Corn Population Research Articles

Root diseases, weeds, and nematodes with poultry litter and conservation tillage in a sweet corn–snap bean double crop

The effect of continuous applications of poultry litter on root diseases, nematodes, and weeds with different tillage practices in vegetable production in Georgia was investigated. Litter treatments (noncomposted and composted broiler or breeder litter) applied 3–5 weeks before planting were compared with no litter. In sweet corn and snap bean there were differences among years, and tillage and litter treatments had a variable effect on yield, post-emergence damping-off and plant stand. Crown and brace root rot in corn induced by Rhizoctonia solani AG 2-2 increased after 3 years conservation tillage, but there were no differences among litter treatments. Population densities of R. solani AG-4 were increased by conservation tillage before planting snap bean the first year but not in later years, while litter treatments had no effect. After 3 years, populations of Pythium spp., Fusarium solani, and Fusarium spp. did not differ among treatments, but noncomposted broiler litter increased populations of saprophytic fungi in soil compared with no litter. Population densities of stylet-bearing nematodes were low and usually not different among treatments. After 3 years of sweet corn populations of Meloidogyne incognita increased with conventional tillage compared with conservation tillage, populations of Paratrichodorus christiei were reduced by litter treatments and populations of Helicotylenchus dihystera were reduced by noncomposted broiler litter compared with no litter. Weed infestation increased in both tillage systems with time, but in snap bean there was a greater infestation in conservation tillage than in conventional tillage. Litter treatments had little effect on weed infestation.

Comparison of Methods for Amylose Screening Among Amylose‐Extender (ae) Maize Starches from Exotic Backgrounds

ABSTRACTBreeding for high‐amylose corn requires a rapid analytical method for determining starch amylose so that generating wet chemistry values does not pose a major limitation in the volume of materials that can be screened. Two methods for determining apparent amylose content (AAC) were examined and compared with an iodine‐binding method involving the solubilization of isolated starch in a sodium hydroxide solution (method 1). These methods included one based on near‐infrared transmittance spectroscopy (NIRT) (method 2) and another iodine‐binding method involving the solubilizing of starch from ground whole corn with a DMSO‐iodine solution (method 3). These methods were chosen because, aside from initial set up costs, they are relatively rapid and inexpensive to perform. The materials evaluated consisted of various exotic corn populations including plant introductions and experimental materials generated from the Germplasm Enhancement of Maize (GEM) project. Crosses were made between these materials and a Corn Belt dent hybrid (OH43 × H99) converted with the amylose‐extender (ae) allele. Grain from F2 ears, presumed to be homozygous for the ae allele based on visual selection of mutant kernels on F1 ears from which they were planted, were then evaluated to identify possible modifiers of ae conditioning high starch AAC. From a total of 1,006 F2 ears, a core set consisting of 155 samples was established and only these were subjected to starch AAC analysis, using all three methods to compare the methods. Method 2 showed poor correlation to method 1 (r = 0.88), however, NIRT did appear to discriminate between samples converted to ae vs. those with a normal or possibly segregating endosperm type. Method 3 showed a slightly better correlation with method 1 (r = 0.92) and appeared to more fully discriminate among samples with AAC values >65% from those at ≈55%. Results from this study suggest that NIRT may be useful when a quick screening method is needed to discriminate mutant from nonmutant genotypes within grain samples of exotic germplasm especially when visual identification is difficult. In addition, method 3 could be used to replace the more time‐consuming method 1 when trying to identify high AAC levels among ae genotypes, even though some inconsistency was observed between the two methods. Finally, this study revealed that exotic germplasm may be an important source of new modifiers to the ae allele because values as high as 70% AAC were identified.

Genetic variability and diversity of corn breeding material originating from domestic and foreign populations determined on the basis of biochemical-genetical markers

Isozymes can serve as genetic markers and their number should be large enough in order to make the coverage of genomes as complete as possible and in order to use these methods for gene marking for required agronomic traits. These markers are the products of 21 mapped genes, which is relatively reliable number for their application in mapping for certain agronomic traits. Genetic variability and diversity are significant for populations and for selfpolinated lines as basic material in breeding and creation of new corn hybrids. For that reason, several groups of corn populations of different origin were analyzed. Two groups of Yugoslav populations, Italian, Portuguese and French collections were assessed on the basis of detected alleles of 21 loci and standard genetic distances between genotypes. Yugoslav corn collections had shown high heterozygosity, on the basis of isozymes as gene markers. Genetic diversity of Italian populations was pronounced on the basis of some loci, and the Portuguese populations had more polymorphic and more heterozygous loci than French populations Inter-genetic variability between populations and their geographical location are very important in breeding crops for creation of heterosis.

Effects of Cover Crops, Nitrogen, and Tillage on Sweet Corn

Effects of tillage, inorganic N, and winter cover crops on sweet corn (Zea mays) were examined in 1994, 1995, and 1996. Tillage treatments were tillage or no tillage, and N treatments were the addition of inorganic N at 0 (N0) or 200 (N+) kg·ha-1 (0 or 179 lb/acre). Winter cover crops included hairy vetch (Vicia villosa), winter rye (Secale cereale), and a vetch/rye biculture. In the N0, rye treatment, the soil was N deficient in 1994 and highly N deficient in 1995 and 1996. When vetch shoot N content was ≥150 kg·ha-1 (134 lb/acre) (1994 and 1995), addition of inorganic N did not increase corn yields, and it only increased corn foliar N concentrations by 8%. Reductions in corn yields (29%) and foliar N concentrations (24%) occurred when vetch shoot N content was only 120 kg·ha-1 (107 lb/acre) (1996) and inorganic N was not supplied. In 1994, the vetch/rye biculture supplied sufficient N for maximum corn yields, but addition of inorganic N increased yields by more than 50% in 1995 and 1996. Under tilled conditions, the vetch N contribution to corn appeared to equal (1996) or exceed (1994 and 1995) 82 kg·ha-1 (73 lb/acre) of N supplied as ammonium nitrate, whereas a mean value of 30 kg·ha-1 (27 lb/acre) was obtained for the biculture cover crop (1995 and 1996). No significant effects of tillage on sweet corn population densities were detected following vetch, but no-tillage significantly reduced corn population densities following rye (17%) or biculture (35%) cover crops compared to tillage. No-tillage did not reduce yields from emerged seedlings (per plant basis) for any cover crops. Vetch appeared to be a satisfactory N source for sweet corn when vetch N content was ≥150 kg·ha-1, and it could be used with no-tillage without yield reductions.

'NE-EDR sh2': A Yellow shrunken2 Sweet Corn Population with Disease Resistance from Exotic Sources

Additional index words. Zea mays , sugary1 gene, backcross breedingLeonard & Suggs] (NCLB), and evaluatedacross an expanded climatic range. Inbredsderived from this population could likelyprovide breeders with a source of polygenicdisease resistance and another tactic to ac-company monogenic/oligogenic resistance,such as recently developed by Hulbert andDrake (2000).OriginThe NE-EDR sh2 was developed in twophases that included recurrent mass selection(RMS) followed by a backcross procedure tointroduce the recessive sh2 allele into anopen pollinated population. The originalNE-EDR composite was assembled duringSummer 1976 in Waimanalo, Hawaii; the NEis an abbreviation for the NE-124 RegionalHatch Project and the EDR is the exoticdisease resistance supplied by the tropicalgermplasm. It included the following NorthAmerican su1 hybrids: ‘Bonanza’, ‘Gold Win-ner’, ‘Golden Cross Bantam’, ‘Iobelle’, ‘Ju-bilee’, ‘Midway’, ‘NK 51036’, ‘SilverQueen’, ‘Stylepack’, and the Hawaiian hy-brid ‘H 68’ (Brewbaker, 1968), which wereadded to the composite on the basis of ear andhorticultural quality. Also incorporated intothe original composite were an open-polli-nated cultivar, ‘Haw’n Sugar’; a syntheticcultivar, Hisu1 SYN. 2; and 10 disease-resis-tant composites of tropical origin, includingHSX COMPS. 1, 6, 7, 8, 9, 10, and 11, alongwith o2-su1 COMP. 1, 2, and 3 (Brewbaker,1998; Gerdes et al., 1993). Each of thesetropical entries was developed in Hawaii byrecurrent mass selection with the objective ofimproving resistance to a broad spectrum offoliar diseases with either a su1 or brittle1(bt1 ) endosperm (Brewbaker, 1996, 1998).In the parental generation, each temperatehybrid was randomly assigned as a male togroups of three tropical females clustered inall possible permutations. The intent was tofurther deploy broad spectrum disease resis-tance from exotic tropical sources into U.S.sweet corn germplasm, specifically in a su1background.After 11 cycles of RMS, the sh2 gene wasintrogressed into the NE-EDR su1 in Hawaiiand Florida. In Hawaii, version “i” (9th cycleRMS) of the NE-EDR su1 was used as therecurrent parent through to BC

Weed Biomass Production Response to Plant Spacing and Corn (Zea mays) Hybrids Differing in Canopy Architecture1

Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec, Canada, and in 1996 at Ottawa, Ontario, Canada, to quantify the impact of corn hybrids, differing in canopy architecture and plant spacing (plant population density and row spacing), on biomass production by transplanted and naturally occurring weeds. The treatments consisted of a factorial combination of corn type (leafy reduced stature [LRS], late-maturing big leaf [LMBL], a conventional Pioneer 3979 [P3979], and, as a control, a corn-free condition [weed monoculture]), two weed levels (low density [transplanted weeds: common lambsquarters and redroot pigweed] and high density [weedy: plots with naturally occurring weeds]), two corn population densities (normal and high), and row spacings (38 and 76 cm). At all site-years under both weed levels, the decrease in biomass production by both transplanted and naturally occurring weeds was greater due to the narrow row spacing than due to the high plant population densi...

Effect of Glufosinate-Resistant Corn (Zea mays) Population and Row Spacing on Light Interception, Corn Yield, and Common Lambsquarters (Chenopodium album) Growth1

Abstract: Management of corn (Zea mays) row spacings and populations has been used for many years to increase corn productivity. In 1998 and 1999, nonirrigated corn was grown in 38-, 56-, and 76-cm row spacings at populations averaging 59,300, 72,900, and 83,900 plants/ha in Michigan. Glufosinate at 0.29 kg/ha was applied to common lambsquarters (Chenopodium album L.) averaging 5 cm in height in each plot. Corn population and row spacing did not influence weed emergence following application of glufosinate. Common lambsquarters biomass and seed production were reduced when grown under canopies of corn planted in populations exceeding 72,900 plants/ha. Common lambsquarters biomass was reduced as corn row spacings were reduced from 76 to 38 cm. Early-season interception of photosynthetic active radiation (PAR) by corn canopies increased as row spacings decreased, but differences were not apparent later in the season. Interception of PAR was similar throughout the season when corn populations exceeded 72,900...

Crop and weed response to nutrient source, tillage and weed control method in a corn-soybean rotation

The integration of various sustainable management techniques in cropping systems can potentially reduce agro-environmental problems, but may warrant a new approach to weed management, due to changes in weed communities. A 3-yr experiment was conducted to determine the effects and interactions of tillage (moldboard plow or chisel plow), weed control method (chemical or mechanical), and nutrient source (mineral fertilizers or liquid hog manure supplemented with mineral fertilizers) on crops and weeds in a corn (Zea mays L.)–soybean (Glycine max (L.) Merr.) rotation on two soils (a Sainte-Rosalie clay and a Duravin clay loam, Orthic Gleysols), at Saint-Hyacinthe, Québec. In most cases, weed density and biomass were more important with mechanical than with chemical control. Nutrient source did not affect weed density, but weed biomass was higher in the manure than the mineral treatment in 1997. Weed populations on both soils were greater with chisel plow tillage combined with mechanical weed control. The presence of crop residues in chisel plow systems may have hindered the efficacy of mechanical weed control operations, particularly when corn was the previous crop. Soybean populations, mid-season biomass and yields were reduced in chisel plow compared with moldboard plow tillage. Corn populations and mid-season biomass were not affected by any of the factors, whereas corn yields showed variable responses over the years. Efficacy of mechanical weed control would need to be enhanced or complemented with other weed control methods, in order to reduce the risks of weed infestations and lower crop yields, particularly in conservation tillage systems. Liquid hog manure would have little effect on weed populations, but would need to be adequately balanced in order to ensure proper crop nutrition and optimum yields. Key words: Chisel plow tillage, mechanical weed control, liquid hog manure, conservation tillage

A doorman to keep foreign genes out

In October 2000, news reports in the USA described that millions of bushels of genetically engineered corn approved for animal use only, had found their way into taco shells. The producer, Kraft Foods, had to withdraw the taco shells from supermarkets not only in the USA, but as far away as Japan. Only a few days later the media reported that the same corn had been found in other corn products. Investigations to determine how the modified grain found its way into the human food supply are still ongoing, although Aventis has already agreed to buy back the corn, called StarLink, at a premium price of approximately $100 million. Later, the US Department of Agriculture reported in mid‐November that this brouhaha over genetically modified food had resulted in a steady drop in USA corn exports. > The new technology will be used to breed corn with resistance to cross‐pollination—which may be a paradox, using genes to confer resistance to further genetic modification A set of genes from a wild relative of corn could solve the problem of unwanted food contamination by GM crops. Jerry Kermicle, a retired professor of genetics at the University of Wisconsin in Madison, discovered this molecular barrier in teosinte, a weed‐like type of corn that grows naturally in Mexico alongside cultivated hybrid corn. When Kermicle bred the genes into modern hybrid corn, they actually prevented …

Intercropping of Corn with Soybean, Lupin and Forages: Silage Yield and Quality

Intercropping of corn with legumes is an alternative to corn monocropping and has a number of advantages, for example, lower levels of inputs, lower cost of production and better silage quality than monocrop systems. An experiment was carried out at two sites in 1993 and 1994 to investigate 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.; red clover, Trifolium pratense L.) on silage yield and quality. The intercrop plots received 90 kg ha−1 less nitrogen fertilizer than monocrop plots, which received 180 kg ha−1. Corn biomass yield had a variable response to the treatments, but showed no change at most site‐years. Soybean and lupin biomass yields were decreased by intercropping (80–98 % for soybean, and 94–100 % for lupin). However, when corn growth was limited due to poor establishment at one site in 1994, soybean was able to grow well and produce yields similar to those of monocropped soybean. The three underseeded forages did not grow well during the period examined (up to silage harvest) and had no effect on the yield of any crop. Total silage yields were similar to corn monocrop biomass yields even during 1994 at the site with low corn population densities because soybean was able to compensate for reduced corn growth.

Avaliação de progênies de meios-irmãos da população de milho CMS-453 no Nordeste brasileiro

Três ciclos de seleção entre e dentro de progênies de meios-irmãos foram realizados na população de milho Zea mays L. CMS-453, de alta qualidade protéica, no período de 1995 a 1997, no Nordeste brasileiro, visando à obtenção de um material mais produtivo, melhor adaptado, portador de caracteres agronômicos desejáveis, com altos teores de triptofano e lisina na proteína, para divulgação na região. As 196 progênies de cada ciclo foram avaliadas em látice 14 x 14, com duas repetições, e realizaram-se as recombinações das progênies selecionadas, dentro do mesmo ano agrícola, de modo a se obter um ciclo/ano. As magnitudes das estimativas dos parâmetros genéticos decresceram do ciclo original para o ciclo I de seleção, registrando-se um acréscimo do ciclo I para o ciclo II. Os altos valores dessas magnitudes, associados às altas médias de produtividade das progênies e aos ganhos médio esperado e obtido com a seleção entre e dentro de progênies, por ciclo de seleção de 11,62% e 3,0% respectivamente, evidenciam o grande potencial da população em responder à seleção, o que permitirá a obtenção de um material mais produtivo e melhor adaptado às condições edafoclimáticas da região. Os teores de triptofano e lisina na proteína, na média dos três ciclos de seleção foram de 0,88% e 3,91%, respectivamente, o que confere alta qualidade protéica à população CMS-453.

Partitioning soil-water losses in different plant populations of dry-land corn

In situ volumetric soil-water contents were measured on 11 days at 0.20 m depth intervals to 1.0 m in a field experiment with four replicates of a dry-land corn hybrid (Pioneer 3140) at plant populations of 37, 49, and 62 thousand plants ha −1. These measurements were used to estimate total soil-water losses in each of the 12 field plots for each of the 10 measurement intervals. The area of the largest leaf on 10 plants in each plot was measured at 86 days after planting, when all the leaves on the plants were fully developed. Daily green leaf area indexes (GLAI) were calculated from these measurements. Climatic data collected at the experimental site together with the results for GLAI were used to calculate water balances in order to partition the total soil moisture loss for each measurement interval into bare soil evaporation, crop transpiration, and drainage below the root zone. The observed total soil moisture losses between the days of measurement compared well with values from the water-balance calculations. As plant population increased, the time to full canopy cover increased. Therefore, higher fractions of the soil water were lost to bare soil evaporation and drainage over time as the plant population was lowered. At the same time, the fraction lost to crop transpiration decreased as the plant population was lowered. This compensatory effect under dry-land conditions resulted in almost identical total water losses by the three plant populations during the growing period. The calculated partitioning of the soil-water losses served to explain the experimental observations that, under dry-land conditions, it would be unlikely that total soil-water losses would be influenced by different plant populations of corn.

Ear Quality in Three Sweet Corn Populations Selected for Resistance to Common Rust

Research was conducted to evaluate correlated effects of full-sib phenotypic recurrent selection for resistance to common rust (Puccinia sorghi Schw.) on ear quality traits in three sugary1 (su1) sweet corn (Zea mays L.) populations: Minn11, Minn14, and NECDR. Cycles 0, 1, 2, and 3 of each population were evaluated in both rust infested and nonrust infested environments. Generally, selection for rust resistance resulted in significant, but minor, decreases in ear and kernel size. Changes in specific traits varied with population. The nonsignificant cycle × environment interaction indicates similar responses occurred in all environments evaluated. Based on these results, selection for ear quality traits need not accompany selection for resistance to common rust if maintenance of ear quality is desired.

Variability For Grain Yield, its Components and Quality Traits in a Sweet Corn Population

Variability For Grain Yield, its Components and Quality Traits in a Sweet Corn Population

Ear Resistance of Sweet Corn Populations to Sesamia nonagrioides (Lepidoptera: Noctuidae) and Ostrinia nubilalis (Lepidoptera: Pyralidae)

Corn borers are the main pests of maize, Zea mays L., in temperate areas. In Spain and other Mediterranean countries, the principal corn borer is Sesamia nonagrioides Lefebvre, although the European corn borer, Ostrinia nubilalis (Hubner), is also an important pest in sweet corn. The objectives of this work were to study resistance to attack of both species in sweet corn populations and to compare the mechanisms of resistance. Twenty sweet corn populations and 1 field corn population were evaluated for ear resistance under artificial infestation, with eggs of S. nonagrioides and O. nubilalis, under natural conditions, and protected with an insecticide, in 1996 and 1997. There were significant differences between years and the interactions genotype × year and treatment × year were significant for most traits. In 1996, damage produced by S. nonagrioides was greater than damage produced by O. nubilalis. In 1997, attack of O. nubilalis was most important. The insecticide did not protect the crop in 1996, and protection was low in 1997. The field corn synthetic cultivar ‘BSCB1(R)C11’, and the sweet corn synthetic cultivars ‘NE-HY-13A(S)C1’, ‘NE-HY-13B(S)C1’, and ‘AS11’ were resistant to attack by both species in both years. Stowell’s ‘W. Evergreen’ and ‘EPS11’ were resistant to O. nubilalis and showed some resistance to S. nonagrioides. All resistant populations have field corn in their pedigree. Field corn seemed to be more resistant than sweet corn, and mechanisms of resistance to both pests were not entirely independent.

Disease-resistant Tropical Supersweet Corn Populations

Disease-resistant Tropical Supersweet Corn Populations

Establishment of Corn in Rotation with Alfalfa and Rye: Influence of Grazing, Tillage, and Herbicides

AbstractIntegrating livestock into crop rotations offers alternatives for grazing and crop management. Grazing, tillage, and herbicides were evaluated in a randomized block design with four replications for transition from alfalfa (Medicago sativa L.) to corn (Zea mays L.). For the control (T1), alfalfa was overseeded with rye (Secale cereale L.) in October, and corn was no‐till established in early May. For alternative treatments, alfalfa was grazed by cattle (Bos taurus) from July until October. Treatments were: T2, disking prior to rye planting, grazing rye for 12.5 d prior to corn planting, with dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) applied after corn planting; T3, no spring grazing, with glyphosate [N‐(phosphonomethyl)glycine] applied before corn planting; T4, same as T3 plus grazing rye for 1.8 d in early spring; T5, autumn application of glyphosate to alfalfa before planting a rye‐hairy vetch (Vicia villosa Roth) cover crop; and T6, autumn disking before planting rye‐hairy vetch with no herbicides used. System T2 increased suppression of alfalfa and corn plant populations compared with shorter grazing periods. System T4 increased corn plant populations compared with no spring grazing (T3; 3.5 vs. 3.0 plants m−1). Autumn disking (T6) generally provided less control of alfalfa than autumn application of glyphosate (T5). Applying glyphosate before corn planting (T3 and T4) improved corn populations and growth, compared with autumn glyphosate or disking (T5 and T6), and resulted in corn forage yield (23 Mg ha−1) similar to conventional no‐till establishment (T1; 22 Mg ha−1). Herbicides completely killed alfalfa, but grazing alfalfa and rye reduced alfalfa persistence. Grazing could provide benefits to corn production systems while providing forage for cattle.

Agronomics of Corn Production under Different Crop Rotations in New York

The 1996 Federal Agriculture Improvement and Reform Act decouples support payments from production. Consequently, grain producers must devise rotations based on market prices. The objective of this study was to demonstrate to grain producers that soybean [Glycine max (L.) Merr.]-corn (Zea mays L.) or soybean-wheat/red clover (Triticum aestivum L./Trifolium pratense L.)-corn rotations under reduced inputs (banded herbicides plus cultivation, ∼105 Ib N/acre) compared with continuous corn under full inputs (insecticide, broadcast herbicides, ∼140 Ib N/acre) maintains or enhances corn yields. Field-scale demonstrations, with participating farmers performing field operations, were established on four farms in New York in 1993. When averaged across years and sites, the soybean-wheat/clover-corn and soybean-corn rotations compared with continuous corn yielded 10% greater (141, 139, and 127 bu/acre, respectively). Grain yield, however, had site by rotation interactions. The soybean-wheat/clover-corn rotation yielded greater in eight of 12 site-year comparisons, and the soybean-corn rotation yielded greater in seven site-year comparisons with continuous corn. Major production challenges where corn did not respond positively to rotations include adequate stand establishment and weed control in the soybean-wheat/clover-corn rotation and adequate N fertility in the soybean-corn rotation. We successfully demonstrated that soybean-wheat/clover-corn or soybean-corn rotations with reduced inputs compared with continuous corn under full inputs enhanced or maintained corn yield. New York growers, who adopt soybean-wheat/clover-corn or soybean-corn rotations, have the opportunity to reduce corn inputs, thereby improving profitability and reducing potential environmental problems.

Establishment of Switchgrass and Big Bluestem in Corn with Atrazine

AbstractSwitchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) provide abundant forage for livestock and wildlife during hot summer months when cool‐season grass species may decline in production. Little biomass production for grazing may result during warm‐season grass establishment because of weed competition. Chemical methods of weed control are now limited, because application of atrazine [6‐chloro‐N‐ethyI‐N'‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] to switchgrass and big bluestem is no longer allowed according to the label. Using corn (Zea mays L.) as a companion crop could provide potential for high biomass production during warm‐season grass establishment, and allow the use of atrazine for weed control. This study investigated the ability of switchgrass and big bluestem to establish in a corn companion crop. The effects of corn hybrid (short‐ vs. long‐season), population density, row spacing, and harvest date on switchgrass and big bluestem stands and on corn production were quantified. Establishment of switchgrass and big bluestem in corn was successful. Switchgrass mean stands were 26.3 plants m−2 in 1995 and 46.4 plants m−2 in 1996. Big bluestem stands were similar to switchgrass in 1995 (31.7 plants m−2), but were much lower in 1996 (5.2 plants m−2). Long‐season corn hybrids and higherdensity corn populations increased corn silage and grain yield without reducing warm‐season grass stands. Within a season, no difference existed between corn grain yields when grown with either switchgrass (6.7 Mg ha−1 in 1995, 5.3 Mg ha−1 in 1996) or big bluestem (6.9 Mg ha−1 in 1995, 5.7 Mg ha−1 in 1996). Silage dry matter yield was not different between corn grown with switchgrass (12.6 Mg ha−1 in 1995, 16.1 Mg ha−1 in 1996) and corn grown with big bluestem (13.1 ha−1 in 1995, and 16.6 Mg ha−1 in 1996) for a given year. Switchgrass and big bluestem grown in corn with atrazine reduced land production losses during the establishment year, yet allowed adequate establishment of these grasses for future forage production.

Influence of corn (Zea mays) population and row spacing on corn and velvetleaf (Abutilon theophrasti) yield

Research was conducted to determine the optimum population and row spacing for corn production and for suppressing velvetleaf growth and seed production. Corn was grown in a factorial arrangement of three populations targeted at 64,000 (1 ×), 96,000 (1.5 ×), or 128,000 (2 ×) plants ha−1and two row spacings of 38 or 76 cm. Influences on corn were determined in weed-free plots, and influences on velvetleaf were determined for target plants established at 1.5–m intervals along the center of corn interrows. Four velvetleaf plantings were made at weekly intervals beginning at corn planting. Corn row spacing had little influence on corn or velvetleaf. Corn yield exhibited a parabolic response to population with a maximum of approximately 90,000 plants ha−1in one year, no response to population in another year, and a linear decline with increasing population in a dry year. Velvetleaf seed production was reduced 69 to 94% by the 1.5 × population and 99% by the 2 × population compared to the standard 1 × population when velvetleaf emerged with corn. Velvetleaf seed production was eliminated when velvetleaf emerged at or later than corn leaf stages 3, 5, and 6 for corn populations of 2 ×, 1.5 ×, and 1 ×, respectively. Reduced velvetleaf seed production was correlated with lower positioning of plants in the corn canopy and reduced light availability. Results suggest that higher corn populations could aid integrated weed management strategies by reducing seed production and limiting the build-up of weed populations.