Bromus-Poaresponse to defoliation intensity and frequency under three soil moisture levels

Abstract

Smooth brome (Bromus inermis Leyss.) and Kentucky bluegrass (Poa pratensis L.) are important herbage for livestock and wildlife in Aspen-Boreal ecosystems in central Alberta, but there is paucity of information on the relationship between soil moisture and defoliation regimes on herbage production in these ecosystems. In a greenhouse experiment, we evaluated the effect of Bromus-Poa defoliation frequencies (2 or 4 wk) and intensities (2.5, 7.5, or 15 cm above the soil surface) under three soil moisture regimes [field capacity (wet), 50% field capacity (moist), 20% field capacity (dry)] on dry matter (DM) yield. Crude protein (CP) content, crude protein yield (CPY) and neutral detergent fiber (NDF) were also determined for herbage harvested. Total accumulated shoot DM decreased under defoliation compared to the undefoliated control, was higher if plants were clipped every 4 wk, rather than 2 wk, and increased with increasing soil moisture availability. Defoliation regimes decreased root DM Compared to the undefoliated control. Soil moisture regime did not significantly affect below-ground DM production, but root:shoot ratio increased significantly with decreasing moisture supply. The average CP content of grasses ranged from 12 to 23%, but was adequate to meet crude protein requirements of growing, pregnant or lactating grazing cattle (Bos spp.) The CPY decreased with increasing moisture stress, and was greatest when plants were clipped at a 7.5-cm height. Shoot NDF concentration increased with decreasing clipping frequency. These result indicate the need to investigate the relationship between soil moisture and management practices that affect the productivity of tame pastures in Aspen-Boreal ecosystems. Key words: Bromus inermis, Poa pratensis, crude protein, neutral detergent fiber, water

How do severity and frequency of grazing affect sward characteristics and the choices of sheep during the grazing season?

“…However, seasonal changes were highly significant with an overall decrease in crude protein concentration and an increase in NDF concentration and a reduction in OM digestibility. Donkor et al (2002) also showed that high frequency and severity of defoliation decreased NDF concentration and increased crude protein concentration on Bromus-Poa swards. This is consistent with the results of Korte et al (1984), who reported that the difference in accumulation of dead material between high and low severity grazing was reduced during a dry period through the presence of desiccated vegetative tillers on high grazing severity treatments.…”

Effects of seabird nitrogen input on biomass and carbon accumulation after 50 years of primary succession on a young volcanic island, Surtsey

“…Inside the seabird colony, the lack of relationship between R / S and N stock is possibly due to other factors, such as limiting water availability, overruling the effect of N availability on the R / S ratio. Drought has been reported to be an important determinant of R / S ratios (Donkor et al, 2002;Gianoli et al, 2009;Dreesen et al, 2012) and water infiltration in Andosols is rapid compared to most other soils (Basile et al, 2003), especially when the C content is below 12 %, as is the case on Surtsey (Arnalds, 2008). Therefore, we attribute the absence of a clear nutrient influence on R / S ratio to an overruling effect of drought in all occurring nutrient situations.…”

Smooth Brome (Bromus inermis) in Tallgrass Prairies: A Review of Control Methods and Future Research Directions

“…Stacy and colleagues (2005) grazed horses in a cool-season grassland at a reclaimed coal mine during the time of smooth brome tiller elongation. Even at a moderate defoliation rate (7.5 cm vegetation height, 4 wks between clippings), maximum aboveground biomass production in a smooth brome-Kentucky bluegrass (Poa pratensis) sod was achieved (Donkor et al 2002). However, more research into grazing as a control method is needed, as previous research has largely focused on maximizing stocking densities while also maximizing smooth brome herbage yields (Donkor et al 2002).…”