Abstract
Producers of orchardgrass (Dactylis glomerata L.) hay in the Mid-Atlantic US have experienced a reduction in regrowth vigor and a decline in the persistence of their swards. The common management practice for the region is to harvest the first growth of hay by cutting at 2.5–7.5 cm height in May or June. We hypothesize that high temperature and low cutting height interact to limit the regrowth rate. To test this, orchardgrass plants were cut to either 2.5 or 7.5 cm and then placed into environmentally controlled chambers with a constant temperature of 20 or 35°C. Stubble was harvested on days 0, 1, 3, and 11 following cutting and subjected to metabolite analysis. Photosynthetic parameters were measured in the regrown leaves on days 3 and 11, and regrowth biomass was recorded on day 11. Under optimal growth temperature (20°C), vegetative regrowth upon defoliation was significantly enhanced when more stubble tissue remained. However, this advantage was not observed under heat stress. Defoliation generally decreases the abundance of carbohydrate reserves in stubble. Interestingly, high temperature stimulated the accumulation of starch and ethanol-soluble carbohydrates in plants cut to 7.5 cm. The similar trends were also observed in protein, amino acids, nitrate, and ammonium. These responses were not pronounced in plants cut to 2.5 cm, presumably due to inhibited photosynthesis and photosystem II photochemistry. Overall, we anticipated that heat-activated metabolite accumulation is part of adaptive response to the stress. However, modified allocation of carbohydrate and nitrogen reserves leads to reduced vegetative regrowth upon defoliation. These data suggest that cutting height management for orchardgrass may be more effective for its regrowth vigor and productivity in cool seasons or when cool weather follows hay harvest.
Highlights
Orchardgrass is a high yielding cool-season forage grass which is a valuable feedstuff for several classes of livestock
Plants were regrown under control (20◦C) or high temperature (35◦C) conditions for up to 11 days
At optimal temperature for cool-season grasses (20◦C), leaving more stubble tissue resulted in greater biomass regrowth upon defoliation
Summary
Orchardgrass is a high yielding cool-season forage grass which is a valuable feedstuff for several classes of livestock. Orchardgrass is the 4th most produced perennial cool-season forage grass seed and is widely planted in North America, Europe, and East Asia (Stewart and Ellison, 2011). Cutting height is a major determinant of quantity and quality of stubble from which the sward will regrow in perennial glasses. Harvest at a low cutting height will remove the majority or all photosynthetic tissue and some of the stem tissue containing NSC, reducing the energy sources for regrowth. Defoliation suddenly changes the activity of leaf sheath phloem from unloading to loading (Amiard et al, 2003). These results emphasize that the stubble tissue serves as a carbon source to support regrowth upon defoliation
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