Abstract
The objectives of the experiment were to (i) examine the dynamics of WSC use and the recovery of leaf sheaths and blades of Bromus valdivianus Phil. and Lolium perenne L. subjected to two defoliation frequencies (DFs) determined by thermal time (TT); (ii) evaluate how DF influenced regrowth and accumulated herbage mass (AHM) during fall. Defoliation was carried out at frequencies of 135 and 270 accumulated growing degree days (AGDDs) for both species. Twelve plots were arranged in a three-block design. All plots had a conditioning period to establish the assigned DF prior to sampling. From the start of the experiment, “cores” were collected from each plot every three days until the DF was reached. Every core was separated into leaf and sheath material before measuring the WSC concentration. Lolium perenne had concentrated more WSCs than B. valdivianus. Both species adapted their WSC recovery according to the DF. The recovery of WSC was faster under a DF of 135 AGDDs than that of 270 AGDDs. Leaf sheaths contained more WSCs than leaf blades and were identified as WSC storage organs. This period can be used as the optimal defoliation interval in B. valdivianus and L. perenne grazing systems.
Highlights
Along with soil fertility and environmental conditions, defoliation frequency (DF) is one of the main factors related to pasture management that influences the rate of regrowth and accumulated herbage mass (AHM)
Lolium perenne L. and B. valdivianus defoliated after 135 accumulated growing degree days (AGDDs) had similar water-soluble carbohydrate (WSC) levels (p > 0.05, Figure 2a,b) in both the blades and sheaths
When the DF was extended to 270 AGDDs, significant differences (p < 0.05, Figure 3a,b) were found between the two species
Summary
Along with soil fertility and environmental conditions, defoliation frequency (DF) is one of the main factors related to pasture management that influences the rate of regrowth and accumulated herbage mass (AHM). When days are used to assign the interval between defoliations, changes in plant phenology are not considered. Using days as a criterion for DF can reduce pasture growth and longevity. In some perennial crops, such as sorghum and oats growing under field conditions, the thermal time, expressed as accumulated growing degree days (AGDDs), has been widely used to determine sowing data [1,2]. Because there is a positive relation between plant development and temperature [3]. The thermal time (TT) was used as a tool to determine the best DF in Lolium perenne L. and Bromus valdivianus
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