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Lincoln University (1990)

Performance of lucerne/grass mixtures under different grazing durations and soil depths in a dryland environment

Gyamtsho, Pema

Titre : Performance of lucerne/grass mixtures under different grazing durations and soil depths in a dryland environment

Auteur : Gyamtsho, Pema

Université de soutenance : Lincoln University

Grade : Master of Agricultural Science 1990

Résumé
Two studies were conducted on pure WL320 lucerne, lucerne/ ’Grasslands Matua’ prairie grass and lucerne/’Grasslands Maru’ phalaris mixtures at Lincoln University, between April 1988 and September 1989. The 0.042 ha plots were sown in early November 1986 into a Templeton fine sandy loam soil. The weather during the experimental period was very dry during spring and summer, but was warm and moist in winter. The first study investigated the effects of short (3-7 days) and long (6-14 days) sheep grazing durations on the three pastures. Short grazing resulted in 15% more total yield from six grazing cycles (15000 versus 13000 kg DMha⁻¹). There were no significant differences in total yields between the pastures. Total lucerne yields were 20% higher under short duration for pure lucerne and lucerne/phalaris, but were not different for lucerne/prairie grass. The total yield of prairie grass under short grazing (9160 kg DMha⁻¹) was 36% higher than under long grazing (6740 kg DMha⁻¹), but phalaris yields were similar at 2570 and 2320 kg DMha⁻¹ respectively for short and long grazing. The results indicated that short grazing duration was superior to long grazing duration, when rotation lengths were equal. The second experiment compared the performance of lucerne with the lucerne/grass mixtures in shallow (<50 cm) and deep (>80 cm) soils on mini-plots of 8 m² selected from areas within the grazed plots. Water use from the soil was measured using a neutron probe. Root cores were sampled in May 1989 from deep soil plots. On the shallow soils total yields from pure lucerne and lucerne/phalaris were similar (11700 and 11400 kg DMha⁻¹) and were significantly higher than the lucerne/prairie yield of 8500 kg DMha⁻¹. Pure lucerne and lucerne/prairie yields were 17% and 45% higher in the deep soils than in the shallow soils, but in both soil types, lucerne/phalaris yields were similar. Winter yields from pure lucerne and lucerne/prairie were similar on both soils (3000 kg DMha⁻¹), but lucerne/phalaris produced 27% more on shallow (3700 kg DMha⁻¹) than on deep soils (2900 kg DMha⁻¹). Total lucerne production in lucerne/phalaris of 9900 kg DMha⁻¹ was not affected by soil depth but in lucerne/prairie, lucerne yield was 57% less on shallow (3950 kg DMha⁻¹) than on deep soils (9100 kg DMha⁻¹). Total yields from prairie grass and phalaris were higher by 30% and 10% respectively on shallow soils. Total water use was not different between the pastures at 384, 376 and 375 mm respectively for lucerne, lucerne/prairie and lucerne/phalaris, but was 10% higher on deep soils (398 mm) than on shallow soils (360 mm). Seasonal water use was similar for all three pastures and was higher in deep soils by 39% in spring and 20% in early summer. All three pastures showed similar water use efficiency (WUE) in deep soils but in shallow soils, the WUE of lucerne/prairie was significantly lower (10-13 kg DMmm⁻¹ H₂O) than either the lucerne or the lucerne/phalaris mixture (18-24 kg DMmm⁻¹H₂O). Pure lucerne extracted water from greater depth than the mixtures. Under all pastures, water was extracted until soil volumetric water content reached 10%. Pure prairie grass and phalaris had 70% and 50% of their roots in the top 20 cm, and roots of both grasses were traced to 70 cm depth. In the top 20 cm lucerne root yield of lucerne/prairie was only 60% (4 kg DMm⁻³) compared to 88% (9 kg DMm⁻³) of lucerne/phalaris at that depth. The results showed that under the extremely dry conditions of 1988/89, there was no advantage in pasture yield of lucerne/grass mixtures over pure lucerne. However the inclusion of phalaris in shallow soils and prairie grass in deep soils provided effective weed control and good cool season growth without adversely affecting pasture productivity

Sujet : WL 320 Lucerne ; Medicago sativa L. ; Grasslands Matua prairie grass ; Bromus willdenowii Kunth. ; Grasslands Maru phalaris ; Phalaris aquatica L. ; lucerne grass mixtures ; grazing duration ; dry matter yield ; seasonal production ; soil depth ; water use ; water use efficiency ; water extraction pattern ; root yield

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