Effect of stubble-height management on crown temperature of perennial ryegrass, tall fescue and chicory.

Defoliating pasture to shorter stubble heights (height above the soil surface) may increase temperature at the plant crown (plant–soil interface). This is especially relevant to summer C₃ pasture production in parts of south-eastern Australia, where above-optimal ambient temperatures (≥30°C) are often recorded. A rainfed field experiment in north-west Tasmania, Australia, quantified the effect of stubble-height management on the upper distribution of crown temperatures (90th and 75th percentiles) experienced by three pasture species: perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea Schreb.; syn. Schedonorus arundinaceus (Schreb.) Dumort.; syn. L. arundinaceum (Schreb.) Darbysh.), and chicory (Cichorium intybus L.). Three stubble-height treatment levels were evaluated: 35, 55 and 115 mm. Defoliation to shorter stubble heights (35 or 55 mm cf. 115 mm) increased the crown temperature of all species in the subsequent regrowth cycle (period between successive defoliation events). In the second summer, defoliating to shorter stubble heights increased the 90th percentile of crown temperature by an average of 4.2°C for perennial ryegrass, 3.6°C for tall fescue and 1.8°C for chicory. Chicory and second-year tall fescue swards experienced less-extreme crown temperatures than perennial ryegrass. This may partly explain why these two species often outyield perennial ryegrass in hotter summer environments than north-west Tasmania, and hence the increasing interest in their use. Above-optimal ambient temperatures (≥30°C) challenge summer pasture production in south-eastern Australia. A field experiment showed that defoliating to shorter stubble heights (35 or 55 mm cf. 115 mm) contributed to elevating the crown temperature of three pasture species, which may have negative implications for plant growth and survival during hot summers. Chicory and second-year tall fescue experienced less-extreme crown temperatures than perennial ryegrass, which may partly contribute to the superior growth of chicory and tall fescue in hot summer environments. [ABSTRACT FROM AUTHOR]