Effects of pre-sowing herbicide and subsequent sward mass on survival, development, and production of autumn oversown Wana cocksfoot and Tahora white clover seedlings

Abstract

Although oversowing new grass and legume cultivars offers potential for development of hill country, the success of this technique is variable. The objective of this experiment was to assess the effect of pre-sowing herbicide and subsequent grazing management on autumn oversowing into dense, hill country pastures. Three herbicide treatments (paraquat, glyphosate, and unsprayed) and four spring grazing treatments (average cover of 500, 1000, 2000, and 3000 kg DMI ha) were compared. In general, 'Grasslands Wana' cocksfoot (Dactylis glomerata L.) and 'Grasslands Tahora' white clover (Trifolium repens L.) seedlings were more numerous (490 Wana 1m 2 and 90 Tahora 1m 2 versus 35 Wana 1m 2 and 40 Tahora 1m2), larger (6-12 tillers or stolonslplant versus 1 tiller or stolon/plant), and more productive in herbicidetreated than unsprayed swards. Lax grazing ( about 3000 kg DM/ha) did not influence the survival of seedlings during spring, but resulted in smaller cocksfoot and clover seedlings. Rapid growth of these seedlings occurred after uniform grazing (release from competition) and resulted in few subsequent differences in plant size and contribution of Wana to pasture production. Once established, Wana and Tahora seedlings were tolerant of a range of grazing conditions, but with the high fertiliser input in this trial, did not appear to benefit annual production. A92057

Changes in plant population density, composition and sward structure of a hill pasture during a pastoral fallow

“…As both herbicide spraying and pre-sowing defoliant techniques present problems for oversowing, more appropriate techniques are sought for hill pasture improvement (Barker and Dymock, 1993). A pastoral fallow was expected to reduce plant density and create a favourable environment for oversowing.…”

“…McCallum et al (1991) showed that pastoral fallowing (or deferred grazing) improved perennial ryegrass contribution to yield by enhancing natural reseeding of this species, and increased pasture growth by 15-19% in the year following the fallow. Barker and Dymock (1993), reported on the management requirements for the successful establishment of one of the slowestablishing species, cocksfoot, and suggested that a pastoral fallow, rather than herbicide spraying, might bare the soil surface sufficiently, to allow germination and establishment of this slow-growing species.…”

“…The introduction of improved forage legume and grass germplasm is one tool for improving the pattern of forage supply of a typically dense hill pasture low in legume content and dominated by low-fertility grasses. Although herbicide defoliation is not essential for successful oversowing of rapidly germinating species, such as perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) (Chapman et al, 1985;Johnson et al, 1993), it is essential for successful establishment of slow-establishing and -growing species, such as cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea L.) and phalaris (Phalaris aquatica L.) (Chapman et al, 1985;Barker and Dymock, 1993). However, the use of herbicide as a tool for reducing competition from the resident species is limited, because of the cost of defoliants and their application in hill country and, to a lesser degree, the risk of soil loss, invasion by undesirable plant species and the growing environmental concerns regarding chemical use.…”