes it imperative to develop more efficient fallow systems for controlling weeds, to utilize moisture efficiently, and maximize wheat production under limited rainfall.Research was conducted at North Platte and Sidney, Nebr. from 1972 through 1977 to develop a weed control program in a limited and no‐tillage winter wheat (Triticum aestivum L.)‐fallow rotation. The experimental areas in fallow were sprayed with glyphosate [N‐(phosphonomethyl)glycine] at 0.8 kg/ha after harvest to eliminate soil water loss from existing weeds in wheat stubble. Six tillage and/or herbicide treatments were applied to separate replicated plots the first few days of August, October, and April.Atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] + glyphosate at 0.8 + 0.8 kg/ha at Sidney and 1.3 + 0.8 kg/ha at North Platte was the most effective fallow weed control treatment but allowed too much weed growth 65 and 77 Mg/ha, respectively. Downy brome (Bromus tectorum L.) control at North Platte was unsatisfactory with August application of atrazine which left 40 plants/m2. Russian thistle (Salsola kali L. var. tenuifolia Tausch) and volunteer winter wheat were not always controlled in April by herbicides that were applied in August or October. The earlier the herbicides were applied during the fallow period the sooner subsequently emerging weeds appeared the following spring. Tillage reduced wheat residues 42% at Sidney and 78% at North Platte when compared to the no‐tillage plots. April tillage at North Platte had less weed growth because August and October tillage planted volunteer wheat and downy brome. Plots treated with residual herbicides stored 24 and 21% more soil water at Sidney and North Platte than tillage treatments. Wheat yields were increased 11% on no‐till plots only at North Platte when compared to tillage. Grain yields were not significantly different when comparing time of initial fallow treatments.

Changes in fallow weed composition following the use of herbicides in Mareeba-Dimbulah tobacco area of Northern Queensland

Experiments were conducted on fallow tobacco ground in North Queensland to observe changes in volunteer fallow weed communities following the use of the chemicals pebulate, trifluralin, and benefin for weed control. Trifluralin and benefin repressed grasses and most broad-leaved weeds, resulting in almost complete pre-dominance of star burr (Acanthospermum hispidum), which is a noxious weed in Queensland. Pebulate showed good control of this weed and permitted a fallow dominated by green summer grass (Prachiaria miliiformis).

Wheat crop surveys in southern NSW. 3. The incidence of take-all

Heavy take-all (Ophiobolus graminis Sacc.) infection was observed in 24 per cent of the 463 wheat crops surveyed in southern New South Wales in 1963. Simple tests of independence showed that the occurrence of heavy take-all infection was positively associated with weed density and cropping intensity. Clover ley history, nature of the previous crop, length of fallow period, sowing time, and weed type did not appear to be significantly associated with the occurrence of take-all. When the possibility of interactions was considered, heavy take-all was found most commonly in the early sown, heavily weed infested second crops after wheat or barley. Sixty per cent of these crops were heavily infected. The results of this survey suggest that a number of hypotheses developed under controlled experimental conditions do not hold widely in the field

Chemical Fallow in the Southern Great Plains

HE concept of reducing tillage operations with herbicides was 1 first tested in California orchards in 1944 (9). In 1949, Johnston and Sullivan (7) gave a detailed discussion of chemicals and equipment needed for eliminating tillage in orchards. Over a 4-year period chemical weed control proved cheaper than cultural methods. Soil condition and water penetration were improved and soil erosion was reduced by chemical weed control. In the Great Plains area, where residue conservation is needed to control wind erosion, eliminating medhanical tillage operations with herbicides has enormous potential. Recognizing this, T. S. Aasheim started experiments with chemical fallow, i.e. weed control with herbicides during the fallow period in 1948 at the North Montana Branch Station, Havre, Montana. These tests were expanded to 3 locations in Montana and the results were reported by Baker et al. (2) in 1956. They concluded that where chemical fallow controlled weeds, grain yields were comparable to yields from conventional tillage. Reduced yields occurred if chemical residues remained in the soil at planting time. Krall (8) recently noted increased protein content of wheat after using 3-p(chlorophenyl)-l, l-dimethyl urea (monuron) for weed control during the fallow period. Many studies have been conducted to find suitable herbicides for chemical fallow (3, 10, 11, 12, 13). These studies indicate that 2,4-D (2,4-dichlorophenoxyacetic acid) successfully controls broadleaf weeds. However, chemical control of annual grasses or volunteer wheat is often unsatisfactory. Good control of foxtail (Setaria sp.), witchgrass (Panicum capillare), downy brome (Bromus tectorum), and hairy chess (Bromus comutatus) was usually obtained. Stinkgrass (Eragrostis cilianensis) was not controlled with chemicals. Shafer (14) applied 3-amino-1,2,4-triazole (amitrol) and the sodium salt of 2,2dichloropropionic acid (dalapon) with an airplane and observed that a minimum of 5 gallons of carrier per acre was required to obtain control of volunteer wheat and downy brome. In preliminary studies in Wyoming, Barnes et al. (5) observed that water intake rates were higher on chemically fallowed plots than on plowed ground where only a sweepmachine was used. During the second 30 minutes of an hour run, chemically fallowed plots absorbed 0.95 inch of water; an increase of 216%o and 250% over plowed ground and subsurface-tilled plots, respectively. Further studies on fallowed land in Wyoming showed that a chiseling operation in conjuction with chemical fallow gave maximum moisture intake rates (1, 6). Three or four years of fallow with chemicals alone