The effects of simulated weed pressure on early maturity soybeans

Breeding for increased weed suppression would be a sustainable contribution to improved soybean weed management, because weed infestation is a major constraint to soybean production world-wide and in organic farming in particular. However, genetic variation in the soybean–weed interaction would be necessary to enable plant breeders to select soybean genotypes based on a superior weed suppression behavior. As there is a lack of information on variation between soybean cultivars in their competitive ability against weeds, the effects of weed pressure on ten early maturity soybean genotypes were studied in a controlled field experiment over three years in Austria. Winter oilseed rape was sown into the soybean stand to simulate pressure from a seed-propagated type of weed. Weed pressure significantly affected soybean yield as well as other agronomic, phenologic and seed quality characters. In two seasons, strong competition from weeds caused a soybean yield reduction of 370 and 560 kg/ha, respectively. In a third season a significant yield increase over weed-free controls was observed at relatively low levels of weed pressure which is explained by non-competition effects of a weak weed ground cover on soybean growth. Yield loss due to weed pressure was lower in early than in late maturity genotypes which appears to be the effect of a better weed tolerance rather than weed suppression. Genotype by weed treatment interaction was not significant, and genetic variation in ground cover development or leaf area was low or not significant in the early maturity soybean cultivars investigated. As such characters are considered important for weed suppression, their variation needs to be increased to enable selection for improved weed suppressive ability.     

Effect of Weed Removal on Productivity of Chickpea (Cicer arietinum L.) and Lentil (Lens culinaris Med.) in a Mediterranean Environment

Three field experiments were conducted on chickpea ( Cicer arietinum L.) and four on lentil ( Lens culinaris Med.) at different winter-sown rainfed locations in Jordan from 1988/89 to 1990/91 to study the effect of the duration of weed-free and weed-infested conditions on yields and yield components of the crops. Chickpea seed yields were reduced on average by 81 % and straw yields by 63 % when fields remained weed infested until harvest compared with weed-free conditions throughout the growing season. The corresponding lentil seed and straw yield decreases were 63 % and 55 %. As the duration of weed-free period increased and the duration of weed-infested period decreased, yields increased. However, the critical period of weed interference was between 35 and 49 days after emergence in chickpea and between 49 and 56 days after emergence in lentil, when these crops were at an advanced stage of vegetative growth. There were significant negative correlations between the weed dry weight and the seed or straw yields. The reduction in seed yields in both crops because of weed interference occurred mainly through the reduced number of pods /plant, which in turn was partly the result of reduced number of secondary branches. In chickpea, some reduction also occurred through reduced 100-seed weight.     

Effect of Two Row Spacings and Hemp Sesbania Competition on Sunflower

The competitiveness of hemp sesbania ( Sesbania exaltata [Raf.] RYBD. EX A. W. Hill) with sunflower ( Helianthus annuus L.) grown in two row spacings was evaluated at the University of Arkansas at Pine Bluff Agricultural Experiment Station in 1982 and 1983. Sunflower and hemp sesbania at densities of 3 to 5 and 13 to 16 plants per meter row, respectively, were interseeded in 61 and 91 cm row spacings in field test plots. Hemp sesbania plants were removed at different sunflower growth stages. In 1982, weed removal treatments were: (1) weedy check, (2) weed-free check, (3) weed removal at 15-leaf stage, (4) removal at 20%, (5) 50% and (6) 100% sunflower anthesis. Treatments in 1983 consisted of: (1) weedy check, (2) weed-free check, (3) weed removal at 10-leaf stage, (4) bud stage, (5) pre-anthesis, (6) 10% anthesis, and (7) 100% anthesis. Sunflower yields were significantly decreased by hemp sesbania competition each year, except for the weed competition treatments in 91 cm row spacing in 1982. Generally, the longer the weeds were allowed to compete with sunflower, the greater the sunflower yield reduction. Yield reductions of 5% to 6% and 25% or more were observed when hemp sesbania was allowed to compete with sunflower until the 10-leaf and anthesis stages of sunflower growth, respectively. When hemp sesbania was allowed to compete with sunflower for the entire growing season, yield was reduced by as much as 35%. Reducing row width from 91 cm to 61 cm did not improve sunflower's ability to compete with hemp sesbania. Thus, hemp sesbania is quite competitive with sunflower and should be controlled during early vegetative growth in order to minimize yield loss.     

Morphology and yield response to weed pressure by corn hybrids differing in canopy architecture

Recently, corn (Zea mays L.) hybrids accumulating more leaf area above the ear, maturing earlier, yielding better in narrower row spacings and tolerating higher population densities than conventional hybrids have been developed. However, no research has been conducted to assess their ability to compete with weeds. The objective of this study was to quantify morphological and grain yield responses of hybrids with differing canopy architectures to the presence and absence of weeds. Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec and in 1996 at Ottawa, Ontario. Three hybrids, leafy reduced-stature (LRS), late maturing big leaf (LMBL), and conventional Pioneer 3979 (P3979), were evaluated at two population densities (normal and high), row spacings (38 and 76 cm) and weed pressure levels (weed-free and weedy). Weed pressure reduced the plant height of LRS less (only 4 cm) than the tall hybrids (average reduction of 26 cm). The overall grain yield of the LMBL hybrid was much greater (12.7 mg ha⁻¹) than the LRS (9.6 mg ha⁻¹) and P3979 (11.0 mg ha⁻¹) hybrids in the absence, but not in the presence (LRS, 6.5; LMBL, 6.7; and P3979, 6.8 mg ha⁻¹), of weeds. The yield of early-maturing LRS and P3979 (especially LRS) hybrids, were least affected by weed pressure, suggesting better tolerance of, and competition with, weeds. However, further research with more LRS hybrids is needed, as is the development of better yielding LRS hybrids, before they can be recommended over conventional hybrids.     

Genotypic variation for competitive ability in spring wheat

Herbicides are the primary method of weed control for crop production in developed countries. For economic and environmental reasons alternative control strategies are being devised. One of these strategies is the development of competitive crop cultivars. The objectives of this research were to establish whether spring wheat (Triticum aestivum L.) genotypes differed in competitive ability and if those differences were related to specific growth characteristics. Sixteen genotypes of spring wheat were grown under simulated weed competition conditions at Saskatoon, Canada over a 3–year period. Four high and four low tillering genotypes from each of two crosses (Neepawa/M1417 and Ingal/M1417) were studied. Weeds consisted of cultivated oat (Avena saliva cv. ‘Waldern’) and oriental mustard (Brassicajuncea cv. ‘Cutlass’) sown at two densities (48 and 96 seeds/m² per weed species). Seedling establishment, ground cover, and seed yield for the three species were determined, as was wheat tiller number, spike number, maximum height, leaf area index, leaf orientation, and flag leaf length and size. Significant (P = 0.001) weed rate by genotype interactions involving changes in genotype rank were detected for wheat grain yield, indicating that the 16 wheat genotypes differed in competitive ability. Wheat grain yield reductions averaged over the two weed densities ranged from 45% to 59%. The highest-yielding genotypes under weed-free conditions were not necessarily the highest yielding under weedy conditions. Genotypes which suffered smaller yield reductions were more effective in suppressing weed growth. Although competitive genotypes were generally taller than non-competitive genotypes, other traits such as large seedling ground cover and flag leaf length were associated with wheat yield under competitive conditions.     

Weed tolerance in soybean: a direct selection system

Weed competition can severely reduce soybean (Glycine max (L.) Merr.) yields, particularly in organic systems. An efficient screening and breeding approach is needed to increase breeding progress for weed tolerance. This study sought to (i) establish a system for direct selection of competitive genotypes, (ii) evaluate genotypic differences in weed tolerance among six early‐maturing genotypes and (iii) assess the contribution of selected morphological traits to weed tolerance. A direct selection system providing two different levels of weed competition through all development stages of a soybean crop was developed, using mixtures of selected crop species as sown competitors. Two resulting mixtures induced intermediate (<30%) and strong (>50%) yield reduction, respectively. This selection system can be applied in screening and breeding programmes to facilitate breeding for weed tolerance. No significant difference in weed tolerance was detected between six soybean genotypes of maturity groups 000 to 00. Morphological traits that might influence competitive ability, for example light absorption, leaf area and lateral shoots, were assessed, and their potential for indirect selection for weed tolerance is discussed.     

Water Sensitive Periods during the Reproductive Growth Phase of Glycine max L. II Establishing Water Stress Sensitivity

The water sensitivity of soybeans was determined on a day-to-day basis from the onset of flowering to physiological maturity by correlating daily leaf water potential values of 50 different soil water regimes with corresponding grain, vegetative and biomass yields. Days, and consecutive days forming periods, during which significant negative correlations were obtained were regarded as water sensitive periods during the reproductive growth phase of the soybean crop.
Water deficits during flowering significantly inhibited vegetative and biomass production but inhibited grain yields only when occurring during early flowering. During pod elongation and seed development the sensitivity of the soybean plant to water stress was present but diminished in time with regard to vegetative and biomass yields. The effect on grain yields was restricted to pod elongation and to later seed development stages. Water stress affected grain yields to a far greater extent than vegetative growth during seed filling and physiological maturity.     

Assessing innovative sowing patterns for integrated weed management with a 3D crop:weed competition model

Weed dynamics models are needed to design innovative weed management strategies. Here, we developed a 3D individual-based model called FlorSys predicting growth and development of annual weeds and crops as a function of daily weather and cropping practices: (1) crop emergence is driven by temperature, and emerged plants are placed onto the 3D field map, depending on sowing pattern, density, and emergence rate; plants are described as cylinders with their leaf area distributed according to height; (2) weed emergence is predicted by an existing submodel, emerged weed seedlings are placed randomly; (3) plant phenology depends on temperature; (4) a previously developed submodel predicts available light in each voxel of the canopy; after emergence, plant growth is driven by temperature; when shaded, biomass accumulation results from the difference between photosynthesis and respiration; shading causes etiolation; (5) frost reduces biomass and destroys plants, (6) at plant maturity, the newly produced seeds are added to the soil seed bank. The model was used to test different sowing scenarios in an oilseed rape/winter wheat/winter barley rotation with sixteen weed annuals, showing that (1) crop yield loss was negatively correlated to weed biomass averaged over the cropping season; (2) weed biomass was decreased by scenarios allowing early and homogenous crop canopy closure (e.g. reduced interrows, increased sowing density, associated or undersown crops), increased summer fatal weed seed germination (e.g. delayed sowing) or, to a lesser degree, cleaner fields at cash crop sowing (e.g. sowing a temporary cover crop for “catching” nitrogen); (3) the scenario effect depended on weed species (e.g. climbing species were little affected by increased crop competition), and the result thus varied with the initial weed community (e.g. communities dominated by small weed species were hindered by the faster emergence of broadcast-sown crops whereas taller species profited by the more frequent gap canopies); (4) the effect on weed biomass of sowing scenarios applied to one year was still visible up to ten years later, and the beneficial effect during the test year could be followed by detrimental effects later (e.g. the changed tillage dates accompanying catch crops reduced weed emergence in the immediately following cash crop but increased seed survival and thus infestation of the subsequent crops). This simulation showed FlorSys to predict realistic potential crop yields, and the simulated impact of crop scenarios was consistent with literature reports.     

Effect of Soil and Foliar Fertilization on Inoculated and Uninoculated Soybeans

Two experiments of soil N-fertilization and Rhizobium inoculation were conducted in 1981 and 1982 at Giza, Egypt. Soybean was sprayed with a commercial micronutrients mixture, and with urea.
In the first experiment, soil N-fertilization 0, 142.8 and 214.2 kg N/hectare were applied to uninoculated plants, whereas, in the second one, local inoculum was used alone or along with addition of a starter dose of N (47.6 kg N/hectare).
Urea applications were at pod filling period (R₄, R₅ and R₆ stages), whereas, micronutrients mixture was applied at 25 days from planting.
Plant dry weight, leaf area/plant, plant height, pod and seed number/plant, seed weight/plant, seed yield and crude seed protein content increased significantly with nitrogen application to uninoculated soybean plants; whereas the starter dose of N had no significant effect on any of these traits under the inoculated soybean plants.
Foliar application of micronutrients caused significant increases in plant DW, LA, pod and seed number/plant, seed index and seed yield of fertilized and inoculated plants.
Foliar application of urea, to inoculated and uninoculated plants, caused significant increments in plant dry weight, 1A, seed protein content and particular seed index and seed yield.     

Evolution of weed beet (Beta vulgaris L.) seed bank: Quantification of seed survival,dormancy, germination and pre-emergence growth

Weed beet is an important weed of sugar beet crops. Weed and cropped beets can cross easily and the management of weed beet is therefore crucial in the case of the advent of GM sugar beet, especially herbicide-tolerant cultivars, in order to ensure the co-existence of GM and non-GM crops and to avoid the appearance of herbicide-resistant weed beet. The inability of weed beet to compete in most other crops of the rotation makes the seed bank evolution a crucial stage of the life-cycle because in the rotation, sugar beet is at the most cultivated only every 3 years. The present study used seed burial experiments and laboratory analyses to characterise each step of the evolution of the weed beet seed bank and the external factors that could modify seed persistence in the soil. A monthly seed mortality of 10% was observed between October and December, while mortality was nil during the other seasons. Equations were then developed to describe the observed seasonal variations in seed survival. Seed dormancy also varied with season: the proportion of non-dormant seeds increased during winter (appearance of secondary dormancy) and decreased during the remaining seasons (loss of dormancy). In addition, the germinating seeds decreased with seed age and seed depth, while the presence of light stimulated germination. These observations were also translated into equations. Last, the pre-emergence hypocotyl growth and its variability were studied according to seed age, but no significant effect was observed. The results confirm the importance of the effects of cropping system on the evolution of the weed seed bank, especially the effect of soil tillage, which determines the date and conditions of seed burial, seed excavation and germination stimulation.     

不同播期东农42产质量性状动态变化规律研究

本试验通过高蛋白品种东农42的六个播期试验,对品质性状和部分产量性状动态取样分析进行研究。确定不同播期对大豆产质性状影响,为指导大豆生产实践提供理论基础。试验通过对大豆东农42在六个不同播种时期的形态及产质量性状中的九个性状进行动态取样和测量,并通过EXCEL和SPSS10.0对试验数据进行统计分析。通过东农42不同播期动态规律研究表明：不同播期之间对品质性状、产量性状和形态性状影响均较大。随着播期推迟,品质性状蛋白质含量增加,油分含量减少;产量性状的单株荚数、鲜粒荚比降低,而鲜皮荚比升高;形态性状的主茎节数降低。但其它一些性状受环境光温条件和降水量影响较大,如株高,平均鲜粒重和平均鲜荚重等。本实验证明,黑龙江省哈尔滨地区大豆的适宜播种期在4月底至5月上中旬,如果播期太晚,会严重影响大豆产量。     

Cover crops and interrow tillage for weed control in short season maize (Zea mays)

Weed competition can cause substantial maize (Zea mays L.) yield reductions. Interseeding maize with cover crops or a combination of interrow cultivation and interseeded cover crops are possible alternative methods of weed control. This study was conducted to examine the potential of interrow cultivation plus cover crops to reduce weed density in maize without reducing the grain yield. Field experiments were conducted in 1993 and 1994 at two sites in Québec to determine the effects of planting 12 cover crops with maize on weed control. Fall rye (Secale cereal L.), hairy vetch (Vicia villosa Roth), a mixture of red clover (Trifolium pratense L.) and ryegrass (Lolium multiflorum Lam), a mixture of white clover (Trifolium repens L.) and ryegrass, subterranean clover (Trifolium subterraneum L.), yellow sweet clover (Meliotus officinalis Lam), black medic (Medicago lupulina L.), Persian clover (Trifolium resupinatum L.), strawberry clover (Trifolium fragiferum L.), crimson clover (Trifolium incarnatum L.), alfalfa (Medicago sativa L.), and berseem clover (Trifolium alexandrinum L.) were seeded at two planting dates, 10 and 20 days after maize emergence. Interrow cultivation was carried out weekly until forage seeding, with a final cultivation being conducted just prior to cover crop seeding. Cover crop planting date did not affect maize yields or the ability of interrow tillage plus cover crops to suppress the development of weed populations. Maize yield was less affected by the interseeded cover crops under conditions of adequate rainfall. Corn planted in fields heavily infested with weeds resulted in substantial yield reductions even when rainfall was adequate. Except for 1993 at l'Assomption interrow tillage plus cover crop treatments had consistently lower weed biomass when compared to the weedy control. Most of the weed control was due to the interrow cultivation performed prior to seeding of the cover crops. The lowest weed density occurred in the herbicide treated plots. The ability of interrow tillage plus cover crops to suppress the development of weeds was affected by the level of weed infestation, the growing conditions and location. The cover crops provide additional weed control but the interrrow tillage or some herbicide application may still be necessary.     

Effect of 1-Naphthaleneacetic Acid Concentrations and the Number of its Applications on the Yield Components, Yield and Fibre Properties of Egyptian Cotton (Gossypium barbadense L.)

Field experiments were performed in two successive seasons at the Experimental Station, Faculty of Agriculture, Cairo University, Giza, Egypt, on the Egyptian cotton cultivar Giza 75 ( Gossypium barbadense L.). Cotton plants were sprayed with the growth regulator 1-naphthaleneace acid (NAA) once (at 90 days), or twice (at 90 and 105 days) or thrice (90, 105 and 120 days) after sowing, during the square initiation and boiling stage at the concentrations of 5, 10, 15, 20 or 25 p.p.m. The volume of solution was the same for all treatments. 9601 ha⁻¹. The control plants were sprayed with water only. The effect of the previous treatments on yield components, cotton yield and fibre properties was studied.
The application of NAA increased the number of opened bolls plant⁻¹, boll weight, seed index, seed cotton yield plant⁻¹ and seed cotton and lint yields ha⁻¹. The most significant effects were obtained with the 15 and 20 p.p.m. concentrations. Lint percentage, fibre length parameters and micronaire value were not significantly affected by NAA. Flat bundle strength was significantly affected by NAA but with no definite trend. The application of NAA twice or thrice tended to give the best results on yield components and cotton yield compared with one application. The results of this study suggested that 20 p.p.m. of NAA gave the best figures when applied twice on the Egyptian cotton plants.     

Dynamisches Entscheidungsmodell zur Lenkung von Unkrautkontrollmaßnahmen in Wintergetreide mit Hilfe digitaler Bildverarbeitung

Dynamic decision model for weed control methods in cereals by means of digital image analysis
Field experiments were conducted to study weed-crop competition in winter wheat, -barley and -rye. Weed cover and crop cover was determined over time by digital image analysis of slides taken in the field. The relation of percentage weed coverage and crop coverage was most suitable to quantify the competition of weed population on the crop. In addition the model "UNPROG" was established to predict yield losses caused by weed competition and to estimate the profitability of chemical or mechanical weed control. The model was tested on 22 farms in Nordrhein-Westfalia in autumn 1991 and spring 1992. In 65 out of 72 field plots (92 %) of winter cereals "UNPROG" gave correct prediction with respect to necessity of weed control.     

Effect of Field Bean and Soybean Cultivation on Soil Compaction Amelioration and its Influence on Wheat and Barley as subsequent Crops

Effect of field bean and soybean cultivation on soil compaction amelioration and its influence on wheat and barley as subsequent crops
Amelioration effect of field bean and soybean growth on compacted soil and its influence on the following crops of wheat and barley was tested. The performance of both field bean and soybean was affected by compaction. A reduction of 5–16 % in total dry matter, 10–22 % in seed yield, 5–12 % in no. of pods per plant, 4–14 % in plant height, 8–19 % in total accumulated N in plant and 11–22 % in accumulated N in seed of the both crops was registered. The crops were grown at 30 and 60 plants/m² densities. The negative effects of compaction were compensated to some extent by high plant density. Both crops loosened the compacted field, the effect increased with an increase in plant density. Field beans decreased the soil bulk density up to 8 %, increased total porosity up to 8 % and air filled pores up to 19 % till 30 cm soil depth, the effects being higher than produced by soybeans.
The increases in yields of wheat and barley and in their accumulated N were 9–57 % and 11–56 %, respectively after field bean and soybean as preceeding crops than after barley.     

豫北露地直播棉田杂草的发生及其与棉花的竞争作用

 为了明确棉田自然混生杂草对棉花的危害程度及其关键防除时期,通过田间杂草共生期试验,研究了豫北露地直播棉田杂草的发生及其与棉花的竞争临界期。结果表明,豫北地区露地直播棉田的优势杂草为牛筋草、马齿苋、藜和鳢肠,杂草出土高峰期集中在棉花苗期和花蕾期,且存在3个出土高峰,分别在5月中旬、6月上中旬和7月中下旬。当杂草与棉花竞争持续时间少于4周时,由于杂草与棉花植株均较小,且土壤中养分相对充足,因此杂草对棉花生长和产量的影响不大;当杂草与棉花竞争期达8周以上时,杂草对棉花的竞争作用明显增强,棉花的株数减少,茎秆变细,形成瘦高植株,且单株结铃数、铃重等产量指标明显降低。因此,豫北棉田自然混生杂草群落与棉花的竞争临界期为棉花出苗后4～8周,在此期间应采取相应措施,保证田间无草害。     

免耕夏玉米田杂草生态经济阈值研究

为了明确免耕夏玉米田杂草的生态经济阈值,通过田间小区试验,采用添加法对田间杂草的种类和密度进行配置,田间小区完全随机区组排列,通过杂草密度与玉米产量损失率的关系计算杂草的生态经济阈值。结果表明,杂草密度(x)与玉米产量损失率(y)呈正相关,以拟合优度>0.90和残差平方和最小为条件对产量损失率曲线模型进行优选,其关系符合指数方程（y=46.4359-18.518e-x/21.9215-28.5039e-x/126.5527,R2=0.9609）,免耕夏玉米田杂草的生态经济阈值平均为2.27株/m2。通过该模型可明确田间杂草所能允许的最低密度,从而指导对田间杂草的综合治理。     

带状套作荫蔽及复光对不同大豆品种(系)生长及产量的影响

选取我国南方套作模式下20个不同产量水平的大豆品种(系),于2013—2014年采用净作和遮阴(遮阳网或玉米)对比分析了高产和低产大豆品种在荫蔽期及复光期的生长特点。结果表明,荫蔽期间,茎叶干物重显著低于净作,分配规律表现为"茎多叶少",分别为58.4%和41.6%;与高产类型大豆相比,低产类型茎叶干重下降比例、茎长、茎长/茎粗、茎长/地上部干物质、茎长/叶面积显著增加;荫蔽期地上部干物质与产量呈显著正相关,茎干物质比例与产量呈显著负相关。光照恢复后,地上部干物质迅速增加,分配规律表现为"茎少叶多",复光后30 d分别为47.7%和52.3%;高产类型地上部干物质、叶面积、叶干重比例、茎粗均显著大于低产类型,茎长/茎粗、茎长/地上部干物质、茎长/叶面积均显著小于低产类型;地上部干物质、叶面积、茎粗、叶干物质比例与产量呈显著正相关,茎长/茎粗、茎长/地上部干物质、茎长/叶面积与产量呈极显著负相关。通过复光前后生长性状与产量的回归分析,复光后30 d的叶干物质比例、茎长/地上部干物质、茎粗可作为预测套作大豆产量的主要指标。上述结果表明,选择荫蔽期茎长较短、地上部干物质较大、叶面积更大,光照恢复期茎粗较大、叶干物质比例较大、茎长/地上部干物质较小的大豆品种可以在套作下获得高产。     

Suppressing Weeds in Direct-seeded Lowland Rice: Effects of Methods and Rates of Seeding

High weed infestation is a major constraint to widespread adoption of direct seeding of rice (Oryza sativa L.) The experiments were conducted in 1998 wet and 1999 dry seasons in the Philippines to examine the effects of seeding methods and rates on suppressing weeds in direct-seeded lowland rice. Treatments consisted of four seeding methods: conventional and modified broadcast seeding, drill seeding with east–west and north–south row orientations; three seeding rates: 40, 80 and 160 kg seed ha⁻¹ as well as two weed control levels: weed control with herbicide and no weed control. Among the seeding methods drill seeding with east–west row orientation had the lowest rice grain yield loss caused by weeds (38 % in the wet and 20 % in the dry season), whereas the highest losses because of weeds were observed with conventional broadcast seeding (59 % in the wet and 27 % in the dry season). Seeding rate was inversely correlated to weed interference. Severe rice yield reduction (71 %) caused by weeds was found at a seeding rate of 40 kg seed ha⁻¹ in the wet season. Using seeding rates of 80 and 160 kg seed ha⁻¹, respectively, lowered yield loss to 47 and 26 % in the wet season, 32 and 18 % in the dry season. Therefore suitable method and/or rate of seeding can significantly suppress weeds in direct-seeded lowland rice.     

Intercropping corn with soybean, lupin and forages: weed control by intercrops combined with interrow cultivation

Intercropping corn with legumes is an alternative to corn monocropping and is a possible way to reduce the use of inputs, such as herbicides, while maintaining current weed control levels. Two experiments were carried out at each of two sites in both 1993 and 1994. The first experiment investigated the effects of seeding soybean or lupin alone or in combination with one of three forages (annual ryegrass, Lolium multiflorum Lam.; perennial ryegrass, Lolium perenne L.; and red clover, Trifolium pratense L.) on weed control. The second experiment examined the effects of seeding date (simultaneous with corn or 3 weeks later) and number of rows of large-seeded legumes (one or two) seeded between the corn rows, on weed control. Whenever seeding of legumes/forages was delayed, weekly interrow tillage operations were used to control weeds until legume/forage seeding. The density and biomasses of monocot weeds, either on or between the corn rows, were not affected by cultivation or intercropping. The density and biomass of dicot weeds on corn rows were reduced by some intercrop systems. For the various cropping systems tested, the dicot weed biomass and density between corn rows were most affected (in some cases reduced by 73-100% of the weedy control). A more effective dicot weed control was observed in delay seeded treatments, which allowed extra interrow cultivations. Intercrops that included soybean were also more successful at reducing weed populations than those containing lupin. Underseeded forages did not reduce weed biomass or density.