Alfalfa Stands Research Articles

Herbicides for Sod-Seeding Establishment of Alfalfa (Medicago sativa) in Quackgrass (Agropyron repens)-Infested Alfalfa Swards

The herbicides 2,4-D [(2,4-dichlorophenoxy) acetic acid], dalapon (2,2-dichloropropionic acid), glyphosate [(N-phosphonomethyl)glycine], paraquat (1,1’-dimethyl-4,4’-bypiridinium ion), and pronamide [3,5-dichloro-(N-1,1-dimethyl-2-propynyl)benzamide] were applied at selected rates and dates to quackgrass [Agropyron repens(L.) Beauv. ♯ AGRRE]-infested alfalfa (Medicago sativaL.) sod in 1979 and 1980 to suppress vegetation for subsequent establishment of alfalfa without tillage. The influence of herbicides on weed control, alfalfa seedling density and visual stand, and forage yield and quality was assessed for 3 yr. During establishment, all herbicides except 2,4-D effectively controlled quackgrass. Glyphosate applied broadcast increasingly suppressed the existing sod as the rate was increased from 0.6 to 1.6 kg ai/ha. The effectiveness of herbicides as measured by total (old and new) plant density was closely related to the suppression of the sward. While the substitution of new alfalfa plants for old ones was not necessary under dense (40 plants/m2) alfalfa stands, completely controlling the vegetation with glyphosate resulted in sustained productivity throughout the experimental period. After 3 yr, alfalfa percentage and yield were highest when glyphosate was broadcast at 1.6 kg/ha. Improvement in forage quality, as estimated by the concentrations of crude protein and neutral-detergent fiber, was closely related to grass control.

EFFECT OF WEED CONTROL AND A COMPANION CROP ON ALFALFA AND SAINFOIN ESTABLISHMENT, YIELDS AND NUTRIENT COMPOSITION

Alfalfa and sainfoin were sown in 1978, 1979, and 1980 on irrigated land at the Lethbridge Research Station. The forages were established using herbicides for weed control, no weed control, or a barley companion crop. Weed control treatments were applied only during the establishment year (year 1). Alfalfa yields, averaged from the three seedings, were 360 and 200 g/m2 greater during year 1 and year 2, respectively, when diclofop plus 2,4-DB was applied than when the companion crop was grown and no weed control was used. Weed yields were greater in years 2 and 3 where alfalfa was established in competition with weeds or companion crops than where weeds were controlled. Alfalfa yields were similar for all treatments in years 3 and 4. Year 1 treatments in sainfoin produced yield differences similar to those described for alfalfa; however, sainfoin yields tended to be smaller and weed yields larger. Year 1 and year 2 forages with high weed contents have acceptable nutrient composition but may not be saleable as hay or silage or to the dehydration industry. The seeding of pure stands of alfalfa on irrigated land using herbicides for weed control produced sufficient high quality forage, in year 1, to make this practice a viable alternative to seeding with a companion crop.Key words: Alfalfa, sainfoin, 2,4-DB, diclofop, MCPB, fiber, protein

Fall No‐Till Seeding of Alfalfa into Tall Fescue as Influenced by Time of Seeding and Grass and Insect Suppression1

AbstractHigher nitrogen and pasture renovation costs have increased interest in no‐till seeding of legumes into grass pastures, but improved technology is needed for direct establishment of legumes in grass sods. This study was undertaken to quantify and evaluate the effects of seeding date, sward suppression, and insect pests on fall no‐till establishment of alfalfa (Medicago sativa L. cv. Arc) into tall fescue (Festuca arundinacea Schreb.)‐dominant swards. Six field experiments of 1 year duration each were conducted during a 5‐year period on either a Typic Hapludult or Ultic Hapludalf soil in the Piedmont of North Carolina. Paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion) for grass suppression and granular carbofuran (2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranyl methylcarbarnate) for insect control either were not applied or were applied at 0.28 and 3.7 kg active ingredient (a.i.) ha−1, respectively, at two seeding dates (early September and mid‐October) in a 23 factorial combination. Three additional sodsuppression treatments (two trials) included (1) application of paraquat to 13 cm‐wide bands over 25.4‐cm rows at 0.28 kg a.i. ha−1, (2) broadcast application of glyphosate [N‐(phosphonomethyl) glycine] at 3.4 kg a.i. ha−1, and (3) post‐sowing clipping and removal of the fescue regrowth. Insects prevalent during establishment were identified and measurements were made of alfalfa stands, insect damage, winter survival, and dry matter production. Seasonal yields of September seeded alfalfa were increased 76 and 20% by sward and insect suppression during establishment, respectively (average six experiments). Insect damage was greater in early September plantings than in mid‐October plantings. Sward suppression and insect control interacted accumulatively under conditions of intensive insect feeding and moisture stress during establishment. Even though 50 to 100% of October‐seeded alfalfa in control plots had not advanced beyond the two‐trifoliolate‐leaf stage of development by early December, good winter survival occurred. We conclude that suppression of tall fescue was essential for best establishment and 1st‐year production of alfalfa and that insect control must be practiced in September no‐till plantings of alfalfa in some years.

Alfalfa Yield Response to a Between‐Cutting Contact Herbicide1

Alfalfa (Medicago sativa L.) fields sometimes develop weed infestation problems when conditions at harvest favor germination of weed seeds or when the stand begins to thin and lose vigor. A recently approved label for use of the contact herbicide paraquat (1,1′,dimethyl‐4, 4′‐bipyridinium ion) allows application between cuttings for weed control. Label directions require application of no more than 0.28 kg ha−1 within 5 days after cutting. The net result of this practice is increased yields of alfalfa if effective weed control is achieved. Our studies with weed‐free alfalfa stands indicated a 7.8% yield reduction caused by paraquat applied within 5 days after hay harvest. A greater reduction might have occurred if treatment was delayed beyond 5 days. This slight harmful effect was expressed only in the first cutting after treatment of weed‐free stands and always greatly offset by control of weeds in weedy alfalfa stands. The benefit from between‐cutting paraquat treatment was positively related to the degree of weed infestation. Alfalfa yields in two harvests following the between‐cutting paraquat treatment were increased by 2.40 Mg ha−1 as compared with nontreated weedy plots. In an old weedy alfalfa field, yields of alfalfa were increased three‐fold with a 70% decrease in weed composition for the first harvest following treatment. The weed control benefit was also observed in the second harvest after treatment. Stand longevity and sustained high yields should prove to be additional advantages to the practice of between‐cutting weed control using paraquat.

N 2 Fixation, and N and Dry Matter Partitioning During a 4‐Year Alfalfa Stand 1

N ₂ Fixation, and N and Dry Matter Partitioning During a 4‐Year Alfalfa Stand ¹

ESTABLISHMENT AND SUBSEQUENT PRODUCTIVITY OF BROMEGRASS AND ALFALFA SEEDED WITH AN ARGENTINE RAPESEED COMPANION CROP IN NORTHEASTERN SASKATCHEWAN

Yields of pure stands of alfalfa (Medicago media Pers.) and bromegrass (Bromus inermis Leyss.) established on summerfallow with and without an Argentine rape-seed (Brassica napus L.) companion crop were compared at Melfort in three tests, each maintained for 4 yr. In all three experiments, yields over the 4-yr period were greater when the forage was established alone, and in two of the three, bromegrass produced more than alfalfa. When established with rapeseed, forages produced much less dry matter in the seedling year than when established alone, and the effects of the companion crop carried over into the following year. Thereafter, the yield differences between the two establishment methods were small and in the final year had disappeared. Argentine rapeseed suppressed forage seedling growth more in the 2 yr with average or cool summers, than in the year with a hot summer. Alfalfa was more severely suppressed than bromegrass in the year with the best growing season.Key words: Bromegrass, alfalfa, rapeseed, companion crops, forage yield, forage establishment

Controlling Weeds in Dormant and Nondormant Alfalfa (Medicago sativa)

When applied in early February, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], pronamide [3,5-dichloro-(N-1,1-dimethyl-2-propynyl)benzamide], secbumeton [N-ethyl-6-methoxy-N′-(1-methylpropyl)-1,3,5-triazine-2,4-diamine], and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] effectively removed weedyBromusspecies from established alfalfa (Medicago sativaL.) and increased yields of alfalfa forage. Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], terbacil (3-tert-butyl-5-chloro-6-methyluracil), and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine- 2,4(1H,3H)-dione] had no adverse effects on yields of alfalfa when applied in late March. Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was somewhat less effective for controlling weeds when applied in late March than when applied in February. When applied to weed-free stands of alfalfa after dormancy was broken, metribuzin, terbacil, hexazinone, and simazine, but not pronamide, significantly reduced yields of alfalfa. Terbacil applied immediately after the first cutting did not significantly reduce yields of the second cutting. Terbacil and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] applied when alfalfa had 5 cm of regrowth significantly reduced yields.

Sulfur fertilization of two aquic hapludalf soils: I. Effect on alfalfa yield and quality

Abstract Alfalfa is rapidly increasing as a cash forage crop on the more arable soils in south central Missouri. These soils are natively acid and low in fertility having formed from loamy, sandy and cherty alluvium found in the bottom land areas, under forest vegetation with native grasses in the open areas. The two experimental sites selected were recently established alfalfa stands, Site I was under irrigation and Site II nonirrigated. Two S materials (SO4‐S and elemental S) at rates of 0, 34 and 68 kg S ha‐1 in 4 replications were applied. Yields, plant S, crude protein and IVDMD were measured for individual harvests in 1980 and 1981. Alfalfa yields were not increased at both locations with S fertilization. Forage S content was significantly increased and the N/S ratio significantly decreased on the higher yielding irrigated alfalfa, but not with the nonirrigated alfalfa. Forage S levels of 0.19% S and N/S ratio of 17.9 during dry year did not result in yield increase when S fertilized. There was obse...

BROMEGRASS AND ALFALFA ESTABLISHMENT WITH A WHEAT COMPANION CROP IN NORTHEASTERN SASKATCHEWAN

Yields of pure stands of alfalfa (Medicago media Pers.) and bromegrass (Bromus inermis Leyss.) established on summer fallow with and without a wheat (Triticum aestivum L.) companion crop were compared at Melfort in three tests, each maintained for 4 yr. In two experiments out of three, yields over the 4-yr period were greater when the alfalfa or bromegrass was seeded alone; bromegrass produced more dry matter than alfalfa. Both forages produced much more dry matter in the seedling year when seeded without a cover crop, and this effect carried over into the first harvest year. In the second and third crop years, bromegrass seeded with wheat produced more dry matter than when seeded alone, whereas seeding method had no significant influence on alfalfa production. Seeding the wheat at 50 kg/ha, half the normal rate, did not improve forage establishment significantly, and made no consistent difference in the amount of grain produced. In all three experiments, soil fertility was high, and moisture was adequate for seedling establishment. It is argued that low light levels under the companion crop were the primary cause of poorer seedling growth in these conditions.Key words: Bromegrass, alfalfa, spring wheat, companion crops, forage yield, forage establishment

Rhizobium meliloti distribution in the soil following alfalfa inoculation

Alfalfa seeds, inoculated with an antibiotic-resistantRhizobium meliloti strain, were planted in three replicated field plots at Clayton, N.C. Core samples were taken three times in the next year at 0, 10, and 20 cm from the edge of each plot. Soil subsamples were taken from within each core sample at 0, 6, 12, and 18 cm depths. The numbers of the inoculum Rhizobium strain in each soil subsample were determined by inoculation of alfalfa plants with diluted soil samples. In general the distribution of rhizobia showed some movement outward and downward in the soil. Lower counts were obtained at the surface during summer. The Rhizobium persistence pattern in the soil differed in the three plots which is consistent with the variability in Rhizobium numbers often observed in established alfalfa stands.

THE IMPORTANCE OF LEAF FROST RESISTANCE TO THE WINTER SURVIVAL OF SEEDLING STANDS OF ALFALFA

Plants propagated from single plant selections of the alfalfa cultivars Saranac and Luna (Medicago sativa L.), Beaver (M. media Pers.) and Anik (M. falcata L.) were transplanted into the field in May and subjected to a range of freezing temperatures at 3-wk intervals during August and September. A portable field freezing chamber was used to study the influence of frost on leaf injury in the fall and winterkill following the severe 1977–1978 winter. Leaves of all plants had the capacity to harden during the fall, but the selection from Anik was consistently the most frost hardy. Temperatures ranging from −4 to −5 °C in mid-August caused 50% leaf injury to the selections of Beaver, Saranac and Luna, while in late September, temperatures ranging from −9.5 to −10.5 °C were required to produce similar amounts of injury. In the Anik selection, −6 °C in mid-August caused 50% leaf injury, but in late September −12.5 °C caused less than 35% injury. Thus, the Anik selection appeared to start hardening about 3 wk earlier than all other selections. In all plants, the potential for winter injury during the 1977–1978 winter increased as a result of leaf frost damage during mid-August and early September in 1977. The application of these results to the winter survival of seedling stands of alfalfa is discussed.

Alfalfa, Second and Third Cutting Insect Control, Missouri, 1981

Abstract Two locations served as tests sites for potato leafhopper control on established stands of alfalfa. One test was conducted on Jul 8 at Salem, MO on second cutting alfalfa and another at Spickard, MO on Aug 26 on third cutting alfalfa. Evaluations were made 24 h after treatment application. Finished sprays were applied to plots at 12 gpa and 40 psi. An IH cub tractor rigged with a 20 ft spray boom, FS-4 nozzles, 50 mesh filter screens, and a PTO roller pump was used to apply compounds. Temperature at treatment was 80°F at Salem and 75°F at Spickard. Overnight rainfall accumulation was 0.35 in at Spickard. Alfalfa was approximately 10 inches tall. Efficacy evaluation was made by sub-sampling plots with 10 sweeps per plot. Each sweep of a 15 inch net was 180° while moving briskly forward. Each treatment was replicated 4 times. Means present in table are of actual counts.

Pre-Plant Systemic Insecticides for Fall Alfalfa Stand Establishment, 1981

Abstract Furadan was used as soil-incorporated prep I ant treatments to assess the benefit of using systemic insecticides in fall planted alfalfa stand establishment. Experiments were conducted at the Rosemount Agricultural Experiment Station, Dakota Co., MN, on Waukegan silt loam. Treatments were applied Jul 30 to 54 x 40 ft (0.05 acre) plots randomized in a complete block design with 3 replications. Alfalfa was seeded Jul 31 at a rate of 10 lb/acre. Granular applications were made by a Ortho-Whirlybird manual applicator and spray applications were made by tractor-drawn boom sprayer in 27 gal/acre at 100 psi pressure. Insect populations were sampled Sep 1 and Sep 24 using a vacuum machine by taking 15 putdowns-of a 20.3 cm vacuum hose (equivalent to 0.48 m2). Stand counts were taken Sep 11 by counting the number of plants in 10 one ft2 samples/plot.

SOME RESPONSES OF ALFALFA–BIRD’S-FOOT TREFOIL MIXTURES TO SEEDING YEAR MANAGEMENT

The effect of different seeding ratios, drainage conditions, and seeding year harvest management practices on control of alfalfa (Medicago sativa L. ’Iroquois’) competition in mixtures with bird’s-foot trefoil (Lotus corniculatus L. ’Leo’) were investigated in four field experiments. Near-optimum temperature and moisture conditions prevailed for alfalfa growth during the study. As a result, alfalfa plants grew larger and outcompeted the trefoil even on drainage conditions that favored the survival of trefoil and reduced alfalfa stands. When the seeding ratio of alfalfa to trefoil was low, alfalfa compensated by producing larger plants and dry matter yields. The contribution to trefoil to yield was only marginally improved by increasing the proportion of trefoil in the mixture, by raising the cutting height, and by cutting the mixtures at the bud stage of alfalfa development.

Preemergence Systemic Insecticides for Establishment of New Alfalfa Seedings, 1979

Abstract Furadan insecticide was applied as preplant incorporated soil applications to a new planting of alfalfa in spring seeding. These applications were made with both granular and liquid formulations to assess not only the insecficidal benefit of establishing new stands of alfalfa but the effect on stand, reduction of seeding rate, yield, and spectrum of insect control. At planting incorporated broadcast treatments were mode to the seed bed after Eptam and fertilizer were incorporated into the topsoil. Treatments were applied May 11’79 to plots 3 × 15 ft randomized in a complete block design with 3 replications. Granular applications were made with a hand held shaker can combining seed amount and insecticide with a small amount of sand added and thoroughly mixed to aid even distribution of mixture. Liquid Furadan 4F applications were sprayed on with a CO2 bottle sprayer at a volume of 30 GPA after seeding. All treatments were then raked lightly to incorporate seed and treatments into the well fitted soil. Three rates of alfalfa seeding (10, 15 and 20 lb) were used with Furadan 10G. Stand populations were sampled twice with post treatment insect samplings done at 75 days using 5-180° insect sweep net collections per plot. Yields were sampled at 75 days by taking square foot samples out of plot centers and weighing all the cut hay to determine green weights.

Frost Heaving in Alfalfa Establishment on Soils with different Drainage Characteristics1

AbstractThe susceptibility of alfalfa (Medicago sativa L.) to frost heaving is a major problem in stand establishment in southern Illinois. This study was conducted at Carbondale, Illinois, to determine the effects of frost heaving on the establishment and production of alfalfa cultivars in relation to soil drainage characteristics. Four alfalfa cultivars (‘Cody’, ‘Spredor’, ‘Weevlchek’, and ‘WL‐307’) were seeded on three soil series, a deep well‐drained AIford (Typic Hapluadalf, fine‐silty mixed mesic), a moderately well‐drained Hosmer (Typic Fragiudalf, fine‐silty, mixed, mesic) with a fragipan starting at a depth of 60 to 70 cm, and a nearly level poorly‐drained Weir (Typic Ochraqualf, fine, montmorillonitic, mesic). Piezometers were installed in each soil to monitor the presence of perched water tables and their position to the soil surface. Small wooden dowels were used to assess soil movement in relation to alfalfa seedling heave. The higher amount of heaving as measured by the distance wooden dowels were raised above a reference point occurred when the night temperature was a few degrees below freezing and the day temperature was above freezing, with a perched water table near the soil surface. Poorly‐drained, Weir soil had the highest perched water table, most alfalfa seedling heave, greatest alfalfa seedling winterkill, and most dowel heave. In contrast, well‐drained Alford series had no perched water table, no appreciable seedling heave or winterkill, and least dowel heave. No significant differences in amount of frost heaving of seedlings were noted amonga alfalfa cultivars on any drainage site. Highest dry matter yields were obtained on the well‐drained Alford site; significant yield reductions occurred as soil drainage class became more poorly drained. Alfalfa stands were successfully established on the well‐drained Alford series and the moderately well‐drained Hosmer series. Soil drainage characteristics did influence alfalfa establishment and production in the climatic transitional zone of the central U. S. Poorly‐drained soils should not be considered for alfalfa production.

Quackgrass(Agropyron repens)Control in Established Alfalfa(Medicago sativa)With Pronamide

The degree and longevity of quackgrass [Agropyron repens(L.) Beauv.] control provided by autumn applications of pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] was influenced greatly by alfalfa(Medicago sativaL.) stand density, as well as by rate of application and soil type. When applications were made to a field with a sparse alfalfa stand (10 to 20 crowns/m2), quackgrass yields were reduced the year following pronamide application, but quackgrass reinfested the plots the second year after treatment. Quackgrass yields one and two seasons following autumn treatment with 2.2 kg/ha pronamide were 1480 and 3890 kg/ha compared to 4480 and 4870 kg/ha for control plots. Annual applications of pronamide were necessary to maintain quackgrass control in the sparse alfalfa stand. Pronamide application to a vigorous, dense alfalfa stand (40 to 50 crowns/m2) provided quackgrass control which persisted into the second year after treatment. Quackgrass control ratings one and two seasons after application of 1.1 kg/ha pronamide were 100 and 90%. Pronamide treatments reduced first cutting quackgrass yields, and increased first cutting alfalfa yields. Treatment of the sparse alfalfa stand with 2.2 kg/ha pronamide resulted in first cutting alfalfa and quackgrass yields of 2420 and 990 kg/ha compared to 1430 and 3940 kg/ha for controls. Treatment of a dense alfalfa stand with 1.1 kg/ha pronamide resulted in first cutting alfalfa and quackgrass yields of 3850 and 300 kg/ha compared to 1710 and 1660 kg/ha for controls. Total herbage yields from all cuttings were either slightly decreased when fields with sparse alfalfa stands were treated or remained constant or slightly increased when more dense alfalfa stands were treated. Pronamide applied with potash as the carrier was as effective as when applied in water. Pronamide treatment resulted in increased crude protein concentration in first cutting herbage at all locations in all years. Crude protein concentration in first cutting control herbage ranged from 13.3 to 16.1%. Crude protein concentration in first cutting herbage from plots treated with 1.1 kg/ha pronamide ranged from 17.7 to 20.6%, depending on year and location. In vitro digestible dry matter (IVDDM) concentrations were increased by most rates of pronamide in first, second, and third cutting herbage. IVDDM for first cutting control herbage was 51.4% compared to 61.3% for herbage treated with 2.2 kg/ha pronamide. Acid detergent fiber concentration in first cutting herbage was not affected by pronamide.

Influence of 2,4‐D, Pronamide, and Simazine on Dry Matter Production and Botanical Composition of an Alfalfa‐grass Sward1

Pronamide [3,5‐dichloro (N‐l,l‐dimethyl‐2‐propynyl)‐benzamide], simazine [2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine], and 2,4‐D [(2,4‐dichlorophenoxy)acetic acid] were evaluated for management of species composition in established swards of alfalfa (Medicago sativa L.) which had become colonized by orchardgrass (Dactylis glomerata L.), Kentucky bluegrass (Poa pratensis L.), and dandelion (Taraxicum officinale Weber). Dormant application of 2,4‐D ester reduced seedling dandelions, but did not affect mature dandelions, alfalfa stands, or yields. Simazine did not affect total yield or botanical composition of forage in this study. Pronamide application reduced bluegrass and total forage yield in the first harvest. The alfalfa component of the forage and total yield of alfalfa increased with pronamide treatments. Total forage yield for the season was the same for all treatments.Counts of alfalfa plants per m2 were made for individual plots and multiple regression analysis was used to determine the association of percent alfalfa composition of the first harvest and plant density with alfalfa yield. In pronamide treated plots as few as 10 to 20 alfalfa plants per m2 utilized resources made available by reduction of other species and produced acceptable yields. These results contrast to the 50 to 60 plants per m2 commonly considered necessary for productive stands and suggest the possibility that herbicides may be used to extend the productive life of swards containing alfalfa.

Effects of Potassium Topdressing a Low Fertility Silt Loam Soil on Alfalfa Herbage Yields and Composition and on Soil K Values1

AbstractAlfalfa (Medicago sativa L.) uses large amounts of soil K. The purpose of this study was to determine the amount of topdressed K needed to obtain maximum herbage yields from alfalfa under presently recommended harvest schedules. ‘Ranger’ alfalfa was established on a low K Typic Argiudoll (Plano silt loam) and topdressed the first two of three harvest years with zero, 56, 112, 224, 448, 672, 896, and 1120 kg/ha K as KCI. Two annual harvest schedules were used; (a) three cuts at first flower and (b) same as (a) plus an early October cut (4 cuts). Yield responses were similar for the two harvest schedules, but 3‐year average yields were highest with three cuts annually. Residual yields and stands showed that the detrimental effect of an early October cut (4 cuts) was partially alleviated by high K topdressing rates. The 3‐year average yields were highest with 672 kg/ha of topdressed K, and then decreased at higher K rates. Herbage K percentage at 672 kg/ha K averaged 2.8% for the 3 harvest years, and 56% of the fertilizer K was recovered in the herbage. Analysis of total herbage from the third harvest year showed that Mn concentration, as well as K, increased as K topdressing rate increased, whereas concentrations of N, P, S, Ca, Mg, Na, Cu, Zn, and B decreased. There was no effect on IVDDM, Fe, and AI concentrations. It is concluded that higher rates of applied K are needed than presently are being used in order to obtain and maintain high herbage yields and persistence from alfalfa stands.

Effects of Weed Control and N Fertilization at Establishment on the Growth and Nodulation of Alfalfa1

AbstractThe establishment of productive alfalfa (Medicago sativa L.) stands is greatly dependent on competition by other plant species and on the seedling development of the forage legume. The objective of this study was to determine the effects of weed control methods in combination with N fertilization rate on seedling growth and nodulation of alfalfa. ‘Saranac’ alfalfa was established on check (no weed control), handweeded, and herbicide 4‐(2,4‐ dichlorophenoxy)butyric acid + 2,2‐dichloropropionic acid (2,4‐DB ‐f‐ dalapon) plots with N applied at 0, 25, 50 or 100 kg/ha at emergence of the forage legume. Dry matter (DM) yields of alfalfa in the first cutting were significantly increased by N applications of 25 to 50 kg/ha over the check in two out of three experiments. Nitrogen applied at seeding did not influence the DM yields of the second cutting. On plots treated with 2,4‐DB and dalapon, the DM yields of alfalfa in the first cutting were 30 to 81% and 11 to 78% of those of check and handweeded plots, respectively. In the second cutting, DM yields of alfalfa were not affected by the method of weed control. Weed growth was significantly increased by applied N in one experiment only.Nodule size was reduced by N applications of 50 and 100 kg/ha. Similarly, the number of nodules per plant was decreased in one experiment. Percent total N of alfalfa tissue was increased by applied N in the first cutting of two experiments. In the second cutting, high N rates resulted in a lower N content of alfalfa tissue which coincided with poor nodulation. The N rate ✕method of weed control interactions for most criteria were not statistically significant.