|dc.description.abstract||Mixtures of WL 320 lucerne (Medicago sativa L.) with Matua prairie grass (Bromus willdenowii Kunth) or Maru phalaris (Phalaris aquatica L.) were compared with pure lucerne over a one and half year period. Two grazing duration treatments were compared: short grazing duration (three to seven days) and long grazing duration (six to 14 days) to give a 3 x 2 factorial randomized block design laid down in four replications with plots of 0.042 ha. Pasture seeds were drilled into Templeton silt loam in 15 cm rows on November 7, 1986 at rates of 32, 8 and 7.5 kg/ha for Matua prairie grass, Maru phalaris and lucerne. Grasses were sown across the lucerne rows. Limited irrigation (25 mm + 40 mm) was applied 43 days and 66 days after sowing to supplement the lower than average summer rainfall. No irrigation was used after grazing commenced. The 144 day establishment phase ranged from the sowing date (November 7, 1986) to the commencement of the first grazing duration treatment (April 1, 1987). All plots were grazed in common for seven days from January 25 to January 31, 1987. During the grazing duration treatment phase (from April 1, 1987 to January 14, 1988) four grazings with sheep were monitored to investigate the possibility of manipulating the lucerne/grass balance by using short or long grazing durations. Because grass tillers recover more rapidly after defoliation compared with lucerne shoots it was hypothesized that long grazing durations would favour lucerne and short durations would result in grass dominance.
The lucerne/prairie grass mixture produced 11,150 kg DM/ha during the 144 day establishment phase compared with 6,480 DM /ha for lucerne/phalaris and 6740 kg DM/ha for pure lucerne. The contribution of lucerne to total yield of lucerne/prairie grass and lucerne/phalaris mixtures was 16% and 53% respectively. Lucerne/grass mixtures provided better ground coverage and depressed weed invasion compared with pure lucerne.
There was no significant difference in total dry matter yield between the three pasture types during the grazing treatment phase (April 1, 1987 - January 14, 1988), the yields being 13,330, 12,710 and 13,900 kg DM/ha for lucerne/prairie grass, lucerne/phalaris and pure lucerne respectively. However, the total lucerne dry matter yield in lucerne/prairie grass (4,130 kg DM/ha) was half of that in lucerne/phalaris (8,450 kg DM/ha), but total prairie grass yield (9,200 kg DM/ha) was over twice that of the phalaris (4,260 kg DM/ha). All pasture types produced the highest total single harvest yields in the October harvest and lowest at the July harvest, with the herbage yield being 5,450, 4,760 and 4,800 kg DM/ha for lucerne/prairie grass, lucerne/phalaris and pure lucerne at the October harvest, and 1,870, 1,700 and 1,300 kg DM/ha at the July harvest. Lucerne/prairie grass and lucerne/phalaris mixtures produced 45% and 31% more dry matter than pure lucerne in the first winter. Both lucerne/prairie grass and lucerne/phalaris were dominated by lucerne (64% and 96% lucerne in lucerne/prairie grass and lucerne/phalaris) in January/88 harvest, but by grass (95% and 78%) at July harvest.
Long grazing duration significantly depressed total grass yield in the lucerne/prairie grass by 2500 kg DM/ha, but by only 900 kg DM/ha in lucerne/phalaris mixture. At both the October and November harvests long grazing duration depressed prairie grass yield by 1150 and 820 kg DM/ha, and phalaris yield by 540 and 250 kg DM/ha respectively. Long grazing duration increased lucerne dry matter yield in lucerne/prairie grass at November cut. Generally, long grazing duration increased lucerne shoot numbers, shoot size and shoot height, but decreased grass tiller numbers in lucerne/grass mixtures, particularly with lucerne/prairie grass. There was no significant effect of grazing duration on grass tiller size and tiller length. However, the total DM yield from long grazing duration was 13% less than that from short duration (12,400 kg DM/ha vs 14,250 kg DM/ha for long and short durations) because of the confounding effect of shorter regrowth periods with less mature pastures after long grazing duration.
Urine nitrogen stimulated grass growth and increased grass tiller numbers and yield, which in tum depressed lucerne growth and decreased lucerne shoot numbers and yield in lucerne/grass mixtures. Prairie grass was most responsive to urine because the lower lucerne proportion in the mixture resulted in lower nitrogen inputs to the pasture and lower nitrogen content of herbage (2.5%) compared with 3.1% for lucerne/phalaris mixture and 3.5% for pure lucerne.
These results suggested that long grazing durations of lucerne/grass mixtures may encourage lucerne and that short duration will encourage grasses.||en