Shoot and tiller regrowth in lucerne/grass pastures after two grazing durations : a thesis submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science (Honours) in the University of Canterbury [Lincoln College]

Abstract

Post grazing regrowth of lucerne shoots and grass tillers was compared in pure WL320 lucerne, lucerne with Maru phalaris and lucerne with Matua prairie grass, grazed for either short (5 day) or long (11 day) durations. In late summer/early autumn (from 13 March, 1989) after extreme drought, labelled shoots and tillers were measured at regular intervals. Late autumn/winter regrowth (from 12 May, 1989) was measured by cutting and drying shoots and tillers of the mean height. It was hypothesised that long grazing durations would favour lucerne in lucerne/grass mixtures because of the rapid recovery of grass tillers after defoliation and slow recovery of lucerne after rapid defoliation. In the late summer/early autumn regrowth period, lucerne and both grasses recovered more rapidly after short than long grazing duration. Lucerne shoots grew to 247 mm in the short grazing duration treatment but only to 205 mm after long grazing duration. Prairie grass tillers grew 261 mm in short compared to 222 mm in long grazing duration. Phalaris tillers grew to 178 mm in the short compared to 131 mm in the long grazing duration treatments. After 44 days lucerne shoots weighed 0.47g each in short and 0.35g in long grazing duration treatments. Prairie grass and phalaris tillers weighed 0.09g and 0.07g after short and 0.07g and 0.06g after long grazing durations respectively. Despite the difference in tiller length of prairie grass and phalaris, no significant difference in tiller grass weight occurred. This indicated that phalaris tillers and greater weight per unit length than prairie grass. Phalaris tiller populations were low ( 550 tillers m⁻²) compared to prairie grass ( 968 tillers m⁻² at 14 days post grazing. Pure lucerne had the most shoots (1313 shoots m⁻²), lucerne with phalaris was intermediate (1025 shoots m⁻²) and lucerne with prairie grass had the least shoots ( 950 shoots m⁻² ). At 45 days post grazing, long grazing duration treatments had a higher proportion of grass and a lower proportion of lucerne than short grazing duration. The late autumn/winter regrowth cycle gave more dry weight gain in prairie grass ( 0.07g tiller⁻¹) than phalaris ( 0.04g tiller⁻¹) by 117 days post grazing. Grazing duration did not have a significant effect on grass tiller regrowth. Lucerne shoot weight did not respond significantly to grazing duration or· pasture type over winter. This trial considered autumn and winter grazing cycles. A study of shoot and tiller regrowth in other seasons is required and this study needs to be repeated to ensure repeatability between years. The results from this trial suggest that for autumn, short grazing will favour both the grass and lucerne, giving higher yields than after long grazing duration. In winter lucerne and grass are unaffected by late autumn/early winter grazing duration.