Synopsis Plant size and yields of both alfalfa and birdsfoot trefoil were influenced by weed control treatments and seeding rates during the season of establishment. Pre‐emergence control of weeds increased first year yields of both legumes, had no effect on plant numbers but increased size of root‐crowns. Plants were larger at low seeding rates, particularly where weeds were controlled, and initial yields were comparable to those at higher seeding rates. Second year yields were influenced more by plant numbers than size of root‐crowns.

Establishment of legume‐grass mixtures on highway rights‐of‐way is complicated by the requirement that seedings be made over an extended period as construction proceeds and erosion control become critical. Permanent seedings are frequently required during the late spring‐early summer period and the late summer‐early fall period when weather conditions are likely to be critical and competition from grasses and weeds may severely retard legume growth. Studies were conducted to determine the competitive effects of three grasses, perennial ryegrass (Lolium perenne L.), Kentucky bluegrass (Poa pratensis L.), red fescue (Festuca rubra L.) and also weeds on establishment of birdsfoot trefoil (Lotus corniculatus L.) in the field at four times of the year, September, April, May and June. Plots were established on Enfield silt loam (mixed Typic Distrochrepts). Birdsfoot trefoil plant counts at the seedling and bloom stages showed that ryegrass was the most and red fescue the least competitive grass. Plant establishment of birdsfoot trefoil was significantly higher for the April seeding than for other seeding dates. Growth of birdsfoot trefoil was greater when seeded with Kentucky bluegrass or red fescue than when seeded with ryegrass. Weed competition reduced establishment of birdsfoot trefoil and growth of the legume at all seeding dates. When birdsfoot trefoil was grown alone, weeds produced more competing growth than grasses. However, grasses virtually eliminated weed growth. Reduced stands and yields of birdsfoot trefoil when grown with perennial ryegrass appeared to be due to rapid seedling emergence of the grass at a critical stage in the early growth and development of birdsfoot trefoil. The slower growing grasses, Kentucky bluegrass and red fescue, did not inhibit growth of birdsfoot trefoil since yields were comparable to the legume grown alone. An exception was the September seeding when winter‐killing severely depleted stands of birdsfoot trefoil grown alone.

Suppression of woody plants by grasses has been widely reported; but few studies have investigated the factors responsible for the reduced growth and poor appearance often shown by ornamental trees and shrubs planted in association with turfgrass. This research was undertaken to determine the major factors responsible for this phenomenon. A field study, conducted over two growing seasons, evaluated the growth of flowering dogwood (Cornus florida L.) and forsythia (Forsythia intermedia Spaeth.) planted in established sod (Enfield silt loam soil, Typic Dystrochrept). Treatments included different sized areas of turf‐free space (0.3m2, 0.7m2, and 23.7m2), surface and subsurface placement of fertilizer and irrigation, and two mowing heights (10 cm and 4 cm). Turfgrass significantly reduced the growth of both woody species. Although supplementary fertilizer, applied as a topdressing, failed to benefit the ornamentals, subsurface treatments resulted in considerable increases in growth. Competition for moisture did not appear to be responsible for the observed differences in growth, since maintaining a high level of soil moisture failed to overcome the inhibitory effects of the turfgrass. Competition for N, however, was indicated by results of leaf tissue analysis. A bioassay experiment tested the hypothesis that the competitive nature of turfgrasses involves an allelopathic mechanism. Aqueous leachates of the roots of perennial ryegrass (Lolium perenne L.), red fescue (Festuca rubra L.), and Kentucky bluegrass (Poa pratensis L.) were applied to rooted cuttings of forsythia. Top growth of the forsythia was inhibited by leachates from all three turfgrass species. Root growth was suppressed by ryegrass and red fescue leachates. Results of these experiments indicate that the suppression of woody plants by turfgrasses may involve chemical inhibition as well as direct competition for available N.

Planting of a shrub or tree into a mature grass sod may result in poor establishment of the woody species. This experiment was designed to measure the field response of four species of ornamental shrubs to turfgrass competition. The shrubs used were forsythia (Forsythia intermedia zabel), azalea (Rhododendron X), Japanese barberry (Berberis thunbergi DC.) and taxus (Taxus media Rehd.). Turfgrass treatments included plots maintained at high or low rates of N fertilizer and receiving, in some cases, supplemental irrigation to maintain high soil moisture. Treatments with no turfgrass were either bark mulch or bare ground. Turfgrass plots were mowed regularly to a height of 7.6 cm. The effects of these variables were measured by evaluating several aspects of growth and development of each shrub species. Turfgrass established 2 years previously on an Enfield silt loam (Typic Distrochrepts) significantly suppressed the growth and development of all four species of shrubs as compared to plots where turfgrass was not a competitor. Differences in soil moisture or temperature are not believed to have been responsible for the differences observed in these findings. Plant competition for N was suggested by both the color ratings and analyses of leaf tissue of the shrubs during the first year of shrub establishment. Additional fertilizer, applied as a topdressing, was more beneficial to the turfgrass than to the shrubs, and did not significantly increase their growth in most cases. The addition of K and P did not increase growth in any of the treatments and apparently was not a factor in the competition between the grass and the shrubs.

Consistently successful legume establishment using sod‐seeding techniques has been difficult to achieve. There is increasing evidence that substances released from herbicide‐treated grass swards have an inhibitory effect on legume germination and seedling growth. Field, greenhouse, and laboratory studies were undertaken to evaluate the effect of spray/planting intervals of 1, 7, 14, and 28 days on the establishment of alfalfa [Medicago sativa] when seeded into sods of orchardgrass [Dactylis glomerata L.] timothy [Phleum pratense L.], and Kentucky bluegrass [Poa pratensis L.], and to examine a possible phytoxic effect of glyphosate [N(phosphonomethyl) glycine] on germination and sod seedling growth of alfalfa. Identical field tests were conducted in the spring of 1981 and 1982 on an Enfield silt loam (coarse‐silty over sandy or sandy skeletal, mixed, mesic Typic Dystrochrept). With few exceptions, the number of alfalfa seedlings, seedling development and alfalfa yields increased as the interval increased between spraying of the sod and seeding. Rate of alfalfa seedling development was reduced in all sods, with timothy being the most inhibitory. Two harvests of alfalfa following seeding confirmed that yields were reduced by killed sod, particularly in orchardgrass and timothy, at early intervals after spraying. There were significant positive correlations between seedling numbers and first harvest yields and between seedling development and first harvest yields of alfalfa. Alfalfa germination was inhibited, seedling development was delayed and total dry weight was reduced when glyphosate‐sprayed grass shoot tissue was soil incorporated in growth chamber seeding tests. However, unsprayed fresh grass tissue was more inhibitory than sprayed grass tissue. Alfalfa germination and hypocotyl and radicle length were reduced by aqueous extracts from glyphosate‐sprayed grass shoot tissue but less so than with extracts from unsprayed herbage. No evidence for a phytotoxic effect of glyphosate could be detected, and it appeared that the inhibition of alfalfa germination and seedling growth was due to allelochemics released from fresh herbage and during the early stages of decomposition.