The Growth Response of Pasture Brome (Bromus valdivianus Phil.) to Defoliation Frequency under Two Soil-Water Restriction Levels

Abstract

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.

Functional contribution of two perennial grasses to enhance pasture production and drought resistance under a leaf regrowth stage defoliation criterion

“…In addition, the second residual leaf was counted (second leaf from bottom to top, with values of 0.5 or 0.75 according to its length), to capture its continued growth after a grazing event. Thus, Bv tillers at 3.5–4.0 LS had at least 5 leaves, one residual from the previous grazing cycle, at least one or two fully expanded and three growing (García‐Favre et al, 2021; Ordóñez et al, 2021). Therefore, the LS regrowth of Bv can be based on up to 6 live leaves; meanwhile, Lp LS regrowth can be based on 3 live leaves.…”

“…This effect, along with the senescence of the first fully expanded leaf as regrowth progresses (coinciding with a decline in pasture quality), determines an optimum range of LS recommended for grazing (Fulkerson & Donaghy, 2001). It was shown that the optimum LS for production and persistence of Lp lies between 2 and 3.0 leaves/tiller (Fulkerson & Donaghy, 2001), while for Bv, it is between 3.5 and 4.0 leaves/tiller (García‐Favre et al, 2021; Ordóñez et al, 2021). In a mixture, to achieve a good pasture production and persistence, both species should be defoliated close to their optimum LS.…”

Nitrogen Use Efficiency and Partitioning of Dairy Heifers Grazing Perennial Ryegrass (Lolium perenne L.) or Pasture Brome (Bromus valdivianus Phil.) Swards during Spring

“…In the current experiment, several factors related to pasture availability (pre-and post-grazing herbage mass) and quality in terms of nitrogen (CP) were similar between Bv and Lp, suggesting that Bv could be used to replace Lp, especially for the months of the year where the water deficit is increased. Bromus valdivianus is a native grass species from Southern Chile that is characterized by its high DM yield and good forage quality, even under restricted conditions of soil water content [40][41][42], which is related to its deep root system, which enables capture of water from deeper soil strata, increasing its drought tolerance [18][19][20]. It was observed that ADF and NDF content were greater for Bv, while WSC content was greater for Lp.…”

“…Bromus valdivianus is a native species from the humid temperate region of Chile characterized by a high tolerance to restricted conditions of soil water (dry periods), mainly related to its deep root system, allowing for water from lower soil strata to be obtained [18,19]. Additionally, Bv is characterized by a high pasture availability, being similar to Lp, the most common grass species used for pasture-based dairy systems, and therefore has the potential to increase current levels of herbage production and pasture persistence in drylands [20]. Moreover, Bv shows a high content of protein (~19% CP) and fiber (~48% NDF) and a medium content of energy (2.5 Mcal ME/kg DM) [21,22].…”

“…Despite the high nutritive value of Bv, several studies have reported an unbalance in its energy and protein content [21,22], which could reduce the rumen N utilization and increase N excretion into the environment [21]. Although there are studies reporting the good growing potential and nutritive value of Bv in countries such as Chile [22,23] and New Zealand [20], there is a lack of studies evaluating the impact of Bv on animal performance and measures of sustainability such as N excretions. Thus, the aim of the study was to evaluate the effect of grazing Lolium perenne and Bromus valdivianus on average daily weight and nitrogen use efficiency of Holstein Friesian heifers.…”