Abstract
This pot study assessed the effects of deferring forage during autumn and leaving as winter cover on reducing cold damage to plants of 2 tropical (C4) grasses ( Chloris gayana and Panicum coloratum ) in a temperate environment in La Plata, Buenos Aires, Argentina. Mature plants were subjected to the following treatments: (i) autumn-deferred forage retained (DF) as control; and (ii) autumn-deferred forage removed (DFR) cutting at 15 cm from soil level at beginning of winter. This experiment had 10 replicates per treatment and 1 plant per pot (experimental unit). Plants of both species were extracted from a commercial beef farm and transplanted into an experimental garden in pots where they grew outdoors from 2 February to 23 May (111 days) when treatments were applied. After winter, both grasses were cut to 15 cm in early spring (27 September) and spring growth was measured in November. Shoot biomass was harvested at ground level and separated into lower and upper layers (above and below 15 cm), leaf blades, sheaths and stolons. Daily air temperature, relative humidity and frost events were registered. Allometric analysis of shoot biomass was performed to determine the stress incidence by cold. DF plants achieved 55‒80% higher shoot biomass than DFR plants during spring in both species. The allometric analysis revealed for P. coloratum significant relationships between shoot biomass from plant compartments (lower and upper layers, leaf blade and sheath) and total shoot biomass in both treatments, indicating good cold tolerance. However, for C. gayana, unlike DF plants, DFR plants were strongly stressed, showing a lack of shoot biomass fit. These results suggest that deferring autumn forage growth and retaining as winter cover may improve survival during winter and productivity during spring of these two tropical grasses in temperate pastoral systems. However, the study needs to be repeated under field conditions and under grazing or cutting over a number of years in different situations to verify these preliminary results. Keywords : Winter cover, cold damage, frost protection, pasture management.
Highlights
The successful introduction of new forage species into grassland ecosystems or cultivated pasture systems depends on successful establishment, persistence and forage productivity (Baron and Bélanger 2007)
Plants that retained autumn-deferred forage during winter (DF) attained a higher shoot biomass (C. gayana, P
Total shoot biomass accumulated during the experimental period including growth in spring, winter and that removed at the beginning of the experiment (DFR treatment only), was 53 and 80% higher in C. gayana and P. coloratum, respectively, for the treatment where deferred forage was retained (Figure 2B)
Summary
The successful introduction of new forage species into grassland ecosystems or cultivated pasture systems depends on successful establishment, persistence and forage productivity (Baron and Bélanger 2007). In temperate and subtropical areas, tropical (C4) grasses have the potential to increase forage production during summer, when growing conditions are not ideal for C3 temperate grasses (Davies and McNaughton 1980; Johnston 1996; Crush and Rowarth 2007). As well as having better growth potential, some tropical grasses have shown good adaptation to saline soils (Loch et al 2004), drought conditions (Pitman 2001), soils with low or high pH (Robinson et al 1993), infertile soils (Loch 1980), seasonal flooding (Baruch 1994; Imaz et al 2015a) and other environmental stresses, whereas temperate grasses showed poor persistence (Crush and Rowarth 2007). When suboptimal temperatures are recorded for extended periods (i.e. 2‒6 months), significant tissue damage and subsequent plant death can occur (Ludlow 1980; Márquez et al 2006)
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