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Lolium perenne L. (Lp) is the main pasture species in New Zealand, but climate change increases the likelihood of drought during summer and consequently lowers its growth rates. Bromus valdivianus Phil. (Bv) tolerates better the summer soil water restriction, but its competitiveness in a diverse pasture relates to the defoliation management and soil moisture levels. The performance of both species in terms of production, persistence and feed quality across seasons under different defoliation regimens was evaluated when the species were mixed and in monoculture. The treatments were applied in a randomised complete block design with three blocks. Bromus valdivianus and Lp monocultures and the 50/50 mixture (Mx) were grazed at low and high defoliation frequencies (i.e. based on Bv and Lp optimal leaf regrowth stage [LS], respectively). Herbage mass production was 15% higher in the Mx, mainly due to an increase in production in spring and summer. In spring, there was complementarity growth between the species, while during summer/early autumn, the Mx production relayed in the higher participation of Bv. Root biomass at depth (31–70 cm) was 38% greater for Bv monoculture and the Mx compared with Lp monoculture, which demonstrated the contribution of Bv to a better production of the mixture during and following the dry periods. In addition, the maintenance of the Bv tiller population and the higher growth rate during dry periods demonstrated its better fitness to low soil water availabilities than Lp. Although herbage mass was not modified by the defoliation frequency, forage quality of Bv showed values at low defoliation frequency that could compromise animal production during spring. However, there was an increase in root biomass under low defoliation frequencies, which suggested that a flexible grazing management across seasons would increase the niche utilisation between species in the mixture. The defoliation frequency of the mixture could be based on Lp LS during spring and winter, and slowed down, following Bv criteria, during summer and autumn. [ABSTRACT FROM AUTHOR]

Bromus valdivianus Phil. (Bv) is a water stress-tolerant species, but its competitiveness in a diverse pasture may depend on defoliation management and soil moisture levels. This glasshouse study examined the effect of three defoliation frequencies, based on accumulated growing degree days (AGDD) (250, 500, and 1000 AGDD), and two soil water levels (80–85% of field capacity (FC) and 20–25% FC) on Bv growth as monoculture and as a mixture with Lolium perenne L. (Lp). The treatments were applied in a completely randomised block design with four blocks. The above-ground biomass of Bv was lower in the mixture than in the monoculture (p ≤ 0.001). The Bv plants in the mixture defoliated more infrequently (1000 AGDD) showed an increase in root biomass under 20–25% FC compared to 80–85% FC, with no differences measured between soil water levels in the monoculture. Total root length was highest in the mixture with the combination of infrequent defoliation and 20–25% FC. Conversely, frequent defoliation treatments resulted in reduced water-soluble carbohydrate reserves in the tiller bases of plants (p ≤ 0.001), as they allocated assimilates mainly to foliage growth. These results provide evidence that B. valdivianus can increase its competitiveness relative to Lp through the enhancement of the root growth and the energy reserve in the tiller base under drought conditions and infrequent defoliation in a mixture. [ABSTRACT FROM AUTHOR]

Pasture brome (Bromus valdivianus Phil.) has the potential to increase current levels of herbage production and pasture persistence in New Zealand dryland, well-drained soils. However, there is little literature on the effect of defoliation management on growth of this grass under contrasting soil-water restriction levels. The growth physiology and performance of pasture brome were evaluated in pots in a glasshouse. Defoliation frequency (DF) treatments were applied based on three different accumulated growing degree-days (AGDD): 250, 500 and 1000 AGDD (high, medium, and low DF). At end of the first growing cycle (1000 AGDD), water availability was restricted to 20–25% of field capacity (FC) in half of the pots, while the other pots were maintained between 80–85% FC. Total accumulated herbage mass was positively related with the low DF and well-watered conditions (p < 0.05). At the final harvest, plants subjected to low DF had greater root mass than high and medium DF (p < 0.05). At each harvest, the leaf regrowth stage (LS) for low DF was 3.5, while for high and medium DF, the LS was 1.5 and 2.0; respectively. Tiller water-soluble carbohydrates were highest at the low DF and under 20–25% FC. Regardless of soil-water conditions, defoliation at 3.5 LS supports production, enhancing survival during a drought. [ABSTRACT FROM AUTHOR]