The effect of haloxyfop-R-methyl ester and imazamox herbicides, tine or no tillage and nine different medic cultivars on the seed and dry matter production as well as the quality of medic pastures

[摘要] ENGLISH ABSTRACT:The aim of this study was to determine the effect of a grass herbicide, abroadleaf herbicide with some grass control capabilities, method of tillage (tineand no-tillage) at planting of wheat as well as different medic cultivars on theregeneration, dry matter (OM) production and quality of a medic pasture.The trial was conducted at Langgewens experimental farm in the Swartlandwheat producing area. Nine medic cultivars of three different species wereevaluated after being sprayed with either haloxyfop-R-methyl (HAL) ester orimazamox (IMI) and subjected to either a tine tillage or a no tillage treatment atplanting of wheat. Soil samples were taken during January 2000 to determine thesize of the medic and weed seedbank as well as the degree of dormancy in themedic seeds, while OM samples were taken throughout the growing season todetermine the OM production of the different medic cultivars and weed species.OM samples taken during October 1998 on the same pasture, were used todetermine the crude protein (CP) and neutral detergent fibre (NOF) content of thepasture. The samples were subjected to in vitro digestion and the digestibility ofpasture CP (OCP), NOF(ONOF) and DM (DOM)were determined.Results showed that seedling establishment differed between cultivars used,herbicide treatments applied as well as the crop stage in the rotation. Thecultivars produced more seedlings where IMI was applied compared to HAL aswell as where the area consisted of two year pasture compared to one yearpasture (1998) and one year wheat (1999). After a year of pasture and a year ofwheat, cultivars Sephi and Paraggio produced the most seedlings, while Caliphand Orion produced the least. Caliph however, showed a very high degree ofseed dormancy while Orion's low seedling establishment was due to itssensitivity to the IMI herbicide used.Little difference was found between the nine cultivars early in the season (July -August) with regard to cumulative OM production, except for Orion, whosegrowth was severely damaged by the IMI treatment. At the end of the growingseason (October), the cultivar Caliph's cumulative OM production (2010.1 kg/ha) was significantly higher than all the other cultivars, except for Parabinga (1053. 4kg/ha).Oifferent pasture samples, of which the botanical composition was known, wasanalysed for CP, NOF, OOM, OCP and ONOF. There was no significantdifference in pasture composition during 1998 but variation in the pasturecomposition did however cause the IMI treatment, compared to the HALtreatment, to have a lower ONOFand OOMcontent. A modelling procedure wasused to predict the pasture quality parameters (CP, NOF, OOM,OCP and ONOF)from the pasture composition (medic hay, medic pods, grassy and broadleafweeds). This prediction of CP, NOF, OOM, ONOF and OCP from the pasturecomponents had a relative low accuracy (49 -74.1 %) and a further refinement ofthis model for possible use on farms in order to improve grazing managementand animal production is advised.In conclusion it could be said that broadleaf weed control caused a definiteincrease in medic seed and OMproduction, but Orion should not be used with anIMI herbicide. All the cultivars, except for Orion, produced enough seedlings upto the second year to ensure sustainability of the medic pasture. All the cultivars,except for Orion, produced a sufficient amount of OM early in the growingseason. Caliph however, produced by far the most OM later in the growingseason.A reduction of broadleaf weeds and medic pods will increase the digestibility ofNOFand OMand therefore increase the quality of the pasture. Pods however arean important part of summer forage and the aim should therefore rather be toreduce the number of broadleaf weeds in the pasture.

[发布机构] Stellenbosch University